Investigations on growth and structure of silver and silver halide nanostructures formed on amphiphilic dye aggregates Dissertation zur Erlangung des akademischen Grades Doctor rerum naturalium (Dr. rer. nat.) im Fach: Physik Spezialisierung: Experimentalphysik eingereicht an der Mathematisch-Naturwissenschaftlichen Fakult¨at der Humboldt-Universit¨at zu Berlin von Herrn Dipl.-Phys. Egon Steeg Pr¨asidentin der Humboldt-Universit¨at zu Berlin: Prof. Dr. Sabine Kunst Dekan der Mathematisch-Naturwissenschaftlichen Fakult¨at: Prof. Dr. Elmar Kulke Gutachter: 1. PD Dr. Stefan Kirstein 2. Prof. Christoph T. Koch, PhD 3. Prof. Dr. Monika Sch¨onhoff Tag der m¨undlichen Pr¨ufung:31.08.2018 2 3 Abstract Quasi one-dimensional inorganic nanostructures, with diameters in the or- der of several nanometers, received increasing interest over the past decades because of their promising application in the fields of electronics and pho- tonics. Nanowires less than 7 nm in diameter can be grown within tubular aggregates of amphiphilic cyanine dyes by addition of silver nitrate to the aqueous solution as shown in previous work [1][2]. It was concluded that these wires consist entirely of pure silver. This thesis reports on the growth mechanism of these wires as revealed by conventional as well as cryogenic transmission electron microscopy. The growth, initiated by short illumina- tion with UV light, has been observed over time scales ranging from minutes to days. In an early stage, within the tubular aggregates nanoparticles are formed which act as seeds for continuous growth of separate pieces of wires. The diameter of the wires is determined by the inner diameter of the tubes. In the final state, the pieces of wire totally fill the aggregate. The growth process indicates transport of at least silver ions through the tubular wall membrane. After homogeneously filling the template the wires grow on- wards over the diameter of the nanotubes, destroying it in the process. A strategy is presented to stop the growth when the wires are completed by precipitation of excess silver ions via addition of chlorides. The crystal structure of the wires was investigated by means of high reso- lution transmission electron microscopy and selected area electron diffraction. The clarification of the wires crystal structure led to the unambiguous find- ing that the wires consist of silver iodide. The silver iodide could be clearly identified in its β-phase by its typical wurtzite structure. Since only silver nitrate was added to the solutions, the source of the iodide ions could be at- tributed to impurities within the dye powder itself. The fragmented growth of the wires from separate seeds leads to nanowires consisting of single crys- talline domains exceeding 100 nm in length. A preferential orientation of the crystal lattice planes with respect to the aggregate axis was observed which is explained by the molecular structure of the aggregates. Based on these findings a model for the growth of silver iodide nanowires within the inner space of the tubular molecular aggregate is presented. The growth is assumed to start at silver seeds that are formed due to photo- oxidation of the already present iodide ions by the silver ions during the illumination of the sample. These silver seeds facilitate nucleation of silver iodide and subsequent growth into wires. These findings may demonstrate a possible route for growing other metal halide structures within the am- phiphilic cyanine dye tubules. 4 5 Zusammenfassung Quasi eindimensionale anorganische Nanostrukturen, mit Durchmessern in der Gr¨oßenordnung von einigen Nanometern, fanden in den letzten Jahrzehn- ten aufgrund ihrer vielversprechenden Anwendung in den Bereichen Elek- tronik und Photonik zunehmendes Interesse. Durch Zugabe von Silberni- trat zu r¨ohrenf¨ormigenFarbstoffaggregaten in w¨assrigerL¨osungk¨onnenNan- odr¨ahte mit weniger als 7 nm im Durchmesser gez¨uchtet werden [1][2]. Es wurde festgestellt, dass diese Dr¨ahte vollst¨andigaus reinem Silber beste- hen. Diese Arbeit besch¨aftigtsich mit dem Wachstumsmechanismus dieser Dr¨ahte. Das Wachstum wurde initiiert durch Belichtung mit UV-Licht und ¨uber einen Zeitraum von Minuten bis hin zu Tagen untersucht. Im fr¨uhen Stadium bilden sich Silbernanopartikel innerhalb der Farbstoffr¨ohren,welche als Keime f¨urdas weitere Wachstum von isolierten Drahtst¨ucken dienen. Der Durchmesser dieser Dr¨ahte wird durch den Innendurchmesser der R¨ohren definiert. Im letzten Stadium wachsen diese Drahtst¨ucke zusammen bis sie das gesamte Aggregat f¨ullen.Dieser Wachstumsprozess impliziert einen Transport von Silber Ionen durch die Wand der R¨ohre.Das Wachstum der Dr¨ahte setzt sich weiter fort nachdem das Template gleichm¨aßigmit Dr¨ahten gef¨ulltist und zerst¨ortdie R¨ohrenin der Folge. Eine m¨ogliche Strategie zum Stoppen des Wachstum wird vorgestellt. Die Kristallstruktur der Dr¨ahte wurde sowohl mit hochaufl¨osenderElek- tronenmikroskopie als auch Elektronenbeugung untersucht. Diese Unter- suchungen erlaubten die eindeutige Zuordnung der Kristallstruktur zu Silber- jodid. Das Silberjodid konnte aufgrund seiner charakteristischen Wurtzite Struktur in der β-Phase identifiziert werden. Da der L¨osungnur Silber- nitrat beigesetzt wurde, konnte die Quelle der Jod-Ionen als Verunreini- gung im Farbstoffpulver ausgemacht werden. Das fragmentierte Wachs- tum der Dr¨ahte von verschiedenen Startpunkten aus f¨uhrtzu Kristallen mit einkristallinen Dom¨anenvon mehr als 100 nm L¨ange.Eine bevorzugte Ori- entierung der Kristallstruktur relativ zur Aggregatachse wurde gefunden und durch die Molek¨ulstrukturder Aggregate erkl¨art. Basierend auf diesen Ergebnissen wurde ein Model zum Wachstum von Silberjodid Nanodr¨ahten im Inneren eines r¨ohrenf¨ormigenMolek¨ulaggregats entwickelt. Es wurde angenommen, dass das Wachstum an Silberkeimen be- ginnt, die durch Photooxidation der bereits vorhandenen Jod Ionen mit Silber Ionen w¨ahrendder Belichtung der Probe gebildet werden. Diese Silberkeime erm¨oglichen die Bildung von stabilen Silberjodid Kristalliten und das nachfol- gende Wachstum zu Dr¨ahten. Die Ergebnisse zeigen einen m¨oglichen Weg zur Synthese von Metall-Halogenid Strukturen innerhalb von Farbstoffr¨ohren. 6 Contents 1 Introduction 9 2 Fundamentals 13 2.1 J-aggregates from cyanine dyes . 14 2.1.1 Micelle formation . 14 2.1.2 Tubular J-aggregates of C8S3 . 16 2.1.3 C8S3 as template for nanowire growth . 17 2.2 Crystal structure and growth . 20 2.2.1 The cubic closed packed and the hexagonal closed packed crystal structures . 20 2.2.2 Indexing of lattice planes . 21 2.2.3 Diffraction on crystals . 24 2.2.4 Classical nucleation theory . 26 2.2.5 Growth of Crystals . 28 2.3 Transmission Electron Microscopy . 31 2.3.1 Imaging with electrons . 32 2.3.2 Contrast in TEM . 33 2.3.3 Phase-contrast imaging in TEM . 34 2.3.4 Conventional transmission electron microscopy . 36 2.3.5 Cryogenic transmission electron microscopy . 38 2.3.6 High-resolution transmission electron microscopy . 39 2.3.7 Scanning transmission electron microscopy . 40 2.3.8 Energy dispersive x-ray spectroscopy . 42 2.3.9 Selected area electron diffraction . 43 3 Materials and methods 47 3.1 Preparation of J-aggregates . 47 3.2 Preparation of nanowires and addition of sodium chloride . 48 3.3 Absorption spectroscopy . 48 3.4 Transmission electron microscopy . 48 7 8 CONTENTS 4 Results and discussion 51 4.1 Nucleation and growth . 52 4.1.1 Kinetics followed by optical spectroscopy . 53 4.1.2 Early growth phase . 55 4.1.3 Main growth phase . 56 4.1.4 Overgrowth . 60 4.1.5 Addition of chlorides . 61 4.1.6 Influence of oxygen . 63 4.1.7 Multiple stranded cable . 66 4.1.8 Particle analysis . 67 4.1.9 Crystal analysis of particles in an oxygen containing sample . 68 4.1.10 Crystal analysis of particles in a deoxygenated sample . 70 4.1.11 Discussion . 73 4.2 Crystal structure analysis of wires . 77 4.2.1 High-resolution transmission electron microscopy of a particle . 78 4.2.2 Wire analysis . 80 4.2.3 Selected Area Electron Diffraction . 80 4.2.4 Chemical analysis of the wires . 84 4.2.5 High-resolution transmission electron microscopy of wires 86 4.2.6 Crystalline domains of the wires . 92 4.2.7 Discussion . 95 5 Conclusion and outlook 99 5.1 Conclusions . 99 5.2 Outlook . 101 6 Appendix 103 6.1 Calculation of silver and iodine to dye molecule ratio . 103 6.2 Ion concentration inside and outside the tube . 105 6.3 Iodide concentration within the dye salt . 107 6.4 Simulation of HRTEM images . 109 6.5 SAED patterns . 111 Chapter 1 Introduction Nanotechnology is a highly promising research area attracting physicists, chemists, biologists, and engineers. Since \nano" describes just the scale in which concepts are established it allows for an interdisciplinary approach. The joint effort of many disciplines has led to a whole bunch of fascinating new basic principles and applications. Especially the field of optoelectronics has made tremendous progress in the last decades as can be seen for example in the development of new quantum dot light emitting diodes QD-LED [3]. Nanomaterials are defined by having one ore more of it's dimensions con- fined on a scale of less than a 100 nm and this work focuses on quasi one dimensional nanowires. Metallic nanostructures in general have become an interesting research topic mostly because of their applications within the field of plasmonics [4]. Furthermore, they allow for the fabrication of transparent electrodes [5][6], and for the preparation of conducting nanocomposites [7]. Among other metals silver is favorable because of its plasmon resonance that may cover the whole visible spectrum [8][9]. Additionally, silver has the highest electrical conductivity of all pure metals. Another practicable class of nanomaterials are semiconductors and among this whole class of materials silver iodide is of particular interest. Silver iodide offers the possibility for applications in solid-state battery and elec- trochemical sensing systems [10][11][12][13].