Residual stress measurement in PVD optical coatings by microtopography

Residual stress in optical plasma vapor deposited coatings must be carefully measured. The topographic inspection of the coatings’ surface at microlevel allows the assessment of its residual stress. In the present work we will report on the optical non-destructive and non-invasive microtopographic inspection of WO3 PVD thin films for residual stress evaluation. The MICROTOP.06.MFC system, an active optical triangulation sensor developed at the Universidade do Minho, was employed. It allows depth resolutions down to 2 nm and lateral resolutions down to 1 μm. The three dimensional coordinate set obtained on the inspection allow the calculation of the stress distribution over the film

Study of vanadium doped ZnO films prepared by dc reactive magnetron sputtering at different substrate temperatures

ZnO films doped with vanadium (ZnO:V) have been prepared by dc reactive magnetron sputtering technique at different substrate temperatures (RT–500 C). The effects of the substrate temperature on ZnO:V films properties have been studied. XRD measurements show that only ZnO polycrystalline structure has been obtained, no V2O5 or VO2 crystal phase can be observed. It has been found that the film prepared at low substrate temperature has a preferred orientation along the (002) direction. As the substrate temperature is increased, the (002) peak intensity decreases. When the substrate temperature reaches the 500 ºC, the film shows a random orientation. SEM measurements show a clear formation of the nano-grains in the sample surface when the substrate temperature is higher than 400 º C. The optical properties of the films have been studied by measuring the specular transmittance. The refractive index has been calculated by fitting the transmittance spectra using OJL model combined with harmonic oscillator

Effect of the deposition rate on ITO thin films properties prepared by ion beam assisted deposition (IBAD) technique

Indium tin oxide (ITO) thin films have been deposited onto glass substrates at room temperature by ion beam assisted deposition technique at different deposition rates (0.1 -- 0.3 nm/s). The effects of the deposition rate on the structural, optical and electrical properties of the deposited films have been studied. The optical constants of the deposited films were calculated by fitting the transmittance spectra using the semi-quantum model. Considering the application for the electromagnetic wave shielding which needs a high IR reflectance, the optimising deposition rate is 0.2 nm/s. The films prepared at this deposition rate shows a relative high IR reflectance (60%), a good electrical conductivity (5 x 10-3 -cm), and a reasonable transmittance in the visible region (over 80%)

Pulsed DC reactive magnetron sputtering of vanadium dioxide thermochromic thin films

Vanadium oxides are an important class of materials with a large diversity of physical and chemical properties which derive from a range of single or mixed valences and a large variety of structures. They are already being used in many technological applications such as electrical and optical switching devices, light detectors, temperature sensors, etc. There has been a great interest in a particular phase, VO2(M), due to its thermochromic behaviour near room temperature which allows the development of smart windows with active control of the solar spectrum, for energy efficiency purposes. However, stoichiometric VO2 is difficult to deposit because of a narrow stability range due to the complex vanadium–oxygen reactive system. In this work, vanadium oxide thin films were synthesised on glass substrates by reactive pulsed direct current magnetron sputtering from a vanadium metal target in an O2/Ar atmosphere. Different processing conditions have been chosen in order to evaluate their influence on the crystal phases formed, surface morphologies and thicknesses and optical performance. The films were characterised by X-ray diffractometry in order to examine the crystal structure and identify the phases present in different films. The obtained VO2(M) films were thereafter analysed in terms of surface morphology by scanning electron microscopy and the characteristic reversible semiconductor-metal transition of the VO2 films was evaluate by optical spectrophotometry in the ultraviolet-visible-near infrared.Fundação para a Ciência e a Tecnologia (FCT) SFRH/BD/40512/2007

Platinum nanoparticles as pH sensor for intelligent packaging

Pt nanoparticles were produced by reverse micelle templating using DTAB. The resulting nanoparticles showes sizes between 250nm and 500nm and formed clusters. Thioglycolic acid (TGA) was covalently attached to the nanoparticle surface as a stabilizer and as. The Pt nanoparticles were dispersed in water and the dependence of its absorvance on the pH of the solution was studied. The spectra showed surface plamon absorption band at 280nm and also red shifted bands that were attributed to clusters of nanoparticles. It was found that the fraction of cluster population depends on the pH of the aqueous solution and that the response of the Pt nanoparticles to pH variations has a memory effect (hysteresis). The possibility of using these Pt nanoparticles in smart labels for food packaging is outlined.Fundação para a Ciência e a Tecnologia (FCT)FEDERCFUMProject NANO/NTec- SQA/0033/200

The effect of concrete strength and reinforcement on toughness of reinforced concrete beams

The objective pursued with this work includes the evaluating of the strength and the total energy absorption capacity (toughness) of reinforced concrete beams using different amounts of steel-bar reinforcement. The experimental campaign deals with the evaluation of the threshold load prior collapse, ultimate load and deformation, as well as the beam total energy absorption capacity, using a three point bending test. The beam half span displacement was measured using a displacement transducer, and the applied force was monitored using a load cell. The tested samples consists on a set of ten reinforced concrete beams having three different levels of steel-bar-reinforcement percentages and four different concrete compositions (i.e., giving rise to a different values of concrete strength). It was observed that the most influential parameter in the beams energy absorption capacity is the amount of steel-bar reinforcement. The results have presented good agreement between themselves. In fact, for beams with a given concrete compressive strength, a decrease in beam’s deformation was measured for higher steel-bar-reinforcement percentages. Moreover, the results had shown that for a particular steel-bar-reinforcement percentage, the concrete compressive strength have also influence in the total energy absorption capacity of the beam

Study of indium tin oxide thin films deposited on acrylics substrates by Ion beam assisted deposition technique

Indium tin oxide (ITO) thin films have been deposited onto acrylics (PMMA) substrates by ion beam assisted deposition technique at different oxygen flows. The structural, optical and electrical properties of the deposited films have been characterized by X-ray diffraction, transmittance, FTIR, ellipometry and Hall effect measurements. The optical constants of the deposited films have been calculated by fitting the ellipsometric spectra. The effects of the oxygen flow on the properties of the deposited films have been studied. It has been found that 40 sccm oxygen flow is an optimum value for getting the films with good transmittance and low electrical resistivity

Electrochemical Performances of Li+ Intercalation and Deintercalation Processes for Electrochromism of MoO3-Doped V2o5 Films Prepared By The Sol-Gel Method

MoO3-doped V2O5 thin films electrode exhibit much enhanced electrochemical performances than the pure V2O5 counterpart. 1M nonaqueous solution of LiClO4 in propylene carbonate (PC) was the electrolyte solution about cyclic voltammetry (CV) of V2O5/MoO3/ITO glass electrodes at room temperature. With the increasing proportion of MoO3 doped in V2O5, all the redox peak currents of the five samples increased, suggesting that their electrochemical activity increased with the initial CV cycles. Disappearing of some phase transition peaks also show that the MoO3-doped V2O5 film makes cyclic stability declining. Compared with the switching speed of films, the coloring and the bleaching times of the MoO3-doped V2O5 thin films are shorter

Influence of oxygen/argon pressure ratio on the morphology, optical and electrical properties of ITO thin films deposited at room temperature

Transparent conductive oxides (TCOs) such as indium tin oxide (ITO) thin films onto glass substrates are widely used as transparent and conductive electrodes for a variety of technological applications including flat panel displays, solar cells, smart windows, touch screens, etc. ITO films on glass and polycarbonate (PC) substrates were prepared at room temperature (RT) and at different PO2 . The films were characterized in terms of the surface roughness (d), sheet resistance, the refractive index (n) and extinction coefficient (k). The free carrier density (nc) and the carrier mobility (m) of the ITO (In2O3:Sn) films were measured and studied. The nc and m values vary in different ratio of oxygen partial pressure ðPO2 Þ of ITO deposition. The observed changes in the ITO film resistivity are due to the combined effect of different parameter values for nc and m. From AFM analysis and spectra calculations, the surface roughness values of the ITO films were studied and it was observed that the d values were lower than 15 nm. The energy band gap Eg ranges from 3.26 eV to 3.66 eV as determined from the absorption spectrum. It was observed an increase on the energy band gap as the PO2 decrease in the range of 20–2% PO2 . The Lorentz oscillator classical model has also been used to fit the ellipsometric spectra in order to obtain both refractive index n and extinction coefficient k values.Fundação para a Ciência e a Tecnologia (FCT)

Development of photocatalytic ceramic materials through the deposition of TiO2 nanoparticles layers

Urbanism and communities centralization enlarges atmospheric pollution that affects both human beings as well as their constructed buildings. Different scientific and technological studies are being conducted, both in academic and construction industry, aiming the development of new construction materials with properties that can decrease visual pollution of cities, reducing also the number of cleanings required. The present research work aims the study and the production of self-cleaning ceramic surfaces in an economical and viable way without changing aesthetical aspect of material substrates used. The use of TiO2 nanoparticles (TiO2-NNPs) represents an attractive way to generate self-cleaning surfaces, therefore promoting the degradation of pollutant agents and reducing cleaning maintenance costs. In order to impart self-cleaning properties to ceramic surfaces, TiO2-NNPs based layers were deposited on different ceramic material substrates using the dip-coating method. The Photocatalytic activity (degradation of pollutants adsorbed on the surface) of the TiO2-NNPs based layers was characterized via the decomposition rate of an aqueous solution of Methylene blue (MB) under UV light irradiation. Colourless layers were successfully produced onto gray and white ceramic substrates using this sol-gel technique, without changing their aesthetical appearance. It was observed that the best photocatalytic activity was exhibited by the most porous ceramic substrate (gray); nevertheless, all the TiO2-NNPs coated ceramic surfaces showed good photocatalytic efficiency.Revigres® Compan