Membranas auto-sustentáveis compostas por filmes finos com múltiplas camadas SiO2/ ( 30 nm)/CdSe( 3,0nm)/SiO2 (18 nm) e SiO2( 30 nm)/PbSe( 3,0nm)/SiO2( 18 nm) foram produzidas por magnetron sputtering e submetidas à irradiação com feixe de elétrons em microscópios de transmissão eletrônica convencionais na faixa de energia de 80 a 300 keV em densidades de corrente de 0,3 a 8,0 A cm-2. Variações de contraste observadas em micrografias adquiridas com diferentes doses de elétrons sinalizam uma considerável redistribuição atômica nos filmes semicondutores, tal redistribuição é restrita às regiões iluminadas e possui maior dependência em relação à dose do que à densidade de corrente do feixe. Medidas de difração com área selecionada (Select Area Diffraction - SAD), observações em condição de alta resolução (High Resolution Transmission Microscopy - HRTEM) e medidas de dispersão em energia de Raio-X característico (Energy Dispersive Spectroscopy - EDS) indicam que ambos semicondutores mantém a estrutura cristalina e a quantidade de átomos de Cd, Se e Pb durante irradiação. As membranas SiO2/CdSe/SiO2 apresentam uma retração contínua e homogênea das interfaces CdSe/SiO2 ao longo da superfície irradiada, a nucleação e crescimento de regiões com apenas SiO2 dá origem a uma rede percolada de CdSe que é desmembradas em nanofios nodulares e nanopartículas isoladas. Os filmes de PbSe não apresentam um processo homogêneo e contínuo durante irradiação. Inicialmente, as interfaces PbSe/SiO2 apresentam perda das arestas de alto ângulo Neste caso, as modificações microestruturais são mais intensas após uma dose limite e em regiões específicas, próximas a buracos de SiO2 previamente existentes na amostra como depositada. Medidas SAD, micrografias em condição de campo escuro e análises de imagem HRTEM mostram que a irradiação no PbSe causa separação de fases, identificada por distribuições de nanopartículas de Pb interfaceadas com uma rede planar percolada de PbSe. A conservação de matéria nos sistemas permitiu determinar os fluxos atômicos durante irradiação, o que foi realizado pelo tratamento numérico das micrografias adquiridas em diferentes doses. A investigação do aquecimento da amostra e do comportamento dos sistemas quando irradiados em diferentes energias e densidades de corrente sugerem que os deslocamentos atômicos podem ser correlacionados com as probabilidades de interação entre elétrons e átomos alvo. Isto permitiu a comparação entre fluxos atômicos experimentais, obtidos pelo tratamento numérico das micrografias TEM, com fluxos atômicos deduzidos em função das seções de choque para deslocamentos atômicos diretos, induzidos por colisões elásticas entre elétrons e átomos alvo, e deslocamentos indiretos, causados por radiólise. Os fluxos teóricos consideram variações nas taxas de deslocamento dos átomos de Cd, Se e Pb ao longo da interface semicondutor/SiO2, tais variações são entendidas como consequência de mudanças na energia de coesão das interfaces, que foram calculadas em função da curvatura e energia de superfície através do modelo de gota líquida (Líquid Drop Model - LDM) Comparações entre os fluxos atômicos inferidos das micrografias com os fluxos teóricos, obtidos das seções de choque para espalhamento elástico e inelástico de elétrons, permitiram estimar as energias de deslocamento dos átomos na interfaces e elaborar possíveis mecanismos para as mudanças microestruturais durante a irradiação. Os valores calculados de energia de deslocamento são inferiores às energias necessárias para deslocar átomos na superfície ou no interior da rede cristalina, mas podem ser aproximados às energias de migração atômica em interfaces. Os resultados mostram que os mecanismos de deslocamento atômico nos filmes finos de CdSe e PbSe não são os mesmos. As mudanças microestruturais observadas nos filmes finos de CdSe não podem ser explicadas apenas em termos de colisões balísticas dos elétrons, mas poderiam ocorrer por deslocamentos radiolíticos, principalmente se houverem estados de interface e meia banda que permitam excitações com energias transferidas menores que a largura de banda do CdSe. Já os resultados das irradiações no PbSe podem ser explicados como decorrentes de deslocamentos diretos, causados pela colisão balística dos elétrons nos átomos de Pb e Se pouco coesos nos planos PbSe{111}. Contudo, este estudo não permite excluir um possível processo de múltiplas ionizações como causa dos fluxos atômicos durante irradiação de ambas membranas. / Self-standing membranes compounded for multilayers SiO2/( 30 nm)/CdSe ( 3.0nm) /SiO2 (18 nm) and SiO2( 30 nm)/PbSe( 3.0nm)/SiO2( 18 nm) were irradiated in conventional Transmission Electron Microscopes (TEM) at energy range of 80 - 300 keV, current densities 0.3 - 8.0 A cm-2. The image contrasts of the micrographs acquired at different electron doses show an intense atomic redistribution in the semiconductor films. The effects of irradiation are restricted on the irradiated regions and show a dose dependence instead electric current dependence. Select Area Diffraction (SAD), Energy Dispersive Spectroscopy (EDS) measurements and High Resolution Electron Transmission Microscopy (HRTEM) micrographs show that the both semiconductors mantained the crystal structure and quantity of Cd, Se and Pb atoms after irradiation. The SiO2/CdSe/SiO2 membranes have a homogeneously and continuous retraction of the CdSe/SiO2 interfaces along the irradiated regions. The SiO2 holes grow to produce a percolated planar network of CdSe. In larger doses this network is disrupted, producing nodular nanowires and isolated nanoparticles. Otherwise, the PbSe thin films did not show a homogeneous and continuous process. In the first minutes of irradiation, the SiO2 holes lost the edges of high angles, the retraction of the interfaces PbSe/SiO2 occurs only at a specific electron dose, after which there are growth and nucleation of new holes around the previous ones SAD measurements, dark field micrographs and HRTEM images attest phase separation during electron beam irradiation of the PbSe, the results show isolated Pb nanoparticles connected to a planar percolated network of PbSe. The matter conservation at the systems allowed the calculation of an atomic flux during the irradiation, what was made by the numerical treatment of the micrographs acquired at different electron doses. The investigation of the sample heating and the behavior of the systems when irradiated at different energies and current densities suggest that the atomic displacements can be correlated with the probabilities of electron-atom interactions. This allowed the comparison between the inferred atomic fluxes with atomic fluxes deduced by the cross sections for the ballistic displacement induced by elastic collision of the electrons and the atomic fluxes deduced by the inelastic cross sections, which show the probability of the indirect displacements induced by radiolysis. These fluxes consider changes in the displacement rates of the Cd, Se, and Pb atoms along the semiconductor/SiO2 due to changes in the cohesion energy at the interfaces, what was calculated in function of the curvature and surface energy using the Líquid Drop Model - LDM The comparison between the atomic fluxes inferred by the TEM micrographs with the theoretical fluxes obtained by the elastic and inelastic scaterring cross sections allowed extimations of the displacement energies of the Cd, Se e Pb atoms at the interfaces, what was used to argue some possibles mechanisms for the microstructural changes during the irradiation. The calculated displacement energies are lower than the bulk or surface displacement energies, but can be approximated with the migration energies for the atomic diffusion at the interfaces. The results suggest that the mechanisms of atomic displacement can not be the same for the thin films of CdSe and PbSe. The microstructural changes observed in the CdSe thin films can not be explained only in terms of ballistic displacements, but can be explained by indirect displacements induced by the radiolysis, especially if there are intermediate and middle band states that allow excitations with energies below the CdSe band-gap. In other way, the results of the PbSe can be explained by direct displacements caused by the ballistic collision of the electrons at the Pb and Se atoms placed in the unstable PbSe{111} planes. However, this study can not rule out the possibility of a multiple ionization process as the cause of the atomic fluxes in both membranes.

Additive Manufacturing (AM), commonly known as 3D printing is a production method that utilises repeated addition of layers in order to produce a final shape. AM utilises less raw material and does not have drawbacks such as tool wear and material wastage as seen in conventional machining. However, they do have drawbacks such as poor surface and internal defects.  A common practice in AM is the fabrication of contour and bulk region using separate parameters.  The aim of this project was to study the effects of various process parameters on the contour properties. The process parameters considered were scanning speed, beam current and focus offset. The Nickel alloy Inconel 718 was utilised in Electron Beam Melting (EBM) to fabricate the test specimen. The samples used in this project were in an as-built condition which was priorly subjected to tensile testing for a different project. The tests performed in this project are hardness testing and microstructural investigation about grains, precipitates and the various defects.  The test results helped to understand the effect of various process parameters on the hardness and microstructure of the samples. The samples with lower scanning speed had higher hardness and lesser lack of fusion than samples with higher speed. In the case of varying beam current, the samples with higher beam current had higher hardness values and fewer lack of fusions. Similarly, the effects of varying two or more process parameters were also studied and their findings recorded. The microstructure consisted of a large number of shrinkage porosities in the bulk and contour regions. The presence of Niobium rich precipitates at grain boundaries and the grain structure for various process parameters were identified and recorded.

The quasicrystals are characterized by unusual rotational symmetries that are not observed in the crystalline materials, which is the cause of their interesting material properties. Because of that a particular attention was paid to quasicrystalline structures in the literature research. The research also contains a description of electron beam technology, spark plasma sintering method and introduction to the problematics of wear. As the default materials for the experimental part were selected Titanium Grade 2 powder and Cristome A5 powder which was partially composed of quasicrystalline phase. The first series of samples was sintered only from powder Cristome A5. The second series was sintered from the mixture of 80 % Titanium Grade 2 powder and 20 % Cristome A5 powder. For the compaction of samples spark plasma sintering technology was selected. Samples were then systematically modified by electron beam and subjected to pin on disc tests. Samples modified at 750 °C had the best wear resistance. Samples modified at 1150 °C contained increased amount of quasicrystalline phase.

This master’s thesis deals with the possibility of creating a compact nickel-silicide layer on austenitic substrates. The theoretical part describes a variety of surface treatments, silicide division, and basic principles of electron beam. The experimental part contains a description of used experimental methods for evaluation of samples, creation of Ni-Si coating using electroplating, and the parameters of electron beam used for melting the sample coating. The last part is devoted to structural evaluation of the sample coating and its microhardness.

The thesis is focused on microstructural stability of heterogeneous weld joint of ODS steel and tungsten. The theoretical part summarizes the basic information about the structure and properties of ODS steels and describes the methods of joining these steels with tungsten. In the experimental part, materials MA956 and WL10 were welded by using electron beam. The individual samples differ by preheating temperature or use filler material. After annealing at 800 °C/1h and 1000 °C/5h, a change of the weld metal microstructure was evaluated by using scanning electron microscope. The chemical composition was measured by energy dispersive spectroscopy. It has been found that during annealing, massive precipitation of particles occures in the whole volume of the weld metal. These particles were identified as Laves phase.

Tato diplomová práce se zabývá dotováním grafenu nízkoenergiovými elektrony. Na křemíkový substrát pokrytý vrstvou SiO2 jsou pomocí litograficky vyrobené masky nadeponované kovové kontakty z titanu a zlata. Grafen vyrobený pomocí metody depozice z plynné fáze je přenesen na substrát a slouží jako vodivé spojení kovových elektrod, které vytvářejí kolektor a emitor. Na křemík je ze spodu přivedeno napětí, které tak vytváří spodní hradlo. Takto vytvořený grafenový tranzistor je ozařován nízkoenergiovými elektrony, které mění dotování grafenu. Z polohy maxima v závislosti odporu grafenu na hradlovém napětí lze vyčíst typ dotování. Toto maximum udává napětí, při kterém Fermiho meze grafenu prochází Diracovým bodem v pásové struktuře grafenu. Velikost hradlového napětí, primární energie elektronového svazku a proud svazku jsou tři parametry, které mají velký vliv na změny dotování. Při ozařování transistoru dochází ke změně typu dotování právě tehdy, když odpor grafenu v závislosti na hradlovém napětí dosáhne maxima. Vývoj této změny je zkoumán pro různé energie a proudy primárního svazku v závislosti na hradlovém napětí i v čase. Typ dotování je také prozkoumán při zastavení ozařování v různých fázích smyčky hradlového napětí. Dopování grafenu nízkoenergiovými elektrony je popsáno v teoretickém modelu.

This diploma thesis is focused on fabrication of graphene field-effect transistors, characterisation of their transport properties and investigation of low-energy electron beam influence on the devices' properties under UHV conditions. The theoretical part of this work describes graphene fabrication methods, options of graphene transfer onto the substrates for graphene field-effect transistor manufacture. Furthermore, model of graphene doping via electrostatic interaction or photon, resp. electron beam exposition is explained. The experimental part of this work consist of manufacture of the graphene field-effect transistor in order to examine the change of its transport properties induced by doping of the graphene via low-energy electron beam exposition.

The master thesis summarizes the critical situation of the lack of a cobalt used in different industry branches. Due to its increasing price, it will not be possible to use in existing applications. One of these applications is production of cobalt alloys where the replacement of this element is impossible. This type of material keeps mechanical properties at high temperature. However, a suitable choice of technology can achieve at least its savings. In the field of welding, the alloys are joined without any use of an additional material. The possible solution could be the use of hybrid technologies or electron beam. Verification of weldability of both methods was realised in experimental parts and evaluated by destructive methods. The investigation was performed on wear resistant alloy Stellite 6B.

The diploma thesis deals with the switching of spin vortices in magnetic nanodisks. First, the basic concepts of (micro)magnetism are defined and existing theoretical and experimental achievements in the field of switching of the two basic characteristics (chirality and polarity) of magnetic vortex are summarized. Then the principle of dynamic switching of magnetic vortex chirality using in-plane magnetic field pulse with a well defined amplitude and duration is presented. There is no need to use a certain shape of nanodisks or asymmetry in magnetic field distribution. Nanostructures were prepared by the multi-step electron beam lithography and ion beam sputtering. Individual steps of sample preparation and optimization for the magnetization dynamics measurements are described. Finally, the experimental measurements of the dynamic switching of chirality on prepared samples obtained by transmission x-ray microscopy at the synchrotron Advanced Light Source at Berkeley, USA are presented and discussed.

This diploma thesis deals with study of resonance modes of plasmonic structures. First part provides an overview of theoretical models, which explain the resonanace modes in plasmonic structures. Next part describes technology of electron beam lithography. First section of experimental part deas with technological processes leading to an improvement of resulting structures made by electron beam lithography that is followed by lift-off process. Last part focuses on a study of reflectance spactra of plasmonic antenas and the identification of resonance modes.