Methods of Preparation and Characterization of Experimental Field-Emission Cathodes

Téma doktorské práce se zabývá přípravou a popisem katod na bázi autoemise, jenž představují kvalitní a levný elektronový zdroj pro zařízení pracující s fokusovaným elektronovým svazkem. Pro přípravu kompozitní autoemisní katody byla využita elektrochemická metoda výroby. Kompozitní struktura katody zlepšuje proudovou stabilitu ve srovnání s čistě autoemisními katodami na bázi wolframu. Na základě charakterizace katody, jenž byla nově provedena metodou šumové spektroskopie, byla implementována technologická zlepšení stávající výroby. Metoda šumové spektroskopie je založena na analýze emisního proudu v časové a kmitočtové rovině, ale především poskytuje informace o nosiči náboje, o jeho pohyblivosti a dále o životnosti katody. Výsledky experimentální části byly rozšířeny teoretickými simulacemi, vedoucími k návrhu metodiky charakterizace vylepšené autoemisní katody.This PhD thesis describes, and covers the preparation of field-emission cathodes that represent a high-quality, inexpensive source of electrons for devices that work with a focused electron beam. In this work, an improved method of electrochemical fabrication is used for the preparation of a composite field-emission cathode. The composite structure improves current stability in comparison to tungsten-based pure field-emission cathodes. Improvements to the technology used were implemented on the basis of findings obtained using spectrum noise diagnostics, which are based on measuring and evaluating the emission current in the time and in frequency domains. Additionally, noise spectroscopy provides important information about charge transport, electron mobility, and lifespan, which is essential for future research. Results obtained using the experimental method have been further supplemented with theoretical data provided by a computer simulation in order to establish characterization procedures for improved field-emission cathodes.

Pyroelectric detector signal measurement and processing

Práce se zabývá fyzikálními vlastnostmi pyroelektrických senzorů a jejich praktickým využitím. Součástí práce je návrh a realizace měřící aparatury, jež bude využita k měření fyzikálních vlastností senzorů. Pro měření signálů pyroelektrického senzoru bude navržen nízkošumový zesilovač. Součástí práce je také návrh a realizace algoritmu pro lokalizaci infračerveného zdroje záření (plamene) v prostoru, na základě vyhodnoceného analogového signálu.The thesis analyzes the physical properties of the pyroelectric sensors and its practical use. Essential part of the work is the design and realization of the measuring set-up, which is used for the measurements of the sensors physical properties. With this workbench, main parameters of the pyroelectric sensors have been obtained. The second part of the work deals with a low noise preamplifier designing. This device was designed for the pyroelectric sensor signal measurements. The amplifier is designed to be used for a low noise, wide band measuring. During the process of amplifier designing, all the noise components have been investigated separately, using operational amplifiers models. The objective of the last part of this work is to develop the system, which would be able to localize an infrared (IR) emitting source located somewhere in the space between the installed pyroelectric sensors. For this purpose, classical localization methods could be used as well as the artificial neural networks (ANN), which are becoming still more popular these days. The system is able to detect the exact placement of the IR radiation source.

Influence of High Concentration of Silica Nanoparticles on the Dielectric Spectra

In the presented work, we report the dielectricbehavior of epoxy–silicon oxide composites in the temperaturerange 240– 300 K, over the frequency range 10-2 Hz – 107 Hz. Themeasuring apparatus was based on the Novocontrol AlphaAnalyser and the measured data were analyzed and interpretedusing the Havriliak – Negami equation. The master curves of thereal part of permittivity and the dielectric loss number wereobtained by time–temperature superposition principle, and theresults showed that the nano-composite had a much higher lossfactor. Through the analysis of the origin of the dielectric responsein epoxy/silica composite, the reason for the different dielectricrelaxation behaviors of the nano-composite, and the pure epoxywas discussed

Nanostructures for Achieving Selective Properties of a Thermophotovoltaic Emitter

This paper focuses on the research and development of a suitable method for creating a selective emitter for the visible and near-infrared region to be able to work optimally together with silicon photovoltaic cells in a thermophotovoltaic system. The aim was to develop a new method to create very fine structures beyond the conventional standard (nanostructures), which will increase the emissivity of the base material for it to match the needs of a selective emitter for the VIS and NIR region. Available methods were used to create the nanostructures, from which we eliminated all unsuitable methods; for the selected method, we established the optimal procedure and parameters for their creation. The development of the emitter nanostructures included the necessary substrate pretreatments, where great emphasis was placed on material purity and surface roughness. Tungsten was purposely chosen as the main material for the formation of the nanostructures; we verified the effect of the formed structure on the resulting emissivity. This work presents a new method for the formation of nanostructures, which are not commonly formed in such fineness; by this, it opens the way to new possibilities for achieving the desired selectivity of the thermophotovoltaic emitter