One-dimensional analytical model for oxide thin film growth on Ti metal layers during laser heating in air

This paper presents the theoretical and experimental results for oxide thin film growth on titanium films previously deposited over glass substrate. Ti films of thickness 0.1 μm were heated by Nd:YAG laser pulses in air. The oxide tracks were created by moving the samples with a constant speed of 2 mm/s, under the laser action. The micro-topographic analysis of the tracks was performed by a microprofiler. The results taken along a straight line perpendicular to the track axis revealed a Gaussian profile that closely matches the laser's spatial mode profile, indicating the effectiveness of the surface temperature gradient on the film's growth process. The sample's micro-Raman spectra showed two strong bands at 447 and 612 cm -1 associated with the TiO 2 structure. This is a strong indication that thermo-oxidation reactions took place at the Ti film surface that reached an estimated temperature of 1160 K just due to the action of the first pulse. The results obtained from the numerical integration of the analytical equation which describes the oxidation rate (Wagner equation) are in agreement with the experimental data for film thickness in the high laser intensity region. This shows the partial accuracy of the one-dimensional model adopted for describing the film growth rate. © 2001 Elsevier Science B.V.

Protective film growth on tin in perchlorate and citric acid electrolytes

Voltammetry has been employed to study the influence of systematic additions of citric acid on the E-I curves of Tin in 0.5 M NaClO4, in order to verify the film growth in the presence of the organic acid and the inhibition of the pitting corrosion of the metal. The minimum concentration of the organic acid needed to change the GI curves is 10(-2) M, in the pH range 1.0-4.0. At pH 3.0 and 4.0, the scan rate dependence on current density, in the potential region of formation and reduction of the film, showed that in a first stage adsorption occurs. In a second stage, the v(1/2) dependence found can he explained by ohmic resistance control. The formation of tin/citric acid complexes, 10(-2) M, is suggested. The pitting inhibition may be due to the formation of a mixed layer of tin in citric acid concentrations higher than 10(-2) oxide and tin citrate complexes on the electrode surface. (C) 2001 Elsevier Science B.V. All rights reserved.

Growth evolution of ZnO thin films deposited by RF magnetron sputtering

We study the surface morphology evolution of ZnO thin films grown on glass substrates as a function of thickness by RF magnetron sputtering technique. The surface topography of the samples is measured by atomic force microscopy (AFM). All AFM images of the films are analyzed using scaling concepts. The results show that the surface morphology is initially formed by a small grains structure. The grains increase in size and height with growth time resulting in the formation of a mounds-like structure. The growth exponent, beta, and the exponent defining the evolution of the characteristic wavelength of the surface, p, amounted to beta = 0.76 +/- 0.08 and p = 0.3 +/- 0.05. From these exponents, the surface morphology is determined by the nonlocal shadowing effects, that is the dominant mechanism, due to the incident deposition particles during film growth.

Study of the growth process of in situ polyaniline deposited films

Polyaniline (PAni) thin films were deposited onto BK7 glass substrates using the in situ deposition technique. The control of the time and the aniline concentration in the PAni polymerization reaction on the film deposition allowed us to prepare films with different thickness, down to similar to 25 nm. The film growth process was monitored by measuring the UV-vis spectra and the AFM height profiles of the film surface. The curves of adsorption kinetics were analyzed with the Avrami's model, yielding an exponent it n = 3, thus indicating nucleation of spheroids at the initial stages of polymerization that grow through a diffusion process. AFM images of the surface height profiles corroborate this hypothesis, with spheroids growing with no preferred orientation during the in situ deposition. (C) 2007 Elsevier B.V. All rights reserved.

An improved three-dimensional model for growth of oxide films induced by laser heating

In this paper we consider a three-dimensional heat diffusion model to explain the growth of oxide films which takes place when a laser beam is shined on and heats a metallic layer deposited on a glass substrate in a normal atmospheric environment. In particular, we apply this model to the experimental results obtained for the dependence of the oxide layer thickness on the laser density power for growth of TiO2 films grown on Ti-covered glass slides. We show that there is a very good agreement between the experimental results and the theoretical predictions from our proposed three-dimensional model, improving the results obtained with the one-dimensional heat diffusion model previously reported. Our theoretical results also show the occurrence of surface cooling between consecutive laser pulses, and that the oxide track surface profile closely follows the spatial laser profile indicating that heat diffusive effects can be neglected in the growth of oxide films by laser heating. © 2001 Elsevier Science B.V.

Growth and morphology of eumelanin thin films - A future bioelectronic material?

We present a study on the thin film morphology and the optical properties of eumelanin resulting from different synthesis routes: the oxidation of tyrosine with hydrogen peroxide, the auto-oxidation of dihydroxyphenylanaline in water and its auto-oxidation in dimethyl sulfoxid. Atomic Force Microscopy images indicate that the presence of holes and particles depends on the eumelanin synthesis route and the substrate employed. Smooth films with very few defects could be obtained with eumelanin synthesized in dimethyl sulfoxide deposited on glass substrates. Our study shows that all eumelanin preparations are comparable in terms of thin film morphology on the submicrometer scale and UV-visible transmission properties. ©The Electrochemical Society.

Understanding growth mechanisms and tribocorrosion behaviour of porous TiO2 anodic films containing calcium, phosphorous and magnesium

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Monoamine oxidase B layer-by-layer film fabrication and characterization toward dopamine detection

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Physical Vapor Deposited Thin Films of Lignins Extracted from Sugar Cane Bagasse: Morphology, Electrical Properties, and Sensing Applications

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nanostructured hybrid films containing nanophosphor: Fabrication and electronic spectral properties

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Optical and electrical diagnostics measurements of plasmas generated in aromatic compounds

Plasmas generated in de discharges in aromatic compounds have been used for several years in polymerization processes. The chemical kinetics developed in such a plasma environment are extremely complicated. Therefore it is extremely important to set up optical and electrical diagnostics in order to establish the kinetics of the film growth, In this work we studied de plasmas generated ill low-pressure atmospheres of benzene for different values of gas pressure and power coupled to the discharge. The pressure range varied from 0.2 to 1.0 mbar for electric power running from 4 to 25 W, the main chemical species observed within the discharge were CH, H and C. It was observed that the CH relative concentration increases continuously with the power in the range investigated. The electron temperature varied from 0.5 to 2.0 eV with the increase of the power, for a fixed value of gas pressure. The relative dielectric constant of the plasma polymerized benzene was kept around 4.8 from 100 Hz to 10 kHz, presenting a resonance near 25 kHz. This electric behaviour of the film was the same fur different conditions of polymeric film deposition, (C) 1997 Elsevier B.V. S.A.

Influence of solution treatment on the adsorption and morphology of poly(o-methoxyaniline) layer-by-layer films

It is shown that the adsorption and morphological properties of layer-by-layer films of poly(o-methoxyaniline) (POMA) alternated with poly(vinyl sulfonic acid) (PVS) are affected dramatically by different treatments of the POMA solutions employed to prepare the films. Whereas the dimension of the globular structures seen by atomic force microscopy increases non monotonically during film growth in parent POMA solution, owing to a competition of adsorption/desorption processes, it changes monotonically for the fractionated POMA. The roughness of the latter films depends on the concentration of the solution and saturates at a given size of the scan window. This allowed us to apply scaling laws that indicated a self-affine mechanism for adsorption of the treated POMA.

Structural and surface morphology characterizations of oriented LiNbO3 thin films grown by polymeric precursor method

Polymeric precursor solution was used to deposit LiNbO3 thin films by dip coating on sapphire substrates. The effects of processing variables, such as heat treatment conditions and number of deposited layers, on crystallinity and morphology of the final films were investigated. X-ray diffraction patterns show the oriented growth of the films. The rocking curves, obtained around the (006) LiNbO3 peak, revealed that the shape peak and the FWHM value were influenced by the processing variables. According to these parameters, some films presented very homogeneous dense and smooth surfaces, as shown by the SEM and AFM studies.

Crystallization of amorphous GaAs films prepared onto different substrates

This work reports changes in structural properties produced by thermal annealing of flash evaporated amorphous GaAs films using the micro-Raman scattering and the X-ray diffraction (XRD) techniques. Films of about 1 μm were grown on c-Si and glass substrates. The crystallization process is less effective for samples deposited on c-Si. This could be due to the ordering in the first layers of the film imposed by the oriented Si substrates. We propose that this ordering makes the growth of crystallites in these films more restrained than the growth occurring in the completely amorphous films on glass substrates. © 2002 Elsevier Science B.V. All rights reserved.

Application of non-isothermal cure kinetics on the interaction of poly(ethylene terephthalate) - Alkyd resin paints

Samples of paint (P), reused PET (PET-R) and paint/PET-R mixtures (PPET-R) were evaluated using DSC to verify their physical-chemical properties and thermal behavior. Films from paints and PPET-R are visually similar. It was possible to establish that the maximum amount of PET-R that can be added to paint without significantly altering its filming properties is 2%. The cure process (80-203°C) was identified through DSC curves. The kinetic parameters, activation energy (E a) and Arrhenius parameters (A) for the samples containing 0.5 to 1% of PET-R, were calculated using the Flynn-Wall-Ozawa isoconversional method. It was observed that for greater amounts of PET-R added, there is a decrease in the E a values for the cure process. A Kinetic compensation effect (KCE), represented by the equation InA=-2.70+0.31E a was observed for all the samples. The most suitable kinetic model to describe this cure process is the autocatalytic Šesták-Berggreen, model applied to heterogeneous systems. © 2007 Springer Science+Business Media, LLC.