@phdthesis{Lemke2013,
  author    = {Lemke, Karina},
  title     = {Abtrennung und Charakterisierung von Polyelektrolyt-modifizierten Nanopartikeln},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-68133},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {Gegenstand der Dissertation ist die gr{\"o}ßen- und eigenschaftsoptimierte Synthese und Charakterisierung von anorganischen Nanopartikeln in einer geeigneten Polyelektrolytmodifizierten Mikroemulsion. Das Hauptziel bildet dabei die Auswahl einer geeigneten Mikroemulsion, zur Synthese von kleinen, stabilen, reproduzierbaren Nanopartikeln mit besonderen Eigenschaften. Die vorliegende Arbeit wurde in zwei Haupteile gegliedert. Der erste Teil befasst sich mit der Einmischung von unterschiedlichen Polykationen (lineares Poly (diallyldimethylammoniumchlorid) (PDADMAC) und verzweigtes Poly (ethylenimin) (PEI)) in verschiedene, auf unterschiedlichen Tensiden (CTAB - kationisch, SDS - anionisch, SB - zwitterionisch) basierenden, Mikroemulsionssysteme. Dabei zeigt sich, dass das Einmischen der Polykationen in die Wassertr{\"o}pfchen der Wasser-in-{\"O}l (W/O) Mikroemulsion prinzipiell m{\"o}glich ist. Der Einfluss der verschiedenen Polykationen auf das Phasenverhalten der W/O Mikroemulsion ist jedoch sehr unterschiedlich. In Gegenwart des kationischen Tensids f{\"u}hren die repulsiven Wechselwirkungen mit den Polykationen zu einer Destabilisierung des Systems, w{\"a}hrend die ausgepr{\"a}gten Wechselwirkungen mit dem anionischen Tensid in einer deutlichen Stabilisierung des Systems resultieren. F{\"u}r das zwitterionische Tensid f{\"u}hren die moderaten Wechselwirkungen mit den Polykationen zu einer partiellen Stabilisierung. Der zweite Teil der Arbeit besch{\"a}ftigt sich mit dem Einsatz der unterschiedlichen, Polyelektrolyt- modifizierten Mikroemulsionen als Templatphase f{\"u}r die Herstellung verschiedener, anorganischer Nanopartikel. Die CTAB-basierte Mikroemulsion erweist sich dabei als ungeeignet f{\"u}r die Herstellung von CdS Nanopartikeln, da zum einen nur eine geringe Toleranz gegen{\"u}ber den Reaktanden vorhanden ist (Destabilisierungseffekt) und zum anderen das Partikelwachstum durch den Polyelektrolyt-Tensid-Film nicht ausreichend begrenzt wird. Zudem zeigt sich, dass eine Abtrennung der Partikel aus der Mikroemulsion nicht m{\"o}glich ist. Die SDS-basierten Mikroemulsionen, erweisen sich als geeignete Templatphase zur Synthese kleiner anorganischer Nanopartikel (3 - 20 nm). Sowohl CdS Quantum Dots, als auch Gold Nanopartikel konnten erfolgreich in der Mikroemulsion synthetisiert werden, wobei das verzweigte PEI einen interessanten Templat-Effekt in der Mikroemulsion hervorruft. Als deutlicher Nachteil der SDS-basierten Mikroemulsionen offenbaren sich die starken Wechselwirkungen zwischen dem Tensid und den Polyelektrolyten w{\"a}hrend der Aufarbeitung der Nanopartikel aus der Mikroemulsion. Dabei erweist sich die Polyelektrolyt-Tensid-Komplexbildung als hinderlich f{\"u}r die Redispergierung der CdS Quantum Dots in Wasser, so dass Partikelaggregation einsetzt. Die SB-basierten Mikroemulsionen erweisen sich als g{\"u}nstige Templatphase f{\"u}r die Bildung von gr{\"o}ßen- und eigenschaftenoptimierten Nanopartikeln (< 4 nm), wobei insbesondere eine Modifizierung mit PEI als ideal betrachtet werden kann. In Gegenwart des verzweigten PEI gelang es erstmals ultrakleine, fluoreszierende Gold Cluster (< 2 nm) in einer SB-basierten Mikroemulsion als Templatphase herzustellen. Als besonderer Vorteil der SB-basierten Mikroemulsion zeigen sich die moderaten Wechselwirkungen zwischen dem zwitterionischen Tensid und den Polyelektrolyten, welche eine anschließende Abtrennung der Partikel aus der Mikroemulsion unter Erhalt der Gr{\"o}ße und ihrer optischen Eigenschaften erm{\"o}glichen. In der redispergierten w{\"a}ssrigen L{\"o}sung gelang somit eine Auftrennung der PEI-modifizierten Partikel mit Hilfe der asymmetrischer Fluss Feldflussfraktionierung (aF FFF). Die gebildeten Nanopartikel zeigen interessante optische Eigenschaften und k{\"o}nnen zum Beispiel erfolgreich zur Modifizierung von Biosensoren eingesetzt werden.},
  language  = {de}
}
@phdthesis{Glatzel2013,
  author    = {Glatzel, Stefan},
  title     = {Cellulose based transition metal nano-composites : structuring and development},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-64678},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {Cellulose is the most abundant biopolymer on earth. In this work it has been used, in various forms ranging from wood to fully processed laboratory grade microcrystalline cellulose, to synthesise a variety of metal and metal carbide nanoparticles and to establish structuring and patterning methodologies that produce highly functional nano-hybrids. To achieve this, the mechanisms governing the catalytic processes that bring about graphitised carbons in the presence of iron have been investigated. It was found that, when infusing cellulose with an aqueous iron salt solution and heating this mixture under inert atmosphere to 640 °C and above, a liquid eutectic mixture of iron and carbon with an atom ratio of approximately 1:1 forms. The eutectic droplets were monitored with in-situ TEM at the reaction temperature where they could be seen dissolving amorphous carbon and leaving behind a trail of graphitised carbon sheets and subsequently iron carbide nanoparticles. These transformations turned ordinary cellulose into a conductive and porous matrix that is well suited for catalytic applications. Despite these significant changes on the nanometre scale the shape of the matrix as a whole was retained with remarkable precision. This was exemplified by folding a sheet of cellulose paper into origami cranes and converting them via the temperature treatment in to magnetic facsimiles of those cranes. The study showed that the catalytic mechanisms derived from controlled systems and described in the literature can be transferred to synthetic concepts beyond the lab without loss of generality. Once the processes determining the transformation of cellulose into functional materials were understood, the concept could be extended to other metals and metal-combinations. Firstly, the procedure was utilised to produce different ternary iron carbides in the form of MxFeyC (M = W, Mn). None of those ternary carbides have thus far been produced in a nanoparticle form. The next part of this work encompassed combinations of iron with cobalt, nickel, palladium and copper. All of those metals were also probed alone in combination with cellulose. This produced elemental metal and metal alloy particles of low polydispersity and high stability. Both features are something that is typically not associated with high temperature syntheses and enables to connect the good size control with a scalable process. Each of the probed reactions resulted in phase pure, single crystalline, stable materials. After showing that cellulose is a good stabilising and separating agent for all the investigated types of nanoparticles, the focus of the work at hand is shifted towards probing the limits of the structuring and pattering capabilities of cellulose. Moreover possible post-processing techniques to further broaden the applicability of the materials are evaluated. This showed that, by choosing an appropriate paper, products ranging from stiff, self-sustaining monoliths to ultra-thin and very flexible cloths can be obtained after high temperature treatment. Furthermore cellulose has been demonstrated to be a very good substrate for many structuring and patterning techniques from origami folding to ink-jet printing. The thereby resulting products have been employed as electrodes, which was exemplified by electrodepositing copper onto them. Via ink-jet printing they have additionally been patterned and the resulting electrodes have also been post functionalised by electro-deposition of copper onto the graphitised (printed) parts of the samples. Lastly in a preliminary test the possibility of printing several metals simultaneously and thereby producing finely tuneable gradients from one metal to another have successfully been made. Starting from these concepts future experiments were outlined. The last chapter of this thesis concerned itself with alternative synthesis methods of the iron-carbon composite, thereby testing the robustness of the devolved reactions. By performing the synthesis with partly dissolved scrap metal and pieces of raw, dry wood, some progress for further use of the general synthesis technique were made. For example by using wood instead of processed cellulose all the established shaping techniques available for wooden objects, such as CNC milling or 3D prototyping, become accessible for the synthesis path. Also by using wood its intrinsic well defined porosity and the fact that large monoliths are obtained help expanding the prospect of using the composite. It was also demonstrated in this chapter that the resulting material can be applied for the environmentally important issue of waste water cleansing. Additionally to being made from renewable resources and by a cheap and easy one-pot synthesis, the material is recyclable, since the pollutants can be recovered by washing with ethanol. Most importantly this chapter covered experiments where the reaction was performed in a crude, home-built glass vessel, fuelled - with the help of a Fresnel lens - only by direct concentrated sunlight irradiation. This concept carries the thus far presented synthetic procedures from being common laboratory syntheses to a real world application. Based on cellulose, transition metals and simple equipment, this work enabled the easy one-pot synthesis of nano-ceramic and metal nanoparticle composites otherwise not readily accessible. Furthermore were structuring and patterning techniques and synthesis routes involving only renewable resources and environmentally benign procedures established here. Thereby it has laid the foundation for a multitude of applications and pointed towards several future projects reaching from fundamental research, to application focussed research and even and industry relevant engineering project was envisioned.},
  language  = {en}
}
@phdthesis{Stete2020,
  author    = {Stete, Felix},
  title     = {Gold at the nanoscale},
  doi       = {10.25932/publishup-49605},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-496055},
  school      = {Universit{\"a}t Potsdam},
  pages     = {X, 186},
  year      = {2020},
  abstract  = {In this cumulative dissertation, I want to present my contributions to the field of plasmonic nanoparticle science. Plasmonic nanoparticles are characterised by resonances of the free electron gas around the spectral range of visible light. In recent years, they have evolved as promising components for light based nanocircuits, light harvesting, nanosensors, cancer therapies, and many more. This work exhibits the articles I authored or co-authored in my time as PhD student at the University of Potsdam. The main focus lies on the coupling between localised plasmons and excitons in organic dyes. Plasmon-exciton coupling brings light-matter coupling to the nanoscale. This size reduction is accompanied by strong enhancements of the light field which can, among others, be utilised to enhance the spectroscopic footprint of molecules down to single molecule detection, improve the efficiency of solar cells, or establish lasing on the nanoscale. When the coupling exceeds all decay channels, the system enters the strong coupling regime. In this case, hybrid light-matter modes emerge utilisable as optical switches, in quantum networks, or as thresholdless lasers. The present work investigates plasmon-exciton coupling in gold-dye core-shell geometries and contains both fundamental insights and technical novelties. It presents a technique which reveals the anticrossing in coupled systems without manipulating the particles themselves. The method is used to investigate the relation between coupling strength and particle size. Additionally, the work demonstrates that pure extinction measurements can be insufficient when trying to assess the coupling regime. Moreover, the fundamental quantum electrodynamic effect of vacuum induced saturation is introduced. This effect causes the vacuum fluctuations to diminish the polarisability of molecules and has not yet been considered in the plasmonic context. The work additionally discusses the reaction of gold nanoparticles to optical heating. Such knowledge is of great importance for all potential optical applications utilising plasmonic nanoparticles since optical excitation always generates heat. This heat can induce a change in the optical properties, but also mechanical changes up to melting can occur. Here, the change of spectra in coupled plasmon-exciton particles is discussed and explained with a precise model. Moreover, the work discusses the behaviour of gold nanotriangles exposed to optical heating. In a pump-probe measurement, X-ray probe pulses directly monitored the particles' breathing modes. In another experiment, the triangles were exposed to cw laser radiation with varying intensities and illumination areas. X-ray diffraction directly measured the particles' temperature. Particle melting was investigated with surface enhanced Raman spectroscopy and SEM imaging demonstrating that larger illumination areas can cause melting at lower intensities. An elaborate methodological and theoretical introduction precedes the articles. This way, also readers without specialist's knowledge get a concise and detailed overview of the theory and methods used in the articles. I introduce localised plasmons in metal nanoparticles of different shapes. For this work, the plasmons were mostly coupled to excitons in J-aggregates. Therefore, I discuss these aggregates of organic dyes with sharp and intense resonances and establish an understanding of the coupling between the two systems. For ab initio simulations of the coupled systems, models for the systems' permittivites are presented, too. Moreover, the route to the sample fabrication - the dye coating of gold nanoparticles, their subsequent deposition on substrates, and the covering with polyelectrolytes - is presented together with the measurement methods that were used for the articles.},
  language  = {en}
}
@phdthesis{Abouserie2018,
  author    = {Abouserie, Ahed},
  title     = {Ionic liquid precursors for multicomponent inorganic nanomaterials},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-418950},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xx, 193},
  year      = {2018},
  abstract  = {Health effects, attributed to the environmental pollution resulted from using solvents such as benzene, are relatively unexplored among petroleum workers, personal use, and laboratory researchers. Solvents can cause various health problems, such as neurotoxicity, immunotoxicity, and carcinogenicity. As such it can be absorbed via epidermal or respiratory into the human body resulting in interacting with molecules that are responsible for biochemical and physiological processes of the brain. Owing to the ever-growing demand for finding a solution, an Ionic liquid can use as an alternative solvent. Ionic liquids are salts in a liquid state at low temperature (below 100 C), or even at room temperature. Ionic liquids impart a unique architectural platform, which has been interesting because of their unusual properties that can be tuned by simple ways such as mixing two ionic liquids. Ionic liquids not only used as reaction solvents but they became a key developing for novel applications based on their thermal stability, electric conductivity with very low vapor pressure in contrast to the conventional solvents. In this study, ionic liquids were used as a solvent and reactant at the same time for the novel nanomaterials synthesis for different applications including solar cells, gas sensors, and water splitting. The field of ionic liquids continues to grow, and become one of the most important branches of science. It appears to be at a point where research and industry can work together in a new way of thinking for green chemistry and sustainable production.},
  language  = {en}
}
@misc{MeilingCywińskiBald2016,
  author    = {Meiling, Till Thomas and Cywiński, Piotr J. and Bald, Ilko},
  title     = {White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-97087},
  year      = {2016},
  abstract  = {In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1\% up to 28\% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst.},
  language  = {en}
}