93 research outputs found
Optical and structural properties of polycrystalline CdSe deposited on titanium substrates
No full textEffects Of Thermal Annealing On The Confined Electronic States Of Inxga1-xas/gaas Strained-layer Superlattices
No full textWe performed simultaneous Raman and absorption measurements on a In0.12Ga0.88As/GaAs strained layer superlattice which was submitted to annealing at 850°C. The observed changes in both types of spectra are used to construct a superlattice profile for the annealed sample from which we obtain values for the band off-set parameter (Qe), the interdiffusion coefficient (D) and the overall lattice constant of the annealed superlattice. © 1989.52273278Schlesinger, Kuech, (1986) Appl. Phys. Letters, 49, p. 519Lee, Schlesinger, Kuech, Interdiffusion of Al and Ga in (Al,Ga)As/GaAs superlattices (1987) Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 5 B, p. 1187F. Iikawa, P. Motisuke, J.A. Brum, M.A. Sacilotti, A.P. Roth and R.A. Masut, J. Crystal Growth, in pressRoth, Sacilotti, Masut, D'Arcy, Watt, Sproule, Mitchell, (1986) App. Phys., Letters, 48, p. 1452Roth, Sacilotti, Masut, D'Arcy, Watt, Sproule, Mitchell, (1986) J. of Crystal Growth, 77, p. 571F. Iikawa, F. Cerdeira, C. Vazquez-Lopes, P. Motisuke, M.A. Sacilotti, A.P. Roth and R.A. Masut, Solid State Commun., in pressLandolt-Börnstein, (1982) Numerical Data and Functional Relationships in Science and Technology, vol. 3/17a, p. 218. , O. Madelung, Springer-Verlag, Berlin, New SeriesLandolt-Börnstein, (1982) Numerical Data and Functional Relationships in Science and Technology, vol. 3/17a, p. 297. , O. Madelung, Springer-Verlag, Berlin, New SeriesGoeth, Bimberg, Jürgensen, Selders, Solomonov, Glinskii, Razeghi, Optical and crystallographic properties and impurity incorporation of GaxIn1−xAs (0.44<x<0.49) grown by liquid phase epitaxy, vapor phase epitaxy, and metal organic chemical vapor deposition (1983) Journal of Applied Physics, 54, p. 4543F. Iikawa, F. Cerdeira, C. Vazquez-Lopes, P. Motisuke, M.A. Sacilotti, A.P. Roth and M.A. Masut, Phys. Rev. B, in press. See also proceeding of the 19th International Conference on the Physics of Semiconductors, in pressMarzin, Charasse, Semage, (1985) Phys. Rev., 31 B, p. 8298Ji, Huang, Reddy, Henderson, Houdre, Morcoç, (1987) J. of Appl. Phys., 62, p. 3366Menendez, Pinczuk, Werder, Sputs, Miller, Sivco, Cho, Large valence-band offset in strained-layer In_{x}Ga_{1-x}As-GaAs quantum wells (1987) Physical Review B, 36 B, p. 816
Continuous To Bound Interband Transitions In δ-doped Gaas Layers
No full textWe have studied the interband transitions of several silicon δ-doped GaAs samples using the technique of photoreflectance spectroscopy. The features observed in the optical spectra above the GaAs fundamental energy gap are tentatively attributed to transitions involving continuous valence band states and quantum-confined states at the conduction-band. The observed interband transition energies are in qualitative agreement with the self-consistently calculated ones taking into account the spreading of dopants. © 1990.82205208Bottka, Gaskill, Sillmon, Henry, Glosser, (1988) J. Electron. Mater., 17, p. 161Glembocki, Bottka, Furneaux, (1985) J. Appl. Phys., 57, p. 432Glembocki, Shanabrook, Bottka, Beard, Comas, (1985) Appl. Phys. Lett., 46, p. 970Shen, Pan, Pollak, Dutta, AuCoin, (1987) Phys. Rev., 36 B, p. 9384Bernussi, Iikawa, Motisuke, Basmaji, Li, Hipolito, (1990) J. Appl. Phys., 67, p. 4149(1990) Proc. Soc. of Photo-Opt. Instrum. Eng., , and also, to be publishedSnow, Glembocki, Shanabrook, (1988) Phys. Rev., 38 B, p. 12483Aspnes, (1980) Handbook on Semiconductors, 2, p. 109. , T.S. Moss, North Holland, Amsterda
Crystal structure, luminescence, and photoelectrochemistry of thin electroplated Cd-chalcogenide layers
No full textDirect Analysis Of The Photocurrent Transient In Semi-insulating Gaas
No full textWe report the results of a detailed analysis of digitally recorded photocurrent transients in semi-insulating GaAs. These generally consist of a sum of exponentials with decay time constants that can be uniquely determined from the fitting procedure. The obtained values for these time constants are more reliable than those determined from the conventional double gate method, where some questionable approximations are always included. At high temperatures and under a strong background illumination, we observed photocurrent transients with an inverted derivative signal. This signal inversion can be understood if we take into account the background current. © 1990.749935939Chevron,Halliburton,PDVSA,Schlumberger,TotalLang, (1974) J. Appl. Phys., 45, p. 3023Hurtes, Boulou, Mitonneau, Bois, (1978) Appl. Phys. Lett., 32, p. 821Kremer, Arikan, Abele, Blakemore, (1987) J. Appl. Phys., 62, p. 2424Abele, Kremer, Blakemore, (1987) J. Appl. Phys., 62, p. 2432Look, (1983) Semiconductors and Semimetals, 19, p. 75. , R.K. Williardson, A.C. Beer, Academic Press, New YorkZ. Fang, L. Shan, T.E. Schesinger and A.G. Milnes, submitted to J. of Electr. MatBalland, Zielinger, Tapiero, Gross, Noguet, (1986) J. Phys. D, 19, p. 71Young, Tang, Dindo, Lowe, (1986) J. Electrochem. Soc., 133, p. 609Blight, Thomas, (1989) J. Appl. Phys., 65, p. 215Martin, Makram-Ebeid, (1986) Deep Centers in Semiconductors, p. 399. , S.T. Pantelides, Gordon & Breach, New Yor
Thermally Induced In/ga Interdiffusion In Inxga1-xas/gaas Strained Single Quantum Well Grown By Lpmovpe
No full textA strained single quantum well of GaAs/InxGa1-xGa/GaAs (x=0.23) has been grown by low pressure MOVPE on a (100) GaAs substrate at 625° C. Samples were annealed under AsH3/H2 at different temperatures in the range 750 to 900° C. Since the quantum well thickness (∼80 Å) is below the critical value for this lattice mismatched system, we assume that the InGaAs layer is commensurate with the GaAs substrate. We analyse the low temperature (2 K) photoluminescence of the electron to heavy hole transition in the quantum well of these samples to study the In/Ga interdiffusion at the InGaAs/GaAs interfaces. The position in energy of the photoluminescence peaks shift to higher energies when annealing. The shifts are quantitatively interpreted in terms of changes in the quantum well profile due to the In and Ga interdiffusion. We determined the interdiffusion coefficient at 850° C to be 3×10-17 cm2/s, with an activation energy 2.07 eV. The values obtained for the In/Ga interdiffusion coefficient are larger than those published for the Al and Ga interdiffusion in AlGaAs/GaAs heterojunctions. © 1988.931-4336341Sullivan, Asbeck, Chang, Miller, Wang, (1986) Electron. Letters, 22, p. 419Adams, Band-structure engineering for low-threshold high-efficiency semiconductor lasers (1986) Electronics Letters, 22, p. 250Roth, Sacilotti, Masut, D'Arcy, Watt, Sproule, Mitchell, (1986) Appl. Phys. Letters, 48, p. 1452Characterization of GaxIn1−xAs/GaAs heterostructures grown by low pressure MOVPE (1986) Journal of Crystal Growth, 77, p. 571Roth, Sacilotti, Masut, Machado, D'Arcy, (1986) J. Appl. Phys., 60, p. 2003Roth, Masut, Sacilotti, Sproule, Mitchell, Le Page, (1987) Can. J. Phys., 65, p. 909Chang, Koma, (1976) Appl. Phys. Letters, 29, p. 138Meenan, Brown, Gavrilovic, Holonyak, Jr., Burnham, Paoli, Streifer, Thermal-anneal wavelength modification of multiple-well p-n AlxGa1−x As-GaAs quantum-well lasers (1984) Journal of Applied Physics, 55, p. 2672Schlesinger, Kuech, (1986) Appl. Phys. Letters, 49, p. 519Lee, Schlesinger, Kuech, Interdiffusion of Al and Ga in (Al,Ga)As/GaAs superlattices (1987) Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 5 B, p. 1187Fritz, Picraux, Dawson, Drummond, Laidig, Anderson, (1985) Appl. Phys. Letters, 46, p. 967Orders, Usher, (1987) Appl. Phys. Letters, 50, p. 980Anderson, Chen, Kulakovskii, Uddin, Valim, Variation of the critical layer thickness with In content in strained InxGa1−xAs-GaAs quantum wells grown by molecular beam epitaxy (1987) Applied Physics Letters, 51, p. 752Landolt-Börnstein, (1982) Numerical Data and Functional Relationships in Science and Technology, New Series, 17, p. 218. , O. Madelung, Springer, BerlinLandolt-Börnstein, (1982) Numerical Data and Functional Relationships in Science and Technology, New Series, 17, p. 297. , O. Madelung, BerlinChandrasekhar, Pollak, (1977) Phys. Rev., 15 B, p. 2127F. Iikawa, F. Cerdeira, C. Vazquez-Lopes, P. Motisuke, M.A. Sacilotti, A.P. Roth and R.A. Masut, to be publishedA.P. Roth, R.A. Masut, M.A. Sacilotti and B. Watt, unpublished, 1986;Goetz, Bimberg, Jürgensen, Selders, Solomonov, Glinskii, Razeghi, (1983) J. Appl. Phys., 54, p. 4543Bastard, Brum, (1986) IEEE J. Quantum Electron. QE-22, p. 1525Bastard, (1981) Phys. Rev., 24 B, p. 5693Bastard, (1982) Phys. Rev., 25 B, p. 7584Marzin, Charasse, Sermage, (1985) Phys. Rev., 31 B, p. 8298Ji, Huang, Reddy, Henderson, Houdre, Morkoç, (1987) J. Appl. Phys., 62, p. 3366Menendez, Pinczuk, Werder, Sputz, Miller, Sivco, Cho, Large valence-band offset in strained-layer In_{x}Ga_{1-x}As-GaAs quantum wells (1987) Physical Review B, 36 B, p. 8165Greene, Bajaj, Phelps, (1984) Phys. Rev., 29 B, p. 1807Crank, (1975) The Mathematics of Diffusion, p. 1. , 2nd ed., Clarendon, OxfordCrank, (1975) The Mathematics of Diffusion, p. 19. , 2nd ed., OxfordKendall, Semiconductors and Semimetals (1968) Physics of III–V Compounds, 4, p. 163. , R.K. Willardson, A.C. Beer, Academic Press, New YorkSeo, Bhattacharya, Kothiyal, Hong, (1986) Appl. Phys. Letters, 49, p. 96
Hot Electron And Hot Phonon Contributions To Radiative Emission Spectra In Cds At High Excitation Intensities
No full textThe dependence of excitation frequency of photoluminescence spectral shape of CdS at high excitation intensities allowed discrimination between hot phonon and hot electron contributions to the broadening of the emission band on one side and the broadening due to many body effects on the other. It was found that the shift towards lower energies of the emission peak is mainly due to induced high carrier density and that the broadening is related to the presence of high densities of optical phonons and hot carriers. © 1975.166763765Jannuzzi, Meneses, Leite, (1972) Solid State Commun., 10, p. 517Leite, Ripper, Guglielmi, (1964) Appl. Phys. Lett., 5, p. 188Meneses, Jannuzzi, Leite, Band gap reduction in CdS due to high density of photo-injected carriers (1972) Solid State Communications, 10, p. 517Shah, Leite, (1969) Phys. Rev. Lett., 22, p. 1304Meneses, Luzzi, (1973) Solid State Commun., 12, p. 447Shah, Leite, Scott, (1970) Solid State Commun., 8, p. 1089Mattos, Leite, (1973) Solid State Commun., 12, p. 465Mattos, Guimarães, Liete, (1973) Opt. Commun., 8, p. 73LUZZI R. and RAMOS J.G.P., Solid State Commun. (to be published)MENESES E.A. and LUZZI R. (to be published)MENESES E.A., JANNUZZI N., LUZZI R., RAMOS J.G.P. and LEITE R.C.C. (to be published)Shank, Dienes, Trozzolo, Myer, NEAR uv TO YELLOW TUNABLE LASER EMISSION FROM AN ORGANIC DYE (1970) Applied Physics Letters, 16, p. 10Shank, Dienes, Trozzolo, Myer, (1970) Appl. Phys. Lett., 16, p. 40
Otimização das propriedades e da injetabilidade de um cimento de fosfato de cálcio
No full textWorld population is getting older and, as a direct consequence, the cases of osteoporosis and bone mass loss are growing fast. Nevertheless, problems related to bone tissue are not exclusivity of old-aged people since there are a growing number of young people who need to replace bones or treat fractures due to car accidents and extreme sports. Thus, the demand for surgeries to repair and treat bone has increased. Calcium phosphate cements (CPCs) based on ?- tricalcium phosphate (?-TCP) have been highlighted for this application once they are biocompatible, bioactive, resorbable and do not present local or systemic toxicity; despite it behaves as a non-Newtonian fluid it can become injectable from a simple control on its viscosity. However, the synthesis of pure ?-TCP, cement?s solid phase, is not a simple task, since many process conditions can change their final properties, or even inhibit its formation. The quality of the starting reagents is a very important factor because some impurities can raise the temperature of formation of ?-TCP to values as high as 1600 ° C, compromising the reliability of its processing and the reactivity of the material. Therefore reagents were first synthesized with a high purity, i.e magnesium free, the main impurity which interferes on the synthesis of ?-TCP. The standardization of the starting reagents properties ensured the reproducibility of ?-TCP manufacturing process. However, it was still observed small amounts of ?-TCP, due to the insufficient energy for complete ? ? ? transformation or the not enough short dwell time to stabilize the ?-TCP phase, however, this small amount of ?-TCP did not influence on the development of the injectable cement. There are many reports that discuss the development and characterization of injectable CFC pastes; however, there are many barriers that need to be overridden. Many surgeons complain about the difficulty of maintaining the material cohesive after deployment and the loss of mechanical strength is inherent to the decreased viscosity of the paste. In this context, it is important to evaluate the possibility of controlling the viscosity of CFC pastes while optimizing their mechanical behavior. In this work carboxymethylcellulose (CMC) was used to optimize the injectability of a calcium phosphate cement and at the same time to control its mechanical strength. It was possible to develop a cement that the mechanical strength has increased with the increased amount of CMC. This fact is a consequence of the effect that the CMC generates into solutions and suspensions: a greater particle dispersion and also its gelling effect. It was also possible to develop an injectable cement for clinical application since the initial setting time (11 min) and cohesion time (7 min) were satisfactory for the application in question. The injectable cement despite of having a lower mechanical resistance compared to the direct molded cement, due to the increase of the liquid-to-powder ratio L/P, still presents values of axial compression resistance higher (22.74 ± 2,49MPa) than the trabecular bone (1 - 10 MPa). The results obtained in this work show that it was possible to develop an injectable bone cement, enabling less invasive surgery, with the potential for clinical application and more accessible to the population.A busca por hábitos mais saudáveis e o desenvolvimento da medicina preventiva contribuíram para o prolongamento da vida da população. Como consequência, é crescente o número de casos de doenças ósseas relacionadas à velhice, como a osteoporose. Entretanto, problemas do tecido ósseo não são exclusividade da população idosa; é cada vez maior o número de jovens que necessitam de algum tratamento ortopédico e odontológico em decorrência de acidentes em geral e de esportes radicais. Dessa forma, as soluções médicas precisam ser otimizadas levando em consideração a necessidade de uma maior vida útil de próteses e implantes e de procedimentos cirúrgicos mais baratos e menos invasivos. Os materiais que têm merecido destaque para o tratamento do tecido ósseo são os cimentos de fosfato de cálcio (CFC) à base de ?-fosfato tricálcico (?-TCP) pois, são biocompatíveis, bioativos, reabsorvíveis, não apresentam toxicidade local ou sistêmica e sua pasta; apesar de se comportar como um fluido não newtoniano, pode se tornar injetável a partir de um controle em sua viscosidade. Entretanto, a síntese do ?-TCP puro, fase sólida do cimento, não é uma tarefa simples, uma vez que muitas condições de processo podem alterar suas propriedades finais ou, ainda, inibir sua formação. A qualidade dos reagentes de partida são os que mais influenciam, pois algumas impurezas podem elevar a temperatura de formação do ?-TCP para valores tão altos quanto 1600°C, comprometendo a reprodutibilidade de seu processamento e a reatividade do material. Portanto foram primeiramente sintetizados reagentes com elevado grau de pureza, ou seja, livres de magnésio, principal impureza que interfere na síntese do ?-TCP. Verificou-se que a padronização das propriedades dos reagentes de partida garantiu-se a reprodutibilidade do processo de fabricação do ?-TCP e observou-se ainda pequenas quantidades de fase ?-TCP, devido provavelmente à energia não suficiente para total transformação do ? ? ? ou tempo não suficiente para estabilizar a fase ?-TCP, no entanto essa pequena quantidade de fase ??TCP não influenciou no desenvolvimento do cimento injetável. Existem muitos relatos na literatura que discutem o desenvolvimento e a caracterização de pastas de CFC injetáveis; entretanto existem muitas barreiras que precisam ser sobrepostas. Muitos cirurgiões reclamam da dificuldade de manter o material coeso após a implantação e a perda de resistência mecânica é inerente à diminuição da viscosidade da pasta. Neste contexto, torna-se importante avaliar a possibilidade de se controlar a viscosidade de pastas de CFC e ao mesmo tempo otimizar o seu comportamento mecânico. Nesse trabalho a carboximetilcelulose foi utilizada para otimizar a injetabilidade de um cimento de fosfato de cálcio e, ao mesmo tempo, controlar a sua resistência mecânica. Foi possível desenvolver um cimento que com o aumento da quantidade de CMC aumentou-se a resistência mecânica. Esse fato é consequência do efeito que o CMC é capaz de gerar: uma maior dispersão das partículas na pasta e, também, seu efeito gelificante. Foi possível também desenvolver um cimento injetável para aplicação clínica pois, os tempos de cura inicial (11 min) e de coesão (7 min) apresentaram-se satisfatórios para a aplicação em questão. O cimento injetável apesar de apresentar uma resistência mecânica mais baixa em relação ao cimento moldado, devido ao aumento da razão L/P, ainda apresenta valores de resistência à compressão axial maiores (22,74±2,49MPa) do que do osso esponjoso (1 ? 10 MPa). Os resultados obtidos neste trabalho demonstram que foi possível desenvolver um cimento ósseo injetável, possibilitando cirurgias menos invasivas, com potencial para aplicação clínica e que será mais acessível à população brasileira.Dados abertos - Sucupira - Teses e dissertações (2013 a 2016
Effect Of Excited Electron States Lifetime On Gain Spectra Of Ehl In Cds
No full textFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Gain spectra in highly photoexcited CdS have been studied. The results are compatible with the assumption of condensation of the photoexcited carriers into a strongly interacting electron-hole liquid (EHL). A gain tail, which extends well below the renormalized band gap energy, is observed. We show that carrier lifetime accounts for this tail, with the EHL not having achieved equilibrium with the thermal bath during the time it is probed. © 1977.2396176202011/09240-9; FAPESP; São Paulo Research Foundation; 2012/07556-1; FAPESP; São Paulo Research FoundationFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Levy, Grun, (1974) Phys. Stat. Sol., 22 A, p. 11. , and references thereinGay, Screening of Excitons in Semiconductors (1991) Physical Review B, 4 B, p. 2567Keldysh, Silin, (1975) Zh. Eksp. Teor., 69, p. 1053(1976) Soviet Physics ZETP, 42, p. 535Beni, Rice, (1976) Phys. Rev. Letters, 37, p. 874Lysenko, Revenko, Tratas, Timofeev, (1975) Soviet Phys. JETP, 41, p. 163Hildebrand, Faltermeier, Pilkuhn, (1976) Solid State Communications, 19, p. 841Leheny, Shah, (1976) Physical Review Letters, 37, p. 871Motisuke, Arguello, Luzzi, Shaklee, (1977) Solid State Communications, 21, p. 397Mattos, Leite, (1973) Solid State Communications, 12, p. 465Motisuke, (1977) PhD thesis, , I.F. UnicampMotisuke, Arguello, Leite, (1975) Solid State Communications, 16, p. 763Blackemore, (1962) Semiconductors Statistics, p. 184. , Pergamon Press, N.Y, et segHammond, Mc-Gill, Mayer, (1976) Phys. Rev., 13 B, p. 3566. , and references thereinVan Hove, (1954) Phys. Rev., 95, p. 249Zubarev, Double-time Green functions in statistical physics (1960) Uspekhi Fizicheskih Nauk, 71, p. 71DOUBLE-TIME GREEN FUNCTIONS IN STATISTICAL PHYSICS (1960) Soviet Physics Uspekhi, 3, p. 320Pines, (1964) Elementary Excitations in Solids, , W.A. Benjamin, N.YLeheny, Shah, (1977) Phys. Rev. Let., 38, p. 51
Properties Of Alxga1-xas With An Alas Buffer Layer On Si Substrates Grown By Metalorganic Vapor Phase Epitaxy
No full textWe present the details of growth by metalorganic vapor phase epitaxy and characterization of undoped and Sn doped AlxGa1-xAs (0≤ x ≤ 0.3) on Si substrates with AlAs buffer layer. Double X-ray diffraction has been performed on these samples and the estimated dislocation density is in the order of 8x106 cm-2. The carrier concentration in these samples were obtained by Schubnikov-De Haas effect and the observed oscillations compare very well with the AlxGa1-xAs grown on GaAs substrates. The photoluminescence efficiency in the Sn-doped AlxGa1-xAs/Si sample is about 640 times greater than in the undoped one and this is attributed to annihilation of non-radiative centers by Sn atoms. The biaxial stress in these films is estimated from the peak positions in the photoluminescence spectra measured as a function of temperature. © 1991.1083-4615620Fan, Phillips, Tsaur, Heteroepitaxy on Silicon (1987) Mater. Res. Soc. Symp. Proc., 91. , Mater. Res. Soc, Pittsburgh, PAAkyiama, Kawarada, Kaminishi, Growth of GaAs on Si by MOVCD (1984) Journal of Crystal Growth, 68, p. 21Fisher, Masselink, Klein, Henderson, McClinn, Klein, Morkoc, Wasburn, (1984) J. Appl. Phys., 58, p. 344Wang, (1984) Appl. Phys. Letters, 44, p. 1149Tsaur, Metze, (1984) Appl. Phys. Letters, 45, p. 535Basmaji, Li, Hipolito, Allan, Lavielle, Portal, Proc. 4th Brazillian School of Semi-conductors Physics (1989) Proc. 4th Brazillian School of Semi-conductors Physics, , Belo Horizonte, to be publishedGay, Hirsch, Kelley, The estimation of dislocation densities in metals from X-ray data (1953) Acta Metallurgica, 1, p. 315Sheldon, Yacobi, Jones, Dunlavy, (1985) J. Appl. Phys., 58, p. 4186Soga, Hahoi, Sakai, Takayasu, Umeno, (1984) Electron. Letters, 20, p. 916Aspnes, (1980) Handbook of Semiconductors, 2, p. 109. , T.S. Moss, North-Holland, AmsterdamZemon, Shastry, Norris, Jagganath, Lambert, (1986) Solid State Commun., 58, p. 457Kuo, Vong, Cohen, Stringfellow, (1985) J. Appl. Phys., 57, p. 5428Soga, Hattori, Sakai, Umeno, (1986) J. Crystal Growth, 77, p. 49
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