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High-temperature plasmonics deals with optically active nanostructures that can withstand high temperatures. A conventional approach relying on standalone noble metal nanoparticles fails to deliver refractory plasmonic nanomaterials, and an alternative route envisions metal nitrides. The main challenge remains the development of advanced synthesis techniques and the insight into thermal stability under real-life application conditions. Here, hafnium nitride nanoparticles (HfN NPs) can be produced by gas aggregation using reactive magnetron sputtering, a technique with a small environmental footprint are shown. As-deposited NPs are of 10 nm mean size and consist of stoichiometric, crystalline fcc HfN. They are characterized by optical absorption below 500 nm caused by interband transitions and in the red/near-infrared (NIR) region due to intraband transitions and localized surface plasmon resonance (LSPR). The optical response can be engineered by tuning the NP composition as predicted by finite-difference time-domain (FDTD) calculations. Going beyond the state-of-the-art, the HfN NP thermal stability is focued under ultrahigh vacuum (UHV) and in air. During UHV annealing to 850 °C, the NPs retain their morphology, chemical and optical properties, which makes them attractive in space mission and other applications. During air annealing to 800 °C, HfN NPs remain stable until 250 °C, which sets a limit for air-mediated use.

The exceptional properties of nanocrystals (NCs) are strongly influenced by many different characteristics, such as their size and shape, but also by characteristics on the atomic scale, such as their crystal structure, their surface structure, as well as by potential microstructure defects. While the size and shape of NCs are frequently determined in a statistical manner, atomic-scale characteristics are usually quantified only for a small number of individual NCs and thus with limited statistical relevance. Within this work, a characterization workflow was established that is capable of determining relevant NC characteristics simultaneously in a sufficiently detailed and statistically relevant manner. The workflow is based on transmission electron microscopy, networked by a correlative multiscale approach that combines atomic-scale information on NCs obtained from high-resolution imaging with statistical information on NCs obtained from low-resolution imaging, assisted by a semi-automatic segmentation routine. The approach is complemented by other characterization techniques, such as X-ray diffraction, UV-vis spectroscopy, dynamic light scattering, or alternating gradient magnetometry. The general applicability of the developed workflow is illustrated on several examples, i.e., on the classification of Au NCs with different structures, on the statistical determination of the facet configurations of Au nanorods, on the study of the hierarchical structure of multi-core iron oxide nanoflowers and its influence on their magnetic properties, and on the evaluation of the interplay between size, morphology, microstructure defects, and optoelectronic properties of CdSe NCs.:List of abbreviations and symbols 1 Introduction 1.1 Types of nanocrystals 1.2 Characterization of nanocrystals 1.3 Motivation and outline of this thesis 2 Materials and methods 2.1 Nanocrystal synthesis 2.1.1 Au nanocrystals 2.1.2 Au nanorods 2.1.3 Multi-core iron oxide nanoparticles 2.1.4 CdSe nanocr

The surface of any binary or multi-component nanocrystal has imperfections and defects. The number of surface defects depends both on the nature of the nanomaterial and on the method of its preparation. One of the possibilities to confine the number of surface defects is the epitaxial growth of the shell, which leads to a change in the physical properties while maintaining the morphology of the core. To form a shell of the desired thickness, an accurate calculation of the amount of its precursors is substantial to avoid the appearance of individual crystals consisting of the shell material. This study aimed to develop an effective calculation method for the theoretical amount of precursors required for the formation of a ZnS shell on the surface of a Cd0.25Zn0.75Se core, followed by the practical implementation of theoretical calculations and characterization of the prepared nanomaterials. This method allows the complete control of the masses and volumes of the initial reagents, which will in turn prevent undesirable nucleation of nuclei consisting of the shell material. In the synthesis of Cd0.25Zn0.75Se/ZnS core/shell quantum dots (QDs), the sources of chalcogens were substituted seleno- and thioureas, which are capable of not only supplanting modern toxic sources of sulfur and selenium but also allowing one to perform the controlled synthesis of highly photoluminescent QDs with a low number of surface defects. The result of this shell overcoating method was an impetuous augmentation in the photoluminescence quantum yield (PL QY up to 83%), uniformity in size and shape, and a high yield of nanomaterials. The developed synthetic technique of core/shell QDs provides a controlled growth of the shell on the core surface, which makes it possible to transfer this method to an industrial scale., Povrch jakéhokoliv binárního nebo multikomponentního nanokrystalu má nedokonalosti a defekty. Množství povrchových defektů závisí jak na druhu nanomateriálu, tak i na metodě jeho přípravy. Jednu z možností, jak omezit množství povrchových defektů je epitaxní růst vrstvy, který vede ke změně fyzikální vlastností, ale zároveň dochází k zachování morfologie jádra. Pro vytvoření obalu zamýšlené tloušťky je nezbytné provést přesné kalkulace množství prekurzoru, aby bylo zároveň zabráněno vzniku nových individuálních krystalů, které obsahují pouze materiál obalu. tato studie je zaměřená na vyvinutí efektivních metod kalkulací množství prekurzoru nezbytného pro formování obalu ZnS na povrchu Cd0.25Zn0.75Se jádra, následované praktickou implementací teoretických kalkulací a charakterizací připraveného nanomateriálu. Tato metoda umožňuje kompletní kontrolu nad množstvím a objemem vstupních reagentů, což má pak za následek prevenci nežádoucích nukleací materiálu obalu. Během syntézy core/shell kvantových teček Cd0.25Zn0.75Se/ZnS bylo použito různých zdrojů chalkogenů na bázi seleno- a thiomočovin, které jsou schopné nejen nahradit moderní toxické zdroje síry a selenu, ale i umožňují provést kontrolovatelnou syntézu vysoce luminiscenčních kvantových teček s malým množstvím povrchových defektů. Výsledkem této obalové metody je výrazné vylepšení fotoluminiscenčního kvantového výtěžku (až 83%) a uniformity velikosti, tvaru a vysokého výtěžku nanomateriálu. Vývoj syntézní techniky core/shell kvantových teček poskytuje vysoce kontrolovatelnou metodu růstu obalu na povrchu jádra, což ji dělá vhodnou pro transfer na průmyslovou aplikační úroveň.