Repositório RCAAP

Titanium surface was chemically modified with sodium hydroxide, sodium silicate and calcium hydroxide with the purpose of improving metal prosthesis to bone adhesion. Results indicate that Ti modified plates immersed in Hanks solution exhibit increased calcium adsorption in comparison to untreated titanium. Calcium silicotitanate, beta-tricalcium phosphate and apatites were detected on the coating.

ZrO2-3 mol % Y2O3-coated AISI 310 stainless steel was nitrided using plasma produced by dc pulsed discharge in a mixture of N2 and H2 at an equilibrium temperature of 450ºC. Profile chemical analyses with GDOS (glow discharge optical spectroscopy) and XRD showed the formation of Nitrogen/Y-ZrO2 solid solution. Nitrogen atoms enter in the zirconia substituting to the oxygen atoms in the network. Although, the nitrogen content measured in zirconia coating is greater than the allowed maximum nitrogen content in doped-zirconia solid solution, the formation of oxynitrides could not be detected. The phase structure was investigated by X-ray diffractometry The mechanical properties were studied by means ultramicrohardness indentation tests. The nitruration improves the mechanical responses of the ZrO2-3 mol% Y2O3 -coated AISI 310 stainless steel.

The study of dental implant surfaces is relevant in order to better understand the interaction of the titanium surface and the surrounding tissues. Clinical success is achieved not only because of implant material but also because of other properties as implant design, surface treatment and quality. In this work, we report a detailed surface investigation of three major Brazilian made implants and compared them to a world-known implant. The surface composition and morphology were investigated by using X-ray photoelectron spectroscopy and scanning electron microscopy. Results of a biological test implemented in order to verify the bioactivity of the implant surface are also presented.

Strontium Bismuth Tantalate (SBT) ferroelectric thin films have attracted considerable attention for the development of non-volatile ferroelectric random access memories (NV-FRAMs). These films, however, have a critical problem: a high processing temperature ( > 700ºC) is required for the crystallization of the perovskite phase. The thermal evolution of the SBT films prepared by Chemical Solution Deposition (CSD) techniques showed the formation of an intermediate oxygen-deficient fluorite phase at ~ 550ºC. The SBT perovskite phase crystallizes at higher temperatures. To favor an earlier perovskite crystallization, SBT thin films were implanted with oxygen ions pulses produced by a Plasma Focus (1 kJ). The samples were annealed at different temperatures in oxygen atmosphere and characterized by GI-XRD and Atomic Force Microscopy techniques. It was found that oxygen addition into the SBT structure promotes a better crystallization of the perovskite phase.

A pure lattice model for Langmuir monolayers is presented where only nearest neighbor interactions are considered. The flexibility of hydrophobic tails laying on the surface is taken into account but the segments above the surface are taken as upstanding rigid rods without contribution to the entropy. The numerical calculations show that to obtain more than one phase transition the flexibility of these tails has to be taken into account.

Thin films of indium oxide 200 nm thick and indium nitride 150 nm thick were produced by reactive sputtering deposition onto soda lime substrates. The Indium cathode was kept under vacuum attached to a high voltage dc. The In xOy films were obtained in argon-oxygen mixture with total pressure between 2 and 7 Pa, current density between 0.04 and 0.56 mA/cm² and substrate temperature of 300 K. The In xNy films were obtained in argon-nitrogen mixture with total pressure between 1 and 5 Pa, current density between 0.18 and 14 mA/cm² and substrate temperature of 320 K. Results revealed that thin films give rise to high conductivity, are transparent and have a carrier density of 10(19) cm- 3 for In xOy and 10(17) cm- 3 for In xNy. These results were obtained mainly from temperature dependent alpha and sigma measurements. The reduced chemical potential was calculated considering three different scattering mechanisms i.e. interaction with optically polarized phonons, interaction with ionized impurities and interaction with grains, in order to identify the main scattering mechanism, which resulted to be due to impurities.

Porous Silicon thin films were produced in this work by the electrochemical anodizing method. The samples were fabricated anodizing p type Si substrates with different resistivities in hydrofluoric acid. Samples were prepared at different current densities. The films were characterized through reflectance and room photoluminescence (PL) measurements in the visible region. A simple theoretical model is proposed to calculate the Optical constants of the material using a theoretical simulation of the reflectance spectra. The maximum positions of PL signals are shifted to long wavelengths as the porosity increase in samples prepared with substrates of resistivities of 0.1 and 1 omega-cm, while an opposite behaviour is observed in samples prepared on more doped substrates. The optical constants obtained through the calculation are the spectral variation of the refractive index and extinction coefficient, also are obtained the sample thickness and surface roughness.

R6G dye with gold nanoparticles was prepared in water solution. Using a thermal lens experimental setup, the thermal diffusivity of R6G in presence of gold nanoparticles with Au different concentration was measured. The results show that, the thermal diffusivity of R6G dye mixed with gold nanoparticles increases with the increase of particle metallic concentration, enhancing the thermal diffusivity in the solution. The thermal diffusivity of the samples was studied for a constant concentration of R6G dye 0.1 g/L. The diffusivities were obtained by using the thermal lens aberrant model with lasers arranged in the mismatched mode. The characteristic time constant of the transient thermal lens was obtained by fitting the theoretical expression, for transient thermal lens, to the experimental data. UV-Vis spectroscopy and TEM were used to characterize the R6G dye gold nanoparticles.

We apply the complete nonlinear Time Dependent Ginzburg Landau (TDGL) equations to study the vortex dynamics in a mesoscopic type II superconductor using the numerical method based on the technique of gauge invariant variables. The solution of these equations shows how the vorticity penetrates into and goes out of the superconductor through the surface boundary. We calculate the spatial distribution of the superconducting electron density and the phase of the superconducting order parameter in a mesoscopic superconducting square sample containing two holes in the presence of a uniform perpendicular magnetic field. The dynamics of different vortex states are studied as a function of the external magnetic field.

With a view to contribute to the understanding the surface effects on optical properties process, and its hole in the electronic properties of the nanoparticles, CdS based nanoparticles are characterised by different experimental techniques and the experimental results compared to density functional theory calculations. Our results indicate that cubic CdS nanoparticles present a strong structural deformation, hexagonal reconstructed structures preserve their lattice behaviour. Both cubic and hexagonal CdS nanoparticles are S-terminated after relaxation, even when mildly Cd-rich nanoparticles are considered. A broad peak observed in our PL measurements is interpreted as an experimental evidence of the surface related peak observed around 1.8 eV in our calculated DOS for the hexagonal relaxed structure.

We investigate the effect of the hydrogen intentional incorporation on the structural properties of the amorphous gallium arsenide prepared by rf-magnetron sputtering technique. The properties of the non-hydrogenated films are: band gap of 1.4 eV (E04), Urbach energy of 110 meV, stoichiometric composition ([As]/[Ga] = 0.50), and dark conductivity of about 3.2 x 10-5 (omega.cm)-1. Hydrogen was incorporated in the films by the introduction of an electronically controlled H2 flux during deposition, keeping constant the other deposition parameters. It was observed that small hydrogen incorporation produces a great change in the structural properties of the films. The main changes result from the formation of GaAs nanocrystals with mean sizes of about 7 nm into the amorphous network.

The effects of crossed electric and magnetic fields on the electronic and exciton properties in semiconductor heterostructures have been investigated within the effective-mass and parabolic band approximations for both bulk GaAs and GaAs-Ga1-xAl xAs quantum wells. The combined effects on the heterostructure properties of the applied crossed electric/magnetic fields together with the direct coupling between the exciton center of mass and internal exciton motions may be dealt with via a simple parameter representing the distance between the electron and hole magnetic parabolas. Calculations lead to the expected behavior for the exciton dispersion in a wide range of the crossed electric/magnetic fields, and present theoretical results are found in good agreement with available experimental measurements.

Highly transparent and conductive thin films of SnO2:F and In2O3:Sn (ITO) have been prepared on glass substrates using the simple pyrolitic (spray) method. Through an exhaustive parameter study and using as diagnostic method for the film quality a figure of merit defined as a function of both, the transmittance and the electric resistivity, the conditions to prepare the SnO2:F and ITO films, with adequate properties to be used as transparent front contact for solar cells, were achieved. A relevant contribution of this work is related with the deposition of SnO2:F and ITO films with the mentioned characteristics, using a solution synthesized in our laboratory by dissolving the precursor metals in HCl. Transparent conducting oxide (TCO) thin films were obtained, with transmittances greater than 80% and resistivities smaller than 7x10- 4 omega·cm, results which are comparable with those obtained using commercial reactants. Results concerning the influence of the synthesis parameters on the optical, electrical and structural properties of the TCO films are reported.

Polycrystalline SnS thin films were grown on glass substrates using a novel procedure involving a chemical reaction between the precursor species evaporated simultaneously. This is a relatively new material, which exhibits excellent properties to be used as absorbent layer in solar cells. X-ray diffraction (XRD) measurements indicate that the synthesized samples grow in several phases (SnS, SnS2 and Sn2S3) depending upon the deposition conditions. However, through an exhaustive parameter study, conditions were found to grow thin films predominantly in the SnS phase with orthorhombic structure. It was found that this type of compound presents p-type conductivity, a high absorption coefficient (greater than 10(4) cm-1) and an energy band gap Eg of about 1.3 eV, indicating that this compound has good properties to perform as absorbent layer in thin film solar cells.

This work presents results related with phase identification and study of the homogeneity in the chemical composition of Cu(In,Ga)Se2 (CIGS) thin films grown by a chemical reaction of the precursor species evaporated sequentially on a soda-lime glass substrate, in a two or three-stage process. For that, the CIGS samples were characterized through X-ray diffraction (XRD) and Auger Electron Spectroscopy (AES) depth profile measurements, respectively. The presence of secondary phases growing superficially was identified through small angle XRD measurements. Theoretical simulation of the XRD spectra, carried out with the help of the PowderCell package, confirmed this result. The results showed that the deposition conditions affect the homogeneity of the chemical composition of the CIGS films, as well as the phase in which these films grow. In general, the samples grown in a two stage process present a mixture of the Cu(In,Ga)Se2 phase with the secondary In2Se3 and Cu2Se phases, whereas, the films grown in a three stage process do it, mainly, in the Cu(In,Ga)Se2 phase with a tetragonal (chalcopyrite type) structure and better homogeneity. CIGS films with characteristics like those found for the three stage samples, have demonstrated good properties for its use as absorber layers in thin film solar cells.

Cadmium sulphide (CdS) thin films deposited on indium tin oxide (ITO) substrates were prepared by the chemical bath deposition technique at different values of pH and pNH3. This was made in order to analyze the influence of the initial chemical composition of the bath on some physical properties of the final CdS films, used as optical windows for solar cells. The mechanism proposed in the literature for this deposition involves the tetra-ammonium cadmium (II) complex, Cd(NH$_{3})_{4}^{2+}$, at the start of the reaction. Following this mechanism, the change in the concentration of Cd(NH$_{3})_{4}^{2+}$ gives a variation in the rate of deposition with the corresponding modification in the quality of the film. Therefore, the predominance zone diagram of Cd2 + species in solution as a function of the values of pH and pNH3 was used to analyze the reasons why the CdS/ITO thin films are favored in just a narrow range of ammonium and hydroxide concentrations. To obtain useful films, the results showed that low ammonium concentrations must be avoided at high pH values as well as high ammonium concentrations at lower pH values.

Cadmium sulphide (CdS) thin films deposited on indium tin oxide (ITO) substrates were prepared by chemical bath deposition technique by using different conditions to agitate the bath and the substrate. For substrate, an oscillating device working at 37 Hz was adapted to support each ITO substrate in order to agitate the substrate during deposition, meanwhile the chemical solution is heated and/not agitated. The deposited films were characterized on their morphology, on the band gap energy, and on thickness. The implemented novel technique for substrate oscillation has shown to improve the films quality, by the chemical bath without colloidal precipitates and by the clean film surfaces obtained. CdS films with variable deposition time can be achieved depending on the agitating technique. The mean band gap energy obtained around 2.41 eV is similar to the typical value reported in the literature for this material. In addition, by oscillating only the substrate during deposition is possible to obtain clean films and avoid the formation of colloidal precipitates on the chemical bath, normally presented when it is magnetically or ultrasonically agitated.

A novel synthesis method was employed to obtain a new family of lead-free compounds with the general formula: Ba1-yLn2y / 3Ti0.91Zr0.09O3 (Ln= lanthanide element). The thin films were deposited by RF-magnetron sputtering under high-oxygen pressure on different substrates at 873 K. The crystalline phases were studied via x-ray diffraction, showing the 001 epitaxial reflections corresponding to perovskite single-phase compounds. The films revealed high homogeneity and stoichiometries corresponding to BLnZT (Ln=Nd, La). Deposited thin films showed a smooth surface. Ferroelectric measurements through hysteresis curves were obtained in Ba0.90La0.0670.033Ti0.91Zr0.09O3, capacitor structures showing clear ferroelectric behavior with Pr, Ps and Ec of 11.9 µC/cm², 36.8 µC/cm² and 38.6 kV/cm, respectively.

A dynamic scaling and kinetic roughening study was done on digitized atomic force microscope (AFM) images of Pb(Zr0.52,Ti0.48)O3 (PZT) thin films. The films were grown on Si(001) and Nb - SrTiO3(001) (STNO) substrates via rf-sputtering technique at high oxygen pressures at substrate temperatures of 600 ºC by varying the deposition time and keeping other growth parameters fixed. By using a specific self-designed algorithm, we can extract from digitized 512-pixel resolution AFM-images, quantitative values of roughness parameters, i.e., interface width (sigma(l)), lateral correlation length (xi||) and, roughness exponent (alpha). Herein, we report on the sputter-time deposition dependence of the parameters describing roughness for both kinds of substrates. We report alpha-values for different time depositions (between 15 and 60 minutes) close to 0.55 for Si substrates and 0.63 for Nb - SrTiO3 substrates, indicating that the surface becomes more correlated in STNO substrates. The alpha-values are associated to the Lai-Das-Sarma-Villain model.

We studied growth mechanisms in semiconducting Ga1 - xIn xAs ySb1 - y films grown by liquid phase epitaxy on (100) GaSb:Te (10(17) cm- 3) substrates at 600 ºC solution-substrate temperature. Atomic Force Microscopy (AFM) images of these films show step-like corrugations, undulations, grooves, and terraces. The terraces are a few nm in height and hundreds of nanometers in length. Epitaxial Ga1 - xIn xAs ySb1 - y films grow lattice-matched to the (100) GaSb substrates. These narrow-gap quaternary Ga1 - xIn xAs ySb1 - y compounds are suitable materials for heterostructure devices operating in the infrared wavelength range. The estimated x and y values are in the GaSb-rich zone. The step-like corrugations (bunching steps) are formed by different mechanisms, such as pinning effect probably due to impurities on the substrate surface.