In this thesis, research on synthesis, structure and characterization of amorphous carbide-based thin films is presented. Crystalline and nanocomposite carbide films can exhibit properties such as high electrical conductivity, high hardness and low friction and wear. These properties are in many cases structure-related, and thus, within this thesis a special focus is put on how the amorphous structure influences the material properties. Thin films within the Zr-Si-C and Cr-C-based systems have been synthesized by magnetron sputtering from elemental targets. For the Zr-Si-C system, completely amorphous films were obtained for silicon contents of 20 at.% or higher. Modeling of these films, as well as experimental results suggest that the films exhibit a network-type structure where the bond types influence the material properties. Higher hardness and resistivity were observed with high amounts of covalent Si-C bonds. Several studies were performed in the Cr-C-based systems. Cr-C films deposited in a wide composition range and with substrate temperatures of up to 500 °C were found to be amorphous nanocomposites, consisting of amorphous chromium carbide (a-CrCx) and amorphous carbon (a-C) phases. The carbon content in the carbidic phase was determined to about 30-35 at.% for most films. The properties of the Cr-C films were very dependent of the amount of a-C phase, and both hardness and electrical resistivity decreased with increasing a-C contents. However, electrochemical analysis showed that Cr-C films deposited at higher substrate temperature and with high carbon content exhibited very high oxidation resistance. In addition, nanocomposite films containing Ag nanoparticles within an amorphous Cr-C matrix were studied in an attempt to improve the tribological properties. No such improvements were observed but the films exhibited a better contact resistance than the corresponding binary Cr-C films. Furthermore, electrochemical analyses showed that Ag nanoparticles on the surface affected the formation of a stable passive film, which would make the Cr-C/Ag films less resilient to oxidation than the pure Cr-C films.

This thesis present research on synthesis, microstructure, and properties of carbide- and boride- based thin films. The films have been synthesized by dc magnetron sputtering, and their microstructures have been characterized mainly by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and transmission electron microscopy.  One of the main objectives with this research has been to evaluate the thin films potential as materials for sliding electrical contact applications and this have influenced, which properties that have been evaluated. Co-sputtered Nb-C films have a microstructure comprising of nanocrystalline NbCx  (nc-NbCx) grains embedded in a matrix of amorphous C (a-C). A thinner a-C matrix form in the Nb-C films compared to the well-studied Ti-C system. As a consequence, the Nb-C films have a higher hardness and conductivity than previously studied Ti-C sputtered under similar conditions. The promising electrical contact properties are attained for reactively sputtered Nb-C films under industrial conditions, at deposition rates two orders of magnitude higher. A reduction in crystallinity is seen when Si is added to the Nb-C films and amorphous films forms at Si content > 25 at.%. The alloying of Si was however not beneficial for the electrical contact properties. Substoichiometric CrB2-x (B/Cr = 1.5) and NbB2-x (B/Nb = 1.8) films are achieved when deposited from MeB2 targets. Boron segregates to grain boundaries forming a B-rich tissue phase. This result in superhardness for the NbB2-x films (42 ± 4 GPa) as well as a low friction attributed to the formation of a boric acid film. Carbon forms a solid solution in the MeB2 grains as well as segregating to grain boundaries forming an amorphous BCx (a-BCx) phase when alloyed to CrB2-x and NbB2-x films. The formation of the a-BCx phase drastically improves the electrical contact resistance of the NbB2-x films. However, the mechanical properties are degraded, which result in a high friction and wear rate. It was in TEM studies of the metastable amorphous structures for the Nb-Si-C films found that the electron beam induces crystallization. Hence, great care is required when studying these types of metastable structures.

Thermally stimulated current measurements are carried out on as-grown TlGaS2, TlGaSe2 and TlInS2 layered single crystals with the current owing perpendiclar to the c-axis in the wide temperature range of 10-300 K with various heating rates. Experimental evidence is found for the presence of three, two and one trapping centers for TlGaS2 , TlGaSe2 and TlInS2 crystals with activation energies 6, 12 and 26 / 98 and 130 / 12 meV respectively. We have determined the trap parameters using varous methods of analyis, and these agree well with each other. The retrapping process is negligible for these levels, as confirmed by good agreement between the experimental results and theoretical predictions of the model that assumes slow retrapping. Also the calculated values of the capture cross sections, attempt to escape frequencies and the concentration of the traps are reported.

Melanins are a class of bio-macromolecules that are found throughout the biosphere. They fulfill various functions in human beings, which makes them a long studied substance in medicine and biology. Furthermore they possess a set of rare and special physico-chemical properties which include featureless broad band absorption in the UV-Vis spectrum and condensed phase electrical conduction. Many scientists have interpreted their findings in terms of an amorphous semiconductor model, but this was done under the a priori assumption that charge transport in melanin is electronic. However, a very strong dependence of melanin’s electrical properties on its level of hydration has recently led to speculations that the dominant charge carrier for high hydration is of protonic rather than electronic nature. This thesis will present direct evidence for electronic charge transport, found by investigating the influence of different environmental parameters on the conductivity of melanin. It will furthermore be shown that the hydration dependent conductivity of melanin can be understood in terms of a dielectric response model for an amorphous semiconductor. This establishment of the major charge carrier is an important step in the on-going effort to fully map the structure-property relationship of melanin and will help to understand its function in vivo. With the ultimate goal to make use of melanin’s fascinating properties, thin films, a new class of device has been characterized and investigated. These thin films, while exhibiting melanin’s characteristics, show improved mechanical stability, a very uniform morphology and a much faster response than standard pellet samples. They are furthermore applicable to standard polymer processing techniques which brings technological applications within reach.

Les semi-conducteurs moléculaires ont permis la réalisation de dispositifs électroniques, tels que transistors à effet de champ, diodes et autres hétérojonctions. Les matériaux ambipolaires, capables de transporter tant les charges positives que négatives, conduisent à des dispositifs aux propriétés particulières. L’objet de cette thèse est de synthétiser de nouveaux matériaux moléculaires ambipolaires et de développer des dispositifs électroniques originaux, en particulier pour des applications dans le domaine des capteurs de gaz. Nous nous intéressons aux molécules compatibles avec des mises en forme par des techniques dites de solution processing, en particulier des métallo-phtalocyanines. / The molecular semiconductors have enabled the production of electronic devices such as field effect transistors, diodes and other heterojunctions. The ambipolar materials, capable of carrying both positive charges and negative, result in devices with special properties. The purpose of this thesis is to synthesize new ambipolar materials develop original electronic devices, especially for applications in the field of gas sensors. We are interested in molecules capable to lead to thin films with low temperature techniques known as solution processing, particularly metallo-phthalocyanines.

Orientador: Marcelo Ornaghi Orlandi / Banca: Walter Katsumi Sakamoto / Banca: Emerson Rodrigues de Camargo / Resumo: Nanocompósitos são materiais que combinam duas (ou mais) fases sólidas, uma das quais deve possuir dimensões nanométricas, que pode reunir em um único material várias propriedades melhoradas para uma dada aplicação e, portanto, podem permitir a coexistência de propriedades tradicionalmente antagônicas como, transparência e condutividade. O presente trabalho teve como objetivo a obtenção de um nanocompósito polimérico transparente e condutor de polimetilmetacrilato - PMMA com nanofitas do sistema Indium Tin Oxide - ITO. Para isto primeiramente estudou-se a influência da temperatura na síntese das nanoestruturas de ITO e depois de obtida a temperatura de síntese que proporcionou o crescimento de nanofitas de ITO com maior condutividade e maior transparência no espectro visível, estudou-se a influência da inserção destas nanofitas nas propriedades ópticas e elétricas de filmes nanocompósitos de PMMA. Como as nanofitas obtidas são emaranhadas, para a obtenção do nanocompósito foi realizada uma separação prévia das mesmas utilizando duas dispersões distintas: sendo a primeira em um ultrasom convencional e a segunda em uma ponta ultrasônica. Depois de dispersas, as nanofitas foram misturadas ao PMMA comercial dissolvido em concentrações mássicas de 1%, 2%, 5% e 10% de nanofitas. As soluções foram então depositadas sobre substrato de vidro e, depois de secos, os filmes foram destacados. As caracterizações ópticas mostraram que a transmitância no espectro visível dos filmes diminui em função do aumento da quantidade de nanofitas no compósito. Neste estudo, as caracterizações elétricas mostraram que ocorreu percolação das nanofitas no polímero após a inserção de 5% em massa de nanofitas. As imagens de MET para os filmes corroboraram os resultados previstos pelas caracterizações elétricas. Os filmes... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Nanocomposites are materials which have two or more solid phases, and one of these phases should be in nano-sized scale range. These materials can have several properties increased for special application and it is possible to obtain composites with traditionally antagonistic combinations of properties, such as transparence in the visible range of light and good conductivity. The main goal of this work is obtain a transparent and conductive polymer-based nanocomposite using polymethylmethacrylate - PMMA and ITO (Indium Tin Oxide) nanobelts. To reach this goal it was first studied the influence of temperature on the synthesis of nanostructured ITO. Once the temperature of synthesis was optimized to ensure the growth of ITO nanobelts with both good conductivity and good transparency in the visible spectrum, we studied the influence of ITO nanobelts on the electrical and optical properties of nanocomposites of PMMA. Because the synthesized nanobelts are entangled each other, to obtain the composite it was realized a separation of them using two different ways; first using a conventional ultrasound and after an ultrasonic tip. Then, nanobelts were mixed with commercial PMMA dissolved in THF 10% in mass concentrations of 1%, 2%, 5% and 10%. So, the solution was deposited over a glass substrate by casting. The results showed that films transmittance in visible range decreases by increasing the amount of nanobelts. The electrical characterization showed that percolation occurred after 5%wt of filler. TEM images of composites corroborate the results provided by the electrical measures. The films prepared using both dispersions had the same transmittance in the visible spectrum, despite of the films obtained by dispersing the nanobelts in ultrasonic tip had a lower electrical resistance. Thus it can be concluded that the dispersion by ultrasonic... (Summary complete electronic access click below) / Mestre

Este trabalho investigou a deposição dos filmes finos de ferritas de lantânio dopado com estrôncio e cobalto La1-xSrxCo1-yFeyO3-δ (LSCF) através da técnica de spray pirólise empregando precursores inorgânicos e silício como substrato. Foram utilizados água e etanol na proporção de (3:1) como solvente na preparação da solução a ser aspergida. As deposições foram realizadas em diferentes temperaturas: 130ºC, 150ºC, 170ºC e 200ºC. Os filmes de LSCF antes e após o tratamento térmico foram analisados por difração de raios X (DRX) e microscopia eletrônica de varredura (MEV). O spray de deposição dos filmes em função das soluções com diferentes proporções de etanol (0%, 50%, 75% e 100%) foi investigado utilizado uma câmera rápida de alta resolução e um laser com comprimento de onda 532 nm. Os resultados evidenciaram que a temperatura de ebulição do solvente e de deposição são parâmetros importantes na determinação da morfologia dos filmes. Maiores teores de etanol promovem um aumento nos valores do ângulo de cone e que a propriedade da tensão superficial exerce significativamente maior influência nos aspectos que envolvem a estrutura do spray, a atomização do líquido, formação de gotas e no ponto de ruptura das soluções Os resultados de DRX apresentaram a fase cristalina majoritária de LSCF após o tratamento térmico a 750°C por 2 horas e a fase secundária de La2O3. As imagens de MEV evidenciaram a formação de filmes para as distâncias de deposição de 120 mm, embora apenas na temperatura de 200°C apresentasse uma estrutura porosa antes e após o tratamento térmico. A presença de interdifusão e microporosidade foi observada para esse filme. Para as diferentes composições de LSCF nas condições de 120 mm e a 200°C, apenas as composições de La1-xSrxCo0,2Fe0,8 com x = 0,6, 0,9 e 0,7 apresentaram estrutura porosa após o tratamento térmico. O filme de La0,8Sr0,2Co0,2Fe0,8 apresentou maior condutividade iônica/elétrica e energia de ativação. A presença de fases secundárias (La2O3, SrO2 e La2CoO3) contribuiu para a redução da condutividade elétrica e iônica e a energia de ativação. / This work investigated the deposition conditions of thin lanthanum ferrite films doped with strontium and cobalt – La1-xSrxCo1-yFeyO3-δ (LSCF) through the spray pyrolysis technique using inorganic precursors and silicon as a substrate. Water and ethanol were used in the proportion (3:1) as solvent in the preparation of the solution to be sprinkled. The depositions were carried out at different temperatures: 130°C, 150°C, 170°C and 200°C. The films of LSCF were analyzed by X-ray diffraction and scanning electron microscopy before and after thermal treatment. The XRD results showed the obtainment of crystalline phase of LSCF after thermal treatment at 750°C/2hours and secondary phase of La2O3. The sprays of solutions with different proportions of ethanol (0%, 50%, 75% and 100%) were analyzed using a fast high-resolution camera and a laser with a wavelength of 532nm.The results showed those deposition temperature and solvente boiling points are important parameters to determine the thin morphology Higher ethanol levels promote an increase in the cone angle values and that the property of the surface tension exerts significantly greater influence on issues involving the structure of the spray, the atomization of the liquid, the droplets formation and the breaking point of the solutions. The XRD results showed the obtainment of majority crystalline phase of LSCF after thermal treatment at 750°C/2 hours with the presence of secondary phase of La2O3. The SEM images showed formation of films for the distance of 120 mm, although only at the temperature of 200°C it presents porous morphology before and after thermal treatment. The presence of interdiffusion and microporosity was observed for this film. For different LSCF compositions under the conditions of 120 mm and 200°C, the films of La1-xSrx Co0,2Fe0,8 with x = 0,6; 0,9 and 0,7 presented porous morphology after thermal treatment. Otherwise, the film of La0,8Sr0,2Co0,2Fe0,8 showed the highest ionic/electrical conductivity. The presence of secondary phase (La2O3, SrO2 and La2CoO3) evidenced by XRD promoted a decrease in ionic/electrical conductivity and in the activation energy.

Made available in DSpace on 2014-06-11T19:25:32Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-02-18Bitstream added on 2014-06-13T18:53:39Z : No. of bitstreams: 1 arlindo_eps_me_ilha.pdf: 3403830 bytes, checksum: 35e9bb51a7710370f78852b7519f78ec (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Nanocompósitos são materiais que combinam duas (ou mais) fases sólidas, uma das quais deve possuir dimensões nanométricas, que pode reunir em um único material várias propriedades melhoradas para uma dada aplicação e, portanto, podem permitir a coexistência de propriedades tradicionalmente antagônicas como, transparência e condutividade. O presente trabalho teve como objetivo a obtenção de um nanocompósito polimérico transparente e condutor de polimetilmetacrilato – PMMA com nanofitas do sistema Indium Tin Oxide – ITO. Para isto primeiramente estudou-se a influência da temperatura na síntese das nanoestruturas de ITO e depois de obtida a temperatura de síntese que proporcionou o crescimento de nanofitas de ITO com maior condutividade e maior transparência no espectro visível, estudou-se a influência da inserção destas nanofitas nas propriedades ópticas e elétricas de filmes nanocompósitos de PMMA. Como as nanofitas obtidas são emaranhadas, para a obtenção do nanocompósito foi realizada uma separação prévia das mesmas utilizando duas dispersões distintas: sendo a primeira em um ultrasom convencional e a segunda em uma ponta ultrasônica. Depois de dispersas, as nanofitas foram misturadas ao PMMA comercial dissolvido em concentrações mássicas de 1%, 2%, 5% e 10% de nanofitas. As soluções foram então depositadas sobre substrato de vidro e, depois de secos, os filmes foram destacados. As caracterizações ópticas mostraram que a transmitância no espectro visível dos filmes diminui em função do aumento da quantidade de nanofitas no compósito. Neste estudo, as caracterizações elétricas mostraram que ocorreu percolação das nanofitas no polímero após a inserção de 5% em massa de nanofitas. As imagens de MET para os filmes corroboraram os resultados previstos pelas caracterizações elétricas. Os filmes... / Nanocomposites are materials which have two or more solid phases, and one of these phases should be in nano-sized scale range. These materials can have several properties increased for special application and it is possible to obtain composites with traditionally antagonistic combinations of properties, such as transparence in the visible range of light and good conductivity. The main goal of this work is obtain a transparent and conductive polymer-based nanocomposite using polymethylmethacrylate – PMMA and ITO (Indium Tin Oxide) nanobelts. To reach this goal it was first studied the influence of temperature on the synthesis of nanostructured ITO. Once the temperature of synthesis was optimized to ensure the growth of ITO nanobelts with both good conductivity and good transparency in the visible spectrum, we studied the influence of ITO nanobelts on the electrical and optical properties of nanocomposites of PMMA. Because the synthesized nanobelts are entangled each other, to obtain the composite it was realized a separation of them using two different ways; first using a conventional ultrasound and after an ultrasonic tip. Then, nanobelts were mixed with commercial PMMA dissolved in THF 10% in mass concentrations of 1%, 2%, 5% and 10%. So, the solution was deposited over a glass substrate by casting. The results showed that films transmittance in visible range decreases by increasing the amount of nanobelts. The electrical characterization showed that percolation occurred after 5%wt of filler. TEM images of composites corroborate the results provided by the electrical measures. The films prepared using both dispersions had the same transmittance in the visible spectrum, despite of the films obtained by dispersing the nanobelts in ultrasonic tip had a lower electrical resistance. Thus it can be concluded that the dispersion by ultrasonic... (Summary complete electronic access click below)

abstract: Amorphous materials can be uniformly deposited over a large area at lower cost compared to crystalline semiconductors (Silicon or Germanium). This property along with its high resistivity and wide band-gap found many applications in devices like rectifiers, xerography, xero-radiography, ultrahigh sensitivity optical cameras, digital radiography, and mammography (2D and 3D tomosynthesis). Amorphous selenium is the only amorphous material that undergoes impact ionization where only holes avalanche at high electric fields. This leads to a small excess noise factor which is a very important performance comparison matrix for avalanche photodetectors. Thus, there is a need to model high field avalanche process in amorphous selenium. At high fields, the transport in amorphous selenium changes from low values of activated trap-limited drift mobility to higher values of band transport mobility, via extended states. When the transport shifts from activated mobility with a high degree of localization to extended state band transport, the wavefunction of the amorphous material resembles that of its crystalline counterpart. To that effect, crystalline monoclinic selenium which has the closest resemblance to vapor deposited amorphous selenium has been studied. Modelling a crystalline semiconductor makes calculations simpler. The transport phenomena in crystalline monoclinic selenium is studied by using a bulk Monte Carlo technique to solve the semi-classical Boltzman Transport equation and thus calculate vital electrical parameters like mobility, critical field and mobility variations against temperatures. The band structure and the density of states function for monoclinic selenium was obtained by using an atomistic simulation tool, the Atomistic Toolkit in the Virtual Nano Lab, Quantum Wise, Copenhagen, Denmark. Moreover, the velocity and energy against time characteristics have been simulated for a wide range of electric fields (1-1000 $\frac{kV}{cm}$), which is further used to find the hole drift mobility. The low field mobility is obtained from the slope of the velocity vs. electric field plot. The low field hole mobility was calculated to be 5.51 $\frac{cm^{2}}{Vs}$ at room temperature. The experimental value for low field hole mobility is 7.29 $\frac{cm^{2}}{Vs}$. The energy versus electric field simulation at high fields is used to match the experimental onset of avalanche (754 $\frac{kV}{cm}$) for an ionization threshold energy of 2.1 eV. The Arrhenius plot for mobility against temperature is simulated and compared with published experimental data. The experimental and simulation results show a close match, thus validating the study. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2017

Made available in DSpace on 2014-10-09T12:46:43Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:36Z (GMT). No. of bitstreams: 1 08288.pdf: 2858118 bytes, checksum: 5254a04c780740482622c95ca3afa37b (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP