Biblioteca Digital

The goal of this work is to study and relate electrical and optical properties of diamond-like carbon (DLC) thin films for applications in electronic devices. DLC films were deposited in a reactive RF magnetron sputtering system on p-type silicon and glass substrates. The target was a 99.9999% pure, 6 in. diameter graphite plate and methane was used as processing gas. Eight DLC films were produced for each substrate, varying deposition time, the reactor pressure between 5 mTorr and 10 mTorr while the RF power was applied at 13.56 MHz and varied between 100, 150, 200 and 250W. After deposition, the films were analyzed by I-V and C-V measurements (Cheng et al. (2004) [1]) in order to determine the electric resistivity, photo-current response and dielectric constant, optical transmittance, used to find the optical gap by the Tauc method; and by photoluminescence analysis to determine the photoemission and confirm the optical band gap. These characteristics are compared and the influence of the deposition parameters is discussed. (C) 2011 Published by Elsevier B.V.

We have explored the suitability and characteristics of interface tailoring as a tool for enhancing the adhesion of hydrogen-free diamond-like carbon (DLC) thin films to silicon substrates. DLC films were deposited on silicon with and without application of an initial high energy carbon ion bombardment phase that formed a broad Si-C interface of gradually changing Si:C composition. The interface depth profile was calculated using the TRIDYN simulation program, revealing a gradient of carbon concentration including a region with the stoichiometry of silicon carbide. DLC films on silicon, with and without interface tailoring, were characterized using Raman spectroscopy, scanning electron microscopy, atomic force microscopy and scratch tests. The Raman spectroscopy results indicated sp3-type carbon bonding content of up to 80%. Formation of a broadened Si:C interface as formed here significantly enhances the adhesion of DLC films to the underlying silicon substrate. (C) 2012 Elsevier B.V. All rights reserved.; NUS; NUS; [R284000087112]

Neste trabalho filmes finos de silício amorfo hidrogenado (a-Si:H) foram depositados no reator magnetron sputtering do laboratório de sistemas integráveis (LSI), a temperaturas menores que 100 °C, pela introdução do gás hidrogênio junto com o de argônio para pulverização de um alvo de silício policristalino. As condições de deposição investigadas estão compreendidas em pressões totais de 5 e 10 mTorr para as quais a potência de RF variou de 150 a 300 W, para a menor pressão, e de 200 a 300 W, para a maior pressão, sendo que para cada condição de potência a concentração de hidrogênio nos gases de descarga variou de pelo menos 0 % a no máximo 60 %. Como os substratos utilizados foram carbono vítreo, lâminas oxidadas de silício e placas de vidro para microscópio óptico os filmes depositados sobre o carbono foram caracterizados por RBS, os depositados sobre as lâminas oxidadas de silício por FTIR e medidas IV e os depositados sobre o vidro por espectroscopia de absorção óptica na região do ultravioleta-visível. A caracterização RBS forneceu informações tanto sobre o tipo e quantidade de impurezas eventualmente incorporadas durante a deposição como sobre a densidade superficial do silício que permitiu a obtenção da densidade volumétrica pela utilização dos parâmetros de espessura obtidos pela técnica de perfilometria. Através da análise dos espectros FTIR o hidrogênio incorporado pode ser quantificado na forma de mono e polihidretos de silício. As medidas IV foram realizadas através de contatos de alumínio...

Neste trabalho foram produzidos filmes finos de nitreto de carbono pelo método de deposição de íons e vapor (IVD) que consiste em evaporar um material (carbono) sobre um substrato e, simultaneamente, realizar sobre ele um bombardeamento por íons (N POT.+). Foram produzidas amostras com energia dos íons de 0,5, 0,8, 2,0, 5,0 e 10,0 keV e razão de transporte TR(C/N) = 04, 1,0, 1,5, 2,0 e 3,0, onde TR(C/N) é o quociente do número de átomos de carbono evaporados pelo canhão eletrônico e o número de íons acelerados que chegam simultaneamente ao mesmo substrato. Os filmes foram produzidos com espessuras de 200, 500 e 1000 nm sobre substratos de Si(100), sílica fundida e carbeto de tungstênio. As propriedades dos filmes analisadas por meio de espectroscopia de fotoeléctrons induzidos por Raios X (XPS), espectrofotometria do infravermelho por transformadas de Fourier (FT-IR), espectrofotometria do visível e ultravioleta, difração de Raios X (XRD) e ensaios de dureza Knoop. Os espectros de XPS foram utilizados para a análise do estado das ligações entre carbono e nitrogênio e também para se estimar a razão de composição CR(C/N) entre átomos de carbono e nitrogênio presentes nos filmes. Foram analisados os picos de C-1s POT. ½ e N-1s POT. ½ e a relação entre suas áreas forneceu a CR(C/N). Para amostras ricas em nitrogênio...

Neste trabalho, foram produzidos filmes finos de carbono pela técnica de magnetron sputtering usando substratos monocristalinos de alumina com plano-c orientado em (0001) e substratos de Si (111) e Si (100), empregando Co, Ni e Cu como filmes intermediários (buffer-layers). As deposições foram conduzidas em três etapas, sendo primeiramente realizadas com buffer-layers de cobalto em substratos de alumina, onde somente após a produção de grande número de amostras, foram então realizadas as deposições usando buffer-layer de cobre em substratos de Si. Em seguida foram realizadas as deposições com buffer-layers de níquel em substratos de alumina. A cristalinidade dos filmes de carbono foi avaliada por meio da técnica de espectroscopia Raman e complementarmente por difração de raios X (DRX). A caracterização morfológica dos filmes foi feita por meio da microscopia eletrônica de varredura (MEV E FEG-SEM) e microscopia eletrônica de transmissão de alta resolução (HRTEM). Picos de DRX referentes aos filmes de carbono foram observados apenas nos resultados das amostras com buffer-layers de cobalto e de níquel. A espectroscopia Raman mostrou que os filmes de carbono com maior grau de cristalinidade foram os produzidos com substratos de Si (111) e buffers de Cu...

Diverse amorphous hydrogenated carbon-based films (a-C:H, a-C:H:F, a-C:H:N, a-C:H:Cl and a-C:H:Si:O) were obtained by radiofrequency plasma enhanced chemical vapor deposition (PECVD) and plasma immersion ion implantation and deposition (PIIID). The same precursors were used in the production of each pair of each type of film, such as a-C:H, using both PECVD and PIIID. Optical properties, namely the refractive index, n, absorption coefficient, α, and optical gap, ETauc, of these films were obtained via transmission spectra in the ultraviolet-visible near-infrared range (wavelengths from 300 to 3300 nm). Film hardness, elastic modulus and stiffness were obtained as a function of depth using nano-indentation. Surface energy values were calculated from liquid drop contact angle data. Film roughness and morphology were assessed using atomic force microscopy (AFM). The PIIID films were usually thinner and possessed higher refractive indices than the PECVD films. Determined refractive indices are consistent with literature values for similar types of films. Values of ETauc were increased in the PIIID films compared to the PECVD films. An exception was the a-C:H:Si:O films, for which that obtained by PIIID was thicker and exhibited a decreased ETauc. The mechanical properties - hardness...

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); During the extraction of aluminum from bauxite, a waste of oxides containing traces of heavy metals in a highly alkaline matrix, called Red Mud (RM), is produced. In this study RM is characterized and the feasibility of using it as a precursor for the production of thin films by Plasma Sputtering and by Plasma Immersion Ion Implantation and Deposition (PIIID) is demonstrated. The chemical structure and composition, surface morphology, topography, and wettability of the films prepared using such methodologies were investigated. The films consist mainly of the elements aluminum, silicon, iron and carbon. Infrared spectroscopic analyses reveal the presence of C=O, C-H2, Fe(OH), Al-O and Si-C functionalities. RF Sputtering produced films with smoother surfaces, whereas PIIID produced granular surface structures. Surface contact angle measurements showed that despite the presence of oxides and hydroxides, the films are hydrophobic, thus exhibiting an interesting link between the physical and thermodynamical properties.

Neste trabalho foi preparada uma série de filmes de carbono amorfo pelo processo de IBAD (Ion Beam Assisted Deposition), onde foi utilizado um feixe iônico de Xe com energia fixa para todas as amostras em 1500eV para realizar sputtering em um alvo de grafite e, um segundo feixe de Xe + responsável pelo bombardeio do filme durante o crescimento. Para cada amostra foi utilizada uma energia de bombardeio diferente, de 0 a 400eV. Esse bombardeio, além de gerar uma compactação da matriz induzindo uma pressão na rede (stress intrínseco), faz com que uma certa quantidade de Xe seja incorporada pelo filme. Por medidas de RBS foram observadas concentrações de 3 a 4% desse gás nobre na matriz, que são as concentrações nas quais são observadas formações de aglomerados sólidos desse elemento quando implantado em metais ou semicondutores cristalinos. Por medidas de XAS realizadas com radiação com energias no intervalo que envolve a borda L3 do xenônio foi verificada a formação de tais aglomerados sólidos e, em conjunto com resultados obtidos por simulações computacionais obtivemos um entendimento melhor sobre a estrutura fina na região de XANES dessa borda de absorção. A partir da técnica de SAXS foram encontradas estruturas com dimensões características de cerca de 10 a 25nm de forma achatada. Como os filmes de a-C crescidos por essa técnica são altamente grafíticos...

Este trabalho de mestrado teve como objetivos a fabricação e o estudo do comportamento elétrico das ponteiras de silício de emissão de campo a vácuo (PECV) recobertas com filme fino de carbono tipo diamante (DLC). Apresentamos o processo de fabricação das ponteiras de silício que é realizado através das etapas de fotolitografia, corrosão por íon reativo no plasma de SF6 (hexafluoreto de enxofre), oxidação térmica seca para afinamento, e deposição do filme DLC por PECVD (Plasma Enhanced Chemical Vapor Deposition). Mostramos os resultados obtidos da caracterização elétrica das ponteiras sem o filme e com o filme DLC, através do levantamento das curvas características I x V (corrente x tensão) e I x t (corrente x tempo). Verificamos que as curvas I x V obedeceram ao modelo de emissão de elétrons de Fowler-Nordheim. Comparamos estes resultados a fim de avaliarmos as mudanças na tensão de limiar, corrente emitida, e estabilidade de emissão. Neste estudo fabricamos PECV recobertas por filme DLC com espessura de aproximadamente 170 Å; The objectives of this dissertation were the fabrication of silicon field emitter tips coated with diamond like carbon (DLC) thin films, and the study of its electrical behavior. We present the fabrication process of silicon tips that consists on four stages: photolithography...

O princípio de funcionamento da Terapia por Captura de Nêutrons pelo Boro (BNCT, Boron Neutron Capture Therapy) é a entrega seletiva de uma maior quantidade de átomos de boro às células cancerígenas do que àquelas saudáveis, seguida da irradiação com nêutrons que irá induzir a emissão de partículas a e íons de recuo de 7Li através da reação nuclear 10B(n,a)7Li. O objetivo deste trabalho é desenvolver uma metodologia para quantificar a taxa da reação de interesse através do uso da montagem de filmes finos de boro acoplados a detectores CR-39, que detectam as partículas a e os íons de recuo de 7Li. Este detector é composto por átomos de hidrogênio, carbono e oxigênio, os quais interagem com nêutrons rápidos e as partículas resultantes destas reações (de espalhamentos e de captura de nêutrons) também são detectadas pelo próprio detector. Deste modo, é possível quantificar, ao mesmo tempo, a reação 10B(n,a)7Li e a contribuição de nêutrons rápidos do fluxo. Essas medidas são fundamentais para os estudos de biodistribuição de átomos de 10B e de microdosimetria dos tecidos irradiados com nêutrons, levando ao planejamento da terapia em si. Os filmes finos de boro foram confeccionados por dois métodos...

During the extraction of aluminum from bauxite, a waste of oxides containing traces of heavy metals in a highly alkaline matrix, called Red Mud (RM), is produced. In this study RM is characterized and the feasibility of using it as a precursor for the production of thin films by Plasma Sputtering and by Plasma Immersion Ion Implantation and Deposition (PIIID) is demonstrated. The chemical structure and composition, surface morphology, topography, and wettability of the films prepared using such methodologies were investigated. The films consist mainly of the elements aluminum, silicon, iron and carbon. Infrared spectroscopic analyses reveal the presence of C=O, C-H2, Fe(OH), Al-O and Si-C functionalities. RF Sputtering produced films with smoother surfaces, whereas PIIID produced granular surface structures. Surface contact angle measurements showed that despite the presence of oxides and hydroxides, the films are hydrophobic, thus exhibiting an interesting link between the physical and thermodynamical properties.

Thickness dependency of the field emission of amorphous and nanostructured carbon thin films has been studied. It is found that in amorphous and carbon films with nanometer-sized sp2 clusters, the emission does not depend on the film thickness. This further proves that the emission happens from the surface sp2 sites due to large enhancement of electric field on these sites. However, in the case of carbon films with nanocrystals of preferred orientation, the emission strongly depends on the film thickness. sp2-bonded nanocrystals have higher aspect ratio in thicker films which in turn results in higher field enhancement and hence easier electron emission.

Ruthenium thin films were deposited by atomic layer deposition from bis(N,N’-di-tert-butylacetamidinato)ruthenium(II) dicarbonyl and O2. Highly conductive, dense and pure thin films can be deposited when oxygen exposure EO approaches a certain threshold ( Emax ). When EO > Emax, the film peels off due to the recombinative desorption of O2 at the film/substrate interface. Analysis by an atomic probe microscope shows that the crystallites are nearly free of carbon impurity (<0.1 at.%), while a low level of carbon (<0.5 at.%) is segregated near the grain boundaries. The atom probe microscope also shows that a small amount of O impurity (0.3 at.%) is distributed uniformly between the crystallites and the grain boundaries.; Chemistry and Chemical Biology; Engineering and Applied Sciences

Individual carbon nanotubes (CNTs) have superior thermal conductivity than conventional materials. The applications for CNTs range from heat sinks, thin films to thermal interface materials. However, when CNTs are grouped together in macroscopic quantities and embedded in different media their thermal conductivity changes. Therefore, it is important to determine the thermal conductance changes when CNTs are embedded in different media. In my research, CNTs were embedded in thin films and as aligned structures (fins) in water. Analytical and experimental methods were used to determine the thermal conductances of these aligned structures and thin films. The primary goals of this research were to develop novel analytical methods to determine thermal conductivity and also experimental techniques to determine effectiveness of the embedded CNTs as carriers of heat by thermal conductance evaluation. It is observed that CNTs fins are effective carriers of heat and result in up to 57% decrease in thermal resistance. In the case of CNTs embedded in thin films, it is important to consider non Fourier effects and neglecting non Fourier effects would lead to an underestimation of the thermal conductivity. In addition to the thermal conductivity value...

Thermal conductivities $\Lambda $ of amorphous carbon thin films are measured in the temperatures range 80--400 K using the $3\omega $ method. Sample films range from soft a-C:H prepared by remote-plasma deposition ($\Lambda = 0.20$ W m$^{-1}$ K$^{-1}$ at room temperature) to amorphous diamond with a large fraction of $sp^3$ bonded carbon deposited from a filtered-arc source ($\Lambda = 2.2$ W m$^{-1}$ K$^{-1}$). Effective-medium theory provides a phenomenological description of the variation of conductivity with mass density. The thermal conductivities are in good agreement with the minimum thermal conductivity calculated from the measured atomic density and longitudinal speed of sound.; Comment: 4 pages, 4 figures

[Full-text paper not available yet]; A study of the synthesis of carbon nanoparticles embedded in carbon thin films deposited by radiofrequency (RF) (13.56 MHz) Ar/H2 (4 %)/C2H2 plasmas is presented. The carbon nanospheres exhibit an amorphous structure that is clearly observed at 300 W, under 0.1 Torr, and grows in size with increasing C2H2 between 1% and 20 %. Above a C2H2 concentration threshold (20% in this case) carbon nanoparticles are no longer formed. In order to study possible changes in the plasma kinetics, optical emission spectroscopy (OES) is used to evaluate the electron temperature while changing the C2H2 concentration. In addition, an analysis of the temporal evolution of the electron energy distribution function (EEDF) is carried out for various C2H2 concentrations considering the effects produced by electron-vibrational superelastic collisions and relative concentration of excited Ar atoms. Finally, the morphological and tribological features of the deposited films are characterized.; F.J.G-V. acknowledges partial financial support from CSIC-CAM (Project No. 200550M016 and 200650M016) and MEC (Projects No. MAT2006-13006-C02-01 and ENE2006-14577-C04-03). C.G-A. acknowledges partial financial support from MEC (Projects No. MAT2002-04085-02-02 and MAT2006-13006-C02-01). Both authors acknowledge partial support from “Fundación Domingo Martínez” (Project No. 4.2).; Peer reviewed

The secondary electron emission yield of fullerene, graphite, and diamondlike carbon after low-energy N2+ ion bombardment was studied for antimultipactor applications. Nitrogen incorporation into the carbon thin films decreases their secondary emission yield, contrary to the hydrogen or oxygen effect. Carbon nitride surface textured to a nanometric scale had the property of hindering secondary electron emission. Valence bands obtained from photoemission spectroscopy using synchrotron radiation were correlated with secondary electron emission measurements. Multipactor threshold power for carbon nitride was 7.5 kW.; We would like to thank Carlos E. Montesano of EADSCASA for his collaboration. This work was supported by the Ministry of Science and Technology of Spain through the coordinated Project Nos. ESP2002-04509-C04-04 and ESP2002-04509-C04-02, and the TMR Project No. ERBFMGECT950022 of the European Community.; Peer reviewed

This thesis presents the development of chemical vapour deposited (CVD) graphene and multi-walled carbon nanotubes (MWCNTs) as enabling technologies for flexible transparent conductors offering enhanced functionality. The technologies developed could be employed as thin film field emission sources, optical sensors and substrate-free wideband optical polarisers. Detailed studies were performed on CVD Fe and Ni catalysed carbon nanotubes and nanofibres on indium tin oxide, aluminium and alumina diffusion barriers. Activations energies of 0.5 and 1.5 eV were extracted supporting surface diffusion limited catalysis for CNTs and CNFs. For the first time an activation energy of 2.4 eV has been determined for Cu-catalysed growth of CVD graphene. Graphene was shown to deviate significantly from the more traditional rate-limited surface diffusion and suggests carbon-atom-latticeintegration limited catalysis. An aligned dry-transferred MWCNT thin film fabrication technique was developed using MWCNTs of varied lengths to control the optical transparency and conductivity. A process based on the hot-press lamination of bilayer CVD graphene (HPLG) was also developed. Transport studies revealed that these thin films behave, in a macroscopic sense...

Shah, Syed I.; TiO2 is widely used in applications like photocatalysis, sensors, solar cells, and memory devices because it is inexpensive, abundant, nontoxic and stable in aqueous solution. Another exciting application where TiO 2 has the potential to be a very useful catalyst is the clean hydrogen generation using solar radiation. Energy consumption is increasing every year and, as a result, renewable and sustainable alternative energy sources are becoming increasingly important. Therefore, clean hydrogen generation research is becoming more and more important. This study aims at the preparation and characterization of nitrogen and carbon (N-C) codoped TiO 2 photoanode material that could potentially be used in photoelectrochemical cells for hydrogen generation. The solar spectrum peaks around 500 nm (2.48 eV) which is in the visible part of the spectrum. The photoanode material to be used for solar hydrogen generation should absorb visible light photons to yield high efficiency. The challenge with TiO2 is that the wide band gap (3.00-3.20 eV) absorbs only ultra-violet (UV) photons and only a small percentage of the solar spectrum is in the UV range. There are various ways to overcome the challenge of sensitizing the material to visible light absorption and this study focuses on one of the most promising ways: band modification of TiO 2 by N-C codoping. The role of pure oxygen pressure on pulsed laser deposited N-C codoped TiO2 films were investigated. At low pressures rutile phase of TiO2 was dominant and a microstructure with densely packed grains was obtained. However...

In this work, we present the gas-sensing properties of chemically sprayed undoped (ZnO), copper-doped (Cu-ZnO), and chromium-doped ZnO thin films (Cr-ZnO), in an atmosphere of carbon monoxide, CO. Films were deposited at 400°C, using zinc acetylacetonate as zinc precursor. Three different atomic concentration ratios of the dopant were tested. A maximum sensitivity of the order of four orders of magnitude was obtained at measurement temperatures of 200 and 300°C in an atmosphere containing 100 ppm of CO. It was found that chromium doping favors a higher sensitivity at lower measurement temperatures (200°C), whereas the best sensitivity appears in copper-doped ZnO films at higher measurement temperatures (300° C). The thinnest films exhibited higher sensitivities.