In contrast to 1,1'-binaphthyl, racemic 4,4'-dimethyl-1,1'-binaphthyl does not undergo spontaneous resolution upon heating from room temperature to just below the melting point. Optically active dimethyl binaphthyl may be obtained by seeding the racemic melt site optically active naphthidine. The crystal structures of both the racemic and optically active dimethyl binaphthyls were solved in the hope of understanding the above observations. The racemate crystallizes in the monoclinic space group C2/c with cell parameters a=13.225, b=10.768, c= 11.572 Å and β=114.040. There are four molecules per unit-cell; two have the B and two have the S configuration. The structure was solved using direct methods and refined to R=0.074. There is a 3° head in the plane of the naphthalene residues, which are cis-oriented with an angle of 68° between them. The optically active form belongs to one of the tetragonal space groups P4₁2₁2 or P4₃2₁2 with cell parameters a = b = 8.3031 and c = 23.706 Å. Direct methods sere used to solve the structure and the final R was 0.060. There are four molecules per unit-cell of identical configuration, but it could not be determined whether this was R or S. The naphthalene residues show a 2.7° bend and are also cis-oriented, but with an angle of 80° between them. Bond lengths and angles are consistent with values previously reported for 1,1'-binaphthyl and naphthalene. The racemate packs somewhat more efficiently and perhaps for this reason it is slightly more stable than the optically active form- It is difficult however to explain the difference in behaviour between the methylated and unmethylated binaphthyls on the basis of these results alone. Further studies would include the crystal structures of optically active 1,1'-binaphthyl and various naphthidines. / Science, Faculty of / Chemistry, Department of / Graduate

The structures of four 4aβ,5,8,8aβ-tetrahydro-1 -naphthoquin-4-ol derivatives have been studied and related to their observed photochemical reactivity. H-abstractions are dominant in the solid state photolyses of these compounds because of their conformations and the topochemical control by the lattice. All structures have been solved by direct methods and refined by least squares procedures. The 2,3,6,7-tetramethyl-4α-ol derivative, C₁₄H₂₀O₂, is monoclinic, space group C2/c, a = 13.898(3), b = 5.228(1), c = 17.316(3) Å, β = 97.442(7)° and Z = 4. This structure was refined to R = 0.058 for 888 reflections. The 2,3- and 6,7-dimethyl-4α-ol compounds-C₁₂H₁₆O₂, are orthorhombic, space group P2₁2₁2₁, and monoclinic, space group 2₁/c, respectively. For the 2,3-derivative, a = 5.148(1), b = 12.269(2), c = 16.478(3) Å, Z = 4 and the refinement of 671 data led to an R of 0.031. The 6,7-compound, a = 9.242(3), b = 22.724(3), c = 5.139(2) Å, β = 102.7(1)°, Z = 4, was refined to R = 0.032 for 626 data. 2,3,4σ,4aβ,6,7,8aβ-heptamethyl-4β-ol, C₁₇H₂₆0₂, is monoclinic, space group P2₁/c, a = 7.497(2), b = 16.792(3), c = 12.687(3) Å, β = 105.30(1)° and Z = 4. An R-value of 0.041 was obtained from the refinement of 1934 reflections. The above compounds have similar conformations which are favorable to H-abstraction reactions. The 6,7-dimethyl-1α,4α-diol C₁₂H₁₈0₂, crystallizes in the monoclinic system, space group P2₁/c, a = 13.870(2), b = 18.025(4), c = 9.236(1) Å, β = 108.098(6)° , Z = 8 and was refined to R = 0.032 for 1461 reflections. The diol compound adopts the same conformation as those above but is not photoreactive. The following four compounds were derived from either tetrahydronaphthoquinol progenitors or their oxidized forms, tetrahydronaphthoquinones. A twistane-1ike structure, twistenone C₁₀H₁₀0₂, was found to crystallize in the monoclinic system, space group P2₁/n, a = 6.381(2), b = 19.454(2), c = 6.708(2) Å, β = 1 06.24( 1 )° and Z = 4. Refinement of 930 reflections converged at R = 0.037. 5-(2,3-dimethylphenyl)-ƴ-butyrolactone crystals, C₁₂H₁₅O₂ are monoclinic, space group P2₁/n, a = 10.847(3), b = 6.924(1), c = 13.654(4) Å, β = 95.22(1)° and Z = 4. The structure was refined to R = 0.057 for 569 reflections. It was hoped that elucidation of this structure would aid in determining the intermediate compound from which it was formed. The methylene ketone C₁₇H₂₄0, derived from the acetylation product of the previously described heptamethyl-4β-ol, is monoclinic, space group P2₁/a, a = 12.374(2), b = 8.771(1), c = 13.743(2) Å, β = 104.027(6)° , Z = 4 and refined to R = 0.037 for 1369 data. A reaction designed to pinacolize a diketone cage compound resulted in a different product from which the hydroxy mesylate derivative C17H280„S, was formed. The crystals are monoclinic, space group P2,/c, a = 9.246(2), b = 10.938(1), c = 17.335(4) Å, β = 102.11(1)° and Z = 4. Refinement converged at R = 0.042 for 2995 reflections. / Science, Faculty of / Chemistry, Department of / Graduate

ABSTRACT Part one of this thesis contains the x-ray crystal structure analyses of six compounds related to natural product chemistry. The first three analyses were performed in order to identify two isomers, separated by chromatography, that were potential intermediates in the syntheses, of stemodin. and aphidicolin, and differed only in the orientation of a cyclobutyl moiety. The first eluted isomer was shown to be a β-cyclobutyl tricyclic enone (C₂₂H₃₂O₃ monoclinic, space group P2₁/n, a = 11.832(1), b = 11.423(1), c = 14.637(1) Å, β = 98.71(2)°, Z = 4, solved by direct methods and refined to R = 0.034 for 2052 observed reflections). The second eluted isomer was the c-cyclobutyl species (C₂₂H₃₂O₃, monoclinic, space group P2₁/n, a = 15.722(4), b = 7.463(2), c = 17.213(6) Å, β =- 104.67(1) ⁰, Z = 4, solved by direct methods- and- refined to R = 0.040 for 702 observed reflections). The third analysis was of the p-bromobenzoate derivative of the second eluted isomer, and confirmed the c-cyclobutyl structure (C₂₉H₃₇BrO₄, triclinic, space group PT, a = 11.023(2), b = 11.877(1), c = 10.900(1) Å, α = 90.461(8), β = 111.57(1), ƴ = 80.51(1)°, Z = 2, solved by Patterson methods and refined to R = 0.032 for 2715 observed reflect ions). The fourth structure was also a p-bromobenzoate derivative of a system involving a four-membered ring, and was undertaken to verify the 1,4-homoenol structure of camphor-1,4-homoenol p-bromobenzoate (C ₁₇H₁₉BrO₂, orthorhombic, space group P2₁2₁2₁, a = 6.875(1), b = 8.522(2), c = 26.658(6) Å, Z = 4, solved by both direct and Patterson methods and refined to R =0.045 for 697 observed reflections). The last two structures of this part proved to be crystallographically difficult. One was the previously unknown structure of raucubaine, an indole alkaloid isolated from the plant Rauwolfia salicifolia griseb. (C₂₀H2₂₄N₂0₃, monoclinic, space group P2₁, a = 7.2179(3), b = 12.8169(7), c = 9.1996(2) Å, β = 93.040(3)°, Z = 2, solved by direct methods (with great difficulty) and refined to R = 0.046 for 1700 observed reflections). The other was a sugar that had remained unsolved for fourteen years (C₂₄H₂₄Cl₂O₈, monoclinic, space group P2₁, a = 5.752(3), b = 15.436(3), c = 13.698(3) Å, β = 93.74(3)°, Z = 2, solved by direct methods (with great difficulty) and refined to R = 0.042 for 898 observed reflections). Part two contains two optically active structures as part of a project concerning spontaneous resolution in binaphthyl systems: the first being naphthidine (C₂₀H₁₆N₂, tetragonal, space group P4₁2₁2 or P4₃2₁2, a = 7.945(1), c = 24.264(5) Å, Z = 4, solved by direct methods and refined to R = 0.068 for 548 reflections) and the other 1, 1'-binaphthyl (C₂₀H₁₄, tetragonal, space group P4₁2₁2 or P4₃2, a = 7.164(2), c = 27.70(1) Å, Z = 4, solved by direct methods and refined to R = 0.030 for 562 observed reflections). These structures are compared to those of several related compounds. / Science, Faculty of / Chemistry, Department of / Graduate

La nécessité de maîtriser les émissions de GES (CO2, NO), la raréfaction et la hausse du prix des carburants fossiles conduisent à envisager la substitution du C fossile par du C « renouvelable » c'est-à-dire issu de la biomasse végétale. Cette stratégie de substitution doit être durable. En particulier l’exportation massive de biomasse végétale privant le sol des restitutions de résidus végétaux (par exemple pour les pailles de céréales) ; et l’implantation de nouvelles cultures notamment des plantes pérennes (par exemple le miscanthus) interrogent sur les pratiques culturales, notamment les dates et les fréquences d’exportation, indispensables pour le maintien de la fertilité des sols et une bonne gestion des cycles biogéochimiques. Miscanthus×giganteus, plante pérenne à rhizome est une des plantes « candidate » pour la production des carburants de seconde génération, en raison de son fort potentiel de production de biomasse, y compris en conditions tempérées. Dans ce contexte l’objectif principal de ce travail de thèse était de quantifier et caractériser les litières végétales recyclées vers le sol sous culture de Miscanthus, plus précisément les feuilles sénescentes,les racines et rhizomes de Miscanthus et d’étudier la minéralisation du C et N au cours de leur décomposition. Ce travail s’est appuyé sur un essai au champ de Miscanthus×giganteus, âgé de 3 à 5ans, implanté depuis 2006 à Estrées-Mons (Nord de la France), et croisant 2 dates de récolte (une récolte précoce avant l’hiver et une récolte tardive après l’hiver en fin de cycle annuel) et 2 niveaux de fertilisation azotée (0 kg N ha-1 et 120 kg N ha-1). Tout d’abord sur les litières prélevées sur cet essai,nous avons quantifié, caractérisé biochimiquement et étudié la minéralisation en conditions contrôlées des feuilles sénescentes, rhizomes et racines. Ensuite la dynamique de chute des feuilles au cours de la sénescence, leur accumulation sous forme de mulch à la surface du sol et les cinétiques de décomposition ont été étudiées au champ pendant deux années. Enfin nous avons étudié les effets de la disponibilité de l’azote sur la dynamique du C et N, la dynamique microbienne et des fonctions enzymatiques au cours de la décomposition de ces feuilles, en conditions contrôlées. La disponibilité en N a été modulée soit en apportant de l’azote minéral, soit en apportant des quantités croissantes de feuilles pour une quantité d’azote donnée. Nous montrons que le C stocké dans les trois " compartiments " recyclés potentiellement au sol est considérable : feuilles sénescentes (1à 3 t C ha-1 par an), racines (1 à 2 t C ha-1) et rhizomes (7 à 10 t Cha-1). Les rhizomes, ont une teneur en soluble-NDS de 25 à 35% et une teneur en lignine de 11 à 15% selon les prélèvements précoces ou tardifs, et une teneur en N élevée (0.7-1.5%). On observe en 263jours à 15 °C, une minéralisation des rhizomes représentant 61±8% du C apporté, supérieure à celle observée pour les racines (36±8%) et les feuilles sénescentes (53±4%). Nous montrons l’importance des feuilles sénescentes de Miscanthus dans le recyclage de matière organique vers le sol : le scénario de récolte précoce prive le sol d’un recyclage annuel de 1-3 t C ha-1 ; d’autre part qualitativement, la faible dégradabilité observée au laboratoire pour les feuilles est confirmée au champ, ce qui conduit à la formation d’un mulch important en épaisseur (2 à 4cm) et en quantité (équivalent à 6 à 7 t C ha-1).Enfin, une forte disponibilité en N accélère la vitesse de minéralisation du C à court terme. Ceci se traduit aussi par une augmentation du C microbien et de l’ergostérol, marqueur fongique, ainsi que des activités enzymatiques liées à la dégradation du C et N (xylanase, leucine aminopeptidase). En revanche, cette disponibilité forte en N réprime l’activité laccase. Nous montrons aussi que diminuer la disponibilité relative en N pour les décomposeurs, par ajout de quantités croissantes de feuilles dans le sol conduit à ralentir la croissance microbienne et fongique. Cette situation favorise très tôt l’installation de la biomasse fongique (augmentation du rapport ergostérol/C microbien) et son activité(laccase).Ce travail montre que la culture de Miscanthus permet potentiellement une forte accumulation de C organique, ce qui est favorable au maintien de la fertilité des sols à long terme. Il est maintenant essentiel de pouvoir prédire le devenir du C des parties souterraines de Miscanthus, dans la perspective de changement dans l’utilisation des terres. / To control emissions of greenhouse gases (CO2, NO), fossil fuels scarcity and their rising prices lead to consider the substitution of fossil C by the "renewable" C from plant biomass. This alternative strategy must be sustainable. In particular the massive export of plant biomass depriving soil of plant residues (eg cereal straws), and the growing of new crops specially perennial crops (eg miscanthus)questioned the cultural practices (dates and frequency of biomass export) essential for maintaining soil fertility and good management of biogeochemical cycles. Miscanthus × giganteus, a rhizomatous perennial grass is dedicated to second-generation fuels production, because of its high potential biomass production.In this context the main objective of this work was to quantify and characterize Miscanthus plant litter recycled to soil, more precisely senescent leaves, roots and rhizomes of Miscanthus, and to study the C and N mineralization during decomposition of these litters. This work was performed on 3 to 5 years old Miscanthus stands established since 2006 in Northern France (Estrées Mons), either fertilized with120 kg N ha−1 year−1 or unfertilized. The sampling of litters was performed in autumn (maximal biomass production) and winter (maturity). Firstly we quantified and biochemically characterized Miscanthus senescent leaves, rhizomes and roots. Then we studied their decomposition in soil under controlled conditions (15°C, -80 kPa) during 263 days. We also investigated in the field for two years the dynamics of leaf fall during senescence, their accumulation in the form of mulch on soil surface and the kinetics of decomposition. Finally we investigated under controlled conditions the effects of nitrogen availability on C and N dynamics, microbial dynamics and enzymatic functions during the decomposition of these leaves. N availability was modulated either by adding inorganic nitrogen, or by adding increasing amounts of leaves for a given amount of nitrogen in soil.Our results showed that the C stored in the three "compartments" recycled to soil is potentially considerable: senescent leaves (1 to 3 t C ha-1 year), roots (1 to 2 t C ha-1) and rhizomes (7 to 10 t C ha-1). The rhizomes had a high NDS soluble content (25 to 35%), a high N content (0.7 to 1.5%) and low lignin content (11 to 15%) depending on early or late harvest dates. we observed after 263 days of decomposition at 15°C a higher carbon mineralization from rhizomes 61 ± 8%, than that observed for roots (36 ± 8%) and senescent leaves (53 ± 4%). We also showed the importance of senescent leavesin the recycling of organic matter in the soil: the early harvest scenario deprives the soil of an annual leaves of 1-3 t C ha-1. Qualitatively, the low degradability observed in the laboratory experiment for the leaves was confirmed in the field. This leads to the formation of an important thick layer of mulch(2 to 4cm) and quantitatively (6-7 t C ha-1). Finally, a high N availability increases the C mineralization rate in the short term which was reflected by an increase in microbial C, fungal ergosterol, and enzymatic activities related to C and N degradation of (xylanase, leucine aminopeptidase). However, this high N availability suppresses laccase activity. We also showed that decreasing N availability for decomposers by adding increasing amounts of leaves in the soil leads toslow microbial and fungal growth. However, this situation favors an early installation of fungal biomass (increased ergosterol / microbial C ratio) and their activity (laccase).This work showed that the cultivation of Miscanthus potentially allows a large accumulation of organic C which is favorable to the maintenance of soil fertility in the long term. It is now essential to predict the fate of underground C parts of Miscanthus, in the perspective of change in land use, i.e.when the Miscanthus stands is to be replaced in field by another crop.

Orientador: Lisandro Pavie Cardoso / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-13T22:20:46Z (GMT). No. of bitstreams: 1 Morelhao_SergioLuiz_M.pdf: 1417672 bytes, checksum: 4f5418b8c55b1008151e0489903dff5e (MD5) Previous issue date: 1990 / Resumo: Neste trabalho, é desenvolvido um método baseado na técnica de difração múltipla de raios-X, para caracterizar a discordância entre os parâmetros de rede da camada e do substrato, na direção paralela à interface camada/substrato. Esse método utiliza os casos de três feixes envolvendo as reflexões secundárias de superfície, cujo feixe secundário é espalhado paralelamente aos planos atômicos primários, além das difrações múltiplas híbridas, oriundas da interação entre as redes da camada e do substrato. A deteção de ambas num mesmo diagrama Renninger, possibilita a caracterização desejada. Para o estudo da ocorrência das contribuições híbridas, foi necessário considerar a geometria de Kossel para a difração múltipla, utilizada na técnica do feixe de raios-X divergente. A utilização das equações básicas dessa geometria, foi modificada de forma a contemplar o espalhamento pelos planos secundários e de acoplamento, que são importantes na interação das redes camada/substrato. Esse novo tratamento fornece a possibilidade de considerar o efeito de imperfeições cristalinas (largura mosaico como um primeiro exemplo) nas equações desenvolvidas, com facilidade. Também, a partir dele, foi possível traçar diagramas de incidência, que evidenciam tanto os efeitos da divergência do feixe incidente quanto a observação das contribuições híbridas. O método desenvolvido foi aplicado a dois sistemas: GaAs/Si[001] e InGaAsP/GaAs[001], e apresentam resultados muito bons na caracterização deles. Além disso, mostrou que mesmo camadas finas (da ordem de 500Þ neste trabalho) intermediárias entre uma camada externa mais espessa e o substrato, podem ser analisadas com razoável precisão / Abstract: Not informed. / Mestrado / Física / Mestre em Física

Submitted by Rafael Santana (rafael.silvasantana@ufpe.br) on 2017-07-10T19:30:23Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertacao - Pedro Negrão.pdf: 2417925 bytes, checksum: 563fc37dbb3bf794487bc4e3c8fc102a (MD5) / Made available in DSpace on 2017-07-10T19:30:23Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Dissertacao - Pedro Negrão.pdf: 2417925 bytes, checksum: 563fc37dbb3bf794487bc4e3c8fc102a (MD5) Previous issue date: 2016-03-29 / CAPES / As argilas compõem um grupo de matérias-primas muito importante devido a suas múltiplas funções industriais. Em especial o caulim, possui propriedades físicas e químicas que possibilitam a sua utilização no processo industrial de uma grande gama de produtos, desde matéria-prima para a indústria cerâmica, de carga e cobertura de papel, entre outras. Esta pesquisa objetivou descrever, através da caracterização mineralógica, análise química, análise granulométrica, ensaios tecnológicos e de plasticidade, as características do material arenocaulinítico sondado no município de Igarassu – PE, ocorrência localizada próxima ao bairro de Nova Cruz 2. O material foi coletado através de sondagem a trado, tendo as amostras passado por análise mineralógica por difração de raios X, análise química por fluorescência de raios X, análise granulométrica, ensaios de plasticidade e foram confeccionados corpos de prova para a realização de ensaios tecnológicos. Os resultados obtidos foram comparados com as características de caulins de outros jazimentos descritos na literatura e com as especificações dos caulins aproveitados industrialmente. / Clays form a group of so important raw materials due to its multiple industrial functions. In particular, the kaolin has physical and chemical properties which allow its use at the industrial process a wide range of products from a raw material for ceramic industry, filler and paper coating, among others. This research aimed to describe through mineralogical characterization, chemical analysis, particle size analysis, technological tests and plasticity characteristics of sandy-kaolinitic materials collected in the city of Igarassu - PE, occurrence located near the Nova Cruz 2. The material was got by auger boring, the samples submitted to a mineralogical analysis through X ray diffraction, chemical analysis through X ray fluorescence, particle size analysis, plasticity tests and was prepared specimens to be performed for the technological tests. The results obtained were compared with the characteristics of kaolin of other deposits described in the literature and with the specifications of kaolin exploited industrially.

Orientador: Stephenson Caticha-Ellis / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-15T10:45:31Z (GMT). No. of bitstreams: 1 CatichaAlfonso_Ariel_M.pdf: 2763768 bytes, checksum: 29657ada0acd8d3cae092d47ee297020 (MD5) Previous issue date: 1979 / Resumo: Não informado / Abstract: Not informed. / Mestrado / Física / Mestre em Física

Orientadores: S. Caticha Ellis, Shil-Lin Chang / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-17T06:20:38Z (GMT). No. of bitstreams: 1 Savi_ArlindoAntonio_M.pdf: 1519545 bytes, checksum: 32526f5f763de2fedfcf5f7ac53dc254 (MD5) Previous issue date: 1978 / Resumo: Não informado / Abstract: Not informed. / Mestrado / Física / Mestre em Física

Orientador: Stephenson Caticha-Ellis / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-17T21:57:26Z (GMT). No. of bitstreams: 1 Mazzaro_Irineu_M.pdf: 2319444 bytes, checksum: f293db8c0a3eac9405776ae4ca21771f (MD5) Previous issue date: 1979 / Resumo: Neste trabalho são estudados monocromadores assimétricos, isto é, formado por cristais com a superfície cortada segundo um ângulo f0 com os planos refletores. O estudo experimental baseado no método de Evans, Hirsch & Kellar( 11 ) , é feito medindo a intensidade de raios-X espalhada pela reflexão Ge( 111 ), com o cristal montado de forma a poder ser girado ao redor da normal ao plano correspondente. No decorrer do trabalho mostramos que o metodo de Evans, Hirsch & Kellar, que experimentalmente é muito atraente, necessitando-se cortar o cristal com o ângulo f0 e simular diferentes ângulos de corte por meio do giro ao redor da normal aos planos refletores, implica em complicações teóricas bastante difíceis de serem superadas muitas das quais foram resolvidas neste trabalho. Na parte teórica deste trabalho, deduzimos em forma geral as expressões da potência e da intensidade refletidas em reflexão assimétrica por um cristal cortado sob um ângulo f0 em relação aos planos de ref1exão, baseando-nos exclusivamente na teoria da interacão dos feixes multiplamente difratados em cristal mosaico ( Caticha-Ellis S., 1969 ( 9 ) ). Foram encontrados efeitos novos, tal como a rotação do feixe difratado numa reflexão assimétrica, efeito que não tinha sido encontrado pelos demais autores que já trabalharam em problemas de reflexão assimétrica. O acordo entre os resultados teóricos e experimentais é analisado no texto. Experimentalmente, fizemos medidas da potência e intensidade do feixe difratado e do ângulo de rotação da seção transversal deste feixe, assim como medidas da intensidade refletida pelas superfícies paralela e inclinada, em função do tratamento aplicado a elas. As equações desenvolvidas para a potência e intensidade relativas do feixe refletido em função da assimetria, permite afirmar que a máxima relação possivel a ser esperada na intensidade do feixe concentrado com relação a reflexão simetrica, é sempre menor do que 2,0. A variação da potência total concorda bem com os valores previsto pela teoria as máximas discrepâncias ocorrendo para as posições de máxima assimétria. onde os valores experimentais devem ser possivelmente mais influenciados pelos fatores instrumentais e pelo defeitos de regularidade e planaridade da superfície. Dos resultados experimentais concluimos. que para obtermos máxima intensidade com um monocromador assimetrico, o ângulo f0 entre planos refletores e superficie deve ser aproximadamente igual a 4,8° para a Ge( 111 ) e de 5,3 para a Si( 111 ), dando origem a aumento de intensidade da ordem de 41% e 31% respectivamente em relação à superfície paralela aos planos. A posição desses máximos depende do tratamento superficial o que faz então impossível dar uma solução válida para todos os casos. Além do mais o valor correto a ser usado deverá ser obtido após as correções da curva pelos fatores instrumentais, sendo estes muito complicados e atingem grande importância para maiores graus de assimetria, isto é b = +-1. O perfil w obtido apresenta irregularidades ( vários picos com forma esquisitas ), segundo o tratamento superficial da amostra. Os polimentos mecânicos mesmo feitos de forma extremamente cuidado com grãos de até 0,05 mm de diâmetro, não foram capazes de eliminar essas irregularidades. O tratamento químico puro ( etching ) também foi imcapaz de resolver o problema. Somente o tratamento mecânico-químico desenvolvido neste trabalho conseguiu obter pontos de varredura de forma correta, reproduzivel e quase sem variações de um siti o do cristal a outro. Nos tratamentos teóricos feitos até agora, pelos diferentes autores, a partir de Evans, Hirsch & Kellar em diante, faziam depender a intensidade e a potência de um só parâmetro geometri co de assimetria. Neste trabalho mostramos que é necessário introduzir mais um parâmetro que depende da relação entre o ângulo de corte f0 e do angulo, de Brag qB. Foi assim definido o fator de corte do cristal k = tgf0 / tgqB,em função do qual diversas expressões adotam formas convenientes. Finalmente são discutidas prováveis extensões deste trabalho / Abstract: Asymmetric X-ray monochromators, firsts introduced by I. Fankuchen ( 1937 ) with the purpose of concentrating an X-ray beam have been the subject of numerous investigations. Evans, Hirsch and Kellar as early as 1948, based ther well known and hitherto unchallenged study on the hypothetic existence of a non-ref1ecting surface layer with an absorption coefficient different from that of the bulk crystal which they used to fit a "theoretical" curve to their experimental data. In this Thesis it is shown that the physical behavior of asymmetric monochromators can be explained without recourse to any kind of artificial hypothesis, by means of the theory of multiple scattering of X-rays ( Caticha-Ellis, 1969 ). The differential equations governing the interchange of power among the incident and the diffracted waves were solved in the two-beam asymmetric case and the solutions expressed in terms of the asymmetry parameters: R = sen( qB - f ) / Sen( qB + f ) or B = 1 - R / 1 + R, where qB is the Bragg angle and f0 the angle between the reflecting plane and the reflecting surface measured on the plane of incidence. f0 is the dihedral angle between the o plane surface and the reflecting planes. The solutions were found to depend not just on one but on two parameters, one of assimmetry and k = tgf0 / tgqB which was called a "cutting parameter". The experimental method used here is based in that of Evans et al. A crystal cut with f0 > qB, turns around the normal to the reflecting planes thus generating different asymmetry f angles. The experimental advantage is th at only one crystal has to be cut. The theoretical complications involved, most of which are discussed here in detail, are the price for that simplifications. A new effect, the rotation of the asymmetrically diffracted beam was predicted and confirmed experimentally. The theory also demonstrates that the intensity in the concentrated beam can not be move than twice the intensity of the symmetrically reflected beam, a fact already known to previous authors. The measured diffracted power agrees well with the maximum discrepancies occur when approaching of maximum asymmetry b = +-1, where the experimental values are largely affected by surface irregularities as well instrumental factors, which how ever have not yet been studied. w - profiles taken on different regions of the crystal showed pronounced differences according to the suface treatment; even after extremely careful polishing with corrudum powder of 0.05 mm grain size. Etching worsened the situation by splitting the w - peak in several smaller anes. Only a hybrid mechanical - chemical treatment, developped for this purpose was able to produce surfaces whose w - profiles possess a reasonable peak shape and are practically invariant for the differente regions of the crystal. In conclusion the theory used irl this thesis explains well the power and intensity diffracted asymmetrically by a crystal cut with an angle f0 with respect to the reflecting planes except under extreme conditions of asymmetri where the instrumental and surface effects are dominant / Mestrado / Física / Mestre em Física

Orientador: Lisandro Pavie Cardoso / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-20T03:57:48Z (GMT). No. of bitstreams: 1 Avanci_LuisHumberto_M.pdf: 1153304 bytes, checksum: 2d8070b9011e768604711d089c934bad (MD5) Previous issue date: 1995 / Resumo: Neste trabalho, os casos de três feixes de superfície (000 200 111) da difração múltipla de raios-X são utilizados de forma inédita, na caracterização de heteroestruturas InP/GaAs(100) crescidas por epitaxia de feixe molecular com fonte gasosa (GSMBE). Um programa desenvolvido para a simulação do perfil e posição desses casos de três feixes nos diagramas Renninger, foi utilizado na detem1inação da largura mosaico paralela (hf) e perpendicular (hw ) à direção do crescimento da camada. Valores menores de ambas as larguras obtidos para as amostras que sofreram tratamento térmico rápido (RT A), indicam que esse tratamento após o crescimento, realmente melhora a perfeição cristalina das camadas. A análise do parâmetro de rede da camada na direção paralela à sua superfície, também obtido do programa, em função da temperatura de nucleação, mostrou que os resultados seguem o modelo de tensão térmica na camada, no qual a temperatura de nucleação é mais importante do que a temperatura de crescimento das camadas de lnP .A condição angular da difração múltipla, quando analisada em detalhes através da variação do ângulo de incidência w e do ângulo de rotação f em tomo da direção [100], acarreta no mapeamento desta condição. Um método baseado nas varreduras w :f , que permite a análise da desorientação superficial dos blocos mosaicos ou das grandes regiões perfeitas difratantes em cristais quase-perfeitos, foi aplicado pela primeira vez em heteroestruturas, no sistema InP/GaAs deste trabalho. A curvas de isointensidade dessas varreduras para o substrato GaAs, permitiu observar diretamente o efeito da tensão provocada pelo crescimento da camada de lnP , na rede do substrato / Abstract: Not informed. / Mestrado / Física / Mestre em Física