Rodrigo Martins

In this paper an exhaustive analysis is performed on the electrochemical corrosion resistance of Al-doped ZnO (AZO) layers deposited on silicon wafers by a DC pulsed magnetron sputtering deposition technique to test layer durability. Pulse frequency of the sputtering source was varied and a detailed study of the electrochemical corrosion response of samples in the presence of a corrosive chloride media (NaCl 0.06 M) was carried out. Electrochemical impedance spectroscopy measurements were performed after reaching a stable value of the open circuit at 2 h, 192 h and 480 h intervals. Correlation of the corrosion resistance properties with the morphology, and the optical and electrical properties was tested. AZO layers with transmission values higher than 84% and resistivity of 6.54 × 10- 4 â. cm for a deposition process pressure of 3 × 10- 1 Pa, a sputtering power of 2 kW, a pulse frequency of 100 kHz, with optimum corrosion resistance properties, were obtained. © 2015 Elsevier B.V.

In this work we studied indium zinc oxide (IZO) thin films deposited by r.f. magnetron sputtering at room temperature. The films were annealed at high temperature (1100 K) in vacuum, and the oxygen exodiffusion was monitored in-situ. The results showed three main peaks, one at approximately 600 K, other at approximately 850 K and the last one at 940 K, which are probably from oxygen bonded in the film surface and in the bulk, respectively. The initial amorphous structure becomes microcrystalline, according to the X-ray diffraction. The electrical conductivity of the films decreases (about 3 orders of magnitude), after the annealing treatment. This behavior could be explained by the crystallization of the structure, which affects the transport mechanism. Apart from the changes in the material structure, a small variation was observed on the absorption coefficient. © 2007 Elsevier B.V. All rights reserved.

In this work, the relation between oxidant/monomer ratio and the electrical conductivity of polypyrrole was studied using different ratios. We achieved a maximum value for electrical conductivity of 7.5 S/cm for a ratio of 2:1. We also developed a chemical dip-coating process to produce the cathode layer in tantalum capacitors. We obtained capacitances of about 80 μF after 8 cycles using the sequence Monomer/Oxidant.

The effect of substrate temperature (Ts) on the properties of pyrolytically deposited nitrogen (N) doped zinc oxide (ZnO) thin films was investigated. The Ts was varied from 300 °C to 500 °C, with a step of 50 °C. The positive sign of Hall coefficient confirmed the p-type conductivity in the films deposited at 450 °C and 500 °C. X-ray diffraction studies confirmed the ZnO structure with a dominant peak from (1 0 0) crystal plane, irrespective of the variation in Ts. The presence of N in the ZnO structure was evidenced through X-ray photoelectron spectroscopy (XPS) analysis. The obtained high N concentration reveals that the 450 °C is the optimal Ts. Atomic force microscope (AFM) analysis showed that the surface roughness was increased with the increasing Ts until 400 °C but then decreased. It is found that the transmittance of the deposited films is increased with the increasing Ts. The optical band gap calculated from the absorption edge showed that the films deposited with T s of 300 °C and 350 °C possess higher values than those deposited at higher Ts. © 2012 Elsevier B.V.

Indium oxide thin films deposited by spray pyrolysis were irradiated by 100 MeV O7+ ions with different fluences of 5 × 1011, 1 × 1012 and 1 × 1013 ions/cm2. X-ray diffraction analysis confirmed the structure of indium oxide with cubic bixbyite. The strongest (2 2 2) orientation observed from the as-deposited films was shifted to (4 0 0) after irradiation. Furthermore, the intensity of the (4 0 0) orientation was decreased with increasing fluence together with an increase in (2 2 2) intensity. Films irradiated with maximum fluence exhibited an amorphous component. The mobility of the as-deposited indium oxide films was decreased from ∼78.9 to 43.0 cm2/V s, following irradiation. Films irradiated with a fluence of 5 × 1011 ions/cm2 showed a better combination of electrical properties, with a resistivity of 4.57 × 10-3 Ω cm, carrier concentration of 2.2 × 1019 cm-3 and mobility of 61.0 cm2/V s. The average transmittance obtained from the as-deposited films decreased from ∼81% to 72%, when irradiated with a fluence of 5 × 1011 ions/cm2. The surface microstructures confirmed that the irregularly shaped grains seen on the surface of the as-deposited films is modified as "radish-like" morphology when irradiated with a fluence of 5 × 1011 ions/cm2. © 2011 Elsevier B.V. All rights reserved.

When thinking on low cost and sustainable electronic systems, paper can be considered as an interesting option to be used as substrate but also as a component of such systems. In this work we have tailored paper samples that were used simultaneously as physical support and dielectric in oxide based paper field effect transistors (FETs). It was observed that the gate leakage current in these devices depends directly from fibril's dimension and arrangement, being lower for micro/nano fibrillated cellulose paper. Moreover, extra ionic charge added to the paper during its production results in the improvement of FETs' electrical properties, with saturation mobility of 16 cm 2V -1s -1 and on/off current ratio close to 105. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The need to improve the efficiency of the European university system is discussed. It is considered possible to increase university funding by letting students pay for their education. It is suggested that European universities raise more money for research from private sources by selling services. It is found appropriate to strive for excellence at the level of specific departments or schools to begin with.

The effect of oxygen partial pressure on the properties of In2 O3 - Ga2 O3 thin films produced by sputtering at room temperature aimed at thin film transistor (TFT) application is reported in this work. When produced in the absence of oxygen, the films are polycrystalline, while in the presence of oxygen, the films are amorphous. The films' resistivity is tuned between 10-3 and 104 γ cm. Moreover, the films present a high transmittance (> 80%) and a smooth surface (rrms =1.2 nm). The high performance as-produced transistors present high saturation mobility (μsat ≈43 cm2 /V s) and a subthreshold gate-voltage swing of 0.51 V/dec, which is reduced to 0.27 V/dec after 150°C annealing. © 2009 The Electrochemical Society.

Undoped and doped hydrogenated amorphous silicon semiconductors (a-Si:H) have been produced by a two consecutive decomposition deposition chamber (TCDDC) system assisted by electromagnetic static fields. Through this technique, a spatial separation is achieved between the plasma chemistry and that of the deposition to avoid ion and electron (with high energies) bombardment on the growing surface. Besides this, the use of a static magnetic field perpendicular to the substrate will promote plasma confinement, so avoiding its contamination by residual gases adsorbed on the reactor walls. On the other hand, the use of two grids dc biased in the deposition chamber, will allow control of the main film precursors, responsible for the electro-optical and structural properties of deposited films. In this paper we shall discuss the deposition method used as well as the transport, structural and morphological properties presented by deposited films and its dependence on deposition parameters used. © 1989.

In this work we present a study on the effect of annealing temperatures on the structural, morphological, electrical and optical characteristics of gallium doped zinc oxide (GZO), indium zinc oxide (IZO) and indium-tin-oxide (ITO) films. GZO and IZO films were deposited at room temperature by r.f. magnetron sputtering, whereas the ITO films were commercial ones purchased from Balzers. All films were annealed at temperatures of 250 and 500 °C in open air for 1 h. The GZO and ITO films were polycrystalline. The amorphous structure of as-deposited IZO films becomes crystalline on high temperature annealing (500 °C). The sheet resistivity increased with increase in annealing temperature. GZO films showed an increase of 6 orders of magnitude. The optical transmittance and band gap of as-deposited films varied with annealing. The highest transmittance (over 95 %) and maximum band gap (3.93 eV) have been obtained for ITO films. © 2007 Elsevier B.V. All rights reserved.

Metallic nanoparticles (NPs) have received recently considerable interest of photonic and photovoltaic communities. In this work, we report the optoelectronic properties of gold NPs (Au-NPs) obtained by depositing very thin gold layers on glass substrates through thermal evaporation electron-beam assisted process. The effect of mass thickness of the layer was evaluated. The polycrystalline Au-NPs, with grain sizes of 14 and 19 nm tend to be elongated in one direction as the mass thickness increase. A 2 nm layer deposited at 250 C led to the formation of Au-NPs with 10-20 nm average size, obtained by SEM images, while for a 5 nm layer the wide size elongates from 25 to 150 nm with a mean at 75 nm. In the near infrared region was observed an absorption enhancement of amorphous silicon films deposited onto the Au-NPs layers with a corresponding increase in the PL peak for the same wavelength region.

Molybdenum (0.5at%) doped indium oxide thin films deposited by spray pyrolysis technique were irradiated by 100MeV O 7+ ions with different fluences of 5×10 11, 1×10 12 and 1×10 13ions/cm 2. Intensity of (222) peak of the pristine film was decreased with increase in the ion fluence. Films irradiated with the maximum ion fluence of 1×10 13ions/cm 2 showed a fraction of amorphous nature. The surface microstructures on the surface of the film showed that increase in ion fluence decreases the grain size. Mobility of the pristine molybdenum doped indium oxide films was decreased from  122 to 48cm 2/Vs with increasing ion fluence. Among the irradiated films the film irradiated with the ion fluence of 5×10 11ions/cm 2 showed relatively low resistivity of 6.7×10 -4Ωcm with the mobility of 75cm 2/Vs. The average transmittance of the as-deposited IMO film is decreased from 89% to 81% due to irradiation with the fluence of 5×10 11ions/cm 2. © 2012 Elsevier Ltd.

The aim of this paper is to present results on a new soldering process based on the low-temperature solidification of intermetallic phases from the system Cu-Sn-Cu which can be employed to form a heat-resistant die-attach as well as signal and power electric contacts. Because of the total transformation into intermetallic phase, the working temperature of the bond formed is several hundred degrees Celsius higher than the process temperature (around 250°C). This process leads to a homologous temperature T/Tm of about 0.3 compared to 0.7 in the case of soft SnAg solder alloy. Therefore a better reliability of the proposed bonding process is achievable. Results of the match of the predicted volume fraction of the intermetallic forms and the experimentally measured contact volume would be also discussed, for contacts formed in power diodes.

The aim of this research is to study the role of concentration variations on precursor solution of nitrogen doped ZnO (ZnO:N) thin films which has been prepared by spray pyrolysis technique. SEM micrographs show that ZnO:N films in 0.1 ML concentration have a mono-disperse surface with nano-spheres of 50 nm in diameter. In higher molarities the nano-spheres agglomerate leading to particle formation. For 0.4 ML concentrations this change is observed, where plume like particles are seen over the surface of ZnO:N thin film. This change corresponds also to changes observed in the XRD spectra, where crystal orientation of ZnO:N thin films changes from (002) to (100). All of the ZnO:N thin films have kept their sharp ultra violet absorption edge, but the transparency in visible spectra region decreases as the molarities in precursor solution increase. Photoluminescence spectra at room temperature revealed emissions at 2.33 eV, 2.54 eV and 3.16 eV that can be attributed to the presence of nitrogen in ZnO structure. We also observe that all samples analyzed show a p-type Hall effect behavior, and that as the molarities in the precursor solution increase, the electrical resistivity of the films decreases, due to an enhancement of free carriers, while the mobility decreases. These data prove the capability of spray pyrolysis as a viable technique in preparing p-type TCO materials and so, fully transparent CMOS-like devices. © 2009 Elsevier B.V. All rights reserved.

The core of this paper concerns the use of an amorphous transparent conductive oxide (a-TCO), whose performance is on par with the classical indium tin oxide (ITO) films as a transparent contact in organic light emitting diodes (OLEDs). The main advantage of indium zinc oxide (IZO) films relies on their amorphous structure and high mobility that turns them likely to be used with high conductivity and high transmittance even at the infrared region. The mobility of IZO films (47.8 cm2 · V-1 · s-1) surpasses the one exhibited by ITO films (26.4 cm2 · V-1 · s-1), which along with its smoother surface and better current distribution plays an important role on OLEDs performance. Besides their similar turn-on voltage, the devices using IZO anodes exhibit higher power efficiency than the ITO ones, which is 66, 18, and 62% for orange, green, and blue OLEDs, respectively. These results suggest that IZO can potentially be applied as an anode in full color displays based on OLEDs. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this paper, the role of electrode architecture (conventional and interdigital), device structure (vertical or planar), and tungsten oxide (WO3) channel thickness on the electro-optical performances of room temperature sputtered electrochromic transistors (EC-Ts) is reported. A larger number of electro-reducible tungsten sites in thicker WO3 films provide improved optical density and coloration efficiency. However, overall transistor performance is found to suffer in planar EC-Ts with the conventional electrode architecture, where the step to planar interdigital electrodes leaves the devices to be almost insensitive to WO3 thickness. Vertical structures result in improved device properties and stability, given to the shorter distance between gate electrode and semiconductor and to the encapsulation effect provided by such structures. These devices show an On–Off ratio of 5 × 106 and a transconductance (g m) of 3.59 mS, for gate voltages (V G) between −2 and 2 V, which to the authors' knowledge are the best values ever reported for electrochemical transistors. The simple and low-cost processing together with the electrical/optical performances well supported into a comprehensive analysis of device physics opens doors for a wide range of new applications in display technologies, biosensors, fuel cells, or electrochemical logic circuits. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Electrochromic materials have attracted considerable attention during the last two decades as a consequence of their potential application in several different types of optical devices. Examples of these devices include intelligent windows and time labels. In this paper the authors describe results obtained with thin tungsten oxide films produced at room temperature by rf magnetron sputtering under an argon and oxygen atmosphere on transparent conductive oxide coated glass substrates. To protect the surface of the electrochromic film, prevent water absorption and obtain a good memory effect under open circuit voltages, a layer of Ta2O5 was deposited over the WO3 films. In this study, the effect of different electrolyte compositions on the open circuit memory of optical devices has been characterized. The best results were obtained for electrochromic devices with polymer gel p(TMC)3LiC1O4 and p(TMC)8LiClO 4 electrolytes. These prototype devices present an overall transmittance of ∼75% in their bleached state and after coloration 40.5 and 52.5% respectively. These devices also show memory effect and an optical density considered satisfactory for some electrochromic applications.

This paper reports the application of a polymethacrylate hydroxyethylene resin based electrolyte in electrochromic (EC) devices. The electrolyte is characterized by electrochemical impedance spectroscopy, visible spectroscopy, TGA, DSC, and DRX and tested as an ionic conductor in an EC device with the following configuration: Substrate/IZO/WO 3/Polymer Electrolyte/(CeO 2)TiO 2/IZO/Substrate. The electrolyte presents an ionic conductivity of 10 -7S/cm at room temperature and TGA analysis show that electrolyte is thermally degraded at 200°C. The EC device based on this polymethacrylate hydroxyethylene resin electrolyte system shows memory effect and exhibits an excellent optical density. © 2011 John Wiley & Sons, Ltd.

In previous papers the mean excess chemical potential, μ1(E), in ternary systems of the type I sulphate + II sulphate + H2O, at 25°C was determined. Results obtained for systems with CuSO4(I), and ZnSO4(I) respectively, pointed out an obvious disparity between their behaviours. They show the existence of some important association phenomena partially accounting for the substantial deviations from ideal behaviour. The ternary sulphate systems (CuSO4 + Me(I,II)SO4 + H2O; ZnSO4 + Me(I,II)SO4 + H2O) studied were characterized against the binaries of the same ionic strength, experimental data being obtained using both e.m.f. and spectrophotometric methods. Deviations from the ideal behaviour were discussed in terms of thermodynamic excess functions and association constants. A comparative study between the results obtained with the two above mentioned methods is presented. In previous papers the mean excess chemical potential, μ1 E, in ternary systems of the type I sulphate+II sulphate+H2O, at 25 °C was determined. Results obtained for systems with CuSO4(I), and ZnSO4(I) respectively, pointed out an obvious disparity between their behaviours. They show the existence of some important association phenomena partially accounting for the substantial deviations from ideal behaviour. The ternary sulphate systems (CuSO4+MeI, IISO4+H2O; ZnSO4+MeI, IISO4+H2O) studied were characterized against the binaries of the same ionic strength, experimental data being obtained using both e.m.f. and spectrophotometric methods. Deviations from the ideal behaviour were discussed in terms of thermodynamic excess functions and association constants. A comparative study between the results obtained with the two above mentioned methods is presented.

Complex impedance measurements were used to analyze the influence of ultraviolet and ozone gas on the electronic behaviour of ZnO films grown by rf magnetron sputtering. The data show that UV exposure strongly increases the ac conductivity of the film at very low frequencies, and that after ozone exposure it recovers the original value. At high frequencies, however, UV-light exposure it does not change the conductivity but the ozone acts in the sense to decrease it. Two distinct mechanisms, related to two relaxation time distributions are clearly observed: they are superimposed in the virgin sample, but they split forming two semicircles in the z″(f) - z′(f) diagrams when the samples are treated with UV and/or ozone gas. A combination of the bruggeman effective medium approximation (BEMA) with the random free energy barrier model is used to fit the data and to explain the ac conductivity variation phenomena observed. © 2006 Elsevier B.V. All rights reserved.