Taking Advantage of Electrostatic Interactions To Grow Langmuir-Blodgett Films Containing Multilayers of the Phospholipid Dipalmitoylphosphatidylglycerol

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

Optical recording in Se(Te)/As2S3 multilayers

The development of Te containing nanoscaled, compositionally modulated Te/As2S3 multilayer structures enables the realisation of optical recording in real time with a CW He-Ne laser illumination (lambda=633 nm) with improved recording parameters in comparison with known Se/As2S3 structures. It is established that the efficiency of the recording process depends on the light stimulated interdiffusion and thickness of sub-layers.

Reduced graphene oxide multilayers for gas and liquid phases chemical sensing

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effects of surface treatments on the fatigue strength of AISI 4340 aeronautical steel

Internal residual stresses significantly influence the fatigue strength of coated materials. It is well known that chromium plating is the most used electrodeposited coating for important industrial applications. However, pressure to identify alternatives or to improve the chromium electroplating process have increased in recent years, related to the reduction in fatigue strength of the base material and to environmental requirements. The high efficiency and fluoride free hard chromium electroplating there called accelerated) is an improvement to the conventional process. One environmentally safer and cleaner alternative to hard chromium plating is tungsten carbide thermal spray coating applied by the High Velocity Oxy-Fuel (HVOF) process. To increase the fatigue strength of chromium plated materials, coating thickness and microcracks density are important parameters to be controlled. Techniques as compressive residual stresses induced by shot peening and multilayers, are also used. The aim of this study was to analyse the effects on AISI 4340 steel, in the rotating bending fatigue behaviour, of the: tungsten carbide thermal spray coating applied by HP/HVOF process; chemical nickel underplate, and shot peening process applied before coating deposition, in comparison to hard chromium electroplatings. Rotating bending fatigue test results indicate better performance for the conventional hard chromium plating in relation to the accelerated hard chromium electroplating. Tungsten carbide thermal spray coating and accelerated hard chromium plate over nickel resulted in higher fatigue strength when compared to samples conventional or accelerated hard chromium plated. Shot peening showed to be an excellent alternative to increase fatigue strength of AISI 4340 steel hard chromium electroplated. (C) 2001 Elsevier B.V. Ltd. All rights reserved.

First order reversal curve analysis of nanocrystalline Pd80Co20 alloy films

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

Comparison of methods for the detection of biofilm formation by Staphylococcus aureus isolated from bovine subclinical mastitis

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

Dynamic scale theory for characterizing surface morphology of layer-by-layer films of poly(o-methoxyaniline)

The dynamic scale theory and fractal concepts are employed in the characterization of surface morphological properties of layer-by-layer (LBL) films from poly(o-methoxyaniline) (POMA) alternated with poly(vinyl sulfonic acid) (PVS). The fractal dimensions are found to depend on the procedures to fabricate the POMA/PVS multilayers, particularly with regard to the drying procedures. LBL films obtained via drying in ambient air show a more homogeneous surface, compared to films dried under vacuum or a flow of nitrogen, due to a uniform rearrangement of polymer molecules during solvent evaporation.

Nanoscale manipulation of CdSe quantum dots in layer-by-layer films: influence of the host polyelectrolyte on the luminescent properties

Thioglycolic acid-capped Use quantum dots (QDs) were assembled on glass substrates with two distinct polyelectrolytes, viz poly(allylamine hydrochloride) (PAH) and poly(amidoamine) (PAMAM), generation 4 dendrimer, via the layer-by-layer (LbL) technique. Films containing up to 30 polyelectrolyte/QD bilayers were prepared. The growth of the multilayers was monitored with UV-vis spectroscopy, which showed an almost linear increase in the absorbance of the 2.8 nm QDs at 535 nm with the number of deposited bilayers. AFM measurements estimated a film thickness of 3 nm per bilayer for the PAH/Cdse films. The adsorption process and the optical properties of the PAMAM/CdSe LbL films were further analyzed layer-by-layer using surface plasmon resonance (SPR), from which a thickness of 3.2 nm was found for a PAMAM/CdSe bilayer. Photoluminescence measurements revealed higher photooxidation of the quantum dots in PAH/CdSe than in PAMAM/CdSe films. (c) 2004 Elsevier B.V. All rights reserved.

Study of electrical, chemical and structural characteristics of superconductor thin film obtained by polymeric precursors method

Superconductor films of the BSCCO system have been grown by dip coating technique with good success. The chemical method allows us to grow high temperature superconductor thin films to get better control of stoichiometry, large areas and is cheaper than other methods. There is a great technological interest in growth oriented superconductor films due anisotropic characteristics of superconductor materials of high critical temperature, specifically the cuprates, as we know that the orientation may increase the electrical transport properties. Based on this, the polymeric precursor method has been used to obtain thin films of the BSCCO system. In this work we have applied that method together with the deposition technique known as dip coating to obtain Bi-based superconductor thin films, specifically, Bi1.6Pb0.4Sr2.0C2.0Cu3.0Ox+8, also known as 2223 phase with a critical temperature around 110 K. The films with multilayers have been grown on crystalline substrates of LaAlO3 and orientated (100) after being heat treated around 790 degrees C - 820 degrees C in lapse time of 1 hour in a controlled atmosphere. XRD measurements have shown the presence of a crystalline phase 2212 with a critical temperature around 85 K with (001) orientation, as well as a small fraction of 2223 phase. SEM has shown a low uniformity and some cracks that maybe related to the applied heat treatment. WDS has also been used to study the films composition. Different heat treatments have been used with the aim to increase the percentage of 2223 phase. Measurements of resistivity confirmed the presence of at least two crystalline phases, 2212 and 2223, with T-c around 85 K and 110 K, respectively.

Photo-induced transformations in chalcogenide composite layers

Investigations of photo-induced structural transformations (PST) and related changes of optical parameters in the light-sensitive amorphous chalcogenides were extended to composite layers, which consist of a wide band-gap material and an active material, Se60Te40 with a smaller band gap. Photo-stimulated interdiffusion and/or crystallization in layered Se0.6Tc0.4/As0.6Se0.94 and Se0.6Te0.4/SiOx were investigated with respect to their dependence on the compositional modulation of the multilayer at scale-dimensions (similar to3-10nm). It was established that PST due to the interdiffusion and crystallization can be efficiently operated by the composition of the adjacent layers of the multilayer which results in the change of the transformation rate and of the optical relief type (positive or negative). The comparison with a single Se0.6Te0.4 layer and with the known data for amorphous-Se/As2S3 multilayers supports the advantages of composite layers for amplitude-phase optical recording. (C) 2004 Published by Elsevier B.V.

Dielectric properties and microstructure of SrTiO3/BaTiO3 multilayer thin films prepared by a chemical route

Multilayer thin films with perovskite structures were produced by the polymeric precursor method. SrTiO3/BaTiO3 (STO/BTO) multilayers were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by the spin-coating technique and heated in air at 700 degreesC. The microstructure and crystalline phase of the multilayered thin films were examined by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), resolution-high transmission electron microscopy (HRTEM), atomic force microscopy (AFM) and X-ray diffraction. The SrTiO3/BaTiO3 multilayer thin films consisted of grainy structures with an approximate grain size of 60 nm. The multilayered thin films showed a very clear interface between the components. The SrTiO3/BaTiO3 multilayer thin films revealed dielectric constants of approximately 527 and loss tangents of 0.03 at 100 kHz. The dielectric constant calculated for this multilayer film system is the value of the sum of each individual component of the film, i.e. The total value of the sum of each SrTiO3 (STO) and BaTiO3 (BTO) layer. The multilayer SrTiO3/BaTiO3 obtained by the polymeric precursor method, also showed a ferroelectric behavior with a remanent polarization of 2.5 muC/cm(2) and a coercive field of 30 kV/cm. The multilayer films displayed good fatigue characteristics under bipolar stressing after application of 10(10) switching cycles. (C) 2001 Published by Elsevier B.V. B.V. All rights reserved.

The characterisation of the protective film formed by benzotriazole on the 90/10 copper-nickel alloy surface in H2SO4 media

The nature of the protective film formed by benzotriazole (BTAH) on the surface of the 90/10 CuNi alloy in deaerated 0.5 mol L-1 H2SO4 solution containing Fe(III) ions as oxidant was investigated by weight-loss, calorimetric measurements, and by surface-enhanced Raman spectroscopy (SERS). The SERS measurements show that the protective film is composed by the [Cu(I)BTA](n), polymeric complex and that the BTAH molecules are also adsorbed on the electrode surface. A modification of the BET isotherm for adsorption of gases ill solids is proposed to describe the experimental results obtained from weight-loss experiments that suggest an adsorption in multilayers. Electrochemical studies of copper and nickel in 0.5 mol L-1 H2SO4 in presence and absence of BTAH have also been made as an aid to interpret the results. The calculated adsorption free energy of the cuprous benzotriazolate on the surface of the alloy is in accordance with the value for pure copper. (C) 2007 Elsevier Ltd. All rights reserved.

Análise fenotípica e molecular da produção de biofilmes por estirpes de staphylococcus aureus isoladas de casos de mastite subclínica bovina

Biofilm formation is considered an advantage for Staphylococcus aureus mastitis isolates, facilitating bacterial persistence in the udder. It requires attachment to mammary epithelium, proliferation and accumulation of cells in multilayers and enclosing in a polymeric matrix known as exopolysaccharide. The objective of this study was to evaluate the ability of Staphylococcus aureus isolated from bovine subclinical mastitis for formation of biofilms. A total of 94 Staphylococcus aureus strains obtained from milk samples of cows suffering from subclinical mastitis in dairy herds on two properties in the state of São Paulo were evaluated. These strains were characterized by in vitro biofilm formation, and by the presence of icaA and icaD genes which are responsible for intercellular adhesion. The results revealed that 98.9% of the isolates produced biofilm in vitro by adherence in sterile 96-well "U" bottom polystyrene tissue culture plates; 95.7% of the isolates possessed the icaA and icaD genes. These bacterial isolates biofilm producers may impair eradication of chronic mastitis, rendering antibiotherapy less effective. The detection of biofilm forming ability in mastitis isolates may provide useful information for more adequate therapeutic regimen and for preventive actions in the control of those bacterial isolates in bovine herds.

The influence of crystallization route on the SrBi2Nb2O9 thin films

Polycrystalline SrBi2Nb2O9-layered ferroelectric thin films were synthesized on Pt/Ti/SiO2/Si substrate using the polymeric precursors solution. The dip-coated films were specular and crack-free and crystallized during firing at 700 °C. Single-, double-, and triple-layered films were obtained by several dips in the deposition solution, and the influence of crystallization between each dip was studied. Microstructure and morphological evaluation were followed by grazing incident x-ray diffraction (GIXRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Multilayered films obtained using the intermediate-crystallized layer route present a dense microstructure with spherical grains, with a preferential orientation in the 〈215〉 direction; films obtained using the intermediate-amorphous layer route are polycrystalline and present elongated grains around 250 nm in size.

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.