Advanced nanomaterials show a significant improvement in certain physical or functional properties compared to conventional materials. Such advanced materials are, for example, lead halide perovskites (LHP). It is a group of hybrid organic-inorganic materials with a direct bandgap exhibiting unique optical properties. The high quantum efficiency of photoluminescence makes nanocrystals or thin films of LHP suitable candidates for the production of light-emitting diodes, solar cells and LCD displays. Their inexpensive and simple fabrication together with their unique optical properties makes LHP one of the most developed materials of the last decade. This diploma thesis aims to study the optical properties of CsPbBr3 perovskite nanocrystals using high lateral resolution methods. CsPbBr3 perovskite nanocrystals show intense anti-Stokes photoluminescence. These nanocrystals can emit light with a lower wavelength than that of the light that causes their photoluminescence. The nanocrystals are prepared in two different ways: by evaporation or by crystallization of the precursor in a solution of dimethylformamide. The morphology, photoluminescence properties and chemical composition of individual nanocrystals are studied. Each nanocrystal is studied individually and its size, shape, photoluminescence properties and chemical compounds are determined, which leads to a deeper understanding of the anti-Stokes photoluminescence of perovskite nanocrystals.

Nanomaterials such as graphene oxide and carbon nanotubes, have demonstrated excellent properties for membrane desalination, including decrease of maintenance, increase of flux rate, simple solution casting, and impressive chemical inertness. Here, two projects are studied to investigate nanocarbon based membrane desalination. The first project is to prepare hybrid membranes with amyloid fibrils intercalated with graphene oxide sheets. The addition of protein amyloid fibrils expands the interlayer spacing between graphene oxide nanosheets and introduces additional functional groups in the diffusion pathways, resulting in increase of flux rate and rejection rate for the organic dyes. Amyloid fibrils also provide structural assistance to the hybrid membrane, which supresses cracking and instability of graphene oxide sheets. The second project is to fabricate polymer nanocomposite membranes with carbon nanotubes encapsulated by polymerized surfactants. The designed polymerizable surfactant forms lyotropic liquid crystalline mesophases in an aqueous medium with hexagonal packing of cylindrical micelles. The adsorption of surfactants on the surface of carbon nanotubes allows a stable dispersion of carbon nanotubes encapsulated in the cylindrical micelles, resulting in the ordered structure. After photo-polymerization, the composite membranes display enhanced dye rejection. Both projects have shown promising ways to improve membrane filtration by using nanomaterials.

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Diplomová práce se zabývá vlivem uhlíkatého plniva na životaschopnost a produkci extracelulárních látek vybrané bakterie Bacillus subtilis (CCM 1999) a kvasinky Yarrowia lipolytica (CCY 29-26-52). Antimikrobiální aktivita těchto částic, přítomných v kultivačním mediu, byla sledována pomocí následujících parametrů: růst daného mikroorganismu, produkce extracelulárních proteinů a v poslední řadě byla monitorována produkce extracelulárních polymerních substancí, které mají úzkou souvislost s tvorbou biofilmu. Suspenze materiálů (0,135 mg/mL) byly připraveny ve dvou rozdílných kultivačních mediích; tzn. živné medium s obsahem glukózy pro Bacillus subtilis a bazální medium s přídavkem Tweenu 80 pro Yarrowia lipolytica, a media byla inokulována příslušným typem mikroorganismu. Experimenty probíhaly po dobu 6 dnů při rychlosti třepání 160 rpm a teplotě 30 °C pro Bacillus subtilis a 28 °C pro Yarrowia lipolytica. Testovány byly celkem tři typy uhlíkatého nanomateriálu, získané z Katedry anorganické chemie, Vysoké školy chemicko-technologické v Praze. Tyto materiály specifikované jako materiál “A”, “B” a “C” se navzájem lišily velikostí částic a stupněm oxidace. Na základě skríningových studií byla vybrána koncentrace testovaného materiálu 0,135 mg/mL a rychlost třepání 160 rpm. Metodou měření optické hustoty vzorku při 600 nm byly sestaveny a porovnány růstové křivky obou mikroorganismů v přítomnosti testovaných nanočástic po dobu 5 dní. Tímto způsobem bylo zjištěno, že přítomnost nanočástic v mediu nemá velký vliv na růst zkoumaného mikroorganismu. Tato metoda, je však pouze orientační, protože se nevyhneme chybě díky přítomnosti mrtvých buněk. Dále byla testována produkce celkových a extracelulárních proteinů daným mikroorganismem v přítomnosti testovaných nanočástic. Nebyla však pozorována výrazná odchylka hodnot od hodnot kontrolního vzorku, který neobsahoval testovaný materiál. Na základě metod počítání kolonií (Bacillus subtilis) a buněk (Yarrowia lipolytica) byly určeny ztráty životaschopnosti mikroorganismu ve 3 časech (6, 48 a 144 hodin); v kratším časovém intervalu byl růst spíše podporován. Dále byla monitorována produkce extracelulárních polymerních substancí (EPS), tedy proteinů, redukujících substancí a polysacharidů. Tyto látky byly vylučovány daným mikroorganismem do prostředí v průběhu 24 hodin. Bacillus subtilis produkoval EPS ve větší míře než Yarrowia lipolytica. Předpokládáme, že produkce EPS by mohla souviset s tvorbou biofilmu, který chrání buňky před toxicitou nanočástic.

<div> Challenges in the semiconductor industry have resulted in the discovery of a plethora of promising materials and devices such as the III-Vs (InGaAs, GaSb, GaN/InGaN) and 2D materials (Transition-metal dichalcogenides [TMDs]) with wide-ranging applications from logic devices, optoelectronics to biomedical devices. Performance of these devices suffer significantly from scattering processes such as polar-optical phonons (POP), charged impurities and remote phonon scattering. These scattering mechanisms are long-ranged, and a quantitative description of such devices require non-local scattering calculations that are computationally expensive. Though there have been extensive studies on coherent transport in these materials, simulations are scarce with scattering and virtually non-existent with non-local scattering. </div><div> </div><div>In this work, these scattering mechanisms with full non-locality are treated rigorously within the Non-Equilibrium Green's function (NEGF) formalism. Impact of non-locality on charge transport is assessed for GaSb/InAs nanowire TFETs highlighting the underestimation of scattering with local approximations. Phonon, impurity scattering, and structural disorders lead to exponentially decaying density of states known as Urbach tails/band tails. Impact of such scattering mechanisms on the band tail is studied in detail for several bulk and confined III-V devices (GaAs, InAs, GaSb and GaN) showing good agreement with existing experimental data. A systematic study of the dependence of Urbach tails with dielectric environment (oxides, charged impurities) is performed for single and multilayered 2D TMDs (MoS2, WS2 and WSe2) providing guideline values for researchers. </div><div><br></div><div>Often, empirical local approximations (ELA) are used in the literature to capture these non-local scattering processes. A comparison against ELA highlight the need for non-local scattering. A physics-based local approximation model is developed that captures the essential physics and is computationally feasible.</div>

<p>Microparticles have been investigated not only as feedstock spherical or amorphous bulk materials used for shape molding, but also as agents that can perform work in the micron scale. The fabrication of microparticles with active properties of self-propulsion, self-assembly, and mobility with enhanced mechanical, thermal, and chemical properties is of particular interest for emerging technologies such as drug delivery, micro-robotics, micro energy generation/harvesting, and MEMS. Conventional fabrication methods can produce several complex particle shapes in one fabrication session or hundreds of spheroid shaped particles per second. Innovative techniques, as flow lithography, have demonstrated control over particle form and composition for continuous fabrication cycles. In recent years predefined shape polymer microparticles have been fabricated as well as ceramic microparticles through suspension processing with these set of techniques. Even though ceramic materials have been fabricated, there is still a strong need to increment the palette of available materials to be processed via flow lithography. We have pioneered the production of shaped ceramic microparticles by Stop-Flow Lithography (SFL) using preceramic polymers, providing control of particle size and shape in the range of 1 – 1000 μm. The principal arranged technique (SFL) combines aspects of PDMS-based microfluidics and photolithography for the continuous cyclable fabrication of microparticles with predefined shapes. The PDMS microchannel devices used were fabricated with vinyl film molds in a laminar hood avoiding the need for a cleanroom, procedure that reduced fabrication costs. After a fabrication session, the preceramic polymer microparticles were collected, washed, and dried before entering an inert atmosphere furnace for pyrolysis. Additionally, by treating the material initially as liquid polymer, special properties can be added by converting it into an emulsion or a suspension. Microparticles were functionalized by introducing porosity and magnetic nanoparticles in the preceramic polymer matrix. The porous characteristic of a particle leads to an increase in surface area, allowing the particle to be infiltrated with a catalyzer or act as a chemical/physical carrier, and the magnetic behavior of the particles allows a controllable trajectory with defined external magnetic fields. These two properties can be used to fabricate bifunctional microparticles to serve as drug carriers through human arteries and veins for drug delivery purposes. We successfully fabricated solid and functional ceramic microparticles in the 10 – 50 μm range with predefined shapes as hexagons, gears, triangles, and ovals. This system is an economical route to fabricate functional defined shape particles that can serve as microrobots to perform tasks in liquid media.</p>

Schon seit dem 17. Jahrhundert ist bekannt, dass kolloidales Gold in wässrigen Lösungen eine rötliche Färbung hervorruft; ein Effekt der direkt aus der Nanostrukturierung des Goldes resultiert. Neben der Modifizierung optischer Eigenschaften können durch Nano- oder Mikrostrukturierung auch andere, neuartige Charakteristika hervorgerufen werden, wie bspw. an Bi3Ni nachgewiesen werden konnte: Mittels mikrowelleninduzierter, reduktiver Umsetzung in Ethylenglykol (mikrowellenunterstützter Polyol-Prozess) konnten submikroskalige Bi3Ni-Stäbchen kristallisiert werden, die in Magnetisierungsmessungen die überaus seltene Koexistenz von Supraleitung und Ferromagnetismus zeigten. Ein Quanteneffekt, der im entsprechenden Volumenmaterial nicht nachgewiesen werden kann und auf spezielle Oberflächenzustände zurückzuführen ist. Durch Nanostrukturierung können außerdem die chemischen Eigenschaften entscheidend beeinflusst werden, wie an BiRh gezeigt werden konnte. Der mikrowellenunterstützte Polyol-Prozess begünstigt hierbei die Kristallisation von pseudohexagonalen Plättchen mit 60 nm Durchmesser und 20 nm Dicke. Im Gegensatz zum Volumenmaterial zeigten diese in der industrierelevanten Semihydrierung von Acetylen zu Ethylen Bestwerte sowohl in Bezug auf den Umsatz als auch die Selektivität. Basierend auf diesen Erkenntnissen sollten mithilfe des mikrowellenunterstützten Polyol-Prozesses im Rahmen der vorliegenden Dissertation nanostrukturierte, intermetallische Verbindungen des Typs M–M‘ (M = Sn, Pb, Sb, Bi; M‘ = Fe, Co, Ni, Cu, Pd, Ir, Pt) hergestellt und eingehend chemisch sowie physikalisch charakterisiert werden. Als Edukte dienten Metallsalze, die stets in Ethylenglykol als primäres Lösungs- und Reduktionsmittel umgesetzt wurden. Das Polyol nimmt zusätzlich als oberflächenaktive Substanz Einfluss auf Partikelgröße und -gestalt. Zur Optimierung der Synthesen und um möglichst viele Phasen zugänglich zu machen, wurden Art und Konzentration der Metallsalze, pH-Wert, Reaktionstemperatur und -zeit variiert sowie die Zugabe von Oleylamin und/oder Ölsäure getestet. Oleylamin und Ölsäure sind ihrerseits oberflächenaktive Substanzen, wobei erstere zugleich reduktiv wirken kann. Die methodeninhärente Nanostrukturierung der Produkte führte teilweise zu bemerkenswerten Effekten in der Phasenbildung sowie Beeinflussung der chemischen Eigenschaften. Nahezu das komplette binäre Phasensystem Bi–Pd konnte durch Optimierung der Syntheseparameter zugänglich gemacht werden. Die Besonderheit hierbei: Neben den Raumtemperaturphasen Bi2Pd, Bi2Pd5 und BiPd3 konnte Bi12Pd31 als Hochtemperaturmodifikation sowie die neue und zugleich metastabile Modifikation gamma-Bi1.0Pd erzeugt und stabilisiert werden. Das im NiAs-Strukturtyp kristallisierende gamma-Bi1.0Pd zeigte in Magnetisierungs- und Widerstandsmessungen Supraleitung unterhalb von 3.2 K. Mittels mikrowellenunterstütztem Polyol-Prozess gelang bereits in eigenen Vorarbeiten die Synthese von nanostrukturiertem Bi3Ir. Die Verbindung ist ausschließlich in nanopartikulärer Form bei Raumtemperatur empfindlich gegenüber molekularem Sauerstoff und bildet im Zuge einer unkonventionellen oxidativen Interkalation das intermetallische Suboxid Bi3IrOx. Dieses Verhalten ist verknüpft mit einer amorphen Hülle um die Bi3Ir-Nanopartikel, da diese zur Aktivierung des molekularen Sauerstoffs benötigt wird. Unter Einsatz von Reduktionsmitteln — z.B. Wasserstoff, Superhydrid®, Hydrazin — ist der Oxidationsprozess für x < 2 vollständig reversibel. Im Rahmen der vorliegenden Arbeit konnten die Erkenntnisse über Bi3Ir und Bi3IrOx vertieft werden: Bi3IrOx konnte als erster Sauerstoffionenleiter bei Raumtemperatur klassifiziert werden, der darüber hinaus metallisch ist. Dies gelang mittels Röntgen- und Elektronenbeugung, hochauflösender Transmissionselektronenmikroskopie, Röntgenphotoelektronenspektroskopie, quantenchemischen Rechnungen, und Experimenten zur Reaktionskinetik. Mit 84 meV ist die Aktivierungsenergie für die Ionenleitung um eine Größenordnung kleiner als in allen konventionellen Sauerstoffionenleitern. Der Diffusionskoeffizient beträgt für 25 °C 1.2·10–22 m2s–1, was in Anbetracht der 10–19 m2s–1 des Yttrium-stabilisierten Zirkoniumoxids (häufig genutztes Referenzmaterial) bei 150 °C wenig erscheint, aber eben schon für Raumtemperatur gilt. Durch den mikrowellenunterstützten Polyol-Prozess konnten erstmals phasenreine, nanostrukturierte Proben von PbPd3, Pd20Sb7, Pd8Sb3, PdSb, Ni5Sb2, und Pd13Sn9 synthetisiert werden sowie alternative Syntheserouten für weitere Phasen (alpha-/beta-/gamma-Bi2Pt, BiPt, NiSb, beta-Ni3Sn2, Pd2Sn, PdSn, Pt3Sn, PtSn, PtPb) ermittelt werden, wobei mehrfach die Bildung von Hochtemperaturphasen beobachtet wurde. Weiterhin konnten einige Grenzen der Methode aufgezeigt werden: Während blei- und bismutreiche Phasen prinzipiell einfach kristallisiert werden können, sind antimon- und zinnreiche Verbindungen mit der Methode kaum erreichbar. Außerdem zeigte sich, dass in den meisten Phasensystemen nur bestimmte Verbindungen angesteuert werden können; die Bildung der intermetallischen Phasen ist häufig die Triebkraft zur Reduktion der Metallkationen. In den Systemen von Co-Sb, Co-Sn und Ir-Sb konnte bisher keine Feststoffbildung beobachtet werden.

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<div>Over the last decade, Dirac matter has become one of the most prominent fields of research in contemporary material science due to the incredibly rich physics of the Dirac equation. Notable examples are the Dirac cones in graphene, Weyl points in TaAs, and gapless edge states in Bi₂Te₃. These unique phases of matter are intimately related to the topological structure of Dirac fermions. However, it remains an open question if the topological structure of Maxwell's equations predicts yet new phases of matter. This thesis will conclusively answer this question.</div><div><br></div><div>Topological electrodynamics is concerned with the geometry of electromagnetic waves in condensed matter. At the microscopic level, photons couple to the dipole-carrying excitations of a material, such as plasmons and excitons, which hybridize to form new normal modes of the system. The interaction between these bosonic oscillators is the origin of temporal and spatial dispersion in optical response functions like the conductivity tensor. Our main achievement is motivating a global interpretation of these response functions, over all frequencies and wavevectors. This theory led us to the conclusion that there are topological invariants associated with the conductivity tensor itself. In this thesis, we show exactly how to calculate these electromagnetic invariants, in both continuum and lattice theories, to identify unique Maxwellian phases of matter. Magnetohydrodynamic electron fluids in strongly-correlated 2D materials like graphene are the first candidates of this new class of topological phase. The fundamental physical mechanism that gives rise to a topological electromagnetic classification is Hall viscosity which adds a nonlocal component to the Hall conductivity. To study the topological electrodynamics, we propose viscous Maxwell-Chern-Simons theory -- a Lagrangian framework that naturally generates the equations of motion, nonlocal Hall response and the boundary conditions. We demonstrate that nonlocal Hall conductivity is the spin-1 photonic equivalent of dispersive mass and induces precession of bulk photonic skyrmions. Nontrivial photonic skyrmions are associated with Dirac monopoles in the bulk momentum space and a singular Berry gauge. A singular gauge occurs when the photonic mass changes sign. Remarkably, the boundary of this medium supports gapless chiral edge states that are spin-1 helically-quantized and satisfy open boundary conditions.</div>

In the present work new methods were developed for preparation of novel nanosized and nanostructured ceramic materials. Ordered mesoporous silica SBA-15 was found to be useful as a hard template for the nanocasting of silicon carbide and allowed the preparation of high temperature stable mesoporous silicon carbide ceramics. Chemical vapor infiltration of SBA-15 with dimethyldichlorosilane at elevated temperatures yields SiC/SBA-15 nanocomposites. The subsequent HF treatment of those composites resulted in silica removal and preparation of mesoporous silicon carbide with surface areas between 410 and 830 m2g-1 and high mesopore volume (up to 0.9 cm3g-1). The pore size (between 3 and 7nm in diameter) and surface area of mesoporous silicon carbide were controlled by adjusting the infiltration conditions (time, atmosphere). The mesoporous silicon carbide prepared via this method showed high structural thermal stability at 1300 oC, exceeding that of the SBA-15 template. However, the ordering on the mesoscopic scale was low. Nevertheless, highly ordered mesoporous silicon carbide materials were obtained via polymer melt infiltration in SBA-15. The low molecular weight polycarbosilane used as a preceramic precursor was converted at 1300 oC to silicon carbide inside the SBA-15, and after subsequent silica removal by HF, a highly ordered mesoporous material was obtained. Ordered mesoporous silicon carbide prepared by the methods reported here, may be an interesting material as a support due to its high temperature stability, chemical inertness, high thermal conductivity and semiconductor properties. In contrast to the nanocasting approach, based on the complete pore filling, also a new in-situ procedure for the preparation of finely dispersed metal and metal oxide particles inside ordered mesoporous silica was developed. A swelling agent (toluene) was used to deliver a hydrophobic platinum precursor into the surfactant micelles before addition of silica source. Such an in-situ method resulted in very high platinum incorporation (80-100%), not achieved for any other in-situ preparation procedures. Additionally, the presence of platinum allowed to decrease the template removal temperatures. Moreover, the method was also extended to other metal or metal oxide/ordered mesoporous silica systems. This may be especially interesting for the preparation of ordered mesoporous materials with low melting points, where typically the structure collapses during the high temperature calcinations process. The in-situ synthesized V2O5/MCM-41 materials were used to prepare VN/MCM-41 composites via nitridation in ammonia at 800oC. This method allowed to prepare highly dispersed, X-ray amorphous vanadium nitride species, with high activity in the propane dehydrogenation. Compared to nitridation of supported vanadium oxide prepared via the ex-situ procedure, in-situ synthesized materials showed similar catalytic activity, in spite of having significantly lower vanadium loading. As an alternative for the preparation of supported nitride materials, a novel preparation procedure of bulk not supported nanocrystalline vanadium nitride with high surface area was presented. Instead of pure oxide powder (which was typically used in the preparation of high surface area vanadium nitride catalysts), a macroporous amine intercalated V2O5 was used as the starting material. The obtained nitride consisted of small crystallites and had a surface area up to 198 m2g-1. Moreover, this foam-derived VN showed significantly improved activity as a catalyst in propane dehydrogenation. This novel preparation method could also be extended to other systems such as ternary VMoxNy nitrides.