Stream 1: EMAG - 2D Materials 10:00 - 12:00 Tuesday, 6th July, 2021 Sessions EMAG Conference Session Session Organiser Andy Brown, Sarah Haigh

10:00 - 10:30

349 Atomic Imaging in 2D Material Heterostructures : Twist, Defects and Particle Synthesis

Prof Sarah Haigh1, Dr Nick Clark1, Astrid Weston1, Dr Daniel Kelly1, Dr Matthew Hamer1, Dr Yichao Zou1, Dr Vladimir Enaldiev1, Dr Alex Summerfield1, Dr Victor Zólyomi1, Prof Denis Gebauer2, Prof Vladimir Falko1, Dr Roman Gorbachev1 1National Institute, , Manchester, United Kingdom. 2Institute of Inorganic Chemistry, Leibniz Universität Hannover, Hannover, Germany

Abstract Text

This talk aims to demonstrate how atomic resolution scanning transmission (STEM) imaging is being used in Manchester to support and enable the development of 2D materials and their heterostructures. The possibility to create new ‘designer’ materials by stacking together atomically thin layers extracted from layered materials with different properties has opened up a huge range of opportunities, from new optoelectronic phenomena [1], modifying and enhancing electron interactions in moiré superlattices [2], to creating a totally new concept of designer nanochannels for molecular or ionic transport [3]. The impressive progress being achieved in the field crucially depends on knowledge of the atomic structure of these heterostructures [4], which in many cases can only be analysed by transmission electron microscopy (TEM) techniques. In this talk I will try to illustrate this with some of our recent work. I will demonstrate imaging of the unusual lattice reconstruction that occurs in twisted transition metal dicholcogenide bilayers [5]. We reveal that this behaviour is more complex than is seen for twisted heterostructures of graphene and/or hexagonal boron nitride. Complementary scanning probe microscopy (SPM) measurements show that such reconstruction creates strong piezoelectric textures, opening a new avenue for engineering of 2D material properties. I will also illustrate a new TEM support grid where an MoS2 wetting layer is added to improve adhesion, enabling sample transfer and TEM visualisation for even the most challenging 2D heterostructures [6]. Finally I will show that 2D heterostructures can themselves be used to enable new possibilities for STEM imaging. We present a new design of graphene based mixing cell where a monolayer 2D material membrane is fractured by the electron beam enabling the earliest stages of mixing to be observed. We apply this novel platform for the direct visualisation of the entire reaction timeline for calcium carbonate synthesis, including nanoscale imaging of liquid-liquid phase separation, the formation of amorphous calcium carbonate, and particle crystallization. [7]

Keywords

2D materials, CaCO3, scanning transmission electron microscopy, in situ, liquid cell, graphene, transition metal dichalcogenides 10:30 - 10:42

147 Monitoring dynamics of defects and single metal atoms in functionalized graphene by temperature programmed in situ transmission electron microscopy

Dr Rosa Arrigo1, Dr Takeo Sasaki2, Dr Manfred Erwin Schuster3 1Salford University, Manchester, United Kingdom. 2JEOL, Welwyn Garden City, United Kingdom. 3Johnson Matthey, Sonning Common, United Kingdom

Abstract Text

The reactivity of carbon materials in catalysis and electrocatalysis is due to the edges site terminations and point defects (vacancies, non 6-membered rings) on the basal planes of the graphene layers. These sites are often terminated by heteroatoms such as O, N, B, P which impart specific acid/base properties. Furthermore, these heteroatoms can be used as anchoring sites for metal atoms to prepare C-metal hybrid systems. Single metal atom sites and point defects are key structural entities determining the performance of graphene- based catalysts. Not only do they co-participate in the catalytic turn-over, but the carbon defects can also be used to tailor the reactivity and selectivity of the immobilized metal species. In this contribution we are concerned with the case of Fe on N-functionalized few-layer graphene which is widely investigated as alternative to platinum group metals systems in electro-catalytic applications such as the oxygen reduction reaction, the electrochemical CO2 reduction and the electrochemical NH3 synthesis. We apply in-situ thermal programmed scanning transmission electron microscopy to monitor dynamics involving Fe single atoms and their stabilization on N functionalized few-layer graphene. This allows us to identify the nature of the defects initially present on N-functionalised graphene and their property to coordinate Fe atoms. Furthermore, we study how these structural defects change upon annealing in the presence and absence of metal atoms. We will show a high mobility of both defects and metal atoms diffusing rapidly from one defect point to the other. Furthermore, we will show that the presence of metal atoms induces a stabilization of the graphene defects. This study is of relevance for the application of graphene-like materials for low and medium temperature catalysis and electrocatalysis.

Figure 1: temperature induced formation of vacancies on few layer N-doped graphene: 500°C (a) vs 700°C (b)

Keywords in-situ TEM, single site catalysis, graphene 10:42 - 10:54

289 Matching algorithms for elemental quantification and few tilt tomography in 2D materials

Dr. Christoph Hofer1, Dr. Viera Skákalová2, Jonas Haas3,4, Prof. Jannik Meyer3,4, Prof. Timothy Pennycook1 1University of Antwerp, Antwerp, Belgium. 2University of Vienna, Vienna, Austria. 3Eberhard Karl University of Tübingen, Tübingen, Germany. 4Natural and Medical Sciences Institute at the University of Tübingen, Reutlingen, Germany

Abstract Text

Introduction Identifying the position and chemical identity of each atom in a specimen is the ultimate goal of structural characterization. With the rise of aberration correctors in scanning transmission electron microscopy (STEM) the Z-contrast based annular dark-field (ADF) imaging technique even allows to distinguish light elements in single layer materials [1]. However, residual aberrations are difficult to manually detect and correct under the low doses needed for beam sensitive materials hampering the analysis of ADF images. Moreover, a conventional tomographic approach for three-dimensional imaging is difficult due to the requirement of a large number of projections [2]. I will introduce the approach of using matching algorithms to overcome these difficulties. To perform quantification of images that is robust to the presence of both residual aberrations and noise, algorithmic matching of simulated and experimental data can be used [3]. A simulation is performed from an initial guess. Successive simulations are then iteratively optimized to match the experimental data as well as possible by adjusting the aberrations and atomic positions used in the simulation. Once convergence is achieved, the atomic scattering factors are finally included in the optimization. Matching algorithms also enable tomography with a much reduced number or tilt angles. I will present results illustrating 3D structure determination of 2D materials such as graphene [4] directly from just two tilt angles. This is indeed sufficient as long as each atom can be identified individually in each projection and the connectivity matrix can be obtained showing which atom is which in the comparison of each view. Under these circumstances, a very similar optimization process is realized where the model is matched so that the simulated projections in each tilt angle are matched to the corresponding experimental data set. The reconstruction is demonstrated using the ADF signal, but is also expected to work with any other signal providing atomic-resolution. Materials & methods ADF STEM measurements were conducted using a Nion UltraSTEM100 operated at 60~kV and a JEOL JEM- ARM200F operated at 80 kV at a convergence angle of ~30 mrad, and tilts separated by ~20 deg. Ptychography data will be collected using a microsecond dwell time capable custom camera at EMAT. Results and Discussion Analysis reveals that our novel intensity method achieves more reliable results compared to other quantification methods in the presence of small non-round aberrations. The method even allows us to extract quantitative atomic intensities if the aberrations are strong. As a specific example, this approach allows to quantify different light-elements in graphene in the presence of a slight three-fold astigmatism which wouldn’t have been possible via other established approaches. The three-dimensional analysis reveals significant deformation of defect sites in 2D materials. Specifically for graphene grain boundaries, a correlation between the deformation amplitude and the misorientation angle is demonstrated. Figure 1 shows one example of a reconstructed grain boundary using two atomically resolved STEM images captured at tilt angles separated by 20 degrees. The analysis also enables one to study single- atomic out-of-plane dynamics, which we have demonstrated for impurities in graphene. We will discuss the extension of the few tilt tomography method to thicker 2D materials such as transmission metal dichalcogenides, and the addition of simultaneous ptychographic data to the ADF signal to facilitate the simultaneous location of both heavy and light atoms. The dose-efficiency of ptychography should also allow a lower dose to be used for such tomography. Alternatively, the dose efficiency can be used to image at more tilts for a given dose budget. With more tilts it becomes easier to handle materials that are thicker than a single atomic layer. In order to further improve the reliability of the reconstruction, a hybrid approach is introduced, where the energy of the model is included into the optimization. Conclusions Our new methods provide reliable intensities from atomically resolved STEM images. They allow one to decouple intensity variations arising from aberrations, beam tails and varying bond distances from those arising from sample variations. For light-element samples, they allow sharp intensity distributions around single elements to be obtained. They also allow the three-dimensional structure of graphene to be obtained showing that atomically thin materials are far from being flat, especially at defect sites. An extension of the algorithm to a wide range of 2D materials is further discussed.

Figure 1: Two-tilt reconstructed graphene grain boundary showing a significant out-of-plane deformation induced by the line defect

Keywords

2D materials, Quantitative STEM, 3D imaging

References

[1] Krivanek, O. et al., Nature 464, 571–574 (2010). [2] A. C. Kak et al., IEEE Engineering in Medicine and Biology Society, New York: IEEE Press (1988). [3] Hofer C. et al., submitted [4] Hofer C. et al., 2D materials 5, 045029 (2018) [5] Research funded by the Ministry of Science, Research and Art Baden-Württemberg and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme via Grant agreement No. 802123-HDEM. 10:54 - 11:06

303 Highly aligned crystallography of 1-1.5 nm Sb2Te3 nanowires embedded in single walled carbon nanotube bundles leading to reversible in situ Phase Change Behaviour at the 1 nm3 scale.

Dr. Jeremy Sloan1, Dr. Reza Kashtiban1, Dr. Charlotte Slade1, Ms. Kiran Bal1, Dr. Samuel Marks1, Dr. Kryzstof Morawiek2, Mr. Yong Zhao Zhang3, Mr. Zhong Wen Li3, Prof. Ana Sanchez1, Prof. Slawomir Kret2, Prof. Richard Walton1, Prof. Piotr Dluzewski2, Dr. Andrij Vasylenko4, Dr. James Lloyd-Hughes1, Prof. Huai Xin Yang3 1University of Warwick, Coventry, United Kingdom. 2Institute of Physics, Warsaw, Poland. 3Institute of Physics, Beijing, China. 4University of Liverpool, Liverpool, United Kingdom

Abstract Text

Phase change materials (PCMs) have been intensively studied due to their promising utility as non-volatile memory and switching devices.1,2 The fundamental mechanism exploited in these applications is the change in electronic properties upon crystalline-to-amorphous structural transition. Structural changes are responsible for localization of charge, impeding electronic transport. Reversibility of the temperature induced crystalline- to-amorphous phase transition in PCMs makes these materials promising candidates for a variety of device applications and their miniaturization offers increased densities for data storage. Our recent studies have focused on confining PCMs to a volume density of ~1nm2 with a potential volume ‘bit’ density of ~1 nm3 by confinement in single walled carbon nanotube (SWCNT)3,4 bundles with constituent tubules exhibiting diameters from 1.4-1.7 nm. When these are infiltrated with layered PCM materials such as Sb2Te3 (the synthesis of this sample is described in Ref. 4) these composites present with highly aligned inclusion crystal growth leading to Bragg reinforcement of electron scattering in electron diffraction obtained from aligned bundles (i.e. Fig. 1(a) and (b, left)).4,5 This occurs in spite of the fact that the filled nanotubes are in a random orientation (i.e. Fig. 1(c)) because a sufficient number of them have (-11-5), (-120) and (015) reflections 4-6 corresponding to equivalent lattice planes derived from the bulk R-3mh Sb2Te3 crystal structure to elicit the Bragg scattering observed in Fig. 1(b). Note that the 10-10 and 11‑20 diffraction rings from the encapsulating SWCNT bundle as well as the equatorial line (ELSWCNT) are also observed. The general crystallography of a five atomic layer thick Sb2Te3 fragment defined relative to the R-3mh Sb2Te3 unit cell is depicted in Fig. 1(d). This highly orientated crystal growth behaviour facilitated the direct observation of crystalline/amorphous phase change when Sb2Te3/SWCNT bundles are subjected to increased electron beam fluence at 80 kV in an ARM200F electron microscope from 0.8 to 1.5 pA/cm.2 In the present study, we show that the same behaviour can be reversibly induced when the Sb2Te3/SWCNT composite is heated from room temperature (i.e. RT) to 400° C and then cooled back down to RT. We also further expand on the crystallography of these embedded phases as a function of SWCNT diameter and introduce the narrowest 3-atom thick structure from a homologous series of SbxTeystructures in which the thickness of successive 3-, 4- and 5-atomic layer thick nanowires varies in thickness by +/-1 atomic layers in cross-section as shown by the three ADF images in Figs. 1(e)-(g) which correspond to the three composite models in Figs. 1(h)-(j) respectively. It is noteworthy that the same three (-11-5), (-120) and (015) reflections (i.e. as represented in Figs. 1(d) and Fig. 1(h)-(j)) are clearly visible in all three crystals, as depicted in Fig. 1(h)-(j). In Fig. 2 we see how the aligned crystal growth behavior outlined in Fig. 1(a-j) assists with observing reversible temperature induced Phase Change in an aligned bundle of SWCNTs (i.e. Fig. 1(a)) as indicated by the disappearance of the (-120) reflection and fusing of the (-11-5) 4 and (015) reflections to form a single RGSb2Te3 feature corresponding to the glassy phase. This sample was heated in an ARM200F (Beijing IoP) equipped with a Protochips heating holder and the sample was heated initially in steps of 25 °C to 100 °C and then in steps of 20 °C to 500 °C. Fig. 2 shows the sample being heated up from 25 °C to 200 °C, 300 °C and 400 °C and then cooled down from 400 °C to 300 °C, 200 °C and 25 °C. Note that the RGSb2Te3 feature disappears at 400 °C (heating up) and reappears at 300 °C (cooling down). We further observed this sequence is both reversible and cyclable (i.e. vertical arrow, far left of Fig. 2 with additional thermal cycles being performed in Beijing and Warwick (JEOL 2100, DENS Wildfire holder). Acknowledgements We are indebted to financial support from EPSRC grants EP/M010643/1, EP/011925/1, EP/1033394/1, and EP/R019428/1 and, in Poland, for EAGLE project FP7-REGPOT-2013-1. Fig. 1. (a) AC-TEM image of a filled vertically aligned ~17 nm thick SWCNT bundle filled with Sb2Te3. (b) Pre (left) and post (right) heating electron diffraction patterns obtained from the bundle in (a). (c) schematic depiction of an aligned bundle of randomly orientated Sb2Te3 filled SWCNTs rotated in the indicated direction by 40° with respect to the vertical direction which is in the plane of the page. (d) Composite structure model of a five atomic layer thick fragment of Sb2Te3 derived from the R-3mh bulk structure with the unit cell of the latter indicated.5 (e) to (g) three annular dark field (ADF) images (top), corresponding Wien filtered images (middle) and clTEM 3.3 matching ADF simulations (bottom) of 3-, 4- and 5- layer thick fragments observed from individual filled SWCNTs. (h) to (i) models used to simulate the individual fragments in (e) to (g) respectively.

Figure 2.Table of electron diffraction (ED) patterns obtained from an individual aligned SWCNT bundle heated from 25 °C to 200 °C, 300 °C and 400 °C (top ED patterns) and then cooled down from 400 °C to 300 °C, 200 °C and 25 °C (bottom ED patterns) in a JEOL ARM200F (Beijing IoP) equipped with a Protochips heating holder. The arrow at far left indicated that this process is fully cyclable as demonstrated by additional cycles performed in Beijing and Warwick (DENS Wildfire holder).

Keywords

Electron Diffraction, Phase Change Materials, In Situ, Carbon Nanotubes

References

References 1. WW Koelmans, A Sebastian, VP Jonnalagadda, D Krebs, L Dellmann, E Eleftheriou, Nat. Commun. 6 (2015) 8181. 2. K. Shportko, S. Kremers, M. Woda, D. Lencer, J. Robertson, M. Wuttig, Nat. Commun. 7 (2008) 653. 3. CE Giusca, V Stolojan, J Sloan, F Börrnert, H Shiozawa, K Sader, MH Rümmeli, M Büchner, SRP Silva Nano Lett. 13 (2003) 4020. 4. SR Marks, K Morawiec, P Dluzewski, S Kret, J Sloan, Acta Phys. Pol. A, 131 (2017) 1324. 5. KA Kokh, VV Atuchin, TA Gavrilova, NV Kuratieva, NV Pervukhina, NV Surovtsev, Solid State Comm. 177 (2014) 16. 6. To be submitted. 11:11 - 11:14

238 Mapping optical near-field hotspots with multiphoton microscopy in nano/meta- and 2D materials

Prof. Ventsislav Valev University of Bath, Bath, United Kingdom

Abstract Text

We demonstrate that multiphoton microscopy constitutes an important, fast and user-friendly method for visualizing plasmonic hotspots in nano/meta- and 2D materials. Additionally, this type of microscopy can have a significant impact, literally. Imaging of the samples can imprint the plasmonic patterns on the structures’ surface for subsequent study with structural characterization techniques, such as SEM or AFM. Consequently, the plasmonic patterns can be mapped with the resolution of scanning probe techniques.

Although transition metal dichalcogenides (such as WS2, WSe2, MoS2, MoSe2) have emerged as promising two-dimensional (2D) materials for nonlinear optical applications, they are constrained by intrinsically small light-matter interaction length due to (typically) flat-lying geometries. Here, we present the first hyperspectral multiphoton analysis of a 3D network of densely-packed, randomly distributed stacks containing twisted and/or fused 2D nanosheets of WS2 – referred to as “nanomesh”.[1] We map the optical second harmonic generation (SHG) across the three characteristic spectral features (A, B and C) and we establish the 2-photon luminescence and third harmonic generation signatures. We reveal that the nanomesh presents very different and enhanced multiphoton spectral signatures from those of flat-lying WS2 multilayers. We pinpoint the origin of these differences to hotspots whose location changes depending on the wavelength of illumination. We attribute the main SHG enhancements to double resonances due to a modified energy landscape by the presence of defects (such as vacancies and their passivated variants, or grain boundaries) that induce intra- bandgap energy levels. Beyond 2D materials, optical metamaterials are mainly based on surface plasmon resonances – in metallic nanostructures, light can collectively excite surface electron waves. These electron waves have the same frequency as light, but much shorter wavelengths, which allow their manipulation at the nanoscale. We present SHG microscopy images where the origin of the SHG can unambiguously be attributed to maxima of the surface charge density, which in turn depend on the geometry of the structures. Our results suggest that SHG microscopy can be used efficiently for mapping the local field enhancement in nanostructured metamaterials. [2-5] Moreover, we will show that upon illuminating nanostructures made of nickel or palladium, with femtosecond pulses, the resulting surface plasmon pattern is imprinted on the structures themselves.[6] This imprinting is done through the formation of nanojets, allowing for subsequent imaging with scanning electron microscopy (SEM) or atomic force microscopy (AFM). [7] The imprinting method combines aspects of both imaging and writing techniques. The combination offers a resolution on local field enhancements that can, in principle, be brought down to that of the AFM.

Keywords

2D materials, transition metal dichalcogenides, second harmonic generation, nonlinear optics, multiphoton spectroscopy, plasmonics, metasurfaces

References

[1] A. W. A. Murphy, Z. Liu, A. V. Gorbach, A. Ilie, V. K. Valev, Laser Photonics Rev. (2021), In press. [2] V. K. Valev, J. J. Baumberg, B. De Clercq, N. Braz, X. Zheng, E. J. Osley, S. Vandendriessche, M. Hojeij, C. Blejean, J. Mertens, C. G. Biris, V. Volskiy, M. Ameloot, Y. Ekinci, G. A. E. Vandenbosch, P. A. Warburton, V. V. Moshchalkov, N. C. Panoiu, T. Verbiest, Adv. Mater. 26, 4074-4081 (2014). [3] V.K. Valev, N. Smisdom, A.V. Silhanek, B. De Clercq, W. Gillijns, M. Ameloot, V.V. Moshchalkov, T. Verbiest, Nano Lett. 9, 3945 (2009). [4] V. K. Valev, A. Volodin, A. V. Silhanek, W. Gillijns, B. De Clercq, Y. Jeyaram, H. Paddubrouskaya, C. G. Biris, N. C. Panoiu, O. A. Aktsipetrov, M. Ameloot, V. V. Moshchalkov, T. Verbiest, ACS Nano 5, 91-96, (2010). [5] V. K. Valev, B. De Clercq, C. G. Biris, X. Zheng, S. Vandendriessche, M. Hojeij, D. Denkova, Y. Jeyaram, N. C. Panoiu, Y. Ekinci, A. V. Silhanek, V. Volskiy, G. A. E. Vandenbosch, M. Ameloot, V. V. Moshchalkov, T. Verbiest, Adv. Mater. 24, OP208-OP215 (2012). [6] V. K. Valev, D. Denkova, X. Zheng, A. I. Kuznetsov, C. Reinhardt, B. N. Chichkov, G. Tsutsumanova, E.J. Osley, V. Petkov, B. De Clercq, A. V. Silhanek, Y. Jeyaram, V. Volskiy, P. A. Warburton, G. A. E. Vandenbosch, S. Russev, O. A. Aktsipetrov, M. Ameloot, V. V. Moshchalkov, T. Verbiest, Adv. Mater. 24, OP29-OP35 (2012). [7] V. K. Valev, A. V. Silhanek, Y. Jeyaram, D. Denkova, B. De Clercq, V. Petkov, X. Zheng, V. Volskiy, W. Gillijns, G. A. E. Vandenbosch, O. A. Aktsipetrov, M. Ameloot, V. V. Moshchalkov and T. Verbiest, Phys. Rev. Lett.106, 226803 (2011). 11:17 - 11:20

319 Identification and analysis of ion-implanted chromium dopants in monolayer MoS2

Mr. Michael Hennessy1, Dr. Eoghan O'Connell1, Mr. Manuel Auge2, Mr. Stefan Rost3, Mr. Minh Bui3, Mr. Eoin Moynihan1, Prof. Beata Kardynal3, Prof. Hans Hofsäss2, Prof. Ursel Bangert1 1University of Limerick, Limerick, Ireland. 2Georg-August-Universität Göttingen, Göttingen, Germany. 3Peter Grünberg Institute, Jülich, Germany

Abstract Text

The remarkable physical properties of monolayer thick transition metal dichalcogenides (TMDCs), resulting from their two dimensional (2D) geometry and lattice symmetry, make them an exciting platform for developing photonic devices with new functionalities [1]. Monolayer TMDCs can be easily incorporated into electrically driven devices, which in turn can be coupled to optical microcavities or photonic circuits [2]. In order to make such devices a reality, modification methods tailored for these materials must be developed. Ultra-low energy (10-25 eV) ion implantation [3,4] of monolayer TMDCs is carried out using the ADONIS mass-selected ion beam deposition system at the University of Gottingen [5]. This novel technique allows for highly pure, clean and selective substitutional incorporation of dopants [6] and is compatible with standard semiconductor processing. Additionally, post-growth doping [7] of TMDCs offers an expanded selection of possible dopants compared to the popular method of doping via CVD growth.

Here we present results of ultra-low energy ion implantation of chromium into monolayer MoS2. Ab initio band structure calculations are first used to analyse the suitability of MoS2 for electronic tailoring via ion implantation. Atomic resolution high angle annular dark field (HAADF scanning transmission electron microscopy (STEM), together with core-loss electron energy loss spectroscopy (EELS) analysis, is used to identify individual dopant atoms in the host lattice and examine the atomic structure of the defects and dopants in the monolayers. Strain induced at dopant sites in the lattice is analysed and quantified using 4D- STEM. Analysis of experimental HAADF STEM and 4D-STEM data is carried out using the Temul Toolkit Python library [8], based on Atomap [9]. Low loss EELS is used in conjunction with low temperature photoluminescence to study excitonic behavior at the strained implantation sites.

This work constitutes a proof-of-principle study to incorporate implanted TMDCs into non-classical single photon emitting diodes [10]. The development of such devices has far-reaching implications for emerging technologies such as quantum cryptography and quantum metrology.

The authors gratefully acknowledge funding from Volkswagenstiftung.

Keywords

2D materials, HAADF STEM, EELS, ion implantation, semiconductors

References

[1] K. Mak, C. Lee, J. Hone, J. Shan, and T. Heinz, Phys. Rev. Lett. 105, 136805 (2010). [2] K. Mak and J. Shan, Nat. Photonics 10, 216 (2016). [3] K. Dolui, I. Rungger, C. Das Pemmaraju, and S. Sanvito, 1 (2013). [4] V. P. Pham and G. Y. Yeom, Adv. Mater. 28, 9024 (2016). [5] M. Uhrmacher and H. Hofsäss, Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 240, 48 (2005). [6] J. W. Mayer, 1973 Int. Electron Devices Meet. 3 (1973). [7] A. Azcatl, X. Qin, A. Prakash, C. Zhang, L. Cheng, Q. Wang, N. Lu, M. J. Kim, J. Kim, K. Cho, R. Addou, C. L. Hinkle, J. Appenzeller, and R. M. Wallace, ArXiv In Press, 1 (2016). [8] E. O’Connell, M. Hennessy and E. Moynihan, PinkShnack/TEMUL: DOI Release. https://doi.org/10.5281/ZENODO.3832143 (2020). [9] M. Nord, P. E. Vullum, I. MacLaren, T. Tybell, and R. Holmestad, Adv. Struct. Chem. Imaging 3, 9 (2017). [10] M. D. Eisaman, J. Fan, A. Migdall, Acta Med. Okayama 67, 259 (2013). 11:25 - 11:55

6 Electron-beam manipulation of lattice impurities

Ass.-Prof. Dr. Toma Susi University of Vienna, Vienna, Austria

Abstract Text

Covalently bound impurity atoms in crystal lattices can be manipulated using the atomically focused electron probe of an aberration-corrected scanning transmission electron microscope. This has revealed inspiring new perspectives for top-down atomic engineering, with the potential to surpass existing techniques in both versatility and capabilities. Manipulation was first realized for incidental silicon impurities in single-layer graphene. Elastic backscattering of a probe electron from a moving C nucleus [1] causes the Si to directly exchange places with one neighboring C atom via an out-of-plane displacement [2], and such dynamics can be controlled by directing the focused electron beam at the desired atomic site [3]. Our manipulation rate is nearly on par with any atomically precise technique [4], and such control is also possible in single-walled carbon nanotubes [5]. Phosphorus dopants in graphene can be manipulated with difficulty [6], and there seem to be physical limits on what is feasible assignificantly heavier Ge impurities cannot [7]. The curious replacement of irradiated impurities by C atoms has also emerged as a practical hurdle for the further scaling of the technique. However, similar irradiation-induced atomic dynamics have been observed for many impurity elements [8], and based on our modeling, several transition metals also appear as promising targets. Perhaps even more excitingly, the electron-beam manipulation of Bi dopants in bulk silicon was recently reported [9], although the precise mechanism was left unclear. We have now applied our established ab initio modeling methodology [10] to address this question, revealing a novel type of non-destructive mechanism we call indirect exchange. Further, we demonstrate that the promising nuclear spin qubit Sb can likewise be manipulated. Support from the European Research Council (grant 756277-ATMEN) and computational resources provided by the Vienna Scientific Cluster (VSC) are gratefully acknowledged.

Keywords scanning transmission electron microscopy, electron-beam manipulation, first principles modeling, heteroatoms, graphene, silicon