Thesis (Ph. D.)--Lehigh University, 2000. / Includes bibliographical references and vita.

A review of phthalocyanine materials is presented, their history, properties, applications, and potential. The two materials under investigation in this thesis (A410 H[2] and A40iso6 H[2]) are introduced as metal free, non-peripheral octa-substituted phthalocyanines, molecularly engineered for Langmuir-Blodgett deposition by M. Cook at the University of East Anglia. The Langmuir-Blodgett method is used to deposit the two materials in the Y-form, onto substrates of glass and gold plated glass, and on quartz with interdigitated platinum electrodes. Optical absorption spectra are obtained for the materials, and the linear relation between the absorption intensity and thickness confirmed. The variation in optical absorption with polarisation and angle of incidence is used to obtain the molecular orientation of the two phthalocyanines. The polarisation results confirm earlier observations. The molecular orientation angles (with respect to the substrate) obtained in this thesis are novel for these materials, and confirm the Herringbone alignment of molecular pairs. Surface Plasmon resonance is used to obtain a refractive index of 1.629, and a thickness of 17.2 nm for a 6 layer film of the A410 material. The electrical properties were measured using samples of the film deposited on substrates with interdigitated electrodes. The spectral photocurrent, conductivity, and activation energy under illumination were investigated for both materials. The electrical response of the films to temperature, voltage and gaseous environment is presented with the time dependent photocurrent response. The characterisation measurement techniques are discussed and suggestions for improvements and further work are made.

In this thesis, the potential of all-spinel oxide tunnel junctions in the field of spintronics has been investigated. In particular, the suitability of the metallic and superconducting LiTi2O4 as non-magnetic electrode in an almost defect-free CoFe2O4-based spin-filter tunnel junction has been explored. For this purpose, high-quality spinel LiTi2O4 and CoFe2O4 thin films have been deposited by pulsed laser deposition on MgAl2O4 substrates. Both films were extensively characterised in terms of structural, surface, magnetic and transport properties. The LiTi2O4 showed metallic and superconducting properties, and the CoFe2O4 had insulating and ferromagnetic properties. A careful tuning of the different growth conditions of these oxides followed in order to grow CoFe2O4/LiTi2O4 bilayers in which LiTi2O4 maintains its metallic and superconducting properties and CoFe2O4 its insulating ferromagnetic characteristics. Transport measurements at low temperature have been carried out to explore details of the tunnelling in symmetric tunnel junctions of the form LiTi2O4/CoFe2O4/LiTi2O4. The measured current–voltage characteristics of these junctions revealed clear Josephson junction behaviour due to superconductivity of the LiTi2O4 electrodes. This conclusive evidence of the tunnel nature of these junctions proves that LiTi2O4 can be used as bottom electrode in all-spinel oxide tunnel junctions.

This thesis reports a study of certain aspects of ion beam mixing in amorphous silicon. The amorphous silicon films are deposited by RF sputter deposition technique, and heavy metal markers of gold and tantalum are used to section these films. Mixing in the amorphous silicon films is brought about by energetic argon ions of various energies (100 keV to 300 keV) and an estimate of mixing is made by observing the shift and broadening in the marker profile using Rutherford backscattering spectrometry. Mixing versus depth as a function of the angle of incidence is investigated experimentally, by implanting at ten different angles (0° to 85°), films, with the marker at various depths. A comparison of the experimental results is made with the Wilson and Webb model, the average diffusion model, and a computer simulation code TRIM-Cascade. All the comparisons show evidence of radiation enhanced diffusion in the experiment. The presence of radiation enhanced diffusion is confirmed when a double marker technique is employed to determine the effect of sputtering, contraction and swelling, in an amorphous silicon film, due to mass transport under argon ion irradiation, both at room temperature and at LN2 temperature. Finally, as an application of the ion beam mixing process, silicide formation at the interface of a Ni-Si and an Fe-Si system is considered. The need to form useful silicides is evident from the recent developments in VLSI technology where transition metal silicides have been explored for interconnect metallization, gate metallization and low resistivity contacts. In the research work presented here, it is found that both the Ni-Si and Fe-Si systems show cascade type of mixing but silicide formation is more evident in the Ni-Si system.

Orientador: Carlos Frederico de Oliveira Graeff / Banca: Monica Alonso Cotta / Banca: Fenelon Martinho Lima Pontes / Resumo: A síntese DMSO foi proposta a cerca de seis anos e o resultado mais importante foi o fato da melanina obtida ser solúvel em DMSO o que permitiu a produção de filmes finos de alta qualidade. Para tal fim, a L-Dopa foi utilizada como reagente principal, em sínteses onde se variou: a concentração de perióxido de benzoíla e a concentração de água no DMSO. A síntese em água foi realizada para fins de comparação. A síntese em DMSO apresentou-se mais lenta em comparação a síntese de melanina em água através dos resultados obtidos pela técnica UV-Vis. O peróxiso de benzoíla tem influência significativa na síntese, agindo diretamente na oxidação do DMSO e na oxidação da L-Dopa. Teste de solubilidade com diferentes solventes foi realizado nas amostras de H2O-melanina, DMSO-melanina recém sintetizada e DMSO-melanina envelhecida com tempo de estocagem de quatro anos. Os solventes utilizados foram; água, DMSO, DMF, THF, acetonitrila e acetato de etila. Os resultados mostraram a insolubilidade da H2O-melanina e da DMSO-melanina envelhecida em todos os solventes e somente a solubilidade da DMSO-melanina recém sintetizada no solvente DMSO foi observada. Indicando novamente que as amostras possuem estruturas diferentes e que a DMSO-melanina sofre alterações estruturais quando exposta no ar. Nos espectros da FTIR, grupos sulfonados só foram observados na DMSO-melanina recém sintetizada, que desapareceram nas amostras envelhecidas, e que não estão presentes na H2O-melanina. Ou seja, os grupos sulfonados responsáveis pela solubilidade da DMSO-melanina com o passar do tempo sofrem degradação e saem da estrutura da DMSO-melanina, explicando assim a insolubilidade da amostra de DMSO-melanina envelhecida. O mesmo foi observado para os espectros de 13C RMN. Para entender esse processo de degradação utilizamos o NaOH2 cuja a ação é a retirada dos grupos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Synthesis in DMSO was proposed about six year and the most important result was the fact that it is soluble in DMSO which allowed the production of thin films of high quality. To this end, the L-Dopa was used as primary reagent in primary reagent in syntheses where varied: the concentration of benzoyl peroxide and water concentration in DMSO. The synthesis was carried out in water for comparison purposes. The synthesis presented in DMSO is slower than the synthesis of melanin in water for analysis of the results obtained with the technique of UV-vis. When we analyzed the effect of the concentration of benzoyl peroxide in the synthesis, we found that the concentration of 0.5 moles of benzoyl peroxide gave summary more efficient to malanin in DMSO. Benzoyl peroxide has significant influence on the synthesis, acting directly on the oxidation of DMSO and the oxidation of L-Dopa. Solubility test was carried out with different solvents in the samples of H2O-melanin, DMSO-melanin newly synthesized and old DMSO-melanin with storage time of four years. The solvents used were: water, DMSO, DMF, THF, acetonitrile and ethyl acetate. The results showed the insolubility of H2O-melanin and old DMSO-metanin in all solvents and only the solubility of newly synthesized DMSO-melanin in the solvent DMSO was observed. Indicating again that the samples have different structures and that the DMSO-melanin undergoes structural changes when exposed to air. In FTIR, sulphonated groups were only observed in DMSO-melanin newly synthesized, which disappeared in the old samples, which are not present in the H2O-melanin. That is, the sulfonated groups responsible for the solubility in DMSO-melanin suffer degradation over the time and leave the structure of DMSO-melanin, thus explaining the insolubility of old DMSO-melanin. A chemical model was proposed, using tools... (Complete abstract click electronic access below) / Mestre

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-01-19Bitstream added on 2014-06-13T20:53:34Z : No. of bitstreams: 1 moralesmorales_o_me_ilha.pdf: 672260 bytes, checksum: 722e9d33ee2b26bf51fb6c4b9a1ef435 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho, o objeto de estudo foi células Solares CdS/CdTe. Estas células usam o filme de sulfeto de cádmio (CdS) como semicondutor do tipo n e o filme de telureto de cádmio (CdTe) como semicondutor do tipo p. O recorde mundial, alcançado no laboratório, para estas células é 16,5% de eficiência. Nos Laboratórios do Departamento de Física e Química de Unesp - Ilha Solteira, este trabalho é pioneiro na fabricação de Células Solares de CdS/CdTe. Para realizar este trabalho foi necessário melhorar o sistema de deposição por spray de SnO2:F já existente, acondicionar o sistema de banho químico para deposição do filme de CdS e implementar o sistema de sublimação para depositar a camada de CdTe. Todos estes sistemas de deposição de filmes finos foram implementados no laboratório do Grupo de Desenvolvimento e Aplicação de Materiais (GDAM). A fabricação da Célula Solar CdS/CdTe consistiu na deposição sequencial sobre vidro de a) Eletrodo condutor transparente utilizando óxido de estanho dopado com Flúor (SnO2:F) pelo método de spray, com controle automático de jato; b) deposição de sulfeto de Cádmio (CdS) pelo método de banho Químico (CBD); c) deposição de Telureto de Cádmio (CdTe) pela técnica de sublimação no espaço fechado (CSS) e d) deposição do contato metálico traseiro de prata por colocação de camada liquida e posteriormente a melhora deste contato com grafite-prata. A estrutura final destas células foi: Vidro/SnO2:F/CdS/CdTe/contato. A caracterização estrutural e óptica das camadas destas células foi realizada pelas técnicas de DRX e UV-vis; os parâmetros elétricos das células foram determinados pela construção da curva I-V. A camada CdTe da célula solar foi tratada termicamente com dicloreto de cádmio (CdCl2) para comparar a sua eficiência com outra célula que não foi tratada... / The object of this work was the study solar Cells CdS/CdTe. These cells use a cadmium sulfide film as an n-type semiconductor and a cadmium telluride film as a p- type semiconductor The world record for maximum efficiency achieved in laboratory for these cells is 16.5%. In laboratories of Departament of Physics and Chemistry of Unesp-Ilha Solteira, this work is a pioneer in the manufacture of CdS/CdTe Solar Cell. To carry out this work it was necessary to improve the existing system of Spray deposition of SnO2: F, conditioning of the system for chemical bath deposition of CdS film and manufacture the sublimation system to deposit the CdTe layer. All of these systems for the deposition of thin films were developed in the laboratory. The manufacture of CdS/CdTe solar cell consisted of sequential deposition on glass of a) transparent conductive tin oxide doped with fluorine (SnO 2:F) using automatic control system of the spray; b) deposition of cadmium sulfide (CdS) for method (CBD); c) deposition of cadmium telluride for technique in closed space sublimation (CSS) and d) the rear metallic contact of silver was deposited by placing the liquid layer and subsequent improvement of contact with graphite-silver. The final structure of cell used in this work was: glass/SnO2:F/CdS/CdTe/contact. The CdTe solar cell layer was heat treated with cadmium dichloride (CdCl2) to compare its efficiency with another cell that was not treated with cadmium dichloride. Then we investigated the performance of only putting back metal contact layer of silver of silver and silver-graphite layer, the latter was giving better results, achieving an efficiency is a well more than 5%

Made available in DSpace on 2014-06-11T19:30:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-05-10Bitstream added on 2014-06-13T19:00:06Z : No. of bitstreams: 1 goncalves_tm_me_bauru.pdf: 1834288 bytes, checksum: 9d41cc9f6ebce4061033368ea92fec9c (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Filmes finos de carbono amorfo hidrogenado contendo silício e dopados com flúor foram produzudos pelos métodos de Deposição de Vapor Químico Assistido e Plasma (PECVD) e Deposição e Implantação Iônica por Imersão em Plasma (PIIID). Para PECVD foi utilizada uma pressão total de gases/vapor de 100 mTorr e inicialmente, 100W de potência de excitação. A proporção dos gases foi estudada, mantendo a concentração do hexametildisiloxano (HMDSO) em 75% e variando a proporção do argônio (Ar) e do hexafluoreto de enxofre (SF6). As porcentagens de flúor utilizadas na alimentação do plasma variaram em 0,6,9 e 12,5%. Visando maior concentração atômica de flúor na estrutura dos filmes, determinou-se a proporção de gases/vapor mais apropriada (75% HMDSO, 19% Ar e 6% SF6), e posteriormente, foi realizado um novo estudo da potência de excitação. Variando a potência entre 40 e 70 W, 50 W foi considerada como sendo a melhor condição de excitação para a descarga luminosa, considerando os efeitos causados pela corrosão relacionada ao flúor e a incorporação do elemento. Um estudo sobre as mesmas proporções foi realizada pela técnica de PIIID, com uma pressão total de 50 mTorr, potência de 50 W e pulsos negativos com magnitude de 800 V. Para este método o filme produzido com 12,5% de SF6 foi escolhido como sendo a melhor opção, tendo em vista que apresentou a maior quantidade atômica de flúor em sua estrutura. Posteriormente, a intensidade dos pulsos aplicados foi variada entre 544 e 14801 V, onde verificou-se que o aumento da intensidade dos pulsos resulta na diminuição da incorporação de flúor / Hydrogenated amorphous carbon films containing silicon and doped with fluorine were produced by two methods: Plasma Enhanced Chemical Vapor Deposition (PECVD) and Deposition (PIIID). For PECVD a total pressure of 100 mTorr was used at a excitation power of 100 W. The gas/vapor proportion was studied, keeping 75% hexamethyldisiloxane and varying the argon (Ar) and sulfur hexafluoride (SF6) ratio. The following proportions of SF6) ratio. The following proportions of SF6 were examined: 0, 6, 9 and 12.5%. Aiming for the highest atomic concentration of fluorine in film structure the best condition (75% HMDSO, 19% Ar and 6% SF6) was determined and a new study of the influence of the radiofrequency power. Considering the corrosion effects gernerated by fluorine in the plasma, variation of the applied power between 40 and 70 W, allowed the selection of 50 W as the best conditions. A study employing the same proportior PIIID was performed using 50 mTorr of total pressure, an applied power of 50 W and a pulse bias of 800 V. Considering the results of the chemical characterizations, films were produced with 12.5% of SF6 in the plasma feed. Subsequently, bias voltage was varied between 544 and 1480 V, where it was observed that the increasing the pulse bias decreased the fluorine concentration in film structure

Made available in DSpace on 2014-06-11T19:30:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-05-29Bitstream added on 2014-06-13T19:39:42Z : No. of bitstreams: 1 silva_vdl_me_bauru.pdf: 1285191 bytes, checksum: cca22db63612f5a769cb9b3084296342 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O objetivo principal deste trabalho é elucidar quais são os mecanismos de transporte de portadores de carga presentes na interface entre SnO2 e o contato metálico, pois tal conhecimento é fundamental para a aplicação na eletrônica. Além disso, é objetivo aqui também, estudar características de transporte em SnO2 dopado com alguns íons terras-raras. As amostras de SnO2 dopadas em Eu3+ e Ce3+ utilizadas nesta pesquisa foram sintetizadas a partir do método sol-gel e os filmes finos depositados pela técnica dip-coating. Os contatos estudados foram feitos a partir dos metais In, Sn e Al, depositados via evaporação resistiva. Medidas de resistência em função da temperatura nas amostras dopadas com Eu indicaram uma variação significativa da resistividade, de até 10 vezes, quando alterado o metal do contato. Isto se deve a diferença entre a função de trabalho de cada metal, que consequentemente acarreta em variação da barreira de potencial na junção metal-semicondutor. Pela característica das curvas de corrente medida em função da tensão aplicada, observou-se que os dois mecanismos de condução elétrica dominantes na interface são a emisssão termiônica, quando em baixas temperaturas e tensões de menor intensidade, e o tunelamento através da barreira, quando em temperaturas mais altas e tensões de maior intensidade. Com base nesses resultados e na aplicação do método proposto por Rhoderick estimou-se os valores da altura da barreira de potencial na junção metal-semicondutor, em 132 meV, 162 meV e 187 meV para os metais In, Al, Sn, respectivamente. Além disso, o tratamento térmico realizado nas amostras promoveu, de modo geral, a diminuição da resistividade do dispositivo devido, provavelmente, ao estreitamento da barreira de potencial e consequente aumento da... / The main goal of this work is the verification of electrical transport mechanisms of charge carriers at the interface between SnO2 and the metallic contact, because this knowledge is fundamental for electronic applications. Besides, another goal here is to investigate transport characteristics of rare-earth doped SnO2 samples doped with Eu3+ and Ce3+ used in this research were made from the sol-gel method and the thin films were deposited via dip-coating technique. The analyzed contacts were deposited from metals In, Sn and Al, via resistive evaporation technique. Resistance as function of temperature measurements applied to Eu-doped samples indicates a significant resistivity, up to 10 times, when the contact metal is varied. This is due to the differences in the work function of each metal, leading to variation in the potential barrier at interface of the metal-semiconductor junction. The characteristics of the current-voltage curves yield two dominant electrical mechanisms at the interface: thermo-ionic emission, for low temperatures and higher applied bias, and quantum tunneling through the barrier, when the temperature is higher and so is the applied bias magnitude. Based on these results and the application of the method proposed by Rhoderick, the potential barrier height of metal-semiconductor junction values were evaluated, yielding 132 meV, 162 meV and 187 meV for the metals In, Al and Sn, respectively. Besides, generally speaking, thermal annealing promotes the resistivity decrease, probably due to the potential barrier narrowing, increasing the tunneling probability. The variation of Ce3+ concentration, from 0,1% also leads to variation in the device resistivity, but this is not related to the potential at the junction interface, instead it is related with other bulk factors, as the charge... (Complete abstract click electronic access below)

Magister Scientiae - MSc / The growth of amorphous hydrogenated silicon (a-Si:H) thin films deposided by hot wire chemical vapor deposition (HWCVD) has been studied. The films have been characterised for optical and structural properties by means of UV/VIS,FITR,ERDA, XRD.XTEM and Raman spectroscopy. Low subtrate heater temperatures in the range form 130 to 200 degrees celcius were used in this thesis because it is believed to allow for the deposition of device quality a-Si:H which can be used for electronic photovoltaic devices. Furthermore, low temperatures allows the deposition of a-Si:H on any subtrate and thus offers the possibility of making large area devices on flexible organic substances. We showed that the optical and structural properties of grown a-Si:H films depended critically upon whether the films were produced with silane gas or silane diluted with hydrogen gas. We also showed that it is possible to to deposit crystalline materials at low temperature under high hydrogen dilution ratio of silane gas. / South Africa

Epitaxial oxide thin films are used in many technologically important device applications. This work deals with the deposition and characterization of epitaxial WO3 and SrBi2Ta2O9 (SBT) thin films on single crystal oxide substrates. WO3 thin films were chosen as a subject of study because of recent findings of superconductivity at surfaces and twin boundaries in the bulk form of this oxide. Highly epitaxial thin films would be desirable in order to be able to create a device within a film without patterning it, by locally creating superconducting regions (e.g. twins) within an otherwise defect free film by reducing or doping the film with Na. Films were deposited by reactive magnetron sputtering at various temperatures on single crystal SrTiO3 (100) and R-sapphire substrates. X-ray diffraction studies showed that the optimised films were highly (001) oriented, quality of epitaxy improving with decreasing deposition temperature. AFM studies revealed columnar growth of these films. Films were heat treated with Na vapour in order to reduce or dope them with Na. Low temperature measurements of the reduced films did not show existence of any superconductivity. SBT is a ferroelectric oxide and its thin films are attractive candidates for non-volatile ferroelectric random access memory (FRAM) applications. High structural anisotropy leads to a high degree of anisotropy in its ferroelectric properties which makes it essential to study epitaxial SBT films of different orientations. In this study, SBT films of different orientations were deposited on different single crystal substrates by pulsed laser ablation. Highly epitaxial c-axis oriented and smooth SBT films were deposited on SrTiO3 (100) substrates. AFM studies revealed the growth of these films by 3-D Stranski-Krastanov mode. However, these films did not exhibit any ferroelectric activity. Highly epitaxial (116)-oriented films were deposited on SrTiO3 (110) substrates. These films were also very smooth with root mean square (RMS) roughness of 15-20 Å. Films deposited on TiO2 (110) were partially a-/b-axis oriented and showed the formation of c-axis oriented SBT and many impurities. Completely a-/b-axis oriented SBT films were deposited on LaSrAlO4 (110) substrates. Films deposited at non-optimal growth temperatures showed the formation of many impurities. Attempts were also made towards depositing Sr2RuO4 films on LaSrAlO4 (110) substrates, which can act as a bottom electrode for ferroelectric SBT films.