International Symposium on Advances in Nanoscience October 25-26, 2010 Campus Garching

Center for Nanotechnology and Nanomaterials (ZNN) and TUM Institute for Advanced Study (IAS) ORGANIZERS The Symposium is hosted by Nanosystems Initiative Munich and TUM Institute for Advanced Study Gerhard Abstreiter, Hendrik Dietz, Jonathan J. Finley, Dirk Grundler, Alexander Holleitner, Paolo Lugli, Friedrich Simmel, Martin Stutzmann

CONTACT Irmgard Neuner (Ofﬁ ce Prof. Gerhard Abstreiter) Walter Schottky Institut (TU München) Am Coulombwall 3 D-85748 Garching Tel: +49-(0)89-289-12771 Fax: +49-(0)89-289-12704 [email protected]

VENUE TUM Institute for Advanced Study (IAS) and Center for Nanotechnology and Nanoma- terials (ZNN) of Walter Schottky Institut in Garching

Content

3 | Introduction

5 | Invited Talks

31 | Poster Presentations

77 | Useful Information

78 | List of Participants

2 Advances in Nanoscience - Garching 2010 INTRODUCTION

The “International Symposium on Advances in Nanoscience” is the Inaugural Symposium for the new center for nanotechnology and nanomaterials (ZNN) at the TUM in Garching that was offi cially opened on July, 19th, 2010. After a fast planning phase and only one year of construction, the building is now almost fully operational. It offers 2000 square meters of offi ces and laboratory space with modern equip- ment for nanoscientists of various directions. In the last few months, research groups have moved into the building and now start to work in several exciting areas of nanoscience, as they are also represented by the different sessions of this symposium – Quantum Nanosystems, Hybrid Nanosystems, Nano and Energy, and Bio-Nanoscience. These areas also represent the major research directions of the DFG funded Excellence Cluster “Nanosystems Ini- tiative Munich“ (NIM), where the ZNN researchers are heavily involved. The ZNN is an extension of the well-known Walter Schottky Institute (WSI) that was founded in Gar ching over 20 years ago. The extremely successful activities of the WSI led to a continuous demand for more lab and offi ce space, a trend that was considerably reinforced by the success of the Excellence Cluster NIM. This triggered the plan for a new building fully devoted to nanoscience. The concept for the new building was developed by Gerhard Abstreiter (WSI) and co-workers and was jointly funded by the Bavarian State and the Federal Government. While the main focus of the WSI still lies in semiconductor materials technology, in the ZNN modern nanofabrication techniques and research at the nano/bio interface will be more prominent. The ground fl oor will host a modern clean room facility for micro- and nanofabrication, and also instrumentation for the characterization of nanomaterials. The fi rst fl oor is devoted to cutting-edge optical and electronic experiments with solid state nanostructures, but also on hybrid nanosystems. The second fl oor contains “wet” labs and physical labs for research in bionanotechnology. Thus, the new building will be perfectly suited for internationally competitive, interdisciplinary research in nanoscience.

Advances in Nanoscience - Garching 2010 3 Talks

4 Advances in Nanoscience - Garching 2010 INVITED TALKS

Session 1: Quantum Nanosystems Session 3: Nano and Energy Experiments on the ultimate „Black Silicon“: Nanotextured Silicon two-dimensional electron system ...... 6 Surfaces for Photovoltaics ...... 20 Klaus von Klitzing Martin Stutzmann

Graphene quantum circuits ...... 7 Role of Nanotechnology in Klaus Ensslin Third Generation Photovoltaics ...... 21 Stephen Goodnick Exploring and harnessing cavity-QED phenomena in single and few quantum Nanostructured organic and dot photonic crystal nanostructures ...... 8 hybrid solar cells ...... 22 Jonathan Finley Lukas Schmidt-Mende

Periodic Nanowire Structures...... 10 Heusler Compounds: Erik Bakkers Novel Materials for Energy Applications ...... 23 Claudia Felser Ga-assisted MBE grown GaAs nanowires and related quantum heterostructures TiO2-Nanotubes in Energy Research ...... 24 for solar applications ...... 11 Julia Kunze Anna Fontcuberta i Morral

Session 4: Bio-Nanoscience Session 2: Hybrid Nanosystems Synthetic Biology of Cell Division ...... 25 Voltage-sustained self-oscillation of Petra Schwille a nanomechanical electron shuttle ...... 12 Eva Weig DNA Nanotechnology for Protein Science ...... 26 Hendrik Dietz Cooper-pair splitter: towards an efﬁ cient source of spin-entangled EPR pairs ...... 13 The Bio-Electronic Synapse – Christian Schönenberger Fusing Electronics with Molecular Biology ...... 27 Uri Sivan Pure spin current based spintronics in metallic nano-structures ...... 14 Molecular Interactions on Yoshichika Otani Dynamically Actuated Surfaces and in Artiﬁ cial Nanopores ...... 28 Carbon nanostructures Ulrich Rant for quantum spintronics ...... 15 Jörg Wrachtrup Stochastic gene expression and the decisive role of noise in microbial genetic networks ...... 29 Plasmonic control of elementary emitters ...... 16 Joachim Rädler Joachim Krenn Nanoscale structures and molecular The perfect wave ...... 17 devices made from DNA ...... 30 Achim Wixforth Friedrich Simmel Optoelectronic dynamics in hybrid nanoscale circuits ...... 18 Alexander Holleitner

A Quarter Century of Quantum Dots: From Science to Practical Implementation ...... 19 Yasuhiko Arakawa Talks

Advances in Nanoscience - Garching 2010 5 Experiments on the ultimate two-dimensional electron system Klaus v. Klitzing and co-workers Max Planck Institute for Solid State Research, Heisenbergstraße 1, D-70569 Stuttgart, Germany

he title of the symposium “Advances in Nanoscience” provokes a presentation about the Tthinnest two-dimensional electron system known as graphene. The presentation will sum- marize own experiments on graphene mono- and bilayers (produced either by epitaxial growth or by exfoliation), including Raman experiments, magneto-transport results, TEM investigations and ARPES data. The focus will be on transport measurements at low temperatures and strong magnetic ﬁ elds. Session 1: Quantum Nanosystems Talks

6 Advances in Nanoscience - Garching 2010 Graphene quantum circuits K. Ensslin F. Molitor, J. Güttinger, S. Schnez, S. Dröscher, M. Hufner, A. Jacobsen, C. Stampfer, T. Ihn and K. Ensslin Laboratorium f. Festkörperphysik, ETH Zürich, Schafmattstr. 16, CH-8093 Zürich, Switzerland

raphene quantum dots and constrictions have been fabricated by mechanical exfoliation of Ggraphene followed by electron beam lithography and dry etching. The single layer quality of graphene has been checked by Raman spectroscopy. The electron hole-crossover can be investigated by linear transport experiments as well as using non-linear effects in three-terminal junctions. A variety of nanostructures such as graphene constrictions, graphene quantum dots and graphene rings have been realized. Of particular interest is the electron hole crossover in graphene quantum dots, spin states as well as the electronic transport through graphene double dots. The goal is to establish the peculiar consequences of the graphene bandstructure with its linear dispersion for the electronic properties of nanostructures. Session 1: Quantum Nanosystems Talks

Advances in Nanoscience - Garching 2010 7 Exploring and harnessing cavity-QED phenomena in single and few quantum dot photonic crystal nanostructures Jonathan Finley Walter Schottky Institut, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany

olid-state cavity quantum electrodynamics (QED) systems offer a robust and scalable plat- Sform for quantum optical experiments and may even provide a route towards “on-chip” photon based quantum information processing technologies. In particular, systems based on photonic crystal nanocavities containing one or more semiconductor quantum dots (QDs) have developed at a rapid pace over the past few years. A diverse range of experiments have been reported in both the weak1 and strong2,3,4 coupling regimes of the light matter interaction. In the weak coupling regime, the direction and rate of QD spontaneous emission can be tailored1 and novel “non-resonant” dot-cavity coupling mechanisms have been identifi ed due to cavity enhanced few-particle scattering5 and phonon mediated processes6. In the strong coupling regime, the QD strongly modifi es the cavity spectrum due to the coherent exchange of energy between dot and the vacuum radiation fi eld. Several proposals for scalable quantum information networks and quantum computation rely on such strongly coupled systems and have begun to exhibit measurable quantum (photon number) effects in atomic systems7, superconducting Session 1: Quantum Nanosystems circuit QED systems8 and QD cavity QED devices9. In this talk, I will discuss recent optical studies of single QD photonic crystal nanocavities operating in both weak and strong coupling regimes of the light matter interaction. Topics that will be addressed include (i) the observation of highly effi cient single photon generation inside a photonic bandgap and nano-cavity, (ii) the identifi cation of a non-resonant coupling of the quantum dots into the cavity mode and an explanation of its fundamental origin, (iii) studies of phonon mediated coupling between a single dot and the nanocavity mode, (iv) investigations of the spectrum and dephasing of QD exciton polariton entangled states as a function of dot- cavity detuning as dynamical variables (incoherent pumping and lattice temperature) are varied and (v) the observation of coherent coupling between two quantum dots coupled to a common nanocavity mode. In contrast to most previous studies, where the QD-cavity spectral detuning is controlled by varying the lattice temperature or by the adsorption of inert gases at low temperatures, we have develop electro-optical tuning methods. This approach has enabled us to electrically control spontaneous emission2 and probe the emission spectrum in the strong coupling regime as a function dot-cavity detuning (Fig 1a) and external control parameters, such as the incoherent excitation level or the lattice temperature (Fig. 1b). Our studies provide insights into the nature of the strong coupling and processes responsible for dephasing of 0D-exciton polaritons.3 Most recently, in nanocavities containing two QDs that are simultaneously tuned into resonance with each other and the cavity mode we observe a triple peak at resonance (Fig. 2) - a signature of coherent cavity mediated coupling between the three quantum states.10 1 M. Kaniber et al. Phys. Rev. B77, 073312, (2008) 2 A. Laucht et al., New J. Phys. 11, 023034 (2009). 3 A. Laucht et al., Phys. Rev. Lett. 103, 087405 (2009). 4 M. Nomura et al. Nature Physics, 6, 279, (2010) 5 M. Winger et al. Phys. Rev. Lett. 103, 207403 (2009) 6 U. Hohenester et al. Phys Rev. B80, 201311, (2010) 7 K. M. Birnbaum et al. Nature 436, 87–90 (2005). 8 D. I. Schuster et al. Nature 445, 515–518 (2007). 9 D. Englund et al. Nature 450, 857, (2007) 10 A. Laucht et al., Phys. Rev. B 82, 075305 (2010) Talks

8 Advances in Nanoscience - Garching 2010 Fig. 1: (a) Plot of photoluminescence spectra for different applied bias voltages. The grey points correspond to the experimental data, while the black lines are ﬁ ts to the theory. When the voltage is varied, the exciton transition is tuned through resonance with the cavity mode. The formation of a clear double-peak for zero detuning is an unambiguous sign for strong photon-matter interaction. (b) Reso- nant spectra for different excitation power densities as indicated in the graph. Again, the grey points correspond to the experimental data, while the black lines are ﬁ ts to the theory. The observed splitting at zero detuning reduces for high excitation power densities until only a single broadened peak is visible Session 1: Quantum Nanosystems (top spectrum).

Fig. 2: Comparison between the observed and calculated spectral functions of two quantum dots in resonance with one cavity mode, showing the excellent agreement between the measured spectrum (open circles) and the theoretical spectral functionﬁ tted to the data (black solid lines). The small arrows indicate the third peak in resonance which is proof for the coupling of three quantum states. The grey solid lines were calculated assuming that the two quantum dot states cannot coexist at the same time

as it would be the case for e.g. exciton and charged exciton of the same quantum dot. Talks

We gratefully acknowledge ﬁ nancial support of the DFG via SFB-63, the German Excellence Initiative via the Nanosystems Initiative Munich and the EU via SOLID.

Advances in Nanoscience - Garching 2010 9 Periodic Nanowire Structures Erik P.A.M. Bakkers Erik P.A.M. Bakkers,1,2,3 Rienk Algra,3,4 Moira Hocevar,2,3 Magnus T. Borgström,3 George Immink,3 Bas Ketelaars,3 Lou-Fe Feiner,1,3 Willem J.P. van Enckevort,4 Elias Vlieg,4 Marcel A. Verheijen1,3 1 Eindhoven University of Technology, The Netherlands 2 Delft University of Technology, The Nehterlands 3 Philips Research Laboratories, Eindhoven, The Netherlands 4 Radboud University Nijmegen, The Netherlands [email protected] emiconducting nanowires offer the possibility of nearly unlimited complex bottom-up design Son intrawire and interwire level, which allows for new (opto-)electronic device concepts, such as single-photon nanowire quantum dot emitters. On the interwire level, a lot of progress has been made on control of the nanowire position and appreciation of absolute growth rates. Here, we show recent advances on inducing periodicity on both intra- and interwire level, such to obtain 3-dimensional position control. The nanowire position is determined by that of the catalyst particle. We have developed a generic soft nano-imprint lithography process to fab- ricate arrays of metal particles [1]. From these structures nearly defect free arrays of InP and GaP nanowires have been grown. This approach gives in-plane periodicity. Next, we demonstrate control of the crystal structure of indium phosphide (InP) and gallium phosphide (GaP) nanowires by impurity dopants. More importantly, we demonstrate that we can, once we have enforced the zinc blende crystal structure, induce twinning superlattices with long-range order in the z-direction in the nanowires [2]. The spacing of the superlattices is tuned by the wire Session 1: Quantum Nanosystems diameter and the zinc dopant concentration. These ﬁ ndings have been quantitatively modelled based on the cross-sectional shape of the zinc-blende nanowires. [1] A. Pierret, M. Hocevar, S.L. Diedenhofen, R.E. Algra, E. Vlieg, E.C. Timmering, M.A. Verschuuren, G.W.G. Immink, M.A. Verheijen, E.P.A.M. Bakkers. Nanotechnology 2010, 21, 065305 [2] R.E. Algra, M.A. Verheijen, M.T. Borgström, L.F. Feiner, G. Immink, W.J.P. van Enckevort, E. Vlieg, E.P.A.M. Bakkers, Nature 2008, 456, 369

Figure 1. a,b) Scanning and transmission electron microscopy images of a nanowire with a twinning superlattice. c) SEM image of a periodic array of nanowire fabricated by nanoimprint lithography Talks

10 Advances in Nanoscience - Garching 2010 Ga-assisted MBE grown GaAs nanowires and related quantum heterostructures for solar applications A. Fontcuberta i Morral1,2,* 1 Laboratoire des Matériaux Semiconducteurs, Institute of Materials, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland 2 Institute of Advanced Studies, Walter Schottky Institut und Physik Department, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany * Corresponding author: email: anna.fontcuberta-morral@epﬂ .ch

anowires represent model systems for studying a variety of low dimensional phenomena Nas well as building blocks for the future generation of nanoscale devices. The most exploited nanowire growth technique is the vapor-liquid-solid (VLS) method, which very often employs gold as a seed for the growth. We present the method for growing GaAs nanowires by MBE without using gold as a catalyst. Along these lines, we will show how Molecular beam epitaxy offers a unique possibility for obtaining high purity and high quality materials. Additionally, it gives a great fl exibility for the fabrication of many types of nanowire heterostructures. We will present here how radial and axial heterostructures can be obtained and how this combination can be benefi cial for application in third generation solar cell designs. The optical and transport properties will be elucidated by means of luminescence, Raman spectroscopy and microscopy experiments realized on the same single nanowire. Finally, the results are then applied to the realization of nanowire-based solar cells. The future Session 1: Quantum Nanosystems of this research area will be briefl y discussed. Talks

Advances in Nanoscience - Garching 2010 11 Voltage-sustained self-oscillation of a nanomechanical electron shuttle E. M. Weig Center for NanoScience (CeNS) & Department of Physics, Ludwig-Maximilians-University Munich, [email protected]

n the past years high stress silicon nitride has received considerable interest as a robust and Ihigh Q material for nanomechanical systems. Here we present a nanomechanical charge shuttle, which is a model system to investigate the coupling of electronic transport properties and mechanical degrees of freedom: A nanoscale metal island hosted by a resonator that is oscillating between two opposing electrodes can be used to mechanically transport charge and thus produce an electric current [1]. We have realized such an electron shuttle on a doubly clamped silicon nitride string subject to high intrinsic tensile stress. Typical devices consist of large arrays of shuttles with customized mechanical resonance frequencies in the range of 1 – 10 MHz that are shunted between the source and drain electrode. Frequency multiplexing is employed to individually address single shuttles. Stable shuttling operation in the quasi-ohmic, high tem-

Session 2: Hybrid Nanosystems perature regime could be demonstrated in an acoustically actuated shuttle at 20 K [2]. While acoustic operation im- plemented by a piezo transducer ensures complete decou- pling of the measured electrical signal from the drive and thus allows for clean transport measurements with linear current – voltage curves, it complicates low-temperature operation due to the inevitable dissipation of the piezo. De- spite ongoing island miniaturization to increase the shuttle’s charging energy this has so far impeded the transition to the Coulomb blockade regime. An alternative approach to efﬁ cient nanomechanical systems relies on self-oscillation, i.e. the generation of a pe- Nanomechanical charge shuttle riodic vibration by a constant driving force. Self-sustained oscillation in nanomechanical systems has been observed in optomechanical systems driven by bolometric forces or radiation pressure, or in electromechanical systems with both external or internal feedback. Voltage-sustained self-oscillation of a nanomechanical charge shuttle has been theoretically predicted [1]. Here we present a nanomechanical electron shuttle operated solely by a DC-Voltage that is applied between source and drain [3]. After triggering the resonator via conventional actuation, the oscillation is sustained by repetitive charge reversal at the electrodes. Due to the minimal energy input of this driving scheme, operation at millikelvin temperatures becomes feasible. This may pave the way into the Coulomb blockade regime of discrete mechanical single electron shuttling. [1] L. Y. Gorelik et al., Phys. Rev. Lett. 80, 4526 (1998). [2] D. R. Koenig, E. M. Weig, J. P. Kotthaus, Nature Nanotechnology 3, 482 (2008). [3] D. R. Koenig, J. P. Kotthaus, E. M. Weig (in preparation). Talks

12 Advances in Nanoscience - Garching 2010 Cooper-pair splitter: towards an efﬁ cient source of spin-entangled EPR pairs L. Hofstetter1, A. Kleine1, S. Csonka1,2, A. Geresdi2, M. Aagesen3, J. Nygård3, A. Baumgartner1, J. Trbovic1, and C. Schönenberger1 1 Department of Physics, University of Basel, Klingelbergstr. 82, CH-4056 Basel,Switzerland 2 Department of Physics, Budapest University of Technology and Economics, Budafoki u. 6, 1111 Budapest, Hungary 3 Nano-Science Center, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark

n quantum mechanics the properties of two and more particles can be entangled. In basic Iscience pairs of entangled particles, so called Einstein-Podolsky-Rosen (EPR) pairs, play a special role as toy objects for fundamental studies [1]. They provide such things as “spooky interaction at distance” [2], but they also enable secure encoding and teleportation and are thus important for applications in quantum information technology. Whereas EPR pairs of photons can be generated by parametric down conversion (PDC) in a crystal, a similar source for EPR pairs of electrons does not exists yet. In several theory papers, it has been suggested to use a supercondcutor for this purpose. The superconducting ground state is formed by a condensate of Cooper-pairs which are electron pairs in a spin-singlet state. Since there are many Cooper pairs in a metallic superconductor like Al, the main task is to extract Cooper pairs one by one and to split them into different arms. This has recently been demonstrated by two groups [3,4] using hybrid quantum-dot devices with both superconducting and normal metal contacts. The quantum dots were realized in semiconducting nanowires [3] and carbon nanotubes [3]. Session 2: Hybrid Nanosystems In this source, Cooper pairs are fi rst extracted from a superconducting contact onebe-one by tunneling. The real challenge lies in the separation of the two electrons. Since electrons are charged it has been proposed to use Coulomb repulsion to separate the two electrons [5]. This can be achieved by introducing two quantum dots. The enhancement of Cooper pair splitting follows, because the transfer of a Cooper pair through a single QD cost twice as much charging energy than the transfer of two split electrons traversing the two arms separately. At low temperatures, this selection rule can lead to a 100% effi cient Cooper pair splitter [5]. The two recent experiments demonstrated a remarkably high effi ciency of up to 50 %. This has to be contrasted with optical PDC where effi ciencies of only < 10 − 6 are achieved. The new experimental results [3,4] are an important milestone in the realization of a solid-state source of entangled electron pairs. Such a source will make possible new experiments aiming at properties of solid-state devices beyond single electron physics. If one is able to convert electrons in the photons without loosing entanglement, this approach may even provide an effi cient source of EPR photons. [1] A. Aspect, P. Grangier, and G. Roger, Phys. Rev. Lett. 49, 91-94 (1982). [2] A. Einstein, B. Podolsky, N. Rosen, Phys. Rev. 47, 777-780 (1935)- [3] L. Hofstetter, S. Csonka, J. Nygard, and C. Schönenberger, Nature 460, 906 (2009). [4] L.G. Herrmann, F. Portier, P. Roche, A. Levy Yeyati, T. Kontos, and C. Strunk, Phys. Rev. Lett. 104, 026801 (2010). [5] P. Recher, E. V. Sukhorukov, and D. and Loss, Phys. Rev. B 63, 165314 (2001). Talks

Advances in Nanoscience - Garching 2010 13 Pure spin current based spintronics in metallic nano-structures Y. Otania,b a Institute for Solid State Physics, University of Tokyo, 5-1-5 Kahiwanoha, Kashiwa, Chiba 277-8581, Japan b RIKEN ASI, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

he basic science for electronic devices aiming at manipulating the spin degree of freedom is Tspintronics, which provides a possible means to realize advantageous functionalities for spin based recording and information processing. For such functions, the usage of spin-current, a ﬂ ow of spin angular momentum, is indispensable. Thus establishing elemental technologies shown as building blocks for efﬁ cient injection (input), manipulation, and detection (output) of spin-currents is a key for further advancement of spintronic devices. In this talk I will discuss the recent research progresses in terms of the spin-current induced phenomena in metallic nano-structures. One of the spin-current induced phenomena responsible for the input is the non-local spin injection where the spin accumulation is induced by the direct injection of spin po-

Session 2: Hybrid Nanosystems larized current from a ferromagnetic metal to a non-magnetic metal, such as Cu or Ag. Fabricating clean interfaces or inserting MgO interface layers were recently found to increase the magnitude of spin accumu- Figure: Building blocks for a spin current circuit. lation in the non-magnetic metal tenfold [1, Diagram shows possible spin current circuit, which 2]. This enables us to switch the magneti- exploits phenomena such as spin accumulation, zation of a ferromagnetic nano-pillar by us- spin transfer torque, and direct and inverse spin ing the pure spin current [2, 3]. Furthermore Hall effects. the spin transport along a 6 μm Ag wire is now possible in the lateral spin valve with MgO interface layers. The spin Hall Effect (SHE) is also an interesting phenomenon where the spin-orbit interaction converts the spin-current into a charge current and vice versa, known as the “direct” and “inverse” SHEs. The SHE was ﬁ rst demonstrated on semiconductor systems by means of optical detection [4]. In diffusive metals, the electrical observation of the charge accumulation due to the inverse SHE was ﬁ rst performed by using a nonlocal spin-injection in a lateral ferromagnetic / nonmagnetic Al metallic nano-structure [5]. This experiment was however successful only at low temperatures simply because of the long spin diffusion length, large enough with respect to the device dimensions, i.e. the small spin-orbit interaction of Al. Separately performed inverse SHE measurement using spin pumping technique ascertained that platinum with a large spin-orbit interaction, i.e. a short spin diffusion length of about 10 nm is a good candidate for further study of this sort [6]. Recent development of spin-current absorption technique enabled to detect electrically reversible SHE comprising the direct and inverse SHEs even at room temperature [7, 8]. More recently giant SHE in Au [9] was demonstrated by using the same method in Ref. [5]. This result opens up a new possibility to use normal metals with high spin-orbit interaction as spin-current sources operating at room temperature for the future spintronic applications. [1] Y. Fukuma, et al., Appl. Phys. Lett. 97, 012507 (2010). [6] E. Saitoh, et al., Appl.Phys. Lett. 88, 182509 (2006). [2] T. Yang, T. Kimura and Y. Otani, Nature Phys. 4, 851 (2008). [7] T. Kimura, Y. Oani, et al., Phys. Rev. Lett., 98, 156601 (2007). [3] T. Kimura, Y. Oani, et al., Phys. Rev. Lett., 96, 037201 (2006). [8] L. Vila, T. Kimura, and Y. Otani, Phys. Rev. Lett., 99, 226604 [4] Y. K. Kato, et al., Science, 306, 1910 (2004). (2007). [5] S. O. Valenzuela and M. Tinkham, Nature (London) 442, 176 [9] T. Seki, et al Nature Materials, 7, 125 (2008) (2006). Talks

14 Advances in Nanoscience - Garching 2010 Carbon nanostructures for quantum spintronics J. Wrachtrup 3rd Institute of Physics and Research Center SCoPE, Pfaffenwaldring 9, 70569 Stuttgart, Germany

anostructured carbon materials have become a versatile tool in modern electronic and Nquantum applications. Structures ranging from the well-known carbon nanotube over graphene or carbon dots are well intensely studied for their novel charge transport and optical properties. Additionally carbon is outstanding because of its low spin orbit coupling. Hence, spins are well isolated form the lattice and form a valuable resource for quantum spintronics. The talk will describe how to engineer spin structures in diamond and other carbon structures. Precise read-out and control of spin states as well as coupling to external devices like optical and microwave cavities will be discussed. Session 2: Hybrid Nanosystems Talks

Advances in Nanoscience - Garching 2010 15 Plasmonic control of elementary emitters Joachim R. Krenn Institute of Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria, [email protected]

urface plasmons are electromagnetic modes at the interface of a metal and a dielectric that Scan be focused to nanoscale volumes and that feature resonantly enhanced near fi elds. Coupling plasmonic modes to quantum emitters as molecules or semiconductor nanocrystals is of specifi c interest, as this coupling can strongly alter both, the emitter excitation and emission rates. Here, we focus on the emission process that is governed by the photonic local density of states. This quantity can be tailored by controlling the geometry-dependent resonance frequencies of plasmonic nanostructures by lithographic means. On this basis we report emission rate engineering of fl uorophores [1], redirecting the energy fl ow in molecular resonance energy transfer [2] and refi ned insight in surface enhanced Raman scattering [3]. For better controlling the mutual position of plasmonic nanoparticles and molecules we apply lithographic methods to combine metal nanoparticles with molecule-doped polymer nanoparticles. We demonstrate that the local density of states of the plasmonic particles can be imaged by Moire patterns gen- Session 2: Hybrid Nanosystems erated by combining incommensurable regular arrays of both types of nanoparticles [4]. [1] S. Gerber et al, Phys. Rev. B 75, 073404 (2007) [2] F. Reil et al., Nano Lett. 8, 4128 (2008) [3] E. Le Ru et al., J. Phys. Chem. 112, 8117 (2008) [4] D. M. Koller et al., Phys. Rev. Lett. 104, 143901 (2010) Talks

16 Advances in Nanoscience - Garching 2010 The perfect wave Achim Wixforth University of Augsburg, Experimental Physics 1, Universitätsstr. 1, 86159 Augsburg, Germany

any materials provide quite remarkable features in terms of their mechanical, electronic, Mmagnetic or optical properties. Semiconductor structures and layered systems thereof for example have revolutionized our daily life over the last few decades. Morover, if reduced to the nanometer scale, a wealth of novel properties and physical effects emerged that are partially already exploited technologically. However, some other materials have their own particular specialities that cannot be accomplished by semiconductors alone. By the deliberate realization of hybrid nanostructures consisting of semiconductors and piezoelectric oxides, or soft matter materials like supported membranes and elastomers we are able to create functional nanosystems that aim towards ‘the best of both worlds’ in such hybrids. In my talk, I will present a few examples for functional hybrid nanosystems for photonic, electronic and biological applications. By letting surface acoustic waves interact with these hybrids,

novel tuneable functionalities can be created that are only possible by combining very different Session 2: Hybrid Nanosystems material classes. Talks

Advances in Nanoscience - Garching 2010 17 Optoelectronic dynamics in hybrid nanoscale circuits A.W. Holleitner Walter Schottky Institut and Physik-Department, Technische Universität München, Am Coulombwall 4, 85748 Garching, Germany.

n order to fully exploit the potential of the diverse range of organic and inorganic nanosys- Items that exist, an extremely important step is the development of reliable electrical contacts to connect them to the outside world and electrically manipulate and readout their properties. We investigate the possibility to build novel types of photo-electronic systems that consist of mixed organic and inorganic nanosystems such as nanocrystals [1], carbon nanotubes [2], semi¬conductor nanowires [3,4], and photosynthetic “light harvesting” proteins [5]. We explore the optoelectronic transport properties of single nanostructures to be probed by measuring the photocurrent response in an external electrical circuit. We focus on charge, energy, and heat transfer processes within the hybrid nanostructures [1-5], on excitonic optical excitations [6], as well as on so-called “ballistic” electron transport that occurs without energy relaxation [7]. In most recent experiments, we succeeded in resolving the real-time motion of photo-generated charge carriers in nanoscale circuits with a picosecond time resolution [8]. Session 2: Hybrid Nanosystems We thank our collaborators for very fruitful cooperations and the German excellence initiative via the “Nanosystems Initiative Munich (NIM)” for ﬁ nancial support.

Photosynthetic protein covalently bound to carbon nano-tubes [5].

[1] M. A. Mangold, C. Weiss, M. Calame, A. W. Holleitner, Appl. Phys. Lett. 94, 161104 (2009). [2] B. Zebli, H. A. Vieyra, I. Carmeli, A. Hartschuh, J. P. Kotthaus, A. W. Holleitner, Phys. Rev. B 79, 205402 (2009). [3] S. Thunich, L. Prechtel, D. Spirkoska, G. Abstreiter, A. Fontcuberta i Morral, A. W. Holleitner, Appl. Phys. Lett. 95, 083111 (2009). [4] C. Ruppert, S. Thunich, G. Abstreiter, A. Fontcuberta i Morral, A.W. Holleitner, and M. Betz, Nano Lett. 10 (5), 1799 (2010). [5] S. M. Kaniber, M. Brandstetter, F.C. Simmel, I. Carmeli, A.W. Holleitner, J. of the Am. Chem. Soc. 132, 2872 (2010). [6] X. P. Vögele, D. Schuh, W. Wegscheider, J. P. Kotthaus, A. W. Holleitner, Phys. Rev. Lett. 103, 126402 (2009). [7] K.-D. Hof, F.J. Kaiser, M. Stallhofer, D. Schuh, W. Wegscheider, P. Hänggi, S. Kohler, J.P. Kotthaus, A.W. Holleitner, Nano Lett. accept., http://pubs.acs.org/doi/full/10.1021/nl102068v (2010). [8] L. Prechtel, S. Manus, D. Schuh, W. Wegscheider, A.W. Holleitner, Appl. Phys. Lett. 96, 261110 (2010). Talks

18 Advances in Nanoscience - Garching 2010 A Quarter Century of Quantum Dots: From Science to Practical Implementation Yasuhiko Arakawa Hans Fischer Senior Fellow of TUM Institute for Advanced Study Institute for Nano Quantum Information Electronics, The University of Tokyo 4-6-1 Komaba, Meguro, Tokyo 153-8505 Japan [email protected]

ollowing Esaki’s pioneering work on superlattices and quantum wells, the concept of quan- Ftum dots was proposed by Arakawa and Sakaki in 1982 for application to semiconductor lasers with the theoretical prediction of temperature insensitive threshold current characteristics. Full conﬁ nement of electrons in the quantum dots has brought up unique features of artiﬁ cial atoms, such as discrete energy states and correlation effects due to spin/charging effects. This has resulted in a wide variety of experimental investigations into semiconductor physics as well as device applications. A successful demonstration of highly temperature-stable quantum dot lasers in 2004 by the University of Tokyo and Fujitsu [2] was led to the launch of a spin-off venture company called QD Lasers Corporation in 2006. In 2010, the quantum dot lasers have been delivered to a telecom commercial market. In addition to nanophotonic device applications, single or coupled

quantum dots are promising for quantum information technologies, such as single photon emit- Session 2: Hybrid Nanosystems ters and quantum-bit devices, with manipulating single photon-electron interaction and quantum entangled states based on electron spins, charges, and nuclear spins. For aiming at future establishment of “quantum mechanical engineering”, a national big project named Nano Quantum Information Electronics (NanoQuine) was started in 2006 in Japan. This is a joint project between the University of Tokyo and major electronics companies (NEC, Hi- tachi, Fujitsu, Sharp and QD laser). This project receives, as a 10 years’ project, the total budget of ~80 M$ from the government and corresponding matching funds from the companies. We started a new research center named Institute of Nano Quantum Information Electronics attached directly to the president of the University of Tokyo. The purpose of this project is to bring innovation in device and system technologies based on quantum dot and related nanoscience. The project has already attained several signiﬁ cant results such as highly temperature stable quantum dot lasers with 25 Gbps modulation, the ﬁ rst transmission experiment of quantum keys over 50 km using quantum-dot single-photon source at 1.5 μm wavelength and the highest speed operation in both p- and n-MOS organic transistors. In this presentation, prospects of quantum dot research for future innovation will be addressed including the effort of the Japanese government through the NanoQuine project. Moreover, I will also overview an additional national project, Photonics Electronics Convergence System Technology (PECST), which was selected as one of 30 projects in the framework of the program, Funding Program for World-Leading Innovative R&D on Science and Technology. We started the new project in collaboration with companies (NEC, Hitachi, Fujitsu, NTT, Oki, AIST) in March 2010, aiming at demonstrating a photonics system on LSI plat-form as well as exploring innovative technologies including Si-based light sources. The total budget is 55M$ for 4years. The WSI-TUM is also one of the collaborating members for this project. Talks

Advances in Nanoscience - Garching 2010 19 „Black Silicon“: Nanotextured Silicon Surfaces for Photovoltaics Svetoslav Koynov, Martin S. Brandt, and Martin Stutzmann Walter Schottky Institut, Technische Universität München, Garching, Germany

ffi cient anti-refl ection coatings are an important component of all high-effi ciency solar cells. EToday, mainly anisotropic etching of Si(100) surfaces or of transparent conductive oxides (for single crystalline Si and thin fi lm solar cells, respectively) as well as λ/4-Si3N -layers (for multicrystalline Si solar cells) are used in production. From a basic point of view, however, the ultimate broadband antirefl ection behavior can be achieved by a conical nanotexturing of the surface with feature sizes in the sub 100 nm range. Such a surface texture acts as an effective medium with a continuos variation of the refractive index from air to that of the bulk solid, independent of the wavelength of the incident light. As no discontinuity of the refractive index occurs, the refl ectivity of such a textured surface is essentially zero. We describe how such a texture can be realized by a fast, self-organized chemical etch in all forms of silicon (single-, multi, nano-crystalline, and amorphous) and discuss the optical and electronic properties of Session 3: Nano and Energy such surfaces, as well as their implementation in solar cells. The possibility to transfer such a texture to other surfaces (glass substrates, GaN) will also be mentioned. Talks

20 Advances in Nanoscience - Garching 2010 Role of Nanotechnology in Third Generation Photovoltaics Stephen M. Goodnick Stephen M. Goodnick and Christiana Honsberg Solar Power Laboratory, Arizona State University, Tempe, AZ 85287-9309, USA

n the present talk, the impact of nanotechnology innovation on current photovoltaic technol- Iogy trends is discussed, with a focus on the expected role that nanotechnology will have on current fi rst and second generation solar production. In particular, the trend in Si production is towards ultrathin Si, thus reducing material cost, and increasing performance. However, in order to scale Si thicknesses to micron scale dimensions requires innovations in terms of optical absorption and energy capture, which requires advancements in present cell design. Spe- cifi cally, so called ‘third generation’ nanotechnology based concepts of light trapping through nanoplasmonic arrays, carrier multiplication through up-down conversion, or multiple-exciton effects in quantum dots, intermediate bands, etc. can allow for scaling to thin dimensions while signifi cantly improving effi ciencies. Here we discuss several different approaches, including Si nanowires for reducing the effective volume of Si, through effi cient light trapping in junction nanowires, strain grown InGAs quantum dots for intermediate band applications, and Si nano- Session 3: Nano and Energy particles for multiexciton generation. Talks

Advances in Nanoscience - Garching 2010 21 Nanostructured organic and hybrid solar cells Lukas Schmidt-Mende Ludwig-Maximilians University (LMU) Munich, Dept. of Physics and Center for NanoScience (CeNS), Amalienstr. 54, 80799 Munich, Germany

orphology control is a key issue towards more efﬁ cient organic solar cells. However, it Mis difﬁ cult to achieve the desired control in purely organic materials. In this presentation several approaches towards control of nano-morphology in organic, hybrid and inorganic solar cells will be discussed. Nano-imprint methods can lead to nanostructured organic solar cells [1]. Metal-oxide nanostructures are used as template and combined with organic materials for hybrid solar cells [2]. Novel fabrication methods allow the controlled fabrication of structures in nano-meter size designed for solar cell applications. Also in inorganic solar cells the nanostructure can to increased photocurrent [3]. Recent results of the group will be discussed in this presentation. [1] G. Scarpa, A. Abdellah, A. Exner, S. Harrer, G. Penso-Blanco, W. Wiedemann, L. Schmidt-Mende, P. Lugli, IEEE Transactions on Nano- technol., 10.1109/TNANO.2010.2048433, 2010

Session 3: Nano and Energy [2] K. P. Musselman, G. J. Mulholland, A. P. Robinson, L. Schmidt-Mende, J. L. MacManus-Driscoll, Advanced Materials 2008, 20, 4470. [3] K. P. Musselman, A. Wisnet, D. C. Iza, H. C. Hesse, C. Scheu, J. L. MacManus-Driscoll, L.Schmidt-Mende, Advanced Materials 2010, DOI: 10.1002/adma.201001455 Talks

22 Advances in Nanoscience - Garching 2010 Heusler Compounds: Novel Materials for Energy Applications Claudia Felser Institute of Inorganic Chemistry, Johannes Gutenberg University Mainz, Mainz, Germany

n 1905 Fritz Heusler discovered that the compound Cu2MnAl is ferromagnetic, even though Inone of its elemental constituents are themselves magnetic. This remarkable material and its cousins, a vast collection of more than 1500 compounds, are now known as Heusler and Half Heusler compounds. Surprisingly, the properties of many of the Heuslers can be forecast simply by counting the number of their valence electrons [1]. One sub-class of more than 250 Heus ler compounds are semiconductors. Recent potential for applications are in electronic devices and green energy. Their band gaps can readily be tuned from zero to ~4 eV by changing their chemical composition. These materials have thus attracted attention as potential candidates for both solar cell and thermoelectric applications. Indeed, excellent therxcmoelectric properties have recently been demonstrated with ﬁ gure of merit higher the 1.4. [1] C. Felser, G. H. Fecher, and B. Balke, Angew. Chem. 46, 668 (2007) Session 3: Nano and Energy Talks

Advances in Nanoscience - Garching 2010 23 TiO2-Nanotubes in Energy Research Celine Rüdiger1, Silvia Leonardi1,2, Florian Wiesinger1, Odysseas Paschos1, Fabio Di Fonzo2, Andrea Li Bassi2, Ulrich Stimming1 and Julia Kunze1 1 Institute for Advanced Study (IAS) and Department of Physics E19, Technische Universität, München, Germany 2 Politecnico di Milano NEMAS - Center for NanoEngineered MAterials and Surfaces, Milano, Italy

elf-organized nanostructured oxides grown by optimized metal anodization have attracted Sremarkable interest in the past decades. Starting with the growth of nanoporous alumina [1], this type of anodic oxide ﬁ lms can nowadays be grown on various valve metals and their

alloys using dilute ﬂ uoride based electrolytes. Upon all valve metal oxides, nanotubular TiO2 on Ti [2,3] is among the most promising structures since it offers several interesting functional

properties. The growth mechanism of nanotubular TiO2 layers was investigated in glycerol/ NH4F electrolytes. At low water concentration, smooth side walls are obtained. A comparison of the length of these tubes and the charge density fl owing during the anodization process shows that in certain cases the tubes grow longer than expected i.e. with an effi ciency > 100%. This phenomenon may be explained by an oxide fl ow model [4,5,6].

Session 3: Nano and Energy While the semiconductive nature of TiO2 is crucial for many applications in ﬁ elds such as biotechnology, photo-catalysis or dye-sensitized solar cells, the limited conductivity prevents an even broader and efﬁ cient use in applications that require a fast electron transport, such as functional electrodes or electrocatalyst supports. For the use of titania as a catalyst support in electrocatalysis, it has to be made conductive and inert towards reoxidation in the electrolyte.

This can be achieved by using a carbo-thermal reduction treatment converting the TiO2 into an

oxy carbide compound (TiOxCy) that shows stable semimetallic conductivity [7].

We are currently exploring ﬂ at and nanotubular TiOxCy as support material in electrocatalysis. After the deposition of an electrocatalytically active metal, like Pt or Pd, reactions such as alcohol oxidation and oxygen reduction (ORR) will be studied. We will investigate the inﬂ uence of the metal coverage, the particle thickness and shape, and the metal oxidation state on the

catalytic activity for ORR and alcohol oxidation. The inﬂ uence of the TiOxCy support will be studied by looking at different oxygen to carbon ratios. [1] H. Masuda, K. Fukuda, Science, 268 (1995) 1644. [2] V. Zwilling, M. Aucouturier, E. Darque-Ceretti, Electrochim. Acta 45 (1999) 921. [3] J.M. Macak, H. Tsuchiya, A. Ghicov, K. Yasuda, R. Hahn, S. Bauer, P. Schmuki, COSSMS (2007). [4] S. Berger, J.M. Macak, J. Kunze, P. Schmuki, Electrochem. Solid-State Lett. 11 (2008), C37. [5] D.J. LeClere, A. Velota, P. Skeldon, G.E. Thompson, S. Berger, J. Kunze, P. Schmuki, H. Habazaki, S. Nagata, J. Electrochem. Soc. 155(9) (2008) C487-C494. [6] S. Berger, J. Kunze, P. Schmuki, D. LeClere, A. Valota, P. Skeldon, G. Thompson, Electrochim. Acta 54 (2009) 5942-5948. [6] R. Hahn, F. Schmidt-Stein, J. Salonen, S. Thiemann, Y.Y. Song, J. Kunze, V.-L. Lehto, P. Schmuki, Angewandte Chemie Int. Ed. (VIP Paper) 48 (2009) 7236. Talks

24 Advances in Nanoscience - Garching 2010 Synthetic Biology of Cell Division Petra Schwille Biophysics - Schwille Lab, Biotechnologisches Zentrum der TU Dresden (BIOTEC), Tatzberg 47-51, 01307 Dresden, Germany

n recent years, biophysics has accumulated an impressive selection of novel techniques Ito analyze biological systems with ultimate sensitivity and precision. Single molecule imaging, tracking and manipulation have enabled us to unravel biological phenomena with unprecedented analytical power, and to come closer to revealing fundamental features of biological self-organization. On the other hand, our knowledge about biological systems has in the era of genomics and proteomics become vast and impossible to fully comprehend. The power of physics has always been the reductionist approach, i.e. the possibility to deﬁ ne an appropriate subsystem simple enough to be quantitatively modeled and described, but complex enough to retain the essential features of its real counterpart. Transferring this approach into biology has so far been extremely challenging, because most “modern” biological systems usually comprise so many modules and elements, many of them still awaiting to be functionally resolved, that it is Session 4: Bio-Nanoscience a risky, and thus, often frustrating task to deﬁ ne truly essential ones. Nevertheless, the strive for identifying minimal biological systems, particularly of subcellular structures or modules, has in the past years been very successful, and crucial in vitro experiments with reduced complexity can nowadays be performed, e.g., on reconstituted cytoskeleton and membrane systems. As a particularly exciting example for the power of minimal systems, self-organization of essential proteins of the bacterial cell division machinery could be shown in a simple assay, consisting of only two protein species, an energy source, and a membrane. In the In my talk, I will discuss some recent results of our work on membrane-based systems, using single molecule optics and biological reconstitution assays. I will further discuss the perspective of assembling a minimal system to reconstitute bacterial cell division. Talks

Advances in Nanoscience - Garching 2010 25 DNA Nanotechnology for Protein Science

Hendrik Dietz Dietz Lab, Physik Department, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany

caffolded DNA Origami [1] is a molecular self-assembly method that enables folding a mul- Stiple-kilobase ‘back-bone’ DNA molecule into complex nanoscale shapes by introducing interactions between different segments on the backbone molecule. Interaction patterns are expressed by sets of synthetic ‘staple’ molecules that are added to the much longer backbone molecule. Based on this concept we have developed a general approach to the construction of custom three-dimensional shapes that can be conceptualized as creating custom-crossection bundles of DNA double helices [2] where the number, arrangement, and lengths of helices can be freely designed. We further found a way for building shapes that also twist and bend in desired ways [3]. Importantly, DNA origami retains spatial registry over each of thousands of DNA bases that are installed in a constructed shape.

Session 4: Bio-Nanoscience Molecular self-assembly with DNA origami thus affords truly unique positional control on the nanoscale. Our current efforts are centered on taking advantage of DNA origami for building nanoscale “gadgets” for applications in the molecular biosciences. One of our main goals is to develop a toolbox for the quantitative study of protein-protein and protein-DNA interactions on the single molecule level. [1] PWK Rothemund: NATURE 2006 [2] SM Douglas, H Dietz, T Liedl, B Hogberg, F Graf, W Shih: NATURE 2009 [3] H Dietz, SM Douglas, W Shih: SCIENCE 2009 Talks

26 Advances in Nanoscience - Garching 2010 The Bio-Electronic Synapse – Fusing Electronics with Molecular Biology Arbel Artzy-Schnirmana,b,c, Elad Broda,c, Dan Blatdd, Rami Fishlera,c, Dori Gertmanb, Ravit Orenb, Tova Waksd, Yoram Reitera,b, Itai Benhare, Zelig Eshhard, Uri Sivana,c a The Russell Berrie Nanotechnology Institute, b Biology, Technion – Israel Inst. of Technology, Haifa, Israel c Physics, Technion – Israel Inst. of Technology, Haifa, Israel d Biology, Weizmann Inst. of Science, Rehovot, Israel e Biotechnology, Tel Aviv University, Tel Aviv, Israel

anmade electronics and living systems are foreign to each other in all aspects. They are Mconstructed from dissimilar materials using different strategies, employ different charge carriers, and use distinctively different logic for their computation. The fusing of these two vast ﬁ elds therefore poses major conceptual and practical challenges but at the same time holds great promise. Learning a lesson from biology where functional interfaces are realized through mutual recognition of two molecules we propose and demonstrate a generic approach to the integration of electronics with biology. In our bio-electronic synapse one of the recognizing molecules is replaced by an electronic device having two states while for the other molecule we choose an antibody selected in-vitro to discriminate between the two electronic states. Application of 0.6V to the device sets it in the “on” state where the antibody binds the device. A subsequent application of -0.6V to the same device turns it to the “off” state where the anti- Session 4: Bio-Nanoscience body detaches from the device. The power of such an electrical control over recognition will be demonstrated by its implementation to the control of T-cell activation by ﬂ ipping an electrical switch. If time allows, the physics underlying the operation of our bio-electronic synapse will be explained. Talks

Advances in Nanoscience - Garching 2010 27 Molecular Interactions on Dynamically Actuated Surfaces and in Artiﬁ cial Nanopores Ulrich Rant Walter Schottky Institute & Institute for Advanced Study, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany

will present two methods to analyze molecular interactions which rely on functionalities aris- I ing from nano-scale dimensions. The ‘switchSENSE’ principle is based on an electrically actuated bio-interface. DNA molecules are driven to oscillate (switch their conformation) on microelectrodes through the application of AC potentials. The switching behavior serves as a universal parameter to infer the molecular state of the bio-interface and permits to detect the binding of target molecules (proteins or nucleic acids) to the layer. In addition to the quantitative analysis of ‘classical’ interaction parameters like afﬁ nity constants or association/dissociation rates, previously inaccessible information about the target molecule size and shape are obtained from a molecular dynamics analysis. The implications of the switching dynamics measurement for a novel type of on-chip

Session 4: Bio-Nanoscience protein analysis will be discussed, in particular with respect to the engineering of antibodies. Moreover, the application of the switchSENSE principle for the detection of a cancer associated single nucleotide mutation in the p53 gene is demonstrated. Artifi cially engineered nanopores in solid state membranes constitute versatile and robust devices to examine nano-scale objects. Single molecules leave a characteristic footprint in the trans-membrane current when passing a single pore of nanometer dimensions. By placing individual molecular receptors inside the pore we are able to study the interaction time of binding partners one-by-one. As a paradigm for stochastic sensing, we exemplarily analyze single protein interactions at hand of the NTA/His-tag affi nity system and demonstrate how the action of a competitive binder affects the association and dissociation constants. Moreover, we ad- vance the nanopore concept by introducing the pore-cavity-pore device, which consists of two nanopores forming the in- and outlets to a femto-liter volume, and demonstrate the electrically controlled injection, storage, and ejection of individual nano-objects. Furthermore, we employ the pore-cavity-pore structure to obtain experimental single-particle data on fundamental problems like confi ned diffusion and the escape of nano-objects across entropy barriers. Talks

28 Advances in Nanoscience - Garching 2010 Stochastic gene expression and the decisive role of noise in microbial genetic networks Joachim O. Rädler Fakultät für Physik, Ludwig-Maximilians-Universität München, Geschwister-Scholl-Platz 1, 80539 München, Germany

olecular fl uctuations can cause signifi cant cell-to-cell variations in the phenotype of ge- Mnetically identical bacterial populations. Gene regulatory networks, which determine the cellular response to environmental signals, are subdued to noise at the molecular concentration levels leading to broadened distribution in expression timing or in other cases bimodal expression profi les. We use green fl uorescent protein to record the protein expression at the single-cell level for the arabinose utilization system of E.coli and the quorum sensing system of Putida. The experimental outcomes are compared to stochastic models of the underlying gene-regulatory networks. Session 4: Bio-Nanoscience Talks

Advances in Nanoscience - Garching 2010 29 Nanoscale structures and molecular devices made from DNA F. Simmel Biomolecular Systems and Bionanotechnology, Physics Department and ZNN/WSI, Technische Universität München, Am Coulombwall 4a, D-85748 Garching, Germany

he sequence-dependent molecular recognition properties of nucleic acid molecules such Tas DNA and RNA can be utilized for the programmable assembly of molecular nanostructures and nanodevices. For instance, the recently developed “DNA origami technique” enables molecular assembly of two- and even three-dimensional nano-objects with almost arbitrary shape. Such structures can be used as a scaffold for the positioning of other nanoscale objects such as small molecules, nanoparticles or proteins into speciﬁ c arrangements. In addition to several examples for such assemblies, we will show how recently developed super-resolution microscopy techniques such as Blink Microscopy or STORM allow for an optical characterization of these sub- wavelength structures.

Session 4: Bio-Nanoscience In addition to the realization of static nanostructures, one of the visions in the ﬁ eld of molecular nanotechnology is the realization of nanoscale “machines” inspired by the dynamic molecular assemblies found in biological systems. In fact, DNA can be utilized to construct also dynamic nanostructures that are controllably driven through a series of distinct conformational states. One of the major goals in this area is the operation of artiﬁ cial molecular devices in biological systems, where they may act as sensors or actuators in vivo. Talks

30 Advances in Nanoscience - Garching 2010 POSTER PRESENTATIONS

Quantum Nanosystems

High frequency tuning of photonic Spin-Orbit coupling effects in the quantum crystal nanocavity modes using surface oscillatory magnetization of asymmetric acoustic waves ...... 33 InGaAs/InP quantum wells ...... 40 D. A. Fuhrmann B. Rupprecht

Electrostatic control of the charge state Dynamic carrier injection into individual of nitrogen-vacancy centers in diamond ...... 34 self-assembled quantum dots controlled M. V. Hauf by surface acoustic waves ...... 41 F. J. R. Schülein Growth kinetics in position-controlled and catalyst-free InAs nanowire arrays Single material band gap engineering on Si (111) grown by selective area in GaAs nanowires ...... 42 molecular beam epitaxy ...... 35 D. Spirkoska S. Hertenberger Spatially resolved ﬂ ow of ballistic electrons Raman spectroscopy and electrical transport measured by quantized photocurrent investigations of InAs nanowires grown spectroscopy ...... 43 on Si (111) by molecular beam epitaxy ...... 36 M. Stallhofer N. Hörmann Towards nuclear spin free qubits based Non-resonant feeding of photonic on Si/SiGe heterostructures ...... 44 crystal nanocavity modes by quantum A. Wild dot multi-exciton states ...... 37 A. Laucht Spatially resolved polarization dependent Raman spectroscopy and pressure induced Ultrafast photocurrent response of resonant Raman on GaAs nanowires ...... 45 freely suspended graphene ...... 38 I. Zardo L. Prechtel

Autocatalytic growth of GaAs nanowires on Si (111) by molecular beam epitaxy using different SiO2 templates ...... 39 D. Rudolph Poster Presentations Hybrid Nanosystems

Organic Functionalization of Spin wave resonances in ferromagnetic thin Group IV-Semiconductors ...... 46 ﬁ lms prepared via atomic layer deposition ...... 52 M. Auernhammer R. Huber

Organized growth of bifunctional oligoarenes A Bose-Einstein condensate coupled and organometallic complex linkers on to a micromechanical oscillators ...... 53 semiconductor nanoscale devices ...... 47 D. Hunger A. Cattani-Scholz Optomechanical coupling of ultracold Optoelectronic properties of two-dimensional atoms and a membrane ...... 54 gold nanoparticle arrays ...... 48 M. Korppi B. Dirks Photoconductance of a submicron Spin waves in individual and periodic permalloy oxidized line in surface conductive single nanostructures ...... 49 crystalline diamond ...... 55 G. Duerr M. Seifert

Graphene solution-gated ﬁ eld effect transistor Polymer Brushes on Graphene ...... 56 arrays for sensing applications ...... 50 M. Steenackers L. Hess Spatially resolved optoelectronic measurements AlGaN/GaN semiconductor biosensors of organic thin ﬁ lm transistors ...... 57 for applications in radiation biophysics ...... 51 C. Westermeier M. Hofstetter

Advances in Nanoscience - Garching 2010 31 POSTER PRESENTATIONS

Nano and Energy

Compact and Nanotubular TiO2 Investigation of different interface in Energy Research ...... 58 morphologies in organic solar cells ...... 60 C. Rüdiger W. Wiedemann

Investigation of the thermal conductivity of GaAs nanowires by Raman spectroscopy combined with laser heating...... 59 M. Soini

Bio-Nanoscience

Regulation of Cellular Signaling Pathways A Thermal Trap for DNA Replication ...... 69 by Spatial Organization of Molecular C. B. Mast Extracellular Matrix Cues ...... 61 H. Böhm Biochemistry on a leash ...... 70 M. Schickinger Expanding the Scope of Single Molecule FRET with DNA Origami ...... 62 Synthetic Assembly of Non-Peptidic Ligands for Constructing α β - and α β -Integrin based Fo- C. Castro v 3 5 1 cal Adhesions ...... 71 Sensing applications of GaN-based devices...... 63 A. Schwede J. D. Howgate Single Molecules as Energy, Force, Organic Thin-Film Transistors for Applications Friction and Structure Sensors ...... 72 in Radiation Biophysics ...... 64 F. Stetter A.-L. Idzko Single-Molecule Cut and Paste for DNA Origami as a Molecular Platform Functional Assembly ...... 73 for Bionanotechnology ...... 65 M. Strackharn R. Jungmann Analysis of proteins on a chip with Towards studying equilibrium unbinding/ the switchSENSE platform ...... 74 binding transitions of single protein complexes R. Strasser under force – enabled by DNA Origami ...... 66 F. Kilchherr Protein Binding Assays in Biological Liquids using Microscale Thermophoresis ...... 75 Fabrication and Electrical Characterization C. J. Wienken of a Pore-Cavity-Pore Device ...... 67 M. Langecker Formation of Nanoparticle Structures with a Combination of Protein and DNA Linkers ...... 76 DNA origami supports for the analysis V. B. Zon of complex samples by singe-particle electron microscopy ...... 68 T. G. Martin Poster Presentations Poster

32 Advances in Nanoscience - Garching 2010 High frequency tuning of photonic crystal nanocavity modes using surface acoustic waves D. A. Fuhrmann1,2, S. M. Thon3, H. Kim2, D. Bouwmeester3,4, P. M. Petroff2, A. Wixforth1 and H. J. Krenner1 1 Lehrstuhl für Experimentalphysik I, Universität Augsburg, Universitätsstr. 1, 86159 Augsburg, Germany 2 Materials Department, University of California, Santa Barbara, CA 93106, USA 3 Physics Department, University of California, Santa Barbara, CA 93106, USA 4 Huygens Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands

e propose and demonstrate high frequency dynamic modulation of localized optical modes Wof photonic crystal membrane (PCM) defect nanocavities employing surface acoustic waves (SAWs). The mechanical deformation induced by SAW distorts the PCM periodicity and gives rise to pronounced modulation of the nanocavity mode. We probe the cavity line as a function of the local phase of the SAW and resolve a dynamic and periodic modulation with tuning speeds >1.5 GHz. We resolve amplitudes ∆λC > 2 nm corresponding to > 15 cavity lin- ewidths for the cavities (Q > 7000) studied without signiﬁ cant degradation of the quality factor. These observations are found in excellent agreement with FDTD simulations for the same cavity design and realistic amplitudes < 2 nm. Our calculations show no resolvable redistribution of the ﬁ eld distribution of the cavity mode making our technique attractive for both solid state Quantum Nanosystems cQED and cavity optomechanical systems. Poster Presentations

Advances in Nanoscience - Garching 2010 33 Electrostatic control of the charge state of nitrogen-vacancy centers in diamond M.V. Hauf1, M. Dankerl1, M. Stutzmann1, J.A. Garrido1, B. Grotz2, F. Reinhard2, B. Naydenov2, J. Wrachtrup2 and F. Jelezko2 1 Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany 2 3. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany

itrogen vacancy defects (NV) in the diamond lattice have been extensively studied in the Npast for several reasons. NV centers can act as non-bleachable single photon emitters in the visible range [1]. Furthermore, they exhibit extraordinary spin coherence times of T2 = 1.8 ms at room temperature, which makes them promising candidates for realizing quantum computation and communication. In this context it is of great interest to achieve electrostatic control over the charge state of the NV in diamond. We have shown that by changing the surface termination from oxygen to hydrogen, the fl uorescence of the negatively charged NV (NV-) can be suppressed. This effect is attributed to the band bending that occurs at hydrogen-terminated diamond surfaces according to the transfer- Quantum Nanosystems doping model [2]. A two-dimensional hole gas is formed at the surface which leads to a deple- tion from electrons and therefore the NV centers are expected to be discharged to the neutral state NV0 or a positively charged state NV+. This is confi rmed by observing the quenching of the fl uorescence of NV centers located under the hydrogenated diamond surface. Furthermore, the charge in the subsurface region of hydrogen-terminated diamond can be controlled by using an electrolyte gate electrode. We use this effect to achieve for the fi rst time an electronic control of the charge state of the NV centers in diamond, allowing us to switch the fl uorescence of NV centers on and off. Self-consistent numerical simulations, where the single-band effective mass Schrödinger equation is solved and coupled to the Poisson equation via the charge density, can reproduce the surface band bending and the concurrent control of the NV-fl uorescence. [1] T. Gaebel et al, Appl. Phys. B 82, 2 (2005) [2] F. Maier, M. Riedel, B. Mantel, J. Ristein, and L. Ley, Phys. Rev. Lett. 85, 16 (2000) Poster Presentations Poster

34 Advances in Nanoscience - Garching 2010 Growth kinetics in position-controlled and catalyst-free InAs nanowire arrays on Si (111) grown by selective area molecular beam epitaxy S. Hertenberger*, D. Rudolph, M. Bichler, J. J. Finley, G. Abstreiter and G. Koblmüller Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany Corresponding author e-mail: [email protected]

e report self-induced selective area epi- Wtaxy (SAE) of well-oriented, free-standing InAs (111) nanowires (NWs) on Si (111) substrates by solid-source MBE. Utilizing lithographically defi ned SiO2 nanomasks on Si (111) with periodic hole patterns of specifi c diameters and pitches (Fig. 1a), SAE of InAs NWs was performed under As-rich growth conditions in a completely catalystfree fashion. Adjustment of the proper substrate tem- Quantum Nanosystems perature was necessary to achieve highly selective growth, where InAs NWs nucleated only in the predefi ned holes with very high Fig. 1 (a) AFM image of a patterned SiO2/Si(111) yields of around 90 % (ratio of vertically grown substrate. The diameter of the holes is 80 nm and the nanowires versus total number of holes) (Fig. hole-to-hole distance (pitch) 2 μm. (b) SEM image 1b). of selectively grown InAs NWs on the template described in (a) with an As-BEP of 2.6*10-6 mbar. (c,d) Based on this scheme, we showed that the InAs NWs grown with a higher As-BEP of 5.2*10-6 yield of vertically ordered NWs was indepen- mbar and a pitch of 500 nm and 250 nm, respec- dent of the interwire distance (pitch) and the tively. initial growth stages as opposed to previous

observations by chemical vapor phase growth methods. Poster Presentations Furthermore, we investigated three distinct growth series, i.e., by variation of (i) growth temperature at fi xed III/V-ratio, (ii) growth time for different pitches (interwire distance) and (iii) III/V-ratio at fi xed growth time, to derive the underlying growth kinetics in MBE–grown SAE InAs NWs. Figs. 1c,d show representative electron micrographs of InAs NWs grown from growth series (iii) with two different pitches (i.e., 500 nm - Fig. 1c and 250 nm pitch - Fig. 1d) and an As-fl ux twice as high as compared to NWs grown in Fig. 1b. Most interesting, signifi cant size variation of the NWs was found depending critically on the pitch and growth time. Two growth regimes were identifi ed – (i) a competitive growth regime with shorter and thinner nanowires for narrow interwire distances, and (ii) a diffusion-limited growth regime for wider distances providing good estimates for the surface diffusion lengths. Surprisingly, despite these size-dependent effects the nanowire geometries remained unal- tered with uniform, al-most non-tapered morphologies even over large variation in nanowire density (~mid–106-109 cm-2 range). In terms of material properties, X–ray diffraction further revealed that the NW arrays were pre- dominantly single-crystalline zincblende and further confi rmed the vertical (111) directionality with low crystal tilt by rocking curve widths ( scans) as low as ~0.6 °. These crystal properties are further corroborated by TEM and PL measurements and will also be presented. Our fi ndings demonstrate the capability to precisely tailor the position and size of well-oriented III–V semicon-ductor NWs through non-catalytic MBE selective area growth and provide an important step toward fully integrated, uniform vertical III–V nanowire array-on-Si devices.

Advances in Nanoscience - Garching 2010 35 Raman spectroscopy and electrical transport investigations of InAs nanowires grown on Si (111) by molecular beam epitaxy N. Hörmann, E. Forster, S. Hertenberger, I. Zardo, D. Spirkoska, G. Koblmüller and G. Abstreiter Walter Schottky Institut, Physik Department, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany Corresponding author e-mail: [email protected]

II–V semiconductor nanowires (NWs) directly grown on Si substrate have gained a lot of Iinterest in recent years, due to the potential for low-defect density high-performance nanostructure devices on Si platform. Also, as a result of their low dimensionality they exhibit peculiar physical properties, very different from bulk materials. The epitaxial growth of InAs NWs on Si (111) by ultra-high purity molecular beam epitaxy (MBE) was recently demonstrated in our group [1,2] using different substrate preparation and templates. Morphological parameters such as NW length and diameter were infl uenced strongly not only by growth conditions, but also substrate preparation resulting in either self-assembled or site-selectively grown NWs. We present here investigations of the lattice dynamics of such InAs NWs by Raman spectros- Quantum Nanosystems copy, which has proved to be a powerful tool to investigate the structural properties in a non- destructive way. Furthermore, we analyzed the electrical transport properties in specifi c sets of single NWs. Raman investigations performed on ensembles of as-grown NWs showed an unexpected downshift of the transverse optical (TO) phonon peak compared to the InAs bulk reference sample [3], as opposed to a slightly upward shifted longitudi- nal (LO) phonon peak (Fig. 1). Size effects were found to be negligible for the investigated range of NW diameters (~50 – 220 nm). All measurements were done excluding heating artifacts and phonon-plasmon coupling at the e-rich InAs surface. Also, we have identifi ed the crystalline quality in dependence of growth conditions and substrate preparation method, based Figure 1 Raman spectra of bulk on the full width at half maximum values for the TO and LO InAs and an InAs nanowire with phonon peak widths. downshifted TO. Polarization dependent Raman spectroscopy experiments were also carried out on single InAs NWs. We were able to resolve at least two different TO-like Raman peaks, i.e., a downshifted peak and another one near the bulk TO position. The observed split was induced by breaking of cubic symmetry, with several possible underlying effects being discussed in detail. For electrical transport measurements, the InAs NWs were contacted using Ni/Au metallizat¬ion. Room temperature I-V characterization showed a linear Ohmic behavior with total resistances in the range of ~1.5 – 50 kΩ. Back-gate dependent measurements identifi ed an n-type behavior as expected due to intrinsic bulk electron conductivity and surface electrons arising from strong Fermi level pinning at the surface. Subsequently the NWs were cooled down to 4.2 K and 1.4 K. The I-V characteristics remained linear, but the measurements showed a slight increase of the resistance. Furthermore, a magnetic fi eld perpendicular to the NW growth axis was applied and magneto-resistance measurements were performed, which will be discussed in detail. [1] G. Koblmüller, S. Hertenberger, K. Vizbaras, M. Bichler, F. Bao, J.-P. Zhang, and G. Abstreiter, Nanotechnology 21, 365602 (2010). [2] S. Hertenberger, D. Rudolph, M. Bichler, J. J. Finley, G. Abstreiter, and G. Koblmüller, submitted to JAP (2010). [3] R. Carles, N. Saint-Cricq, J. B. Renucci, M.A. Renucci, and A. Zwick, Phys. Rev. B, 22, page 4804 (1980). Poster Presentations Poster

36 Advances in Nanoscience - Garching 2010 Non-resonant feeding of photonic crystal nanocavity modes by quantum dot multi-exciton states A. Laucht1, A. Mohtashami1, M. Bichler1, M. Kaniber1 and J. J. Finley1 1 Walter Schottky Institut, TU München, Am Coulombwall 3, D-85748 Garching, Germany E-mail: [email protected]

hotoluminescence studies of photonic crystal defect nanocavi- Pties containing single quantum dots typically reveal intense, highly correlated emission from the cavity mode, even when the discrete quantum dot transitions and mode are spectrally detuned (|∆E|>20 meV) [1,2,3]. Here, we show experimentally that such off- resonance emission from the cavity mode arises from multi exciton- continuum transitions during the cascaded emission from the dot. Experimentally, we track the temporal evolution of the emission spectrum and fi nd that the mode emission is temporally correlated with quantum dot multi-exciton emission but becomes much weak- Quantum Nanosystems er after the population in the dot reduces towards the single exciton level [4]. Our results lend further support to recent pump power dependent cross-correlation measurements [5] identifying such multi exciton-continuum transitions as being responsible for the emission from the cavity mode. Figure – Typical time resolved emission spectra recorded Photon cross-correlation measurements between the quantum dot from a single dot nanocavity and the far detuned cavity mode unambiguously prove that the cav- with |∆E|~16meV. Strong emis- ity mode is fed by the same quantum dot. For small dot-cavity detun- sion is observed from the cavity ings (|∆E|<3 meV), acoustic phonon mediated dot - cavity coupling mode in the fi rst 1-2ns, becom- gives rise to cavity emission [6, 7]. However, for larger detunings ing much weaker as the excitation level in the system reduces acoustic phonon mediated coupling becomes ineffective and the Poster Presentations toward the single exciton level. cavity mode emission stems from optical transitions between higher excited multiexciton states and an energetically lower quasi continuum of multi exciton states [4]. This naturally results in several photons per excitation cycle at the cavity mode frequency, manifest- ing itself as Poissonian statistics of the cavity mode. At the same time, strong cross correlations exist in the conditional emission statistics of the quantum dot and cavity. These apparently contradictory observations are fully explained by our measurements. Time resolved luminescence spectra with sub nanosecond resolution show that the cavity mode is temporally correlated with the p-shell emission from the quantum dot (see fi gure). In contrast, the s-shell emission is delayed due to the cascaded emission process and only weak cavity mode emission is observed for low excitation levels. Power dependent time-resolved measurements lend further support to our interpretation and allow us to extract quantitative information about the strength of the off-resonant coupling. An understanding of this non-resonant dot-cavity coupling is of the utmost importance for low threshold quantum dot nano lasers, where it is expected to be the dominant source of optical gain. We gratefully acknowledge fi nancial support of the DFG via SFB 631 B3, and the Nanosystems Initiative Munich. [1] Hennessy K, Badolato A, Winger M, Gerace D, Atatür M, Gulde S, Fält S, Hu E L, and Imamoglu A, Nature 445, 896 (2007) [2] Press D, Götzinger S, Reitzenstein S, Hofmann C, Löffl er A, Kamp M, Forchel A, and Yamamoto Y, Phys. Rev. Lett. 98, 117402 (2007) [3] Kaniber M, Laucht A, Neumann A, Villas-Bôas J M, Bichler M, Amann M-C, and Finley J J, Phys. Rev. B 77, 161303(R) (2007) [4] Laucht A, Kaniber M, Mohtashami A, Hauke N, Bichler M, and Finley J J, in course of preparation (2009) [5] Winger M, Volz T, Tarel G, Porolan S, Badolato A, Hennessy K J, Hu E L, Beverator A, Finley J, Savona V, and Imamoglu A, Phys. Rev. Lett 103, 207403 (2009) [6] Hohenester U, Laucht A, Kaniber M, Hauke N, Neumann, A, Mohtashami A, Seliger M, Bichler M, Finley J J, Phys. Rev. B 80, 201311(R) (2009) [7] Suffczynski J, Dousse A, Gauthron K, Lemaître A, Sagnes I, Lanco L, Block J, Voisin P, and Senellart P, Phys. Rev. Lett. 103, 027401 (2009)

Advances in Nanoscience - Garching 2010 37 Ultrafast photocurrent response of freely suspended graphene L. Prechtel1, L. Song2, D. Schuh3, W. Wegscheider3 and A.W. Holleitner1 1 Walter Schottky Institut and Physik-Department, Technische Universität München, 85748 Garching, Germany. 2 Center for NanoScience (CeNS), Ludwig-Maximilians-University, Geschwister-Scholl-Platz 1, 80539 Munich, Germany. 3 Institut für Angewandte und Experimentelle Physik II, University Regensburg, Universitätsstrasse 31, 93040 Regensburg, Germany

ecently, photocurrent generation at the interface between a mono- and a bi-layer of gra- Rphene has been attributed to the photo-thermoelectric effect [1]. Even though there are indications that this effect is also accountable for the photocurrent generation at a graphene- metal interface, there is still debate whether intrinsic fi elds (similar to those in Schottky-contacts [2]) are separating the optically excited charge carriers. We address these questions by a novel ultrafast photocurrent spectroscopy [3], which is based on a common pump-probe technique [4]. The experimental setup with a picosecond time-resolution will be introduced, and fi rst results of the time-resolved photocurrent of freely suspended graphene will be shown. We will discuss both the photo-thermoelectric effect and intrinsic fi elds Quantum Nanosystems at graphene-metal interfaces, as well as charge carrier relaxation effects by THz-generation within the graphene. We acknowledge fi nancial support by the DFG excellence initiative “Nanosystems Initiative Munich” (NIM), the DFG project HO 3324/2 and Ho 3324/4, and the Center for NanoScience (CeNS) in Munich. 1. X. Xu, N. M. Gabor, J. S. Alden, A. M. van der Zande, and P. L. McEuen, Nano Lett. 10, 562-566 (2010). 2. S. Thunich, L. Prechtel, D. Spirkoska, G. Abstreiter, A. Fontcuberta i Morral, and A. W. Holleitner, Appl. Phys. Lett. 95, 083111 (2009). 3. L. Prechtel, S. Manus, D. Schuh, W. Wegscheider and A. W. Holleitner, Appl. Phys. Lett. 96, 261110 (2010). 4. D.H. Auston, IEEE J-QE 19, 639 (1983). Poster Presentations Poster

38 Advances in Nanoscience - Garching 2010 Autocatalytic growth of GaAs nanowires on Si (111) by molecular beam epitaxy using different SiO2 templates Daniel Rudolph1, Simon Hertenberger1, Xiaodong Wang1,2, Watcharapong Paosangthong1, Max Bichler1, Gerhard Abstreiter1, Jonathan J. Finley1 and Gregor Koblmüller1 1 Walter Schottky Institut, Technische Universität München, Garching, Germany; and 2 Pohl Institute of Solid State Physics, Tongji University, Shanghai, P. R. China Corresponding author e-mail: [email protected]

ue to their peculiar geometry semiconductor nanowires (NWs) are highly promising for Dthe realization of future optoelectronic and quantum devices. The enhanced lateral strain relaxation allows the heteroepitaxial integration of highly lattice–mismatched systems, such as III-V semicon-ductor NWs, into established silicon (Si) technologies. However, the growth of high quality GaAs NWs with low defect densities, low impurity incorporation and superior electronic properties re-mains a major challenge since GaAs NWs are mostly grown by vapor- liquid-solid (VLS) processes using foreign catalysts, such as gold (Au). Au forms unwanted deep level traps in semiconductors and, thus, a self-catalyzed Ga-assisted VLS growth method was developed at our institute to grow gold-free GaAs NWs on GaAs substrates [1,2]. In this study, we investigated the autocatalytic growth of GaAs NWs on Si (111) grown by ultra– Quantum Nanosystems high purity solid source MBE. Three different kinds of substrate templates were used, namely

Si (111) coated with (a) an ultrathin layer of amorphous SiOx, (b) an ultrathin layer (~2nm) of thermal SiO2, and (c) a layer of thermal SiO2 with periodic hole patterns deﬁ ned by electron beam lithogra-phy and reactive ion etching (RIE). Scanning electron microscopy (SEM) con- ﬁ rmed that growth on the former two substrates resulted in random self-assembled formation of vertical GaAs NWs along the <111> direction with an average area density of ~108cm-2, while the latter resulted in site-selective growth of NWs [cf. Fig. 1(a)] with a predetermined area-density (107–108cm ). For the site–selectively grown NWs we have further investigated the effect of growth temperature and V/III ratio on the vertical NW growth yield and growth selectivity. The results indicate a narrow growth window for optimum NW growth.

SEM images revealed a clear droplet at the apex Poster Presentations of the NWs indicating that growth is mediated by the VLS mechanism. This was confi rmed by in-situ studies of the nucleation dynamics using refl ection high energy electron diffraction (RHEED). The time evolution of the RHEED Bragg spot intensity [Fig. 1(b)] revealed a pronounced intensity decrease and delay of NW growth with respect to the exposure to the Ga fl ux. This delay was found to depend on the V/III ratio and was attributed to the initial for- Figure 1 (a) SEM image of a GaAs NW grown site- mation of Ga droplets on the substrate. selectively on Si(111) using a patterned SiO2 mask, (b) Time evolution of RHEED intensity shows a de- The structural quality of the grown GaAs NWs lay between exposure to Ga and NW growth. was investigated by high resolution x-ray diffraction (HRXRD). The epitaxial relationship between NWs and Si substrate was confi rmed and the dominant refl ections were found for zinc blende (ZB) (111) GaAs (2θ=27.3°) and Si (111) (2θ=28.4°). Optical characterization of single NWs via photoluminescence spectroscopy revealed further information about the crystal structure: For high V/III ratio (~5) a pure ZB structure was found, while for lower V/III ratio (<2) a mixed crystal structure consisting of ZB and wurtzite phases was observed. This is in good agreement with earlier fi ndings for GaAs NWs grown on GaAs substrate [3]. [1] A. Fontcuberta i Morral et al., Appl. Phys. Lett. 92, 063112 (2008) [2] C. Colombo et al., Phys. Rev. B 77, 155326 (2008) [3] D. Spirkoska et al., Phys. Rev. B 80, 245325 (2009) Advances in Nanoscience - Garching 2010 39 Spin-Orbit coupling effects in the quantum oscillatory magnetization of asymmetric InGaAs/InP quantum wells B. Rupprecht1,*, Ch. Heyn2, H. Hardtdegen3, Th. Schäpers3, M.A. Wilde1 and D. Grundler1 1 Lehrstuhl für Physik funktionaler Schichtsysteme, Physik Department, Technische Universität München, James-Franck-Straße 1, D-85747 Garching bei München, Germany 2 Institute of Applied Physics, Jungiusstraße 11, D-20355 Hamburg, Germany 3 Institute for Bio- and Nanosystems (IBN-1) and JARA Jülich-Aachen Research Alliance, Research Centre Jülich GmbH, D-52425 Jülich, Germany * B. Rupprecht, e-mail: [email protected], Tel: +49-89-289-12409, Fax: +49-89-289-12414

n 1984, Bychkov and Rashba proposed in a semi- Inal paper [1] to measure the magnetic suscepti- bility and the de Haas-van Alphen (dHvA) effect to observe and quantify the spin splitting induced by spin-orbit interaction (SOI) in a structure inver- sion asymmetric two-dimensional electron system (2DES). At low temperature, the magnetization M = -∂U/∂B reﬂ ects in particular the evolution of the ground state energy U with the magnetic ﬁ eld B. For

Quantum Nanosystems over two decades, the predicted beating pattern in the quantum oscillatory behavior of M has not been observed experimentally due to the experimental Fig. 1: Magnetization measured at 0.03 K (symbols), compared to theoretical modeling challenge posed by the detection of the small mag- (line). netic moment associated with the low number of charge carriers. Instead, beating patterns in the magnetoresistance R(B) of a 2DES were evaluated to explore Rashba type SOI [2]. Recently, cantilever magnetometers using the torque τ = M × B have been proven to be very powerful to study 2DES magnetization [3,4]. The beating pattern in M(B) was detected for a high-mobility 2DES in an AlGaAs/GaAs heterostructure. High tilt angles δ between the sample normal and the external fi eld were used to enhance the torque [5]. Here, we report the experimental observation of SOI induced beating patterns in M in a nearly perpendicular magnetic fi eld B using cantilevers. We address M of a 2DES in asymmetric InGaAs/InP quantum wells [6]. We observe a pronounced beating pattern below 1 T. The magnetization data allow for a quantitative modeling based on the theory outlined in Ref. [7]. By this means we extract the Rashba coeffi cient αR as well as the band structure parameters such as the effective mass m*, Lande factor g* and the Landau level broadening Γ. In particular the full fi eld dependence of the total spin splitting γ(B) is obtained. This goes beyond the evaluation of γ from beat nodes in R(B) where only special fi eld positions are addressed. We will compare our results with simulations where we consider SOI in, both, perpendicular and tilted fi elds. We thank D. Heitmann for continuous support and K. Groth for technical help. We gratefully acknowledge fi nancial support by the DFG via the German Excellence Cluster “Nanosystems Ini- tiative Munich (NIM)” as well as the SPP 1285 Halbleiter-Spintronik via Grant No. GR1640/3. [1] Y. A. Bychkov and E. I. Rashba, J. Phys. C 17, 6039 (1984) [2] J. Nitta, T. Akazaki, H. Takayanagi, and T. Enoki, Phys. Rev. Lett. 78, 1335 (1997) [3] M.A. Wilde, J.I. Sprinborn, O. Rösler, N. Ruhe, M.P. Schwarz, D. Heitmann, and D. Grundler, Phys. Stat. Sol. (b) 245, 344 (2008) [4] A.C. Bleszynski-Jayich, W.E. Shanks, B. Peaudecerf, E. Ginossar, F. von Oppen, L. Glazman, J.G.E. Harris, Science 326, 272 (2009) [5] M. A. Wilde, D. Reuter, Ch. Heyn, A. D. Wieck, and D. Grundler, Phys. Rev. B 79, 125330 (2009) [6] V.A. Guzenko, Th. Schäpers, and H. Hardtdegen, Phys. Rev. B 76, 165301 (2007) [7] W. Zawadzki, P. Pfeffer, Physica E 13, 533-537 (2002) Poster Presentations Poster

40 Advances in Nanoscience - Garching 2010 Dynamic carrier injection into individual self-assembled quantum dots controlled by surface acoustic waves Florian J.R. Schülein1, Dirk Reuter2, Andreas D. Wieck2, Achim Wixforth1 and Hubert J. Krenner1 1 Lehrstuhl für Experimentalphysik I, Universität Augsburg, Universitätsstraße 1, 86159 Augsburg, Germany 2 Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum, Germany

e investigate the emission of single In(Ga)As/GaAs quantum dots (QDs) under the infl u- Wence of surface acoustic waves (SAWs). Carriers are generated by a pulsed diode laser (t < 100 ps) actively phase locked to the SAW. The SAW (f = 490 MHz) induces a switching of the QD emission from one single peak without SAW to three characteristic emission lines in the time-integrated spectrum with a SAW applied (cf. Fig 1(a)) [1]. By tuning the relative phase between laser excitation pulse and SAW, we observe a pronounced intensity modulation of these three peaks with the fundamental period of the SAW (cf. Fig 1(b)) explained by acoustically driven carrier injection and conveyance which is less effi cient for holes. In addition, we observe a weaker modulation with the double period explained by electron tunneling out of the QD (two maxima per cycle) triggered by strong piezoelectric fi elds induced by the SAW. Quantum Nanosystems [1] S. Völk et al., Nano Letters 10 3399-3407 (2010), doi:10.1021/nl1013053 Poster Presentations

Advances in Nanoscience - Garching 2010 41 Single material band gap engineering in GaAs nanowires D. Spirkoska1,*, A. Efros2, S. Conesa-Boj3, J. Arbiol3, J. R. Morante3, A. Fontcuberta i Morral1,4 and G. Abstreiter1 1 Walter Schottky Institut, Technische Universität München, 85748, Garching, Germany 2 Naval Research Laboratory, Washington, DC 20375, USA 3 TEM-MAT, Servies Cientiﬁ cotècnics, Universitat de Barcelona, Barcelona, CAT, Spain 4 Laboratoire des Matériaux Semiconducteurs, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland * D. Spirkoska, e-mail: [email protected], Tel: +49-89-289-13873, Fax: +49-89-289-12704

emiconducting nanowires are rapidly developing research ﬁ eld with many possibilities for Simplementation in the next generation opto-electronic devices. Additionally, they represent important platform for studying fundamental physical phenomena, generally not accessible in bulk materials. One striking example is the existence of the wurtzite (wz) crystal structure in III-V compounds, which have only zinc-blende (zb) structure in the bulk form. Their nanowire counterparts can grow with pure zb structure as well, but also with pure wz or a mixture of both. Due to the different band gaps of the wz and the zb structure, as theoretically predicted [1], nanowires with mixed wz/zb structure offer unique possibility for band gap engineering with only one material. In this work we investigated the optical properties of GaAs nanowires with a

Quantum Nanosystems mixed wz/zb structure, with special accent on the polarization properties of the emitted light. GaAs nanowires were grown using the Ga assisted Molecular Beam Epitaxy growth technique [2]. By varying the As pressure during the growth the crystal structure of the nanowires can be changed from pure zb to a mixture of zb and wz, evidenced by high resolution transmission electron microscopy (HRTEM) (see Figure 1 a)) [3]. This enables the formation of quantum wells (QW) along the growth direction of the nanowires, with electrons confi ned in the zb region and holes confi ned in the wz region. A typical photoluminescence (PL) spectrum from one nanowire exhibiting a variety of QWs is presented on Figure 1 b). The polarization properties of the emitted PL are depending from the splitting between the heavy holes (hh) and light holes (lh) levels in the wz GaAs. The PL emission at 4.2 K is polarized perpendicular to the nanowire growth direction in most of the investigated nanowires, indicating that the heavy hole level is the ground state. With increasing the temperature we still observe perpendicular polarization of the emitted light (though with decreased polarization ratio), pointing out a relatively large splitting between hh and lh levels (Figure 1 c)). To explain these experimental fi ndings we developed a theoretical model that enabled us to extract some fundamental parameters of the wz GaAs from our measurements such as the splitting between the heavy hole and light hole states. [1] M. Murayama and T. Nakayama, Phys. Rev. B 49, 4710 (1994). [2] D. Spirkoska, C. Colombo, M. Heiss, G. Abstreiter and A. Fontcuberta I Morral, J. Phys.: Condens. Matter. 20, 454225 (2008). [3] D. Spirkoska, J. Arbiol, A Gustafsson et al. Phys. Rev. B, 80, 245325 (2009).

Figure 1. a) HRTEM image from GaAs nanowire exhibiting both zb and wz crystal structure. b) PL spectrum from a GaAs nanowire exhibiting a mixed wz/zb structure. c) Polarization dependence of the emission at E=1.483 eV. Poster Presentations Poster

42 Advances in Nanoscience - Garching 2010 Spatially resolved ﬂ ow of ballistic electrons measured by quantized photocurrent spectroscopy K.-D. Hof1, F. J. Kaiser2, M. Stallhofer3, D. Schuh4, W. Wegscheider4,5, P. Hänggi2, S. Kohler2,6, J. P. Kotthaus1 and A. W. Holleitner3,* 1 Fakultät für Physik and Center for NanoScience (CeNS), Ludwig-Maximilians-Universität München, Germany 2 Institut für Physik, Universität Augsburg, Germany 3 Walter Schottky Institut and Physik Department, Technische Universität München, Garching, Germany 4 Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Germany 5 Laboratorium für Festkörperphysik, HPF E 7, Eidgenössische Technische Hochschule Zürich, Switzerland 6 Instituto de Ciencia de Materiales de Madrid (CSIC), Madrid, Spain * A. W. Holleitner, email: [email protected], Tel: +49-89-289-12775, Fax: +49-89-289-12704

uantum point contacts (QPCs) have re- Qcently been exploited in very sensitive detection schemes to quantify charge and spin states in nanoscale circuits and to image the coherent charge ﬂ ow in two-dimensional electron gases (2DEGs) [1]. Here, we demonstrate the use of GaAs-based QPCs to spatially resolve the ballistic ﬂ ow of photo-generated electrons in a 2DEG [2]. To this end, electron- hole pairs are optically generated in a 2DEG Quantum Nanosystems by focused interband laser excitation at typically 1.552eV with 76 MHz repetition rate. The resulting optical beam induced current (OBIC) through an adjacent QPC is measured with radio frequency lock-in detection as a function of the laser spot position (see scheme in Figure 1). We observe that photo-generated electrons can ballistically propagate across several microm- eters, before they tunnel through the QPC (Figure 2). As will be discussed in the presentation, the transmission of photo-generated electrons through the QPC is governed by the quantized energy and momentum values of the electron modes in the QPC. Hereby, the measured photocurrent across the QPC exhibits characteristic quanti-zation steps. [1] M. A. Topinka, B. J. LeRoy, S. E. J. Shaw, E. J. Heller, R. M. Westervelt, K. D. Maranowski, and A.C. Gossard, Science 289, 2323-2326 (2000). [2] K.-D. Hof, F. J. Kaiser, M. Stallhofer, D. Schuh, W. Wegscheider, P. Hänggi, S. Kohler, J. P. Kotthaus, and A. W. Holleitner, Nano Lett., article

ASAP, publication date (Web): September 20, 2010 Poster Presentations

Advances in Nanoscience - Garching 2010 43 Towards nuclear spin free qubits based on Si/SiGe heterostructures A. Wild1 , J. Sailer1, K.M. Itoh4, E. E. Haller5, G. Abstreiter1, S. Ludwig3 and D. Bougeard1,2 1 Walter Schottky Institut, Technische Universität München, Germany 2 Institut für Experimentelle und Angewandte Physik, Universität Regensburg, Germany 3 Fakultät für Physik, Ludwig-Maximilians-Universität, Germany 4 Department of Applied Physics and Physico-Informatics, Keio University, Japan 5 Lawrence Berkeley National Laboratory, Materials Sciences Division, USA

oupled quantum dots (QD) are presently Cintensely investigated as possible spin qubits for quantum information processing (QIP). The electron spin coherence time in the curently most advanced GaAs based systems is limited by the hyperne interaction of a conned electron with the many nuclear spins of the surrounding host crystal. Using Silicon (Si) as the host material oers a promising alterna-

Quantum Nanosystems tive route towards solid state based QIP. For Si in its natural isotopic composition, substan- tially longer decoherence times are expected compared to GaAs as a result of reduced hyperne interaction and weak spin-orbit coupling. The possibility of isotopic purication of Figure 1: Charge stability diagram, gate design of the Si crystal which contains no nuclear spins double quantum dot device and Si/SiGe heterostruc- promises even superior coherence properties ture layout. for electron spins. We chose strained Si in SiGe as host material for conning electrons. This approach enables high electron mobilities and allows for isotopic engineering of the host crystal. By using single crystals enriched in certain isotopes as source materials in our molecular beam epitaxy (MBE) system we are able to create virtually nuclear spin free hosts [1] or to decorate the host crystal lattice with a variable concentration of nuclear spins to investigate the in uence on qubit decoherence for prospective quantum dot circuits. We have established the Si/SiGe heterostructure development and processing of two-dimensional electron gases (2DEG) and devices suitable for the denition of coupled QDs. The 2DEG densities can be tuned via front and backgates from 1 to 5·1011 cm-2. Thereby we achieve 2DEG mobilities in the range of 30,000 – 100,000 cm2(Vs)-1 for Si/SiGe in its natural isotopic composition and 10,000 – 40,000 cm2(Vs)-1 for 28Si/SiGe 2DEGs. Based on these 2DEGs we have already dened rst double QDs. Here we present rst characterization measurements of electrostatically dened double QD devices in natural Si. Full tunability of our double QDs is shown, including transport and charge spectroscopy. Preliminary pulsed-gate measurements demonstrate the suitability of our devices for coherent spin experiments and as spin qubits. Our rst double QD devices dened in 28Si 2DEGs are currently under investigation. These samples will allow coherent experiments on spin qubits in a nuclear spin free environment. [1] J. Sailer et al., Phys. status solidi RRL 3, 61 (2009) Poster Presentations Poster

44 Advances in Nanoscience - Garching 2010 Spatially resolved polarization dependent Raman spectroscopy and pressure induced resonant Raman on GaAs nanowires I. Zardo1,*, S. Conesa-Boj2, E. Uccelli1,3, F. Peiro2, Y. Xiang1, J. R. Morante2, J. Arbiol4, G. Abstreiter1 and A. Fontcuberta i Morral1,3 1 Walter Schottky Institut, Physik Department, Technische Universitaet Muenchen, Am Coulombwall 3, D-85748 Garching, Germany 2 Departament d’Electrònica, Universitat de Barcelona, E-08028 Barcelona, CAT, Spain 3 Laboratoire des Matériaux Semiconducteurs, Institut des Matériaux, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland 4 ICREA Research Professor at Institut de Ciència de Materials de Barcelona, CSIC, 08193 Bellaterra, CAT, Spain * Corresponding author: email: [email protected]

emiconductor nanowires will play an important role in several areas of nanotechnology, Ssuch as electronics, sensing and energy conversion. The functional properties of nanowires are inﬂ uenced by different factors, the structure being one of the most determining. Spatially resolved Raman spectroscopy is a non-destructive technique used for the structural characterization of materials, which enables to determine the crystalline phase and presence of strain. In this work, the structural properties of gallium arsenide nanowires have been studied. The structural homogeneity of the nanowires is studied by spatially resolved Raman spectroscopy, and the obtained results are compared with Transmission Electron Microscopy measurements.

The GaAs nanowires present a mixture of zinc-blende and wurtzite structure [1,2]. The Ra- Quantum Nanosystems man selection rules are determined (see Figure 1) and strain related effects underlined [3].

The E1-A1 splitting due to anisotropy of the crystal in wurtzite GaAs nanowires was found. The activation of the LO and SO modes was attributed to the presence of faceting on the nanowire sidewall. We present also light scattering experiments on zinc-blende GaAs nanowires under hydrostatic pressure up to 20 GPa with a Diamond Anvil Cell. The applied hydrostatic pressure drives the tuning of the direct E0 nanowire band gap with respect to the excitation energy, leading to resonant Raman scattering. The dispersion of the Raman cross section of the TO, of the forbidden LO and second or higher order scattering processes has been measured at various pressures. The obtained results indicate a different response of the nanowires with respect to the bulk. The resonance proﬁ le of the 2LO mode suggests a stronger Fröhlich coupling. The Grüneisen Poster Presentations parameters were also found to be different from those obtained from bulk GaAs. Finally, there is evidence for a structural transition for P > 16 GPa. This work shows that Raman spectroscopy of individual nanowire is a powerful technique for revealing the structural properties of nanostructures such as nanowires. [1] C. Colombo et al., Phys. Rev. B 77, 155326 (2008) [2] D. Spirkoska et al., Phys. Rev. B 80, 245325(2009) [3] I. Zardo et al., Phys. Rev. B 80, 245324 (2009)

Advances in Nanoscience - Garching 2010 45 Organic Functionalization of Group IV-Semiconductors M. Auernhammer, M. Hoeb, M. S. Brandt, J.A. Garrido, M. Stutzmann and I.D. Sharp Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, 85748 Garching, Germany

he covalent bonding of organic molecules to semiconductor materials allows the design of Thybrid systems suitable for biosensor and (bio)molecular electronic applications. Silicon carbide and diamond are promising substrate materials for such devices since they offer a unique combination of a number of desirable bulk and interfacial properties, including optical transparency, biocompatibility, and chemical stability. In this work, we demonstrate a technique for thermally activated formation of alkene-derived self-assembled monolayers on oxygen-terminated surfaces by reaction with 1-octadecene

(C18H36). In 1993 Linford et al. introduced a wet-chemical process, commonly known as hydros- Hybrid Nanosystems ilylation, which yields organic thin ﬁ lms on silicon surfaces [1]. During this chemical reaction, the alkenes spontaneously self-assemble on H-terminated silicon surfaces and form covalent silicon-carbon bonds. The alkyl-monolayers show exceptional oxidation resistance in ambient air and electrically passivate the surface via the reduction of surface states. Here, a similar process is studied on SiC and diamond surfaces, which are primarily oxygen- or hydroxyl-terminated following HF or plasma treatment, respectively [2,3]. The reaction of alkenes with OH- terminated surfaces yields dense and chemically stable organic monolayers. The layers were characterized using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), Thermal desorption spectroscopy (TDS) and water contact angle measurements. This investigation reveals that alkenes selectively attach to the oxygen-terminated sites via a covalent oxygen bridges. This work thus increases the range of available functionalization protocols and provides a new means of straightforwardly forming self-assembled organic monolayers on semiconductors in order to engineer their surface properties. [1] M.R. Linford, P. Fenter, P.M. Eisenberger, C.E.D. Chidsey, Journal of the American Chemical Society 117 (1995) 3145. [2] U. Starke, Ch. Bram, P.R. Steiner, W. Hartner, L. Hammer, K. Heinz, K. Müller, Applied Surface Science 89 (1995) 175. [3] H. Notsu, I. Yagi, T. Tatsuma, D.A. Tryk, A. Fujishima, J. Electroanal. Chem. 492 (2000) 31.

Fig. 1: Schematic representation of the alkyl self- assembly via functionalization of diamond-and silicon carbide surfaces. Poster Presentations Poster

46 Advances in Nanoscience - Garching 2010 Organized growth of bifunctional oligoarenes and organometallic complex linkers on semiconductor nanoscale devices Cattani-Scholz1, K-C. Liao2, A. Bora3, A. Pathak3, I.D. Sharp1, C. Hundschell4, B. Nickel4, J. Schwartz2, M. Tornow3, G. Abstreiter1 1 Walter Schottky Institut, Physik Department, Technische Universität München, Germany 2 Department of Chemistry, Princeton University, NJ, USA 3 Institut für Halbleitertechnik, TU Braunschweig, Germany 4 Department of Physics, Ludwig Maximillian Universität München

e report on the successful deposition of self-assembled monolayers (SAMs) of sexithio- Wphene- and anthracene bisphosphonates onto silicon dioxide/silicon substrates. These SAMs further served as a basis for the preparation of novel three-dimensional, organized bilayers of sexithiophene- and anthracene bisphophonates, using techniques of coordination chemistry under controlled conditions by deposition of organometallic linkers onto the monolayers. We have characterized the mono- and bilayer systems on planar surfaces by XPS, AFM and XRR measurements. Our preliminary results indicate a high structural quality regarding layer composition, thickness and density.

Further, we discuss ﬁ rst electrical characterization data of our aromatic organophosphonate Hybrid Nanosystems systems, both in vertical transport using a metal top electrode, and laterally in-between nano- gap electrodes. Poster Presentations

Advances in Nanoscience - Garching 2010 47 Optoelectronic properties of two-dimensional gold nanoparticle arrays B. Dirks, C. Weiß, M.A. Mangold, A.W. Holleitner Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany

he fi eld of plasmonics deals with the interaction of light with metal clusters. It has drawn Ta lot of interest in recent years due to possible applications for surface enhanced Raman spectroscopy and biosensing. The absorption of light by nanoparticles induces surface plasma oscillations of the conduction electrons. At fi rst, this leads to a strongly enhanced electrical fi eld at the surface of the particles and, secondary, the plasmons decay and heat up the particles. We use self-assembled two dimensional arrays of alkane coated gold nanoparticles to investigate the impact of these two effects on the transport properties of such arrays. By probing the photoconductance of a contacted gold nanoparticle array we fi nd a clear en-

Hybrid Nanosystems hancement of the photoconductance at the surface plasmon resonance. This can be explained by bolometrically enhanced tunnel rates between adjacent nanoparticles [1]. Furthermore, fi - nite difference time domain simulations have shown a strong fi eld enhancement between the nanoparticles in the array under optical excitation of the surface plasmons. This fi eld enhancement leads to a strongly increased optoelectronic response of the nanoparticle array [2]. We acknowledge a fruitful collaboration with M. Calame and C. Schönenberger. This work has been supported by the “Deutsche Forschungsgemeinschaft” through project HO 3324/2, the excellence program “Nano Initiative Munich” (NIM), and the Center for NanoScience (CeNS) in Munich. [1] Mangold, M.A.; Weiss, C.; Calame M.; Holleitner A.W.: Appl. Physics Letters 94, 161104 (2009). [2] Mangold, M.A.; Weiss, C.; Dirks, B.; Holleitner A.W.: arXiv: 1004.5353 (2010). Poster Presentations Poster

48 Advances in Nanoscience - Garching 2010 Spin waves in individual and periodic permalloy nanostructures G. Duerr, K. Thurner, F. Brandl, S. Neusser, R. Huber, T. Schwarze and D. Grundler Lehrstuhl für Physik funktionaler Schichtsysteme, Technische Universität München, Physik-Department, James-Franck-Strasse, 85748 Garching b. Muenchen, Germany

he research fi eld of magnonics addresses the generation, manipulation and detection of Tspin waves (SWs) on the nanoscale [1]. For SW wave guiding individual as well as interconnected ferromagnetic nanowires have been found to be promising [2]. Characteristic lateral feature sizes of such devices range from a few 10 nm up to several 100 nm. Periodically patterned ferromagnets are also of particular interest as they can form artifi cial crystals and provide ultimate control of the fl ow of spin waves [3]. We present three recent advances in our study of structured and unstructured ferromagnetic thin fi lms.

Magnonic devices are prepared from 25 nm thick permalloy (Ni80Fe20) fi lms. To explore in detail the spin wave propagation properties and damping characteristics prior to nanopatterning we Hybrid Nanosystems use all-electrical spin wave spectroscopy (AESWS) [4] and vary the temperature from 4 K up to 400 K. Applying out-of-plane fi elds of up to 2.5 T we study the intrinsic damping parameter of the permalloy thin fi lms used for the magnonic nanodevices. To form SW wave guides we prepare 300 nm wide nanowires using electron beam lithography and lift-off processing of polycrystalline permalloy. Using an in-plane magnetic fi eld H applied in different spatial directions we vary the domain confi guration and local magnetization in the nanowires. This gives rise to different spin wave modes. We focus on the magnetic zig-zag confi guration which has been reported earlier to provoke deep-submicron SW channels [5]. Using AESWS we determine the resonance frequencies of these modes and study the propagation behavior. Antidot lattices, i.e., periodic arrays of holes in a ferromagnetic thin fi lm such as permalloy, rep- Poster Presentations resent interconnected networks of nanochannels and might provoke artifi cial crystal behavior [1,2]. We have studied holes with a diameter of 120 nm arranged on squared periodic lattices with different lattice constants. The arrays have been etched using focused ion beam lithography. By means of AESWS propagation of spin waves has been studied depending on the in- plane fi eld H [4]. Propagation velocities and intensities are found to vary signifi cantly depending on the strength and orientation of H [4,6]. Such characteristics are interesting for tunable wave guiding and applications in the framework of the emerging research fi eld of magnonics. We thank A. Holleitner, T. Rapp, J. Topp, and P. Weiser for experimental support. The research leading to these results has received funding from the European Community’s Seventh Frame- work Programme (FP7/2007-2013) under Grant Agreement n° 228673 MAGNONICS and the German excellence cluster “Nanosystems Initiative Munich (NIM)”. [1] V.V. Kruglyak, S.O. Demokritov, and D. Grundler, J. Phys. D: Applied Physics 43, 264001 (2010). [2] S. Neusser and Dirk Grundler, Advanced Materials 21, 2927 (2009). [3] J. Topp, D. Heitmann, M. Kostylev, and D. Grundler, Phys. Rev. Lett. 104, 207205 (2010). [4] S. Neusser, G. Duerr, H.G. Bauer, S. Tacchi, M. Madami, G. Woltersdorf, G. Gubbiotti, C.H. Back, and D. Grundler, Phys. Rev. Lett. 105, 067208 (2010). [5] J. Topp, J. Podbielski, D. Heitmann, and D. Grundler, Phys. Rev. B 78, 024431 (2008). [6] S. Neusser, G. Duerr, S. Tacchi, M. Madami, G. Gubbiotti, and D. Grundler, in preparation.

Advances in Nanoscience - Garching 2010 49 Graphene solution-gated ﬁ eld effect transistor arrays for sensing applications L. Hess1, M. Dankerl1, M. Hauf1, A. Lippert1, S. Birner1, I.D. Sharp1, M. Stutzmann1, J.A. Garrido1 1 Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany

iosensing and bioelectronic applications have enormously profi ted from employing fi eld Beffect transistors as transducing devices, mainly due to their intrinsic amplifi cation capability and the high integration offered by semiconductor technology. Due to the maturity of Si technology, most of the work with the so-called solution-gated fi eld effect transistors (SGFETs) has been done based on Si-MOSFETs. However, several disadvantages of the Si technology, such as high electronic noise and poor stability, have motivated the search for more suitable materials. The sensitivity of SGFETs devices largely depends on the distance between the conductive channel and the surface. Therefore, the use of FETs structures with surface channels

Hybrid Nanosystems offer clear advantages. In this respect, the surface conduction of graphene appears as an ideal candidate for the development of highly sensitive SGFETs. A few recent studies have shown that the conductivity of graphene ﬁ lms can be modulated using an electrolyte gate1,2. Here, we demonstrate a facile route for the scalable fabrication of transistor arrays that operate in aqueous environments using epitaxial graphene on SiC3

and CVD-grown graphene on SiO2. Furthermore, we utilize an on-chip structure for Hall effect measurements which allows direct determination of carrier concentrations and mobilities under electrolyte gate control. The study of the graphene/electrolyte interface reveals a high interfacial capacitance (few μF/cm2), resulting in a high transconductance and correspond- ingly high sensitivity of the SGFETs. Through direct measurement, together with application of a model which considers the microscopic structure of water at the interface, we analyze the effect of gate potential on both hole and electron transport. Finally, the low-frequency noise of graphene SGFETs operating in electrolyte is investigated, revealing an effective gate noise of tens of μV, which compares very well with low-noise Si devices currently used in bioelectronic applications. Our study3 demonstrates that graphene SGFETs, with their facile technology, high transconductance, and low noise promise to far outperform state-of-the-art Si-based devices for biosensor and bioelectronic applications. [1] P.K. Ang, W. Chen, A.T.S. Wee, and K.P. Loh, J. Am. Chem. Soc. 130, 14392 (2008) [2] Y. Ohno, K. Maehashi, Y. Yamashiro, and K. Matsumoto, Nano Lett. 9, 3318 (2009) [3] M. Dankerl, V.M. Hauf, A. Lippert, L. Hess, S. Birner, I.D. Sharp, A. Mahmood, P. Mallet, J.Y. Veuillen, M. Stutzmann, and J.A. Garrido, Adv. Funct. Mater., accepted (2010) Poster Presentations Poster

50 Advances in Nanoscience - Garching 2010 AlGaN/GaN semiconductor biosensors for applications in radiation biophysics M. Hofstetter1, J. Howgate2, I. D. Sharp2, M. Stutzmann2 and S. Thalhammer1 1 Helmholtz Zentrum München, Institute for Radiation Protection, Ingolstädter Landstraße 1, D-85764 Neuherberg, Germany 2 Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany

n recent decades, signiﬁ cant efforts have been devoted to the development of biosensors that Iare capable of measuring changes and responses at a cellular level. Semiconductor sensors based on gallium nitride and its alloys are particularly promising and devices capable of biosensing on a cellular and tissue level have been already demonstrated [1]. Here, we present a new concept in radiation biophysics for in situ monitoring of alterations in the microenvironment of cellular systems. We record the sensor response to X-ray irradiation in real-time with charge and pH sensitive solution gate AlGaN/GaN high electron mobility transistors (HEMTs). At the interface of the two materials, the difference in polarizations leads to a ﬁ xed space charge

and a two-dimensional electron gas (2DEG) is produced. The electrical properties, and there- Hybrid Nanosystems fore the conductivity, of the system strongly depend on the surface potential of the chip. We demonstrate that the devices are stable and show reproducible behaviour under constant and pulsed X-ray radiation [2]. The HEMT devices are biocompatible and can be simultaneously operated in aggressive ﬂ uids and under hard radiation. We have performed tests regarding cell proliferation and growth dynamics on GaN sensor surfaces to ensure biocompatibility as well as biofunctionality. Titration measurements in solution reveal that the linear pH response and sensitivity are retained under X-ray irradiation and devices can be simultaneously operated as radiation dosimeters. [1] G. Steinhoff et al., Appl. Phys. Lett. 86 (2005) 033901 [2] M. Hofstetter et al., Appl. Phys. Lett. 96 (2010) 092110 Poster Presentations

Advances in Nanoscience - Garching 2010 51 Spin wave resonances in ferromagnetic thin ﬁ lms prepared via atomic layer deposition R. Huber1, P. Berberich1, T. Rapp1, J. Bachmann2, K. Nielsch2, and D. Grundler1 1 Lehrstuhl für Physik funktionaler Schichtsysteme, Physik Department E10, Technische Universität München, James-Franck-Str., D-85748 Garching b. München, Germany 2 Institut für Angewandte Physik und Mikrostrukturzentrum, Universität Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany

n the way to artifi cially designed three-dimensional magnetic structures atomic layer de- Oposition (ALD) is a promising thin-fi lm deposition technique. We have produced different ferromagnetic thin fi lms by an ALD from the company PicoSun. The fabrication is based on the

oxidation of FeCp2 (NiCp2). [1,2] Afterwards iron oxide (nickel oxide) is reduced inside the ALD

reactor by H2 at 400°C. The multi-source ALD reactor allows us to provide a cap layer of Al2O3 which prevents the magnetic thin ﬁ lm from oxidation. We have studied the quasistatic and dynamic properties via the magneto-optical Kerr effect and broadband spin-wave spectroscopy, respectively. In the latter case we mount the thin ﬁ lm on top of a coplanar waveguide with an

Hybrid Nanosystems inner conductor exhibiting a width of 20 μm. Using a vector network analyzer we measure spin wave resonances. They depend characteristically on an applied in-plane fi eld and follow the well-known Kittel formula. We will discuss the magnetic properties of different ferromagnetic thin fi lms such as Fe and Ni fabricated by ALD. We thank Sebastian Neusser for experimental help in the initial stage of the experiment. We acknowledge fi nancial support through the European Community’s Seventh Framework Pro- gramme (FP7/2007-2013) under Grant Agreement no. 228673 MAGNONICS. [1] J. Bachmann et al., J. Appl. Phys., 2009, 105, 07B521 [2] M. Daub et al., J. Appl. Phys., 2007, 101, 09J111 Poster Presentations Poster

52 Advances in Nanoscience - Garching 2010 A Bose-Einstein condensate coupled to a micromechanical oscillators D. Hunger1,2, S. Camerer1,2, T. W. Hänsch1,2, D. König1, J. P. Kotthaus1, J. Reichel3 and P. Treutlein1,2,4 1 Ludwig-Maximilians Universität, Munich, Germany 2 Max-Planck Institute of Quantum Optics, Garching, Germany 3 Laboratoire Kastler Brossel, E.N.S, Paris, France 4 University of Basel, Basel, Switzerland

ltracold atoms can be trapped and coherently manipulated close to a surface using chip- Ubased magnetic microtraps on so-called atom chips. This opens the possibility of studying interactions between atoms and on-chip solid-state systems such as micro- and nanostructured mechanical oscillators. Such oscillators have attracted attention due to the extreme force sensitivity and the novel manipulation techniques of cavity optomechanics. The question is raised whether the toolbox for quantum manipulation of ultracold atoms could be employed to read out, cool, and coherently manipulate the oscillators’ state. Several theoretical proposals show that sufﬁ ciently strong and coherent coupling between atoms and oscillators would en-

able studies of entanglement, quantum state transfer, and quantum control of mechanical force Hybrid Nanosystems sensors. In our experiment we demonstrate a ﬁ rst step in this direction and couple the vibrations of a micromechanical cantilever to the collective motion of Bose-condensed atoms in a trap. The interaction relies on surface forces experienced by the atoms at about 1μm distance from the cantilever. We observe resonant coupling to several well-resolved mechanical modes of the condensate, including in particular the center of mass mode and the breathing mode. We use trap loss as the simplest way to detect the atomic motion induced by the coupling. With this method we are able to sense cantilever oscillations with a minimum resolvable amplitude of 13 nm, limited by the atomic trap lifetime and trap anharmonicity. Coupling via surface forces does not require magnets, electrodes, or mirrors on the oscillator and could thus be employed to couple atoms to molecular-scale oscillators such as carbon nanotubes. Poster Presentations

D. Hunger et al., Phys. Rev. Lett. 104, 143002 (2010)

Advances in Nanoscience - Garching 2010 53 Optomechanical coupling of ultracold atoms and a membrane Maria Korppi1,2,3, A. Jöckel1,2,3, D. Hunger1,2, S. Camerer1,2, M. Mader1,2, T.W. Hänsch1,2 and P. Treutlein1,2,3 1 Ludwig-Maximilians-Universität, München, Germany 2 Max-Planck-Institut für Quantenoptik, Garching, Germany 3 Universität Basel, Switzerland

e report the recent results of our experiment, where we couple a single mode of a high-Q Wmembrane-oscillator to the motion of laser-cooled atoms in an optical lattice. The optical lattice is formed by retrorefl ection of a laserbeam from the oscillator surface. Quantum fl uctuations of the lattice laser light mediate coupling between the motion of the atoms and the membrane1. When the trap frequency of the atoms is matched to the eigenfrequency of the membrane, the coupling leads to resonant energy transfer between the two systems. We have observed such resonant energy transfer both from the membrane to the atoms and, more signifi cantly, the back-action of the atoms on to the membrane.

Hybrid Nanosystems In the long term, such coupling mechanism could be exploited in developing hybrid quantum systems between atoms and solid-state devices. As another intriguing perspective, a new generation of optical lattice experiment is in sight, where the mirrors creating the laser standing waves are micromechanical oscillators which interact with the atoms, and, which ultimately must be described quantum mechanically. 1 Optical Lattices with Micromechanical Mirrors, K. Hammerer, K. Stannigel, C. Genes, P. Zoller, P. Treutlein, S. Camerer, D. Hunger, T.W. Haensch, arXiv:1002.4646

Figure: Optical lattice mediates the coupling between ultracold atoms and a membrane placed in separate vacuum chambers. Poster Presentations Poster

54 Advances in Nanoscience - Garching 2010 Photoconductance of a submicron oxidized line in surface conductive single crystalline diamond M. Seifert, M. Stallhofer, M. V. Hauf, G. Abstreiter, M. Stutzmann, J. A. Garrido and A.W. Holleitner Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, 85748 Garching

ndoped single crystalline hydrogen-terminated diamond exhibits a p-type surface conduc- Utivity. This surface conductivity originates from a two-dimensional hole gas formed due to a band bending beneath the surface [1]. An oxygen-terminated diamond surface, however, shows no surface conductivity and, therefore, thin oxidized lines can act as efﬁ cient energy barriers within the two-dimensional hole gas [2]. We investigate the sub-bandgap optoelectronic phenomena induced by such a barrier in hydrogenated diamond at room temperature. The submicron oxidized lines are deﬁ ned in single-crystalline diamond by electron beam lithography in combination with an oxygen plasma treatment. We observe a photoconductive gain of the hole

conductivity across the barrier for sub-bandgap illumination [3]. The fi ndings are consistent with Hybrid Nanosystems the infl uence of photogenerated electrons being trapped in defect levels within the oxidized lines. We discuss the spatial and energetic characteristics as well as typical timescales of the optoelectronic phenomena. Our fi ndings suggest that surface conductive diamond circuits can be tailored by submicron oxidized lines in order to build photodetectors in the ultraviolet range at room temperature. We acknowledge fi nancial seed-funding by the German excellence initiative via the “Nanosys- tems Initiative Munich (NIM).” [1] F. Maier, M. Riedel, B. Mantel, J. Ristein, and L. Ley, Phys. Rev. Lett. 85, 3472 (2000). [2] J. A. Garrido, C. E. Nebel, R. Todt, G. Rösel, M.-C. Amann, and M. Stutzmann, Appl. Phys. Lett. 82, 988 (2003). [3] M. Stallhofer, M. Seifert, M. V. Hauf, G. Abstreiter, M. Stutzmann, J. A. Garrido, and A.W. Holleitner, Appl. Phys. Lett. 97, 111107 (2010). Poster Presentations

Advances in Nanoscience - Garching 2010 55 Polymer Brushes on Graphene Marin Steenackers WACKER-Lehrstuhl für Makromolekulare Chemie, Technische Universität München, Lichtenbergstraße 4, 85747 Garching, Germany

raphene has been attracting great interest because of its distinctive band structure and Gphysical properties. Here, we report on the preparation of large-area and free-standing fi lms of the order of centimeters consisting of a single graphene layer covalently modifi ed with a soft and fl exible functional polymer brush layer. These self-supporting nanomembranes, also referred to as “polymer carpets”, were prepared by a two-step procedure: fi rst, a high quality and uniform single graphene layer, prepared by chemical vapor deposition on copper foils, was functionalized with polymer brushes by direct photografting of styrene. In a second step, the

copper foil was etched away in an aqueous (NH4)2S2O8 solution resulting in a ﬂ oating graphene/

Hybrid Nanosystems polymer brush membrane which could easily be transferred to other substrates. The introduction of complex chemical functionalities within the polymer carpet can be prepared directly by polymer analogue reactions of the polystyrene brushes. Polymer carpets, based on crosslinked monolayers, were found recently to exhibit remarkable and unprecedented properties combining extreme thinness, mechanical and chemical stability, robustness, ﬂ exibility and (chemical) sensitivity. Our results provide a new set of tools for covalent chemical functionalization and manipulation of single graphene layers for the development of new integrated micro-/nanotech- nological devices. Poster Presentations Poster

56 Advances in Nanoscience - Garching 2010 Spatially resolved optoelectronic measurements of organic thin ﬁ lm transistors Christian Westermeier, Matthias Fiebig, and Bert Nickel Department für Physik and CeNS, Ludwig-Maximilians-Universität, Geschwister-Scholl-Platz 1, 80539 München, Germany

entacene is a promising candidate for organic electronics and optoelectronic applications Pdue to its high charge carrier mobility and strong absorption properties. Its optical properties are highly anisotropic. Therefore, the thin-fi lm-phase texture of pentacene grains should be visible in polarized light due to anisotropic absorption. Being the initialising step to generate excitons, absorption is crucial for the photoresponse of transistors. Consequently, the polycrystalline thin-fi lm-phase texture might be directly related to the photoresponse of pentacene based OFETs. Here, we use local illumination of the transistor channel in a confocal laser scanning setup with submicron resolution which allows us to excite single pentacene grains. Due to the random Hybrid Nanosystems orientation of the single crystals on the substrate, the refl ection from different grains varies depending on the polarization direction of the incident light, as expected. The sharp luminescence image mirrors the thin-fi lm texture and thus absorption and luminescence measurements match up perfectly. However, the spatially resolved photoresponse of the pentacene OFET shows an extrinsic structure which is diffuse and almost independent of the polarization. To disentangle the different contributions of the underlying transport phenomena, we perform time resolved photoresponse measurements. Apart from a heat-induced homogeneous mechanism, these measurements also reveal two spatially inhomogeneous processes with different timescales. A structured and slow component is observed within the transistor channel, whereas a faster mechanism occurs close to the positive electrode. The obtained results for the photoresponse of pentacene based OFETs are explained by a model of triplet exciton assisted hole detrap-

ping. Poster Presentations

Advances in Nanoscience - Garching 2010 57 Compact and Nanotubular TiO2 in Energy Research Celine Rüdiger1, Silvia Leonardi1,2, Florian Wiesinger1, Odysseas Paschos1, Fabio Di Fonzo2, Andrea Li Bassi2, Ulrich Stimming1 and Julia Kunze1 1 Institute for Advanced Study (IAS) and Department of Physics E19, Technische Universität, München, Germany 2 Politecnico di Milano NEMAS - Center for Nano-Engineered Materials and Surfaces, Milano, Italy

alloys using dilute ﬂ uoride based electrolytes. Upon all valve metal oxides, nanotubular TiO2 on Ti [2,3] is among the most promising structures since it offers several interesting functional properties.

The growth of self-organized TiO2 nanotube arrays on electropolished and not electropolished Nano and Energy Ti sheets was investigated for three different electrolytes, being ﬂ uoride ion containing sulphate and phosphate buffer solutions as well as glycerol-based electrolytes. A systematic structural and morphological characterization was performed revealing an interdependence of the crys- tallographic orientation of the grains in polycrystalline Ti and the growth rates and properties of

nanotubular TiO2 layers.

While the semiconductive nature of TiO2 is crucial for many applications for example in photo- catalysis, the limited conductivity prevents an efﬁ cient use in applications that require a fast electron transport, functional electrodes or electrocatalyst supports. For the latter application

TiO2 has to be made conductive and inert towards reoxidation in the electrolyte. This can be

achieved by a carbo-thermal reduction treatment converting the TiO2 into an oxy-carbide com-

pound (TiOxCy) that shows stable semimetallic conductivity [4].

A parameter study has been performed for compact TiO2 fi lms on Ti sheets to optimize the carbo-thermal reduction. The composition, morphology and structure of the fi lms before and after the conversion have been studied with XPS, SEM, AFM and XRD. The conductivity of the 3-/4- fi lms was electrochemically investigated with the well understood redox system Fe(CN)6 .

With the aim to investigate the nanotubular and compact TiOxCy layers as support materials for

electro catalytically active metals like Pt and Pd, a study of Pt-deposition on compact TiOxCy ﬁ lms was performed. Further effort will be devoted to the investigation of the inﬂ uence of the metal coverage, the particle thickness and shape, and the metal oxidation state on the catalytic

activity for ORR and alcohol oxidation. The inﬂ uence of the TiOxCy support will be studied by looking at different oxygen to carbon ratios. [1] H. Masuda, K. Fukuda, Science, 268 (1995) 1644. [2] V. Zwilling, M. Aucouturier, E. Darque-Ceretti, Electrochim. Acta 45 (1999) 921. [3] J.M. Macak, H. Tsuchiya, A. Ghicov, K. Yasuda, R. Hahn, S. Bauer, P. Schmuki, COSSMS (2007). [4] R. Hahn, F. Schmidt-Stein, J. Salonen, S. Thiemann, Y.Y. Song, J. Kunze, V.-L. Lehto, P. Schmuki, Angewandte Chemie Int. Ed. (VIP Paper) 48 (2009) 7236. Poster Presentations Poster

58 Advances in Nanoscience - Garching 2010 Investigation of the thermal conductivity of GaAs nanowires by Raman spectroscopy combined with laser heating Martin Soini1, Ilaria Zardo1, Emanuele Uccelli1,2, Stefan Funk1, Gregor Koblmüller1, Anna Fontcuberta i Morral1,2, and Gerhard Abstreiter1 1 Walter Schottky Institut, Technische Universität München, Garching, Germany 2 Laboratoire des Matériaux Semiconducteurs, Institut des Matériaux, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland

n order to make thermoelectrics a competitive technology, materials with high electric and Ilow thermal conductivity are required. Recently, this has increased the interest in nanoscale systems for thermoelectric application. Nanowires are promising candidates for the reduction of the thermal conductivity due to increased boundary scattering, while keeping the electrical conductivity high [1,2]. We investigated the thermal conductivity κ of GaAs NWs. Our method is based on the laser heating of freely suspended NWs and the determination of the local temperature by μ-Raman spectroscopy. Nano and Energy The thermal profi le measured for homogeneous nanowires shows parabolic behavior, which is in agreement with the simple model proposed by Hsu et al. [3]. The fi t to the temperature profi le is used to extract κ. The absolute value of the laser power absorbed inside the nanowire, which is needed for the determination of κ, is determined by fi nite differences simulations. The conductivity is found to be in the range of 10 to 35 Wm-1K-1 and therefore to be signifi cantly lower than in bulk GaAs. Furthermore, our results confi rm recent theoretical calculations by Martin et al. [4]. The exposition to laser light with high power induces the oxidation of the GaAs, affecting the properties of the nanowires in an irreversible manner. We determined a systematic increase of the thermal resistance with increasing laser power. The reliability of the determination of the local temperature on a micrometer scale by Raman spectroscopy is demonstrated by applying this method to nanowires with morphological inho- Poster Presentations mogeneities. Furthermore, the measurement on tapered nanowires proofs the decrease of the thermal conductivity for smaller diameters.

Upper left: Typical sample confi guration: The nanowire is freely suspended between two gold pads. Scale bar: 1 μm. Lower left: Spacially resolved Raman measurement on a single nanowire. The shift of the TO peaks is used to calculate the local temperature. Right: Parabolic temperature profi le measured on a homogeneous nanowire. The solid lines are the fi t curves to the experimental points. [1] A. I. Hochbaum, R. Chen, R. D. Delgado, W. Liang, E. C. Garnett et al., Nature 451, 163 (2008) [2] G. J. Snyder, and E. S. Toberer, Nature Materials 7, 105 (2008) [3] I-K. Hsu, R. Kumar, A. Bushmaker, S. B. Cronin, M. T. Pettes et al., Appl. Phys. Lett. 92, 063119 (2008) [4] P. N. Martin, Z. Aksamija, E. Pop, and U. Ravaioli, Nano Lett. 10, 1120 (2010)

Advances in Nanoscience - Garching 2010 59 Investigation of different interface morphologies in organic solar cells Wolfgang Wiedemann1, Alaa Abdellah2, Holger Hesse1, Jonas Weickert1, Robert Meier3, Kevin P. Musselman4, Judith L. MacManus-Driscoll4, Peter Müller-Buschbaum3, Giuseppe Scarpa2, Paolo Lugli2, and Lukas Schmidt-Mende1 1 Dept. of Physics & Center for NanoScience (CeNS), Ludwig-Maximilians University, Munich, Bavaria, Germany. 2 Institute for Nanoelectronics, Technical University Munich, Munich, Bavaria, Germany. 3 Physik-Department LS E13, Technical University Munich, Munich, Bavaria, Germany. 4 Dept. of Materials Science and Metallurgy, University of Cambridge, Cambridge, United Kingdom.

he morphology in organic photovoltaics plays a key role in determining the device effi cien- Tcy. We present polymer solar cells with different interfacial geometry and their fabrication processes to investigate the exact role of this morphology. We compare different device architectures: bilayer, blend, stratifi ed and nanostructured bilayer solar cells. The bilayer solar cell is fabricated by a transfer technique, where [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) is laminated on top of a poly(3-hexylthiophene) (P3HT) fi lm. The blend device is spincoated from a mixed solution of both materials and shows a homogeneous intermixing of the donor and ac-

Nano and Energy ceptor material. The stratifi ed solar cell has a continuous transition between each active material and can be obtained by spincoating a PCBM layer from an orthogonal solvent for P3HT on top of the P3HT fi lm. The nanostructured device is a bilayer architecture with controlled nanostructured interfaces by combining nanoimprinting and lamination techniques: before laminat- ing the second organic layer, the fi rst is imprinted by an anodic aluminum oxide (AAO) stamp. This technique allows us to achieve a network structure of donor-acceptor material with a ~80 nm periodicity and ~40 nm width. These structures have an abrupt interface between the donor and acceptor materials and show an increased effective interfacial area and photovoltaic performance compared to bilayers. In contrast to blend fi lms, they allow an in depth analysis of the infl uence of morphology on interfacial physical processes. To get an insight into the recombination- and dissociation process and also the carrier transport, we apply transient measurements, such as photovoltage decay (PVD). Photoluminescence (PL), temperature- and light intensity dependent I-V measurements provide additional information about the device physics. Gracing small and wide angle X-ray scattering data are shown to reveal imformation about the interfacial morphology and the polymerchan orientation. The studies of the different device architectures provide insights to the ideal device morphology. Poster Presentations Poster

60 Advances in Nanoscience - Garching 2010 Regulation of Cellular Signaling Pathways by Spatial Organization of Molecular Extracellular Matrix Cues Yvonne Schön1, Vera C. Hirschfeld-Warneken1, Heike Böhm1, Stefanie Neubauer2, Horst Kessler2, and Joachim P. Spatz1 1 Max-Planck-Institut für Metallforschung, Stuttgart, Germany 2 Institute for Advanced Study at the Department Chemie, Technische Universität München, Lichtenbergstr. 4, D-85747 Garching, Germany

patial patterning of biochemical cues on the micro- and nanometer scale controls numer- Sous cellular processes such as spreading, adhesion, migration, and proliferation. Espe- cially αvβ3 integrin mediated cell adhesion is crucially inﬂ uenced by ligand design, spacing and global ligand density. With synthetic cell environments we are able to precisely control integrin activation by the presentation of the activating ligand: the gold nanoparticles employed as an- chorpoints can be positioned by a self-assembly technique assigning particle spacing and con- sequentially global particle density. Moreover, further developments of this method also allow

the independent adjustment of local spacing and global density by a combination of micro- and Bio-Nanoscience nanostructuring approaches or the variation of the particle spacing in a gradient along the patterned glass slides. In combination with ligands speciﬁ cally designed to match the addressed integrins these adhesive nanostructured surfaces are a versatile tool to analyze cell attachment, spreading and migration. In combination with single cell force microscopy the adhesion strength of cells in dependence of their integrin activation and focal contact formation can be controlled and analyzed at the subcellular level. Poster Presentations

Advances in Nanoscience - Garching 2010 61 Expanding the Scope of Single Molecule FRET with DNA Origami Carlos Castro, Hendrik Dietz Dietz Lab, Physik Department, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany

ypical dimensions of cellular components are on the order of a few nanometers and their Tdiverse cellular functions often involve conformational changes that require movements ranging from fractions of a nanometer up to tens of nanometers. The current state of the art tool for studying conformational dynamics is single molecule Fluorescence Resonance Energy Transfer (FRET), whereby energy transfer between two ﬂ uorescent dyes is correlated to their spatial separation; however, quantitative distance predictions require case-speciﬁ c calibrations and are only accurate in the range of ~ 3-7 nm. Furthermore, the working range is limited to

Bio-Nanoscience below 10 nm. Here we present a nanoscale device constructed by DNA origami that improves the quantitative accuracy of FRET distance predictions and expands its potential working range. The device integrates 3d structures built from self-assembled DNA, attachment sites for molecules of interest, sites for surface immobilization, and ﬂ uorescent markers for the direct visualization of biomolecular dimensions and dynamics by FRET. The device takes advantage of a distance calibration that can be generally applied to any molecule of interest. We have demonstrated that the device can easily achieve 1 nm distance resolution. For the purpose of proof-of- concept studies we speciﬁ cally integrated a piece of double stranded DNA (dsDNA) containing a recognition sequence for Catabolite Activator Protein (CAP), which is know to bend dsDNA upon binding, between the arms of this device. The bending angle will be evaluated with single particle electron microscopy (EM), and FRET microscopy will be employed in solution to resolve real-time kinetics and deformations of CAP-DNA binding. Poster Presentations Poster

62 Advances in Nanoscience - Garching 2010 Sensing applications of GaN-based devices John D. Howgate1, Markus Hofstetter2, Sebastian Schoell1, Stefan Thalhammer2, Ian D. Sharp1 and Martin Stutzmann1 1 Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, 85748 Garching, Germany 2 Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany

ur research is dedicated to the investigation of interfaces between wide bandgap semicon- Oductors and organic systems for biosensing and bioelectronic applications. For this purpose, the fundamental operation of electrolyte-gated high electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures is studied in terms of ionic interactions at the surface, pH sensitivity, and charge transfer processes. A particular emphasis of this work is the development of top-down techniques for miniaturization of the HEMT channel in order to enhance sensitivity, with an end goal of reaching nanoscale devices. In addition, we have investigated

the catalytic activity of covalently bound enzymes on the transistor gates by immobilization of Bio-Nanoscience penicillinase for detection of the catalytic product penicillic acid from penicillin. Possibilities for direct charge transfer between GaN and grafted biomolecules have also been explored. We have found that the energetic alignment at these hybrid interfaces allows photo-catalytic cleav- age of self-assembled monolayers via UV-induced charge transfer from GaN substrates and have demonstrated that GaN and SiC are promising materials to accommodate direct charge transfer from photosynthetic reaction centers. The high sensitivity of electrolyte-gated AlGaN/ GaN devices is further exploited for real time measurement of ionizing radiation doses and the responses of locally irradiated cells on the surfaces of devices. Poster Presentations

Advances in Nanoscience - Garching 2010 63 Organic Thin-Film Transistors for Applications in Radiation Biophysics A.-L. Idzko1, G. Scarpa2, and S. Thalhammer1 1 Helmholtz Centre Munich, German Research Centre for Environmental Health, Ingolstädter Landstraße 1, D-81377 Neuherberg, Germany 2 Technical University Munich, Institute for Nanoelectronics, Arcisstrasse 21, D-81377 München, Germany

ere we present a biosensor setup based on organic semiconducting material for applica- Htions in radiation biophysics. Organic polymers are extremely sensible on physical as well as (electro-) chemical infl uences so they can be used to detect small pH-value changes and variations in ion concentrations. Both molecular structure and morphology are adjustable to fi ne-tune the chemical and physical properties, thus enhancing sensitivity and selectivity. The layout of the polymeric fi eld effect transistor device consists of a silicon substrate also acting as the gate of the transistor coated with silicon dioxide. On this dielectric an interdigitated pattern

Bio-Nanoscience of electrodes is sputtered, acting as source and drain. The surface of the transistor is coated with the polymer P3HT with spin coating. P3HT is one of the most commonly used polymers as a conducting agent because it forms highly ordered thin fi lms and has the highest reported fi eld-effect mobility in polymer fi eld effect transistors so far, 3*10-3 cm2V-1s-1. To overcome biocompatibility problems protein-based coatings and oxygen-plasma treatments were performed to enable growth of adherent living cells on those modifi ed surfaces. This new approach based on the interplay between organic and biological materials is motivated by the possibility of observing new phenomena or obtaining more detailed information from biologically active systems for example cell-cell communication during and after irradiation. [1] G. Scarpa et al., Organic Electronics 10 (4) (2009) 573-580 [2] S. Thalhammer et al., Macremolecular Bioscience 10 (4) (2010) 378-383 Poster Presentations Poster

64 Advances in Nanoscience - Garching 2010 DNA Origami as a Molecular Platform for Bionanotechnology R. Jungmann1,3, C. Steinhauer2,3, M. Scheible1, A. Kuzyk1, P. Tinnefeld2,3, F.C. Simmel1,3 1 Lehrstuhl für Bioelektronik, Physik-Department, Technische Universität München, James-Franck-Straße 1, 85748 Garching, Germany 2 Angewandte Physik - Biophysik, Ludwig-Maximilians-Universität, Amalienstraße 54, 80799 München, Germany 3 Center for NanoScience, Ludwig-Maximilians-Universität, Schellingstraße 4, 80799 München, Germany

NA is now widely used as a programmable material for the construction of two- and three- Ddimensional nanostructures. Application of hierarchical assembly strategies as well as intramolecular folding as in “DNA origami” has resulted in structures with low assembly error densities [1]. We currently explore the use of DNA origami in the context of biophysics and bionanotechnology. We use rectangular DNA origami labeled with fl uorophores at specifi c positions as a nanoscopic ruler. Super-resolution fl uorescence microscopy based on the subsequent localization of single molecules enables two fl uorophores at a distance of about 90 nm

to be optically resolved. This combination of subdiffraction imaging and DNA nanotechnology Bio-Nanoscience opens up new avenues for studying nanostructures and their dynamics [2]. We have also developed an assay for the investigation of kinetic and dynamic processes on DNA-based nanostructures using transient binding of short ﬂ uorescently labeled imaging strands. The assay allows to routinely perform analysis of binding and dissociation kinetics on the single molecule level. The method, that we term DNA-PAINT, is used to investigate positional effects of DNA hybridization kinetics on DNA scaffolds as well as for super-resolution ﬂ uorescence imaging of DNA nanostructure with a resolution < 30 nm. [1] Rothemund, P.W.K., Folding DNA to create nanoscale shapes and patterns. Nature, 2006. 440(7082): p. 297-302. [2] Steinhauer, C., et al., DNA Origami as a Nanoscopic Ruler for Super-Resolution Microscopy. Angewandte Chemie-International Edition, 2009. 48: p. 8870-8873. Poster Presentations

Advances in Nanoscience - Garching 2010 65 Towards studying equilibrium unbinding/binding transitions of single protein complexes under force – enabled by DNA Origami Fabian Kilchherr, Hendrik Dietz Laboratory for Biomolecular Nanotechnology, Physik Department, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany

dentifying and characterizing ubiquitously found adhesive interactions between biological Imacromolecules is key for understanding regulatory processes in biology. Single-molecule force spectroscopy approaches can provide detailed mechanistic insight into the physical de- tails of intramolecular interactions inside protein structures. In this project we seek to enable the single-molecule study of intermolecular protein-protein and protein-nucleic acid interactions with dual-beam optical traps which has so far remained experimentally challenging. The con- ceived DNA Origami handles enable force spectroscopical measurements of receptor-ligand

Bio-Nanoscience interactions. In addition, the presented handles are stiffer than usually used DNA double helices. This leads to less noise in the force signal and an improved spatial and temporal resolution. Poster Presentations Poster

66 Advances in Nanoscience - Garching 2010 Fabrication and Electrical Characterization of a Pore-Cavity-Pore Device Martin Langecker, Daniel Pedone, Alexandra Mara Münzer, Ruoshan Wei, Robin Daniel Nagel and Ulrich Rant Walter Schottky Institut, Technische Universität München, Germany

ingle engineered nanopores in solid state membranes have attracted broad attention in Srecent years as a tool to study single biological molecules like DNA or proteins. Here we present a novel concept for a nanopore structure in a silicon chip which does not only consist of a single nanopore in a membrane but comprises two stacked nanopores which form the opposing in- and out-lets to a cavity with a volume of 10 femto liter. The ‘pore-cavity-pore’ (PCP) device is fabricated by structuring nanopores into a sandwich SiN/Si/SiN wafer using e-beam lithography, wet chemical etching, and feedback controlled electrochemical etching steps. The in- and outlet nanopores are characterized by transmis- Bio-Nanoscience sion electron microscopy, evidencing that the pore diameters may be controlled independently down to 10 nm. The electrical properties of the PCP structure are investigated by impedance spectroscopy under conditions which are typical for single molecule experiments, that is, when applying potentials across the device in electrolyte solution. Furthermore, we present a ﬁ nite-element simulation of the electric ﬁ eld inside the device. The PCP device can be used to investigate single molecules both optically and electrically. We present a measurement chamber design that is capable of simultaneous electro-optical measurements. Poster Presentations

Advances in Nanoscience - Garching 2010 67 DNA origami supports for the analysis of complex samples by singe-particle electron microscopy Thomas G. Martin and Hendrik Dietz Laboratory for Biomolecular Nanotechnology, Physik Department, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany

e introduce a new approach for imaging molecules with low contrast in an electron micro- Wscope. DNA origami structures are well deﬁ ned structures with a high contrast in transmission electron microscopy. By binding an unknown object to DNA origami supports it is possible to determine its position even if the object’s contrast is lower than the gaussian background noise. Placing markers on the support provides additional information about the orientation which can be used to simplify 3D reconstruction. Bio-Nanoscience Poster Presentations Poster

68 Advances in Nanoscience - Garching 2010 A Thermal Trap for DNA Replication Christof B. Mast and Dieter Braun Systems Biophysics, Ludwig-Maximilians-Universität München, Fakultät für Physik, Amalienstr. 54, D-80799 München, Germany

ormally, genetic information is protected from free diffusion into the environment by cell Nwalls. The cells provide all conditions for the replication and mutation of genetic material - the basic prerequisite for Darwinian evolution. We modeled a fundamental principle in the laboratory, which allows for continuous evolution of genetic material without cell membranes. We ﬁ lled a thin capillary with DNA and nucleotides, solved in buffer as an aqueous solution (Figure c). A moving infrared laser spot then generated a thermal gradient realizing thermophoresis as well as a cyclic convection of the solution. The superposition of both effects caused

the double-stranded DNA molecules to migrate to the cold area (Figure a), while simultane- Bio-Nanoscience ously cycling the DNA between the cold and warm section of the capillary. In the hot area, the DNA separates into single strands. These are then elongated by a polymerase enzyme in the cold region to two double-stranded copies of the original template DNA (Figure b). Therefore, a simple temperature gradient drives both, an exponential replication as well as the selective accumulation of information. This is relevant as presumably similar thermal conditions prevailed in rock pores near hot undersea springs of prehistoric oceans. Our experiment shows how a simple disequilibrium setting may allow life to evolve. Poster Presentations

Advances in Nanoscience - Garching 2010 69 Biochemistry on a leash Matthias Schickinger et al. Laboratory for Biomolecular Nanotechnology, Physik Department, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany

nter-macromolecular interactions play a major role in many biological processes. In order to Ibetter understand these processes it is essential to identify and quantify these protein-protein and protein-nucleic acid interactions. The insights gained may be invaluable to many applications in the ﬁ elds of biotechnology or biomedicine, e.g. for targeted drugdesign. Here, we intend to introduce a new approach to single molecule measurements on receptor-ligand systems that, using a comparatively simple experimental setup, makes it possible to gain deeper insight into the kinetics of these systems. At the heart of this technique is a DNA origami structure

Bio-Nanoscience consisting of two 18-helix blocks and a connecting single- or double-stranded DNA leash. The blocks attach to the respective receptor and ligand, respectively. One of the blocks is fi xed to a surface, the other one is free to move (but kept on the leash) and carries fl uorescent labels. By monitoring the magnitude of the mobile block’s movement in a fl uorescence microscope, we discriminate the bound state from the unbound state and measure directly the binding and unbinding times of our sample system. Once this method has been established, it can serve as a platform for the study of all kinds of inter-biomacromolecular interactions. Owing to its relatively basic instrumental requirements, it should be fairly easily reproducible. Furthermore, it would deliver a means to measure binding kinetics as a function of environmental conditions, under the infl uence of additional ligands and in a high-throughput and highly parallel fashion. Poster Presentations Poster

70 Advances in Nanoscience - Garching 2010 Synthetic Assembly of Non-Peptidic Ligands for Constructing

αvß3- and α5β1-Integrin based Focal Adhesions A. Schwede1, S. Neubauer2, F. Rechenmacher2, H. Kessler2, J. Polleux1,3, H. B. Schiller3, R. Fässler3 and J. P. Spatz1 1 Department of New Materials and Biosystems, Max-Planck-Institute for Metals Research, Heisenbergstr. 3, 70569 Stuttgart, Germany 2 Institute for Advanced Study (IAS), Department Chemie, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany 3 Department of Molecular Medicine, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany

he ability of eucaryotic cells to react to their proximate environment, the so-called extracel- Tlular matrix (ECM), is a crucial biological phenomenon. It has been extensively described in literature how cells effectively react in a coordinated, specifi c, localized manner to stimuli coming from their external environment. Depending on the defi ned chemical and physical characteristics of the underlying ECM, cell behaviour such as proliferation, differentiation, motility or even apoptosis can be greatly infl uenced. New technologies and scientifi c approaches give us the thrilling opportunity of gaining innovative, clarifying insights into how cells sense their environment locally and yet react globally dis- Bio-Nanoscience playing a myriad of customized mechanical and biochemical responses. Our system is based on the self-organization of nanoparticles with a spatial control at the nanometer scale, which in turn serve as anchor points to signaling molecules of our choice. More specifi cally we work with gold nano-particles (AuNPs) covalently bound to a biologically inert apolar poly-ethylene-glycol (PEG) scaffold in a defi ned pattern with tuneable spacing. Using ligands covalently bound to these AuNPs that address specifi c signalling pathways offers us the unique possibility to better understand the relevance of these pathways in the formation/maturation/disassembly of focal adhesions (FA). Therefore, these nano-structures offer highest spatial resolution regarding the positioning of single transmembrane receptors activation such as integrin activation and therefore FA formation and enable the testing of cellular response to individual specifi c signal molecules and their spatial patterning. The challenge in this study is to direct FA formation by using different non-peptidic binding ligands at the same substrate on both the micro-scale and the nano-scale. With this technol- Poster Presentations ogy we aim to construct synthetically FAs in living cells. Many questions arise: is it possible to form adhesion complexes consisting of two types of transmembrane receptors? How is signal transduction affected and how is the phenomenological reaction of cells to this directed manipulation?

Advances in Nanoscience - Garching 2010 71 Single Molecules as Energy, Force, Friction and Structure Sensors F. Stetter, T. Pirzer, B. Balzer, M. Geisler und T. Hugel Physik-Department E22, Technische Universität München, James-Franck-Str. 1, D-85748 Garching, Germany

uring the last years we developed molecular sensors consisting of single polypeptides Dand an AFM tip. They allowed us to determine the interaction between single polymers and solid substrates in aqueous environments. In particular we were able to understand how hydrophobic and dispersion forces determine polymer adhesion [1, 2]. Using these probes and single molecule force spectroscopy we study various phenomena and interfaces. In particular we will present how surface properties affect the adhesion force of polymers [3], how friction and adhesion are related on the nano level and how lipid bilayers Bio-Nanoscience determine the structure of amyloids like Alpha-Synuclein, a key peptide related to Parkinson’s disease. 1. Horinek, D., et al., Peptide adsorption on a hydrophobic surface results from an interplay of solvation, surface, and intrapeptide forces. Proc Natl Acad Sci U S A, 2008. 105(8): p. 2842-7. 2. Geisler, M., B.N. Balzer, and T. Hugel, Polymer adhesion at the solid-liquid interface probed by a single-molecule force sensor. Small, 2009. 5(24): p. 2864-9. 3. Pirzer, T., et al., Single molecule force measurements delineate salt, pH and surface effects on biopolymer adhesion. Phys Biol, 2009. 6(2): p. 025004. Poster Presentations Poster

72 Advances in Nanoscience - Garching 2010 Single-Molecule Cut and Paste for Functional Assembly Mathias Strackharn1,2, Stefan. W. Stahl, Stefan K. Kufer, Elias M. Puchner, Hermann Gumpp, Stephan Heucke and Hermann E. Gaub1 1 Center for Nanoscience & Physics Department, University Munich, Amalienstr. 54, 80799 Munich, Germany 2 [email protected]

ingle-molecule cut-and-paste surface assembly (SMCP) [1] was employed for the con- Strolled deposition of individual fl uorophores in well-defi ned nanometer sized patterns. We combined a total internal refl ection fl uorescence microscope (TIRFM) with an atomic force microscope (AFM) and used this ultrastable hybrid TIRF-AFM setup [4] to monitor the deposition process of single fl uorophores in real time and to determine their position with nanometer precision. We were able to demonstrate the precision of the method and to point out the limitations [2]. SMCP allows for the creation of patterns of arbitrary shape and with arbitrary numbers of single molecules consisting of multiple species. By making use of specifi c molecular interac- Bio-Nanoscience tion, like the coupling of streptavidin to biotinylated transfer DNA, we could provide with this technique a scaffold for the controlled self-assembly of nanoparticles [3]. We could further combine the technique with an elaborated superresolution microscopy technique and highlight which role reductants and oxidants play for aquisition speed and resolving power [5]. Recently we could build up from single molecular units a complex with a complete new function that oc- cured only due to the functional assembly. [1] Kufer, S. K., Puchner, E. M., Gumpp, H., Liedl, T. & Gaub, H. E., Single-Molecule Cut-and-Paste Surface Assembly, Science 319, 594-596 (2008) [2] Kufer S.K., Strackharn M, Stahl S.W., Gumpp H., Puchner E.M. & Gaub H.E., Optically monitoring the mechanical assembly of single molecules, Nature Nanotechnology, Vol. 4, (2009) [3] Puchner, E. M., Kufer, S. K., Strackharn, M., Stahl, S. W. & Gaub, H. E., Nanoparticle Self-Assembly on a DNA-Scaffold written by Single-Molecule Cut-and-Paste, Nano Letters, Vol. 8, No. 11 (2008) [4] Gumpp H., Stahl S.W., Strackharn M., Puchner E.M. and Gaub H.E., Ultrastable combined atomic force and total internal refl ection fl uorescence microscope. - Review of Scientifi c Instruments, 80(6) (2009) [5] Cordes T., Strackharn M., Stahl S.W., Summerer W., Steinhauer C., Forthmann C., Puchner E.M., Vogelsang J., Gaub H.E., and

Tinnefeld P., Resolving Single-Molecule Assembled Patterns with Superresolution Blink-Microscopy, Nano Letters, Vol. 10 (2010) Poster Presentations

Advances in Nanoscience - Garching 2010 73 Analysis of proteins on a chip with the switchSENSE platform Ralf Strasser, Jens Niemax, Paul Hampel, Kenji Arinaga, and Ulrich Rant Walter Schottky Institut, Technische Universität München, Am Coulombwall 3, D-85748 Garching, Germany

hile established label-free surface biosensors are restricted to yield mere binding con- Wstants, the platform technology switchSENSE adds the unique capability of a size/shape analysis during the same measurement run. By determining a protein’s hydrodynamic diameter with high accuracy, a wealth of previously inaccessible information can be revealed. Short DNA molecules are chemically tethered to metal microelectrodes at one end. When applying AC voltages (0.1 Hz – 500 kHz) to the electrodes, the DNA molecules are repelled from -or attracted to- the surface. This molecular ‘switching’ is monitored in real time by optical Bio-Nanoscience means. Receptors attached to the DNAs’ upper ends serve as capture sites for target molecules. Label-free targets which bind to the interface alter the switching behavior, and ‘classi-

cal’ binding parameters (KD, kon, koff) can be obtained. Unprecedented for a biochip detection platform, additional information about the target molecule size and shape is inferred from a molecular dynamics measurement. Here we present a measurement device and a biochip developed at the Walter Schottky In- stitute for the parallel and label-free detection and analysis of biomolecules. The utility of the switchSENSE platform for the analysis of protein-protein, protein-DNA, DNA-DNA is demonstrated and application examples with relevance to the engineering of therapeutic antibodies are presented. Poster Presentations Poster

74 Advances in Nanoscience - Garching 2010 Protein Binding Assays in Biological Liquids using Microscale Thermophoresis Christoph J. Wienken1, *, Philipp Baaske2, Stefan Duhr2 and Dieter Braun1 1 Department of Physics and Center for NanoScience (CeNS), Ludwig Maximilians University Munich, Amalienstr. 54, 80799 Munich Germany 2 NanoTemper Technologies GmbH, Amalienstr. 54, 80799 Munich, Germany * Christoph Wienken, email: [email protected], phone: +49 89 2180 1484, fax: +49 89 2180 16558

rotein interactions inside the human body are expected to differ from the situation in vitro. PThis is crucial when investigating protein functions or developing new drugs. We present a sample-efﬁ cient, free-solution method termed Microscale Thermophoresis (MST) that is capable of analyzing interactions of proteins or small molecules directly in biological liquids such as blood serum or cell lysate. The technique is based on the thermophoresis of molecules, which provides information about molecule size, charge and hydration shell. We validated the method using immunologically relevant systems like human interferon gamma or low molecu-

lar weight binders such as calcium binding to calmodulin. The affi nity of the small molecule Bio-Nanoscience inhibitor quercetin for its kinase PKA was determined in buffer and human serum revealing an 400-fold reduced affi nity in serum. This information about infl uences of the biological matrix allows for more reliable conclusions on protein functionality and may aid in more effi cient drug development. Poster Presentations

Advances in Nanoscience - Garching 2010 75 Formation of Nanoparticle Structures with a Combination of Protein and DNA Linkers Vera B. Zon, Matthias Sachsenhauser and Ulrich Rant Walter Schottky Institut, Technische Universität München, 85748 Garching, Germany

he optical properties of metal nanoparticles (NPs) are governed by localized surface plas- Tmon resonances (LSPRs), which result from the interaction of the conduction electrons of the particles with the incident light. The coupling of LSPRs between closely located colloidal metal particles is particularly interesting, because it generates substantial enhancements of the electric ﬁ eld, so called ‘hot spots’, which may be used for surface-enhanced spectroscopy or engineered for energy-transfer constructs. In order to build complex architectures with tailored optical properties (optical circuits) from individual NPs, the protein- and/or DNA-programmed

Bio-Nanoscience assembly of NPs is especially promising, because particles can be deterministically arranged on the nano-scale. Here we present a controlled way to form gold NP dimers and to build chains from the dimers. The chain units are protein-linked NP dimers, which are connected by DNA molecules. We utilize the self-organizing properties of DNA, which allow us to pre-design the desired structures and arrange the building blocks in a deterministic manner. We show the inﬂ uence of the number of the DNA strands per linking protein on the architecture of the obtained structures. The system is examined with respect to its optical properties with UV-VIS spectroscopy and dynamic light scattering; additionally we present TEM images of the NP complexes.

76 Advances in Nanoscience - Garching 2010 USEFUL INFORMATION How to get to the venue

ZNN Center for Nanotechnology and Nanomaterials, Am Coulombwall 4

IAS Institute for Advanced Study (Lichtenbergstraße/ Boltzmannstraße)

Subway station „Garching Forschungszentrum“

PUBLIC TRANSPORT Subway „U6“, direction „Garching Forschungszentrum“

Departure „Marienplatz“ (Munich city center) 7:40 7:50 8:00 Departure „Garching“ (Hotel König Ludwig) 8:03 8:13 8:23 Arrival „Garching Forschungszentrum“ 8:05 8:15 8:25

Subway station - IAS building: 5 min walk, Subway station - ZNN building: 10 min walk

ORGANIZERS Nanosystems Initiative Munich (NIM) & TUM Institute for Advanced Study (IAS): G. Abstreiter, H. Dietz, J.J. Finley, D. Grundler, A. Holleitner, P. Lugli, F. Simmel, M. Stutzmann

CONTACT Irmgard Neuner (Ofﬁ ce Prof. Gerhard Abstreiter) Walter Schottky Institut (TU München) Am Coulombwall 3 D-85748 Garching Tel: +49-(0)89-289-12771 Fax: +49-(0)89-289-12704 [email protected]

Advances in Nanoscience - Garching 2010 77 LIST OF PARTICIPANTS

First Name Last Name Affi liation e-mail Yasuhiko Arakawa University of Tokyo [email protected] Marianne Auernhammer TU München [email protected] Erik Bakkers TU Delft [email protected] Andreas Bausch TU München [email protected] Heike Böhm Max Planck Institute for Metals Research [email protected] Achyut Bora TU Braunschweig [email protected] Dieter Braun LMU München [email protected] Carlos Castro TU München [email protected] Anna Cattani-Scholz TU München [email protected] Hendrik Dietz TU München [email protected] Beate Dirks TU München [email protected] Georg Dürr TU München [email protected] Klaus Ensslin ETH Zürich [email protected] Jochen Feldmann LMU München [email protected] Claudia Felser Johannes-Gutenberg-Universität Mainz felser-offi [email protected] Jonathan Finley TU München jonathan.fi [email protected] Matthias Firnkes TU München matthias.fi [email protected] Anna Fontcuberta i Morral EPF Lausanne anna.fontcuberta-morral@epfl .ch Emanuel Forster TU München [email protected] Daniel Fuhrmann Universität Augsburg [email protected] Stefan Funk TU München [email protected] Jose A. Garrido TU München [email protected] Hermann Gaub LMU München [email protected] Thomas Gerling TU München [email protected] Stephen Goodnick Arizona State University [email protected] Dirk Grundler TU München [email protected] Moritz Hauf TU München [email protected] Norman Hauke TU München [email protected] Simon Hertenberger TU München [email protected] Lucas Hess TU München [email protected] Nicolas Hoermann TU München [email protected] Markus Hofstetter Helmholtz Zentrum München markus.hofstetter@helmholtz-muenchen Alexander Högele LMU München [email protected] Alexander W. Holleitner TU München [email protected] John Howgate TU München [email protected] Rupert Huber TU München [email protected] Thorsten Hugel TU München [email protected] David Hunger LMU München [email protected] Anna-Lena Idzko Helmholtz Zentrum München [email protected] Andreas Jöckel MPQ/LMU/Uni Basel [email protected] Ralf Jungmann TU München [email protected] Horst Kessler TU München [email protected] Fabian Kilchherr TU München [email protected] Florian Klotz TU München fl [email protected] Gregor Koblmüller TU München [email protected] Maria Korppi Universität Basel [email protected] Jörg Kotthaus LMU München [email protected] Joachim Krenn Karl-Franzens-Universität Graz [email protected] Hubert Krenner Universität Augsburg [email protected] Katharina Krischer TU München [email protected] Julia Kunze TU München [email protected]

78 Advances in Nanoscience - Garching 2010 First Name Last Name Afﬁ liation e-mail Anton Kuzyk TU München [email protected] Martin Langecker TU München [email protected] Arne Laucht TU München [email protected] Silvia Leonardi TU München [email protected] Tim Liedl LMU München [email protected] Enrique Lin Shiao TU München [email protected] Bettina Lotsch LMU München [email protected] Paolo Lugli TU München [email protected] Thomas Martin TU München [email protected] Christof Mast LMU München [email protected] Bert Nickel LMU München [email protected] Yoshichika Otani University of Tokyo [email protected] Natan Osterman LMU München [email protected] Milan Padilla TU München [email protected] Anshuma Pathak TU Braunschweig [email protected] Daniel Pedone TU München [email protected] Leonhard Prechtel TU München [email protected] Joachim Rädler LMU München [email protected] Ulrich Rant TU München [email protected] Celine Rüdiger TU München [email protected] Daniel Rudolph TU München [email protected] Benedikt Rupprecht TU München [email protected] Matthias Sachsenhauser TU München [email protected] Giuseppe Scarpa TU München [email protected] Matthias Schickinger TU München [email protected] Lukas Schmidt-Mende LMU München [email protected] Christian Schönenberger Universität Basel [email protected] Yvonne Schön Max Planck Institute for Metals Research [email protected] Florian Schülein Universität Augsburg ﬂ [email protected] Alice Schwede Max Planck Institute for Metal Research Stuttgart [email protected] Petra Schwille TU Dresden [email protected] Max Seifert TU München [email protected] Ian Sharp TU München [email protected] Friedrich Simmel TU München [email protected] Uri Sivan Technion Tel Aviv [email protected] Martin Soini TU München [email protected] Dance Spirkoska TU München [email protected] Markus Stallhofer TU München [email protected] Marin Steenackers TU München [email protected] Frank Stetter TU München [email protected] Mathias Strackharn LMU München [email protected] Ralf Strasser TU München [email protected] Martin Stutzmann TU München [email protected] Almut Tröller LMU München [email protected] Klaus von Klitzing MPI für Festkörperforschung, Stuttgart [email protected] Christian Wachauf TU München [email protected] Eva Weig LMU München [email protected] Christian Westermeier LMU München [email protected] Wolfgang Wiedemann LMU München [email protected] Christoph Wienken LMU München [email protected] Andreas Wild TU München [email protected] Marc Wilde TU München [email protected] Achim Wixforth Universität Augsburg [email protected] Jörg Wrachtrup Universität Stuttgart [email protected] Ilaria Zardo TU München [email protected] Vera Zon TU München [email protected]

Advances in Nanoscience - Garching 2010 79 PROGRAM – MONDAY, OCTOBER 25, 2010 PROGRAM – TUESDAY, OCTOBER 26, 2010

8:30-9:00 OPENING AND WELCOME ADDRESSES SESSION 3: NANO AND ENERGY VENUE: IAS BUILDING SESSION 1: QUANTUM NANOSYSTEMS VENUE: IAS BUILDING 8:30-9:00 Martin Stutzmann (TU München and NIM) „Black Silicon“: Nanotextured Silicon Surfaces for Photovoltaics 9:00-9:40 Klaus von Klitzing (MPI für Festkörperforschung, Stuttgart) Experiments on the ultimate two-dimensional electron system 9:00-9:30 Stephen Goodnick (Arizona State University) Role of Nanotechnology in Third Generation Photovoltaics 9:40-10:10 Klaus Ensslin (ETH Zürich) Graphene quantum circuits 9:30-10:00 Lukas Schmidt-Mende (LMU München and NIM) Nanostructured organic and hybrid solar cells 10:10-10:40 COFFEE BREAK 10:00-10:30 COFFEE BREAK 10:40-11:00 Jonathan Finley (TU München and NIM) Exploring and harnessing cavity-QED phenomena in single 10:30-11:00 Claudia Felser (Universität Mainz) and few quantum dot photonic crystal nanostructures Heusler Compounds: Novel Materials for Energy Applications 11:00-11:30 Erik Bakkers (TU Delft) 11:00-11:30 Julia Kunze (TU München and IAS)

Periodic Nanowire Structures TiO2-Nanotubes in Energy Research 11:30-12:00 Anna Fontcuberta i Morral (EPF Lausanne and TUM-IAS) 11:30-14:30 POSTERSESSION AND BUFFET-LUNCH VENUE: ZNN BUILDING Ga-assisted MBE grown GaAs nanowires and related quantum heterostructures for solar applications SESSION 4: BIO-NANOSCIENCE VENUE: IAS BUILDING 12:00-13:30 LUNCH BREAK 14:30-15:00 Petra Schwille (TU Dresden) Synthetic Biology of Cell Division SESSION 2: HYBRID NANOSYSTEMS VENUE: IAS BUILDING 15:00-15:30 Hendrik Dietz (TU München and IAS) 13:30-14:00 Eva Weig (LMU München and NIM) DNA Nanotechnology for Protein Science Voltage-sustained self-oscillation of a nanomechanical electron shuttle 15:30-16:00 Uri Sivan (Technion, Israel) 14:00-14:30 Christian Schönenberger (Universität Basel) The Bio-Electronic Synapse – Fusing Electronics with Molecular Biology Cooper-pair splitter: towards an efﬁ cient source 16:00-16:30 COFFEE BREAK of spin-entangled EPR pairs 16:30-17:00 Ulrich Rant (TU München, NIM and IAS) 14:30-15:00 Yoshichika Otani (University of Tokyo) Molecular Interactions on Dynamically Actuated Surfaces Pure spin current based spintronics in metallic nano-structures and in Artiﬁ cial Nanopores 15:00-15:30 Jörg Wrachtrup (Universität Stuttgart) 17:00-17:30 Joachim Rädler (LMU München and NIM) Carbon nanostructures for quantum spintronics Stochastic gene expression and the decisive role 15:30-16:00 COFFEE BREAK of noise in microbial genetic networks 16:00-16:30 Joachim Krenn (Universität Graz) 17:30-18:00 Friedrich Simmel (TU München and NIM) Plasmonic control of elementary emitters Nanoscale structures and molecular devices made from DNA 16:30-17:00 Achim Wixforth (Universität Augsburg and NIM) 18:00-19:00 CLOSING AND FAREWELL (BIER AND BREZEN) The perfect wave 17:00-17:30 Alexander Holleitner (TU München and NIM) Optoelectronic dynamics in hybrid nanoscale circuits VENUE 17:30-18:00 Yasuhiko Arakawa (University of Tokyo and TUM-IAS) TUM Institute for Advanced Study (IAS) and A Quarter Century of Quantum Dots: From Science Center for Nanotechnology and Nanomaterials (ZNN) of Walter Schottky Institut in Garching to Practical Implementation ORGANIZERS 18:15-19:00 RECEPTION Nanosystems Initiative Munich and TUM Institute for Advanced Study 19:00-22:00 DINNER Gerhard Abstreiter, Hendrik Dietz, Jonathan J. Finley, Dirk Grundler, Alexander Holleitner, Paolo Lugli, Friedrich Simmel, Martin Stutzmann