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This paper reports on research results from on-going studies in cold welding prevention for space applications. DLC film was tested as a protective coating on devices with texturized Ti6Al4V surfaces to prevent cold welding under conditions of high pressure in a high vacuum environment. Texturized Ti6Al4V surfaces are necessary for the mechanical engagement of movable parts in satellite devices. This kind of application requires very high adherence between the substrate and the film. In this study, the DLC depositions were performed either on smooth or on laser textured Ti6Al4V surfaces. Smooth surfaces were used to measure the friction coefficient on a nanometric scale and the textured surfaces were used to test mechanical engagement. A very thin silicon interlayer was used to improve the DLC adherence to the Ti6Al4V substrates. Both silicon and DLC films were prepared by RF magnetron sputtering with argon as the buffer gas and with an additional DC bias. Raman scattering spectroscopy was used to analyze the existence of sp 2 and sp 3 chemical bonds of DLC films and the nature of silicon structures in the silicon interlayer. The morphology and roughness were evaluated by SEM and AFM; the LFM was used to measure the friction coefficient in nanoscale and, the micro-indentation technique was used for evaluating film hardness. A new system was developed to measure the friction coefficient in microscale in order to measure the friction value between highly texturized surfaces. This paper presents an in-depth description of the testing process and the results of the cold welding prevention test of textured DLC surfaces in a high vacuum environment.

Nitrogen Plasma Immersion Ion Implantation (PIII) has been used to modify the surface chemical structure of Ultra High Molecular Weight Polyethylene (UHMWPE). Grinding and polishing processes based on abrasive papers and alumina pastes have been evaluated with regard to their results on the improvement of polymer surface roughness, which has shown to be of crucial importance for hardness characterization. Raman spectroscopy, XPS, and Nanoindentation tests were used to characterize the modified surfaces. Experimental results has shown that UHMWPE surface mechanical properties such as hardness and elastic modulus can be improved by induced chain cross-linking between the macromolecules on the polymer surface caused by nitrogen PIII. The new material formed on the surface is Diamond Like Carbon (DLC). As a significant improvement in hardness was obtained by DLC synthesis on the treated surface, it is expected a dramatic improvement of abrasion resistance and overall durability of prostheses made with PIII treated UHMWPE.

Surface modification of ultra-high molecular weight polyethylene (UHMWPE) has been explored by using the non-line-of-sight plasma immersion ion implantation (PIII) technique. The polymer specimens, immersed in nitrogen plasma, were pulsed through a metallic grid at repetition rate of 100 Hz with negative high-voltage pulse of 15 kV magnitude and 10 μs duration. The UHMWPE's structural changes induced by the PIII were analyzed by laser Raman spectroscopy (LRS) at 514.5 nm, X-ray photoelectron spectroscopy (XPS) and optical microscopy. From the Raman spectra it is observed that the chain structure of UHMWPE has been damaged due to ion bombardment and a layer of hydrogenated amorphous carbon is formed. The ratio of sp3/sp2 bonded carbon in the modified layer was obtained by suitable fitting of the XPS C 1s energy peak, using a four-curve fitting procedure, which recognizes a portion of C–O and CO surface bonding. The XPS results for N 1s peak show that the implanted nitrogen ions form chemical bonds with the polymer instead of forming precipitates by self-clustering.

Surfaces with very poor mechanical and frictional properties can be improved, or even, acquire new properties similar to diamond if good adherent CVD diamond film is obtained on it. In this work, nitrogen ions were sub-implanted on pure molybdenum as a means to enhance CVD diamond film adherence. Deposition time from 2 up to 60 h were used for deposition of 10 to 400 µm thick CVD diamond films with very good adherence on sub-implanted molybdenum substrate. Characterizations were carried out by XPS, X-ray diffraction and nano indentation on prepared surfaces prior to diamond growth and after the onset nucleation. The ionic sub-implantation with nitrogen possibly assists in adhesion, with the creation of a thin layer of nitrates and complexes.

In this work we study the influence of oxygen addition to several halocarbon-hydrogen gas systems. Diamond growth have been performed in a high power density MWCVD reactor built in our laboratory. The growth experiments are monitored by argon actinometry as a reference to plasma temperature and atomic hydrogen production, and by mass spectrometry to compare the exhaust gas composition. Atomic hydrogen actinometry revealed that the halogen presence in the gas phase is responsible for a considerable increase of atomic hydrogen concentration in the gas phase. Mass spectrometry shows similar results for all gas mixtures tested. Growth studies with oxygen addition to CF4/H2, CCl4/H2, CCl2F2/H2 and CH3Cl/H2 reveals that oxygen increases the carbon solubility in the gas phase but no better diamond growth conditions were found. Halogens are not, per se, eligible for diamond growth. All the possible advantages, as the higher production of atomic hydrogen, have been suppressed by the low carbon solubility in the gas phase, even when oxygen is added. The diamond growth with small amount of CF4 added to CH4/H2 mixture is not aggressive to the apparatus but brings several advantages to the process.

In this work, studies have been carried out on surface modification on a pure molybdenum surface to enhance CVD diamond adherence. Pure molybdenum exhibits a phase transformation temperature close to that of diamond growth, but it is possible to obtain a surface modification by ion sub-implantation at an appropriate lower temperature without phase transformation. In this study, it was possible to create an appropriate interface by using appropriate ion compounds and impact energy on the substrate surface at a very narrow window of working temperature. This interface efficiently avoided carbon diffusion during diamond growth and also improved the chemical bond density between atoms from the interface and carbon from the onset of diamond nucleation. Diamond films from a few micrometers up to millimeters have been obtained with very good adherence. Characterization by XPS and small angle X-ray diffraction of this interface prior to diamond growth and after diamond nucleation reveals different compound contributions to the chemical bonds. Indentation and SEM analyses were also carried out.

Diamond films with small grain size, good quality and high grain density were deposited on Ti6Al4V substrates using a technique assisted by surface wave-guide microwave discharge, the Surfatron system. The grain density was studied as a function of the film growth time in order to compare two different substrate preparation techniques: conventional ultrasonic bath in hexane and diamond powder only, and carbon ion sub-implantation with the same ultrasonic bath. The titanium carbide (TiC) interface formation as a function of the grain density was evaluated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Diamond quality was also analyzed by Raman scattering spectroscopy.

We investigate the residual stress in diamond films grown on (001) silicon substrates as a function of film thickness. The diamond films were deposited at 1070 K by the conventional hot filament technique using a gas mixture of methane (1.0% vol) and hydrogen (99.0% vol). The film thickness, obtained from cross section scanning electron micrographs, varied from 3.0 to 42 μm as the growth time increased from 1 to 10 h. These images evidenced that the columnar growth is already established for films thicker than 10 μm. Top view micrographs revealed predominantly faceted pyramidal grains for the films at all growth stages. The grain size, obtained from these images, was found to vary linearly with film thickness. Using a high resolution x-ray diffractometer, the residual stress was determined by measuring, for each sample, the (331) diamond Bragg diffraction peak for Ψ values ranging from −60° to +60°, and applying the sin2 ψ method. For the micro-Raman spectroscopy, we used the summation method, which consists in recording and adding a large number of spectra in different places of a selected area of the sample. All Raman spectra were fitted with Lorentzian lines to separate the contribution of the pure diamond and the other nondiamond (graphite) phases. This spectral analysis performed in each sample allowed the determination of the residual stress, from the diamond Raman peak shifts, and also the diamond purity, which increases from 70% to 90% as the thickness goes from 3 to 42 μm. The type and magnitude of the residual stress obtained from x-ray and micro-Raman measurements agreed well for films thicker than 10 μm. For films thinner than this value, an opposite behavior between both results was observed. We attributed this discrepancy to the domain size characteristic of each technique.

Stress analysis on chemical vapor deposition (CVD) diamond films has demonstrated an apparent disagreement among various researchers in recent works even for similar deposition conditions. The type and the value of stress have shown a strong dependence on film thickness, which can be attributed to columnar growth and grain size and boundaries. X-Ray diffraction techniques appeared to be more suitable to study these effects and permit the evaluation of the average stress in larger sample areas when compared with micro-Raman spectroscopy, which feels a local strain inside the grains. In the case of boron-doped diamond films, boron incorporation on substitucional or interstitial sites can produce stresses according to the doping level. In order to investigate these effects, a series of diamond films were deposited on silicon (001) substrate in a hot filament (HF)-assisted CVD reactor at 800°C. The CH 4 flow is kept at 0.5 sccm for all experiments and the H 2 and B 2 O 3 /CH 3 OH/H 2 flows are controlled in order to obtain the desired B/C ratios. Stress behavior in HFCVD boron-doped diamond films has been investigated by X-ray diffraction measurements using the sin 2 ψ technique. Tensile and compressive stresses have been observed and the thermal and intrinsic components have been calculated. The diamond films were characterized by scanning electron microscopy and Raman spectroscopy.

Generation of atomic hydrogen in H2/Ar/CCl4 microwave discharges with O2 addition has been investigated. In situ mass spectrometry and emission hydrogen-atom actinometry have been used in the microwave-plasma-assisted chemical vapor deposition (MWPACVD) reactor. Optical emission spectroscopy (OES) was used to study the intensity of Hα, Hβ and Hγ lines using argon as actinometer. The results showed different increases in the atomic hydrogen concentration for the three hydrogen lines analyzed for additions of up to 1.5% CCl4. These results confirm a previous study on the validity of the OES technique using the Hγ line intensity. An additional increase in the atomic hydrogen generation was also observed when O2 was added to the H2/CCl4 mixtures. Chemical reaction products, detected by exhaust-gas mass spectrometry, showed that CCl4 is completely dissociated in the plasma reactor with a fast conversion into hydrocarbons. The effects of O2 addition lead an increase in CO and H2O formation associated with a decrease in CH4 and C2H2 concentration. Oxygen decreases the hydrocarbon concentration for high concentrations of halogenated precursor. This behavior inhibits the formation of solid carbon observed in mixtures with chlorine and permits the production of good-quality CVD diamond films owing to the high generation of atomic hydrogen. The films grown in different concentrations of CCl4 and O2 were analyzed by scanning electron microscopy and Raman spectroscopy.

Boron-doped polycrystalline diamond films have been deposited over silicon substrate by hot-filament chemical-vapor-deposition process. A gas mixture of 0,5 vol. % methane and 1 vol. % methanol on hydrogen at a pressure of 50 Torr, have been used. Boric oxide dissolved in methanol have been used as the boron doping source during the diamond growth process. Raman spectroscopy and Scanning Electron Microscopy (SEM) have been performed on the samples. A change of Raman spectra with film doping was observed. The diamond characteristic line at 1333 cm-1 down shifted and its intensity decreased as the film resistivity decreased. On the other hand, a broad peak around 1220 cm-1 appeared and its intensity increased with decreasing film resistivity. No modifications on films morphology have been observed with different boron doping level. The grains were well-faceted with 2 mm average size

The effects of halogenated precursor associated with O 2 addition in the gas phase for diamond growth have been studied. Optical emission spectroscopy (OES) and exhaust gas mass spectrometry (MS) were used in a microwave plasma-assisted chemical vapor deposition (MWPACVD) reactor. The relative emission intensity of atomic hydrogen line H α (656.3 nm) has been measured with CF 4 and CCl 2 F 2 concentrations in the range of 0–5%. Our results show an increase of atomic hydrogen concentration up to 80 and 200% when CF 4 and CCl 2 F 2 are added in the mixture, respectively. The input gases were chosen in order to discern the oxygen effects for mixtures with different concentrations of CF 4 and CCl 2 F 2 . An additional increase of 50% H generation was observed when O 2 was added in the range of 0–3% for both mixtures with 3% of CF 4 or CCl 2 F 2 . Mass spectrometry was used to analyze the dissociation process of CF 4 and CCl 2 F 2 associated with HF and HCl formation. These dissociation processes are correlated with the increase of atomic hydrogen concentration. For oxygen addition, CO formation is the main final product from the halocarbon. The higher thermodynamic stability of CO enables us to obtain a gas phase with a high concentration of atomic hydrogen and inhibits the formation of solid non-diamond carbon observed in mixtures with high halocarbon concentrations.

Optical emission spectroscopy measurements and exhaust gas mass spectrometry were used for diagnostics in a microwave plasma assisted chemical vapor deposition reactor for diamond growth. An actinometry technique was used to study the atomic hydrogen generation with additions of CF4 and CCl2F2 in the feed gas. The relative emission intensity of the atomic hydrogen line Hα (656.3 nm) was measured with CF4 and CCl2F2 concentrations in the range of 0–5%. The results show an increase in atomic hydrogen concentration up to 80 and 200% when CF4 and CCl2F2 are added in the mixture, respectively. The -ideal actinometry conditions and the validity of the observed increase of atomic hydrogen with an change in electron temperature and density in the plasma was investigated. The dissociation process of CF4 and CCl2F2 associated with HF and HCl formation were discussed by measurements of stable species by mass spectrometry of the exhaust gas. The increase of the atomic hydrogen concentration is correlated with the easy HCl and/or HF dissociation by electron-impact.

Diamond growth on Ti6Al4V substrate has been studied using a hot filament assisted technique. The substrate surface pretreatment consisted of polishing with 1-μm diamond paste using oxalic acid followed by pitting in an ultrasonic bath with a 0.25-μm diamond powder suspension in n-hexane for 20 min. The main parameters of the diamond growth with CH4/H2 gas mixture and the mechanical properties of the substrate have been studied as a dependence of substrate temperature. The film was completely formed after 20 min at a 800°C substrate temperature. The adherence between film and substrate has been shown to be strongly dependent on substrate temperature and growth time. Adherent and good quality CVD diamond films, as thick as 10 μm, have been obtained at a 600°C growth temperature. Stress dependence on growth parameters has been studied by Raman spectroscopy.

In this paper we present the measurement of the activation energy for diamond chemical vapor deposition from carbon tetrachloride mixtures in a hot-filament assisted reactor. Mixtures of 1 vol% CCl4 in H2 have been used in most experiments. Growth rates have been measured in the temperature range from 220 to 820°C to obtain the activation energy. Raman spectroscopy and scanning electron microscopy show that crystalline diamond was obtained only for substrate temperatures over 420°C. We also present an extensive comparison with most activation energy determinations in the literature and propose that there is a common trend in most observations.

Optical emission spectroscopy (OES) and exhaust gas mass spectrometry were used to study the gas phase during diamond growth in microwave plasma-assisted chemical vapor deposition (MPACVD). Mixtures with CF 4 addition in H 2 /Ar and H 2 /Ar/CH 4 have been studied. The relative emission intensity of atomic hydrogen line H α has been measured by actinometry. This work presents a systematic study that has been performed with regard to the dependence of the relative intensity of the H α line (656.3 nm) with CF 4 addition. CF 4 concentrations in the range of 0–5% have been studied. We also investigated the influence of oxygen addition on the relative intensity of the H α line for fixed mixtures with H 2 /Ar/CH 4 and H 2 /Ar/CF 4 . Our results have shown that CF 4 and O 2 addition increases considerably the atomic hydrogen concentration. These results suggest that the CF 4 and O 2 addition can promote diamond growth using systems with lower activation power.

Tetrafluoromethane (CF4) was added to standard CH4/H2 mixtures for diamond growth in hot-filament-assisted chemical vapour deposition. CF4 concentrations in the range of 0.3%–3% were studied. Mass spectrometry of the exhaust gas showed that only a small fraction (< 15%) of CF4 was thermally dissociated for filament temperatures over 1800 °C. The observed stable products of its dissociation were mainly C2H2, CH4 and HF. This CF4 addition considerably enhanced the nucleation and growth characteristics on silicon and molybdenum. Diamond growth was observed with substrate temperature as low as 390 °C. A comparative study for the growth dependence on substrate temperature with and without CF4 addition in the gas mixture is presented. The growth rate was measured by post-growth weighing with a micro balance. An activation energy of 11 kcal mol-1 for growth with CF4 addition was obtained. Raman spectra and atomic force microscopy were used to characterize the diamond films.

We investigated diamond seeding as an efficient method of enhancing the nucleation density in chemical vapor deposition (CVD) diamond growth. We prepared substrates by ultrasonification for a short time in a 0.25 m diamond powder suspension and studied the effects of several dispersion liquids on seeding. We identified five key liquid properties for efficient seeding: zero or low dipole moment, low density, high vapor pressure, low surface tension and low viscosity. n-Hexane and n-pentane are the most suitable liquids, and yield seeding at the limit of the powder grit. We also observed the phenomenon of chemical consolidation of diamond particles onto silicon substrates during the initial growth stages. This consolidation ensures film adherence comparable with that obtained by other methods of nucleation enhancement.

Some studies about application devices that have been developed in our laboratory are presented. Some characterizations show the quality of free-standing CVD diamond film. An improvement of CVD diamond burrs will be presented, including laser cutting of diamond film, processes for soldering the film to the stainless steel tips, and statistical performance of the burrs. Basic studies were carried out in order to improve the film quality. These results gave us support for the scaling-up of a hot-filament system for the manufacturing of CVD diamond burrs.

Universidade Estadual Paulista UNESP Campus de Guaratingueta, C. P. 205, CEP-12500-000, Guaratingueta, SP

We present the scale-up of a hot filament system for manufacturing CVD diamond burr. In our system, the diamond film growth rate reached around 15 μm h −1 on 1 mm diameter molybdenum rods. The burrs were made of 250 μm thick free-standing diamond film. We optimized the gas consumption, power supply, gas flow rate and the number of hot filament reactors for the industrialization of dentist burr. We also discuss the production capabilities of each reactor. Scale-up and price prospective together with exhaustive testing show that CVD diamond burr may have a favorable cost-effectiveness.

Columnar grain structure is always observed in CVD-diamond growth and is an important parameter to identify the morphology of thin and thick films. Structure defects, aspects of onset nucleation and film growth mechanisms can also be related to columnar growth. In this work we focused our attention on the columnar structure of CVD-diamond grown on irregular surfaces. We observed that there is a relationship among curvature radius of the substrate surface, the spread of the column volume and the growth rate of the diamond film. Growth rates on spherical surfaces of around 0.5 mm curvature radius have been observed to be up to three times bigger than the growth rates on planar surfaces. Also, the grain size distribution on planar and on the corner surfaces as a function of the growth rate has been studied. Characterization with scanning electron microscopy (SEM) and Raman scattering spectroscopy (RSS) has been performed.

We report here the improvement of the adhesion of CVD diamond films on WC-Co (6%) tools and the enhancement in the cutting tool life-time by the introduction of CF4 in the CH 4 H 2 gas mixture. By the use of this halogen precursor it was possible to reduce the substrate temperature during the deposition without degradation in the diamond film quality. The low-temperature deposition improves the smoothness of the coating and minimizes the thermal stress induced by the CVD process.

The photoacoustic technique is used to investigate the thermal diffusivity of ${\mathrm{Ge}}_{\mathit{x}}$${\mathrm{Te}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ glasses as a function of composition. The observed dependence on the composition is explained on the basis of the chemically ordered network model. This interpretation is further supported by x-ray and electrical resistivity measurements.

The usefulness of the open photoacoustic cell technique for investigating the effects of air inclusions on the thermal properties of foamed polyurethane is demonstrated. It is shown that the thermal diffusivity and thermal expansion coefficients increase with decreasing values of the resin to catalyst ratio, which corresponds to greater air inclusion in the resin.

The influence of poling fields on the electrical and thermal properties of polyvinylidene fluoride (PVDF) pyroelectric detectors is discussed. It is shown that both the dielectric constant and the thermal diffusivity exhibit a monotonically increasing behavior with the poling field. The detectors were fabricated by solution casting of the PVDF films followed by thermal poling. It is concluded that the predominant crystal phase present in our films is the γ-form. Except for the dielectric breakdown field, all the electrical and thermal properties of these films were found to be in good agreement with the commercially available ones. The thermal diffusivity was measured using the so-called open photoacoustic cell method.

The stress evolution in diamond films grown on Ti6Al4V was investigated in order to develop a comprehensive view of the residual stress formation. Residual stress is composed of intrinsic stress induced during diamond film growth and extrinsic stress caused by the different thermal expansion coefficients between the film and substrate. In the coalescence stage it has been observed that the residual stress is dominated by the microstructure, whereas on continuous films, the thermal stress is more important. In this work diamond thin films with small grain size and good size and good quality were obtained in a surface wave-guide microwave discharge, the Surfatron system, with a negative bias voltage applied between the plasma shell and substrate. For above of -100V applied bias, the ratio of carbon sp³/sp² bond may increase and the nucleation rate increase arising the high value at the -250V applied bias. Stress measurements and sp³ content in the film were studied by Raman scattering spectroscopy. The total residual stress is compressive and varied from -1.52 to -1.48 GPa between 0 and -200 V applied bias, respectively, and above the -200 V, the compressive residual stress increased drastically to -1.80 GPa. The diamond nucleation density was evaluated by top view SEM images.

Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-27T11:18:05Z No. of bitstreams: 0Bitstream added on 2014-05-27T14:28:22Z : No. of bitstreams: 1 2-s2.0-0000950115.pdf: 514956 bytes, checksum: 6c9c0de1741231e5c99740d865b2cd63 (MD5) Made available in DSpace on 2014-05-27T11:18:05Z (GMT). No. of bitstreams: 0 Previous issue date: 1996-05-01 The fabrication of boring tools (burrs) for dentistry with the use of a hot-filament chemical vapor deposition (CVD) system, to form the diamond abrading structure, is reported here. The diamond was synthesized from a methane/freon gas mixture diluted in hydrogen. Comparative drilling tests with conventional diamond burrs and the CVD diamond burrs in borosilicate glasses demonstrated a lifetime more than 20 times larger for the CVD diamond burrs. Also, heat flow experiments in dentine showed that the CVD diamond burrs induce temperature gradients of the same order as the conventional ones. These characteristics of the CVD diamond burrs are highly desirable for odontological applications where the burrs' lifetime and the low temperature processing are essential to the quality and comfort of the treatment. © 1996 American Institute of Physics. Inst. Nac. de Pesquisas Espaciais, 12201-970 Sao Jose dos Campos, SP Universidade Estadual Paulista, 12245-001 Sao Jose dos Campos, SP Universidade Estadual de Campinas, 13081-970 Campinas, SP Universidade Estadual Paulista, Presidente Prudente, SP Universidade Estadual Paulista, 12245-001 Sao Jose dos Campos, SP Universidade Estadual Paulista, Presidente Prudente, SP

In this work we show that the addition of a small amount of CF4 to a regular CH4 -H2 gas mixture allows diamond growth at lower temperatures with reasonable growth rates. We used a hot filament assisted reactor and observed diamond growth with a substrate temperature as low as 390 ଌ. We present a comparative study for the growth dependence on substrate temperature with and without CF4 addition in the gas mixture. The growth rate is measured by post growth weighting with a micro balance. Raman spectroscopy, SEM and AFM images show the good quality of the films grown at low temperatures when CF4 is added to the feeding gas.

Using two different photoacoustic techniques for a two-layer system of variable thickness, we show that the thermal diffusivity and the thermal conductivity are completely determined, based upon the effective-sample model widely used in heat-transfer problems. A procedure to establish a standard photothermal technique for measuring both the thermal diffusivity and the thermal conductivity is also discussed.

The photoacoustic signal of two semiconductor samples is investigated as a function of the modulation frequency in a heat-transmission configuration. It is shown that, in the frequency range where the sample is thermally thick, the signal amplitude and phase can single out the different fast and slow nonradiative recombination heat sources responsible for the photoacoustic signal. The characterization of the thermal and the carrier transport properties is discussed and some practical procedures for this purpose are also outlined.

The photoacoustic signal of a narrow-gap semiconductor and of Si is investigated as a function of the modulation frequency through the use of a heat-transmission configuration. It is shown that in the thermally thick modulation-frequency range the signal amplitude can single out the different heating sources responsible for the photoacoustic signal. It is also shown that from the signal phase data, as a function of the modulation frequency, we can obtain the values of the surface recombination velocity and the nonradiative band-to-band recombination time.

The Ar+ laser‐stimulated desorption of iodine molecules from an impregnated polystyrene film was investigated. The photoprocess induces a color change (from red to the transparent) and leaves in the film a marked print, which is related to the laser beam characteristics. The experimental data was fitted using a set of differential equations relating the time dependence of the film temperature and absorption coefficient. At low‐power levels (

The kinetics of iodine doping of atactic polystyrene films is investigated using photoacoustic spectroscopy. The changes in the photoacoustically measured physical properties, such as nonradiative relaxation time and thermal diffusivity, are present as a function of the doping time. The results show strong evidence that an order‐disorder transition is taking place as a function of the doping time. The suggested order‐disorder transition is also evident in the dielectric constant measurements of the doped films.

Polyethylene (PE) and polypropylene (PP) surfaces can be modified by impregnation with manganese dioxide, either pure or mixed with iron(III) and copper(II) oxides. This is done by immersion of polymer tubing or film in (acidic or alkaline) potassium permanganate aqueous solutions, at 50–80°C. The oxide deposits thus obtained are highly adherent to the polymer surface and resistant to mild (cloth, paper) abrasion. These polymer—oxide composites were studied by electron spin resonance (ESR) spectroscopy. ESR spectra of samples obtained under various conditions showed differences, depending on the preparation technique used and on the sample age. Spectral characteristics of the oxides indicate that the total amount and local concentration of Mn 2+ ions in the oxides can vary, depending on the preparation procedure.

O caráter aleatório e não homogêneo do crescimento de filmes finos, por processo de deposição, leva à formação de uma superfície rugosa que obedece, em geral, a uma geometria fractal. A dinâmica de crescimento da superfície do filme pode ser descrita por meio de modelos de crescimento discretos, simulações numéricas e equações diferenciais estocásticas. Os modelos e as equações nos fornecem os expoentes críticos, que descrevem o comportamento da rugosidade com a escala de observação e tempo de deposição. Crescemos filmes de platina e ouro através da técnica de implantação e deposição de íons por imersão em plasma metálico. Determinamos experimentalmente os expoentes críticos por meio de microscopia de tunelamento. Comparamos os nossos resultados experimentais com previsões dadas por alguns modelos teóricos. Verificamos que há um bom acordo entre eles e as previsões dadas pela equação estocástica de Kardar, Parisi e Zhang. A estrutura cristalina dos materiais também foi analisada por meio de difração de raios x. The randomness and inhomogeneities in the growth of thin films generate a rough surface obeying, in general, fractal geometry. The growth dynamics of film surface can be described by theoretical discrete models, numerical simulations and stochastic differential equations. Models and equations give the critical exponents that describe the behavior of roughness with the observation scale and deposition time. We have synthesized platinum and gold films by metal plasma immersion ion implantation and deposition. We have measured the critical exponents by Scanning Tunneling Microscopy. Our experimental results were compared with some theoretical models predictions. We verified that there is a good agreement between them and the theoretical predictions given by the Kardar, Parisi and Zhang stochastic equation. The crystallographic structure was also analyzed by X-ray diffraction.

Utilizando a Teoria do Funcional da Densidade e uma Dinâmica Molecular Quântica que envolve o formalismo de pseudopotenciais de primeiros princípios, fizemos cálculos de energia total, estrutura atômica e eletrônica, e ligação química para o cristal perfeito e a superfície do GaAs e das fases cúbicas do BN, AlN, GaN e InN para determinar o papel da aproximação do gradiente generalizado (GGA) no funcional da energia de troca e correlação. Nossos cálculos mostram que o efeito combinado da correção não linear de caroço e da aproximação GGA é responsável por mudanças significativas nos parâmetros estruturais e na estrutura eletrônica das superfícies polares (001), independentemente da ionicidade do elemento estudado, mas não é decisivo para o cristal perfeito e para a superfície não polar (110). Nossos cálculos para a superfície (110) sugerem que o ângulo de rotação da ligação entre o cátion e o ânion que compõe a superfície é muito menor para os nitretos: em torno de '15 GRAUS' comparado com '30 GRAUS'^='2 GRAUS' observado para outros semicondutores III-V. Neste trabalho propomos um modelo com uma relação linear entre o deslocamento vertical do cátion e do ânion da camada superficial e o comprimento de ligação superficial após a relaxação para todos os semicondutores III-V e II-VI. Além disso, observamos que a superfície (110) de todos os compostos III-V e II-V apresentam estruturas eletrônicas muito similares. Também procedemos estudos detalhados da estrutura atômica e eletrônica das reconstruções (1x1), (2x2), c(2x2) e (1x4) terminadas em gálio da fase cúbica do GaN crescido na direção (001). Observamos que apenas a reconstrução (1x4) apresenta caráter semicondutor e que é a mais favorável do ponto de vista energético, com um ganho de 0,29 eV por célula unitária (1x1) quando comparada a reconstrução (1x1). A incorporação do nitrogênio em estruturas cristalinas foi inicialmente testada considerando a dissociação e posterior adsorção das moléculas 'NH IND. 3' e 'NF IND. 3' sobre a reconstrução (2x1) da superfície de silício crescida na direção (001). Nossos cálculos apontam que quando da adsorção, em ambos os casos, os dímeros de Si são simétricos e seu comprimento de ligação é maior do que o observado para a superfície livre. As estruturas eletrônicas obtidas indicam que a adsorção das moléculas de amônia e de trifluoreto de nitrogênio resultam na passivação da superfície de silício.

In the present work photoacoustic spectroscopy is applied on a variety of experimental situations, aiming to determine thermal and spectroscopic, properties of materials. Measurements in different polymers were done: glue, grafted polyethylene and copolymer, europium complex doped blendes, human nail and nafion®. The first study was the analysis of residuals in paper manufacture using the absorption spectra. It demonstrated the similarity between the residue after fabrication and the used glue, not supposed to be present. Secondly, the cross-linking process m grafted vinyltrimetoxysilane on low density polyethylene and the copolymer ethylenelvinyltrimetoxysilane, prepared with factorial design, was monitored through pIIotoacoustic intensity and phase. The optimum point for temperature and concentration of catalyst, using statistical design, indicated the same range for both samples (≈ 5 % and 80 °C). In the study of Eu3+ doped polycarbonate/poly(methylmethacrylate) blends, the spectroscopy and photoluminescence suggested the preferable location of europium complex in polycarbonate phase. The doped blendes presented higher lifetimes and higher quantum efficiency values (≈50%). Normalized thermal diffusivity is higher for blend 20/80 (αmean≈5.6x10-3 cm²/s) whilst the specific heat was almost constant (Cp(mean)≈1.7 Jg-1K-1) for all the used compositions. Yet, the study "in vitro" of human nail thermal diffusivity, using "Open photoacoustic Cell" showed an increase and possible saturation with increasing human age. The average value was found to be (13.7 ±3.6) x 10-4 cm²/s. Finally, the study of thermal diffusivity of nafion® as a function of water content showed that thermal properties can be affected when clusters regions present adsorbed water. For samples "in natura" the average value found for the thermal diffusivity was α=(6.5±0.4)x10-4 cm²/s (Open Photoacoustic Cell) and α=(7.0±0.2)x10-4 cm²/s (Thermal Lens) No presente trabalho a Espectroscopia Fotoacústica é aplicada numa variedade de situações experimentais, para determinar propriedades espectroscópicas e térmicas de materiais, associando-as a produtos residuais, reticulação e efeitos da hidratação sobre elas. As medidas foram realizadas em diferentes materiais poliméricos: cola, polietileno enxertado e copolímero reticulados, blendas dopadas com complexo de európio, unha humana e nafion®. O primeiro estudo foi a análise de defeitos residuais na fabricação de papel e, através de comparação espectral, verificou-se a semelhança entre o resíduo proveniente da calandragem de papel e a cola utilizada, sendo não suposta a sua presença. Em um segundo estudo, o processo de reticulação, de polietileno de baixa densidade enxertado com viniltrimetoxisilano e copolímero etileno viniltrimetoxisilano, preparadas usando planejamento fatorial, foi monitorado indiretamente através da intensidade do sinal fotoacústico e fase fotoacústica. O ponto ótimo para os fatores temperatura e concentração de catalisador, usando modelo estatístico, indicou a mesma faixa para as duas amostras (≈ 5 % de catalisador a 80°C). No estudo das propriedades espectroscópicas e fotoluminescentes de blendas de poli(carbonato)/poli(metacrilato de metila) dopadas com Eu3+, constatou-se a localidade preferencial do complexo európio na fase do policarbonato. As blendas dopadas apresentaram alto valor para o tempo de vida e para a eficiência quântica (≈50%), comparada aos sistemas similares. A blenda 20/80 apresentou maior difusividade térmica (αmédia≈5,6x10-3 cm²/s) enquanto que o calor específico mostrou-se quase constante (Cp(médio)≈1,7 Jg-1K-1) para todas as composições usadas. Ainda, o estudo "in vitro" em unhas humanas, usando "Célula Fotoacústica Aberta" mostrou um aumento e possível saturação da difusividade térmica com o aumento da idade. O valor médio para a difusividade térmica encontrado foi de (13,7 ±3,6) x 10-4 cm²/s. Por último, no estudo da hidratação, o monitoramento da difusividade térmica de membranas nafion® mostrou que propriedades térmicas são afetadas quando regiões clusters são preenchidas com água absorvida. Para amostras "in natura" os valores encontrados para a difusividade térmica foram de α=(6,5±0,4)x10-4 cm²2/s (Célula Fotoacústica Aberta) e α//=(7,0±0,2)x10-4 cm²/s (Lente Térmica) v, 161 f