This master thesis is focused on characterization of electrical transport properties of one-dimensional nanostructures. First section of this work deals with theoretical description of the experimental approaches to realization of such measurements. This section involves also a detail discussion of preparation of contacts using e-beam lithography. Next, theoretical description of characterization of nanostructures using photoluminescence measurements is given. Second section describes practical application of the aforementioned electrical transport measurements. Presented results include transport and photoluminescence measurements of WS2 nanotubes, InAs and WO2.72 nanowires. The last section of this thesis deals with nanowire quantum well heterostructures. The section provides both a deeper theoretical view of the problem and results of the photoluminescence measurements are shown.

The presented diploma thesis is focused on the preparation and properties of transparent polycrystalline ceramic materials based on Al2O3. Theoretically, the most important technological aspects of the processing of these materials are presented. Detailed attention is given to transparent Al2O3 polycrystalline ceramics doped with rare earth elements. The influence of microstructural parameters on the optical properties (represented by RIT) is investigated on Al2O3 samples doped and codoped with dysprosium, terbium and chromium. A significant effect of the average grain size on the light transmittance of all samples is observed. The highest RIT = 55 % (measured by a laser beam with a wavelength of 632,8 nm) was achieved by an optimized preparation process for a sample doped with 0,05 at. % of dysprosium. For all samples photoluminescent properties are also analysed. The photoluminescent emission spectra correspond to the activation of doping elements. In case of the terbium and chromium codoped samples, the differences in the activation of individual dopants depending on different excitation wavelengths were demonstrated, resulting in different colour emissions for different excitation wavelengths.

For Raman spectroscopy is a need to introduce a laser light into an optic fiber and analyze a collected light at the same time. Therefore it was proposed a specialized optical system. This system can also be used to measure other spectroscopy methods such as photoluminescence. In the theoretical part of this theses, was discussed both mentioned methods and their instrumentations. In addition to the Raman spectroscopy, was also shown some special cases of Raman spectroscopy for enhanced measurement of Raman scattering. The problem of weak signal detection and its reading is also discussed in the theoretical part of the thesis. In the practical part of this thesis was discussed the mechanical design of the optical system and the choice of optical elements that are used in the system. Next, is introduced the manufactured system, which design is based on the parameters of the chosen optical elements. The practical part of the thesis ends with an assembly and testing of the proposed system.

Philosophiae Doctor - PhD / The framework agreement in the year 2000 by the international community to launch Generation IV program with 10 nations, to develop safe and reliable nuclear reactors gave rise to the increased interest in the studies of SiC and the effect of different irradiations on solids. Silicon carbide is a preferred candidate used in harsh environments due to its excellent properties such as high chemical stability and strong mechanical strength. The PBMR technology promises to be the safest of all nuclear technology that have been developed before. SiC has been considered one candidate material being used in the fabrication of pebble bed fuel cell. Its outstanding physical and chemical properties even at high temperatures render it a material of choice for the future nuclear industry as whole and PBMR in particular. Due to the hostile environment created during the normal reactor operation, some of these excellent properties are compromised. In order to use this material in such conditions, it should have at least a near perfect crystal lattice to prevent defects that could compromise its strength and performance. A proper knowledge of the behavior of radiation-induced defects in SiC is vital. During irradiation, a disordered crystal lattice occurs, resulting in the production of defects in the lattice. These defects lead to the degradation of these excellent properties of a particular material. This thesis investigates the effects of various radiation effects to 6H-SiC. We have investigated the effects of radiation induced damages to SiC, with a description of the beds and the importance of the stability of the SiC-C interface upon the effects of radiations (y-rays, hot neutrons). The irradiated samples of 6H-SiC have been studied with various spectroscopic and structural characterization methods. The surface sensitive techniques such as Raman spectroscopy, UV-Vis, Photoluminescence and Atomic Force Microscopy will be employed in several complimentary ways to probe the effect of irradiation on SiC. The obtained results are discussed in details.

This work deals with measuring of very low temperatures during the detection defects of solar cells by photoluminescence method. Liquid nitrogen is used to cooling solar cells. Properties of liquid nitrogen and safety of handling are described in this work. Themperature in cryo area is measured by the thermocouple senzors. A main part of this work was to concept and creation of equipment for themperature controling in cryo technique. This equipment signalling danger scorch in low temperatures. The device was created to complement work place for the detection defects of solar cells by photoluminescence method.

Orientador: Silvio Rainho Teixeira / Resumo: Cerâmica com estrutura do tipo perovskita e minério recentemente descoberto, o CaZrO3 se aplica, com destaque, em componentes de circuito para sensores de oxigênio, hidrogênio e umidade, além de poder ser utilizado na adsorção de corantes, como material abrasivo, refratário e como matriz em sólidos fósforos dopados com Eu3+. Devido a este leque de aplicações, torna-se imprescindível o estudo de novos métodos de síntese visando a obtenção deste material, principalmente em escala nanométrica. O método Hidrotermal Assistido por Micro-ondas (HAM) é um excelente candidato para tal, já que é empregado na obtenção de cerâmicas avançadas, utilizando menores tempos e temperaturas durante o processo de síntese. Este trabalho apresenta os primeiros resultados da obtenção do CaZrO3 pelo método HAM, no qual diversos parâmetros de síntese foram variados para uma melhor avaliação de suas características estruturais, morfológicas e ópticas. Partículas CaZrO3 foram nucleados pelo método HAM em 140 ºC durante 1, 10, 40 e 180 min e cristalizados via tratamento térmico de 600 até 1200 ºC. Duas fases principais foram obtidas, uma estequiométrica e outra não estequiométrica, as quais podem ter suas porcentagens modificadas de acordo com os precursores, tempo de síntese e temperatura de tratamento térmico. Três propriedades distintas foram analisadas: (1) sensibilidade à umidade; (2) capacidade de adsorção dos corantes rodamina B, vermelho congo, azul de metileno e alaranjado de metila e; (3) viabi... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Ceramic with a perovskite type structure and recently discovered mineral, CaZrO3 is especially used in circuit components for oxygen, hydrogen and humidity sensors, in addition to being able to be used in the adsorption of dyes, as an abrasive, refractory material and as a matrix in solid phosphors doped with Eu3+. Due to this range of applications, it is essential to study new methods of synthesis in order to obtain this material, mainly on a nanometric scale. The Microwave-Assisted Hydrothermal (MAH) method is an excellent candidate for this, since it is usually used to obtain advanced ceramics, using shorter times and temperatures during the synthesis process. This work presents the first results for obtaining CaZrO3 by the MAH method, in which several parameters of synthesis were varied for a better evaluation of its structural, morphological and optical characteristics. CaZrO3 particles were nucleated by the MAH method at 140 ºC for 1, 10, 40 and 180 min and crystallized via heat treatment from 600 to 1200 ºC. Two main phases were obtained, one stoichiometric and the other non-stoichiometric, which can have their percentages modified according to the precursors, synthesis time and heat treatment temperature. Three distinct properties were analyzed: (1) sensitivity to humidity; (2) adsorption capacity of rhodamine B, congo red, methylene blue and methyl orange dyes; (3) viability of this material as an Eu3+ ion matrix (1, 3 and 5%). All these properties were observed, whe... (Complete abstract click electronic access below) / Doutor

Title: Defects limiting charge collection in semiinsulated CdZnTe Author: Vít Zajac Department: Institute of Physics of Charles University Supervisor: doc. Ing. Jan Franc, DrSc., Institute of Physics of Charles University Abstract: We achieved to detect photoluminescence transitions deep in the band gap in 4 samples cut from 2 different crystals of semiinsulating Cd1-xZnxTe (x = 0,02 - 0,18) in a row of points along the growth axis. The spectral peaks give evidence of the presence of deep levels in the sample and the intensity of the photoluminescence peaks is to a certain extent proportional to the concentration of these levels. A comparison between resistivity and photoconductivity that were measured by a contact-less method showed that the change of photoluminescence intensity of deep levels does not bring about an unambigous change of neither resistivity nor photoconductivity. Correlation analysis of resistivity and photoconductivity of 6 samples from 4 different crystals confirmed the following model: A shift of the Fermi level within the band gap induced by a change of donor-acceptor compensation is accompanied by an unambigous change of resistivity and results in a change in occupation of the deep levels. This causes a change in the photoconductivity of the crystal because the occupation factor of...

Silicon carbide (SiC), is a wide band gap (2.4 eV < Eg < 3.3 eV) semiconducting material well known for its potential applications in high-temperature, high-power, high-frequency or hard radiation resistant devices. In this thesis, we are broadening elementary knowledge about this material. We identify energy levels in the material, using Photo-Hall effect spectroscopy supported by the temperature dependency of classic Hall effect measurement and temperature dependent photoluminescence. This knowledge is essential to allow SiC application as a radiation detector.

This thesis deals with synthesis and characterization of newoligothiophenes and derivatives thereof, for use as organicsemiconductors in optical and electronic applications, such asfield-effect transistors and light-emitting diodes. Much workis devoted to the development of new synthetic strategies forinteresting building blocks, to beused for synthesizing suchmaterials. One series of regio-defined oligothiophenes, up tothe octamer, has been prepared and evaluated. Photoluminescencequantum efficiencies of these were 22-31 % in solution, butdropped to 2-5 % in the solid state. Another project deals withthe development of oligothiophenes with in-chain chirality.These may find use in polarized lightemitting diodes. Finally,two oligothienyl-substituted porphyrins have been synthesizedand are currently evaluated for use in light-emitting diodesand possibly in solar cells. / NR 20140805

We conclusively explain the different lasing mode energies in ZnO nano- and microcavities observed by us and reported in literature. The limited penetration depth of usually used excitation lasers results in an inhomogeneous spatial gain region depending on the structure size and geometry. Hence, weakly or even nonexcited areas remain present after excitation, where modes are instantaneously suppressed by excitonic absorption. We compare the effects for ZnO microwires, nanowires, and tetrapod-like structures at room temperature and demonstrate that the corresponding mode selective effect is most pronounced for whispering-gallery modes in microwires with a hexagonal cross section. Furthermore, the absorptive lasing mode suppression will be demonstrated by correlating the spot size of the excitation laser and the lasing mode characteristic of a single ZnO nanowire.