Os compostos semicondutores ternários, dentre eles o Ga1-xInxSb, têm sido objeto de interesse de pesquisadores e da indústria microeletrônica devido à possibilidade de ajuste da constante de rede, assim como a correspondente modificação da banda proibida de energia e do intervalo de emissão e absorção óptica, com a variação da fração molar de x. A flexibilidade destas propriedades estruturais torna este composto apropriado como substratos para epitaxias de outros compostos ternários e quaternários, na formação de mono e heterojunções. A maneira mais econômica para obtenção de substratos de materiais semicondutores é através do crescimento de cristais a partir da fase líquida. Porém, os parâmetros que regem a obtenção de lingotes de Ga1-xInxSb com qualidade comercial, a partir da fase líquida, ainda não estão bem definidos. O índio tende a segregar para o líquido, pois seu coeficiente de segregação é menor que a unidade (k < 1), resultando num perfil composicional variado ao longo do lingote. Como os binários GaSb e InSb apresentam configurações de defeitos intrínsecos que originam condutividades de tipos opostos, tipo p e tipo n, respectivamente, a mudança na composição da liga, durante o crescimento, provavelmente resulta na modificação da concentração de cada um destes defeitos. A dopagem com telúrio consiste numa alternativa para minimizar a segregação do índio e diminuir a densidade dos defeitos pontuais, melhorando a qualidade estrutural de cristais de Ga1-xInxSb obtidos através do método Bridgman convencional. Desta forma foram crescidos cristais ternários Ga1-xInxSb, com e sem agitação do líquido durante a síntese, com fração molar inicial de índio de 10% e 20%, alguns deles dopados com 1020 átomos/cm3 de telúrio, pelo método Bridgman vertical. A caracterização estrutural em termos de formação de defeitos lineares, interfaciais e volumétricos foi realizada através de imagens obtidas por microscopia óptica, eletrônica de varredura e de transmissão. A homogeneidade composicional e distribuição de fases foi avaliada através de medidas de espectroscopia por dispersão de energia. Medidas de resistividade e efeito Hall foram utilizadas para a caracterização elétrica, enquanto que a transmitância óptica e a banda proibida de energia foram avaliadas por espectrometria FTIR. Os padrões de difração obtidos através da microscopia eletrônica de transmissão foram utilizados para avaliar a cristalinidade das amostras e determinar o parâmetro de rede. Os resultados obtidos indicam que o telúrio atua de forma compensatória, minimizando a segregação de índio e contribuindo para a homogeneidade composicional e redução de defeitos, principalmente de discordâncias. Além disso, altera a condutividade do Ga1-xInxSb para tipo n, mesmo em frações molares de In inferiores a x = 0,5, diminuindo o número de cargas positivas na rede atribuídas aos defeitos tipo GaSb e VGaGaSb e, desta forma, aumenta a concentração de portadores de carga e reduz a resistividade. Na condição de alta dopagem, reduz a transmitância óptica no infravermelho e aumenta a banda proibida de energia através do efeito Burstein-Moss. A avaliação de cristais de Ga1-xInxSb, dopados e não dopados, crescidos pelo método Bridgman convencional contribuiu para o entendimento do comportamento de dopantes em compostos semicondutores ternários. / Ternary compound semiconductors, including Ga1-xInxSb, have been subject of interest of researchers and microelectronics industry because of the possibility of adjusting the lattice constant, as well as the corresponding modification in the band gap energy, and in the optical absorption and emission range, by varying the mole fraction x. The flexibility of their structural properties makes this compound suitable as substrates for epitaxy of other ternary and quaternary compounds, in the formation of mono- and heterojunctions. The most economical way to obtain semiconductor substrates is by crystal growth from the liquid phase. However, the parameters governing the outcoming of Ga1-xInxSb ingots with commercial quality, from liquid phase, are not well defined. Indium tends to segregate to the liquid, since its segregation coefficient is less than the unity (k < 1), resulting in a varied compositional profile along the ingot. As the binary GaSb and InSb have intrinsic defects configurations that originate opposite conductivities, type p and type n, respectively, the change in the alloy composition, while growing, probably results in a modification of the concentration on each of these defects. Doping with tellurium is an alternative to minimize the indium segregation and decrease the density of point defects, therefore improving the structural quality of Ga1-xInxSb crystals obtained through the conventional Bridgman method. Thus, ternary Ga1-xInxSb crystals were grown by vertical Bridgman method with and without stirring the melt during the synthesis, with 10% and 20% initial molar fraction of indium and some of them were tellurium-doped at 1020 atoms/cm3. The structural characterization regarding linear, interfacial, and volumetric defects formation was performed by using images obtained through optical, scanning and transmission electron microscopy. The compositional homogeneity and phase distribution was assessed by energy-dispersive spectroscopy measurements. Resistivity and Hall Effect measurements were used for the electrical characterization, while the optical transmittance and the band gap energy were examined by FTIR spectroscopy. Diffraction patterns obtained by transmission electron microscopy were used to evaluate the crystallinity of the samples and determine the lattice parameter. The results indicate that tellurium acts in a compensatory way, minimizing indium segregation and contributing to the compositional homogeneity and defect reduction, especially in dislocations. In addition, it changes the conductivity of Ga1-xInxSb to n-type, even in mole fraction of In lower than x = 0.5, reducing the number of positive charges on the network assigned to GaSb and VGaGaSb defects, thus increasing the concentration of charge carriers and reducing the resistivity. In high doping condition, it reduces the optical transmittance in the infrared region and increases the energy of the band gap by the Burstein-Moss Effect. The evaluation of Ga1-xInxSb crystals, doped and undoped, grown by the conventional Bridgman method contributed to the understanding of dopants behavior in ternary compound semiconductors.

L'utilisation récente des fibres optiques (FOs) à base de silice dans des environnements extrêmes, a incité les chercheurs à accélérer leurs études de vulnérabilité. De tels défis sont fortement liés à la bonne compréhension des effets à la fois macroscopiques et microscopiques des différents types de radiations sur la réponse des FOs. Cette thèse de doctorat présente une étude complémentaire aux études précédemment menées sur les différents défauts ponctuels dans les FOs à base de silice par Cathodoluminescence (CL). Cette technique offre la possibilité de détecter les centres luminescents mais aussi de suivre leurs distributions spatiales, leurs cinétiques de création et de guérison en fonction de l'irradiation électronique. Dans ce manuscrit, nous introduisons tout d'abord un résumé des connaissances actuelles sur les défauts liés à la silice pure et différemment dopée.Les détails de notre procédure expérimentale sont discutés dans le 2ème chapitre où nous montrons que les doses déposées lors des mesures CL sont très importantes. Dans le 3ème chapitre nous présentons une étude systématique de la réponse en CL des différentes classes de FOs, dans lesquelles différentes bandes d'émission sont discutées. Le 4ème chapitre traite l'impact d'une variation des conditions d'irradiation électronique sur les centres GLPC, l'un des défauts liés au Ge les plus importants. Enfin, dans le 5ème chapitre, nous avons montré la possibilité de produire des nanoparticules à base de silice par ablation laser, et la capacité de la technique CL de caractériser ce type de matériaux, ce qui ouvre la porte à d'autres utilisations de cette technique pour la caractérisation de nanoparticules. / The recent use of silica-based optical fibers (OFs) in harsh environments pushed the researchers to accelerate their vulnerability and hardening studies. Such challenges are strongly linked to the good understanding of the macroscopic as well as the microscopic effects of different types of radiations on the silica-based OF's response. This PhD thesis presents a complementary study to previous researches on the properties of different point defects in silica-based OFs by Cathodoluminescence (CL). Such technique offers the ability to both detect the luminescent centers and to follow their spatial distribution, their growth and decay kinetic as a function of the electron beam characteristics. ln the present manuscript we first summarize the current knowledge regarding point defects in pure silica or silica glass doped with Ge, P, Ce, N or Al. Details of the experimental procedure are discussed in the 2nd chapter in which we highlight that the equivalent dose deposited during the various configuration of CL measurements are very large. ln the 3rd chapter, we perform an overview study of the CL responses of different classes of OFs, in which many emission bands related to the different dopants were discussed. The 4th chapter focuses on the study of the effects of varying beam conditions on the signature of Germanium Lone Pair Center (GLPC), one of the most important Ge-related point defects. Finally, in chapter V, we demonstrate the possibility to produce silica-based nanoparticles by laser ablation process, and the ability of the CL technique to characterize such materials, which opens the door to other employments of this technique for future studies on nanoparticles.

A neutron flux on the order of 2·10²° neutrons/cm² at 0.18 MeV induces formation of point defects (vacancies and interstitials) in single crystal 3C-SiC causing a volume lattice expansion (swelling) of over 3% that can be measured by X-Ray diffraction. The crystal lattice can be completely restored with an annealing temperature equal to or higher than the irradiation temperature. This phenomenon serves as a basis for temperature measurements and allows the determination of the maximum temperature, if the exposure time is known. The single crystal 3C-SiC sensor is applicable to small, rotating and hard to access parts due to its size of 300-500 microns, wide temperature range of 100-1450 °C, "no-lead" installation, inert chemical properties and high accuracy of temperature measurements. These features make it possible to use the sensor in gas turbine blades, automotive engines, valves, pistons, space shuttle ceramic tiles, thermal protection system design, etc. This work describes the mechanism of neutron irradiation of single crystal 3C-SiC, the formation of point defects and their concentration, the different temperature measurement techniques, and the application of Maximum Temperature Crystal Sensors (MTCS) for maximum temperature measurements in both stationary and non-stationary regimes.

Uranium (U) exhibits a high temperature body-centered cubic (b.c.c.) allotrope that is often stabilized by alloying with transition metals such as Zr, Mo, and Nb for technological applications. One such application involves U-Zr as nuclear fuel, where radiation damage and diffusion (processes heavily dependent on point defects) are of vital importance. Metallic nuclear fuels swell under fission conditions, creating fission product gases such as helium, xenon and krypton. Several systems of U are examined within a density functional theory framework utilizing projector augmented wave pseudopotentials. Two separate generalized gradient approximations of the exchange-correlation are used to calculate defect properties and are compared. The bulk modulus, the lattice constant, and the Birch-Murnaghan equation of state for the defect free b.c.c. uranium allotrope are calculated. Defect parameters calculated include energies of formation of vacancies in the α and γ allotropes, as well as self-interstitials, Zr, He, Xe and Kr interstitial and substitutional defects. The results for vacancies agree very well with experimental and previous computational studies. The most probable self-interstitial site in γ-U is the <110> dumbbell and the most probable defect location for dilute Zr in γ-U is the substitutional site. The most likely position for Xe and Kr atoms in uranium is the substitutional site. Helium atoms are likely to be found in a wide variety of defect positions due to the comparable formation energies of all defect configurations analyzed.

Point defects control many properties of technological importance in intermetallic compounds such as atomic diffusion, creep, hardness, mechanical properties and sintering. Farther, since intermetallic compounds are characterized by long range atomic order, the point defects in these compounds can be qualitatively different from those in pure metals and disordered alloys. In the present study, we have chosen β-NiAl for our point defect studies since it is a potential candidate for high temperature applications and a model system for the study of basic phenomena in ordered alloys. We have used a mean field formulation for studying point defect concentrations. The outline of the formulation is as follows: We divide the rigid, body centred cubic lattice into two interpenetrating cubic sublattices called α and j3 which are made up of the cube corners and body centres respectively. We write a generic free energy function (G) that involves the temperature T and the six sublattice occupancies viz., the A (Ni), B (Al) and vacancies (V) on the two sublattices α andβ. We use the constraints on the number of α and β sublattice sites viz., the number of α sublattice sites is equal to the number of β sublattice sites, to write G as a function of four of the six sublattice occupancies and T. We define three auxiliary parameters η1, η2 and η3 which correspond to the vacancy concentration, the differential B species population on the two sublatices (the chemical or atomic order), and the differential vacancy population on the two sublattices, respectively. We then rewrite G as a function of T, xB and ηi. The G can now be minimized with respect to the three auxiliary variables so that we recover the free energy (G) as a function of XB and T only. The formulation requires as inputs the Ni-Ni, Al-Al, Ni-Al, Ni-V and Al-V interaction energies in the nn and nnn shells. We have obtained the Ni-Ni, Al-Al and Ni-Al interaction energies from the effective pair potentials reported in the literature. For the Ni-V and Al-V interaction energies we have used a bond breaking model in which we have assumed that the Ni-V and Al-V interaction energies in the nnn shell to be zero. Using the above interaction parameters in our mean field formulation we have determined the concentrations of various types of point defects in β-NiAL We have specifically chosen the temperature range of 800 - 2000 K and the composition range of 45 - 55 atomic% Al. Our results can be summarised as follows: 1.The predominant defect in the stoichiometric alloy is a combination of an Ni-antisite defect and two vacancies on the Ni sublattice. 2.The Al-rich alloys of composition (50 + ∆) atomic% contain 2∆% vacancies;since the alloys are almost perfectly ordered, these vacancies predominantly occupy the Ni sublattice. Similarly, the Ni-rich alloys of composition (50 — ∆)atomic% contain ∆% Ni antisites. 3.Both the vacancies on the Ni sublattice (in Al-rich alloys) and Ni-antisites (in Ni-rich alloys) show negligible temperature dependence, and hence owe their origin to the off-stoichiometry. 4.In all the alloys, the Al-antisites have the lowest concentration (of the order 10-6 even at 2000 K) and the concentration of the vacancies on the β sublattice is the next lowest. Thus, our results support the view that β-NiAl is a triple defect B2 and, if we consider constitutional vacancies as those which have a little or no temperature dependence, there exist constitutional vacancies in Al-rich β-NiAl. This conclusion is in agreement with some of the experimental results. However, it must be pointed out that there is considerable disagreement among experimental results from different groups.

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xi, 124 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 81-87).

Šiame darbe nagrinėjami radiaciniai defektai bei jų tarpusavio reakcijos silicyje. Atlikti eksperimentai, kurių metu pasitelkus minkštąją Rentgeno spinduliuotę buvo generuojami defektai. Vėliau bandiniai buvo tiriami FT-IR spektroskopijos metodais. Darbo apimtis 52 puslapiai. Darbas susideda iš 5 dalių. Pirmoje dalyje apžvelgiami Rentgeno spinduliuotės šaltiniai ir spinduliuotės savybės. Antroje - dalyje radiaciniai defektai silicyje. Trečioje - defektų tyrimo metodai. Ketvirtoje - dalyje defektų reakcijos. Penktoje - eksperimento metodika ir eksperimento rezultatai. / In this work, we are researching radiation defects and their reactions in silicon. During experiments defects were generated using soft Rentgen radiance. Later samples were researched using FT-IR methods of spectroscopy. Work amount is 52 pages. Work consists from 5 parts. First part - overview of sources and features of Rentgen radiance. Second part – radiation defects in silicon. Third part – methods of defect researching. Fourth part – reactions of defects. Fifth part – Methods and results of experiment.

The climb of dissociated dislocations in FCC materials is known to be complex: Observations of climb under HVEM irradiation in CuAl suggest that it, proceeds via the nucleation of interstitial loops directly onto individual partials. In silver, however, dissociated dislocations appear to constrict at an early stage in the irradiation, and dense vacancy cluster damage is seen to form in their vicinity. This thesis presents results and analysis of a study aimed at the determination of the interaction of HVEM generated interstitials and vacancies with pre-existing dislocations in a range of Fe-17Cr-Ni ternary alloys (with the nickel content varying between 15 and 40%). Two quaternary alloys (Fe-15%Ni-17%Cr-l%Si and Fe-15%Ni-17%Cr-2%Mo) arc also studied. As with earlier studies in CuAl and Ag, pre-existing dislocations in a (111) orientated foil were first characterized at subthreshold voltages employing the weak-becim technique, then irradiated with IMeV electrons at temperatures in the range 400-430°C and finally returned to the low voltage microscope for postirradiation characterization of the observed damage. Analysis of the post-irradiation microstructures indicates that interstitial climb only occurs at particularly favourable sites, such as pre-existing jogs: For the ternary alloys, constrictions are removed along edge and mixed dislocations, whilst zig-zagging of screw and near-screw dislocations may also be attributable to jog climb. After the annihilation of constrictions evidence of climb is not seen and pipe diffusion is thought to be occurring. The precipitation of small clusters, many of which are identifiable as vacancy SFT, is reminiscent of observations in silver. The addition of silicon to the matrix apparently leads to the creation of favourable sites for interstitial climb, as evidenced by the formation of high densities of new jogs after irradiation. Loops are seen to precipitate close to dislocations in the Mo-doped material. The origin of these loops is unclear at this stage. The relevance of the results to the phenomenon of void swelling is discussed.

Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains xiii, 109 p. : ill. Includes abstract. Includes bibliographical references (p. 102-109).

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xiii, 150 p. : ill. Includes abstract. Includes bibliographical references (p. 141-150).