Rodrigo Martins

This new production technique is based on the growth of a-Si films on a reactor where gas decomposition promoted by a capacitively coupled r. f. power system takes place in a chamber separated from that where amorphous films are deposited under the action of an electromagnetic static field. Using this method, we shall reduce films contamination caused by the residual gas desorbed from reactor walls. At the same time, there is a reduction plasma ion and electron damages on the deposited films. The main species impinging upon our substrates will be mainly composed of long life radicals with high mobilities and high diffusion rates, which will give origin to a random silicon network free of long poly-silane chains.

In this paper we report results concerning the use of paper as substrate and as an electronic component for the next generation of sustainable low cost electronic systems, where different examples of applications are given. © 2013 Society for Information Display.

A complementary metal oxide semiconductor (CMOS) device is described. The device is based on n-(In-Ga-Zn-O) and p-type (SnO x) active oxide semiconductors and uses a transparent conductive oxide (In-Zn-O) as gate electrode that sits on a flexible, recyclable paper substrate that is simultaneously the substrate and the dielectric. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A study of intrinsic zinc oxide thin film as ozone sensor based on the ultraviolet (UV) photoreduction and subsequent ozone re oxidation of zinc oxide as a fully reversible process was presented. It was found that the film described were produced by spray pyrolysis, dc and rf magnetron sputtering. The dc resistivity of the films changed more than eight orders of magnitude when exposed to an UV dose of 4 mW/cm2. Analysis shows that the porous and textured zinc oxide films produced by spray pyrolysis at low substrate exhibit an excellent ac impedance response.

The aim of this work is to provide the basis for the interpretation, under steady state and in the low-voltage regime of the dark current-density-voltage (J-V) characteristics of transverse asymmetric amorphous silicon (a-Si:H) p-i-n and n-i-p diodes. The transverse asymmetric a-Si:H diodes present ratios between the metal contact and the underneath doped layer areas larger than five, leading to the inclusion, in the diode equation, of a lateral leakage current, responsible for the high saturation current density and the forward shape of the J-V curves recorded. The leakage current depends on the lateral spatial potential developed with which varies following a power-law dependence. The experimental J-V curves in diodes with the doped layer around the metal contact unetched and etched prove the role and origin of this lateral leakage current and, thus, the proposed model. © 1995 American Institute of Physics.

Amorphous Silicon solar cells have been produced by a two consecutive decomposition and deposition chamber system, using polished S. S. substrates. Through a systematic investigation of the electrical and optical properties of doped and undoped amorphous silicon layers (1) we observe that the deposition conditions (gas partial pressure, density of r. f. power, substrate temperature, electromagnetic static fields applied to the substrate, and gas flow rate) influence films properties. In the course of this investigation we have been studying the role of the sheet resistance, R//s, of the I. T. O. layer on the short circuit current, I//s//c, and on the open circuit voltage, V//o//c, of p. i. n. structures of 16cm**2 in area. The obtained results indicate that V//o//c is almost independent on R//s, while I//s//c variation approaches a square root dependence on R//s.

The aim of this study was to investigate the influence of ultrasound and high-shear mixing on the properties of microparticles obtained by spray congealing. Dispersions containing 10% carbamazepine and 90% carrier Gelucire® 50/13 (w/w) were prepared using magnetic stirring, high-shear mixing, or ultrasound. Each preparation was made using hot-melt mixing spray congealing to obtain the microparticles. All microparticles presented a spherical shape with high encapsulation efficiency (>99%). High-shear mixing and ultrasound promoted a decrease in the size of microparticles (D90) to 62.8 ± 4.1 μm and 64.9 ± 3.3 μm, respectively, while magnetic stirring produced microparticles with a size of 84.1 ± 1.4 μm. The use of ultrasound led to microparticles with increased moisture content as identified through sorption isotherm studies. In addition, rheograms showed distinct rheological behaviour among different dispersion preparations. Therefore, the technique used to prepare dispersions for spray congealing can affect specific characteristics of the microparticles and should be controlled during the preparation. © 2013 Informa UK Ltd. All rights reserved.

We have deposited by Plasma Enhanced Chemical Vapour Deposition phosphorus doped amorphous and microcrystalline silicon films, as a function of the RF power (10-300 W), using a PH3/(SiH4 + H2 + He)mixture. It was found that films microcrystallization occurs for powers above 130 W, where a clear phase transition occurs. The microcrystalline films produced present high dark conductivities and optical band gaps, where the crystalline volume fraction is above 25%, as revealed by micro Raman spectroscopy. The Hall mobility have been also determined for amorphous and microcrystalline films, as a function of temperature, in the range 280-340 K. The data show that for the microcrystalline films the conduction is mainly in the extended states of the microcrystals, confirming also the double sign anomaly. That is, for n-type films, the sign is positive for the amorphous case while it is negative for the microcrystalline case. © 1998 Elsevier Science S.A.

The objective of this work is to provide a basis for the interpretation of the a-Si:H photodiode behaviour under low illumination level conditions, where a lateral leakage current plays an important role on the devices' performances when the doped collecting layer can not be considered a true equipotential. To determine this effect, a-Si:H p.i.n devices with small metal dot contacts, matrix distributed, were produced and analysed before and after etching the surrounding doped region of the metal collecting contact. The experimental data fit a model that includes the contribution of a lateral leakage current influencing the J-V characteristics, responsivity and the apparent light degradation behaviour of the device.

The role of order and disorder on the electronic performances of n -type ionic oxides such as zinc oxide, gallium zinc oxide, and indium zinc oxide used as active (channel) or passive (drain/source) layers in thin film transistors (TFTs) processed at room temperature are discussed, taking as reference the known behavior observed in conventional covalent semiconductors such as silicon. The work performed shows that while in the oxide semiconductors the Fermi level can be pinned up within the conduction band, independent of the state of order, the same does not happen with silicon. Besides, in the oxide semiconductors the carrier mobility is not bandtail limited and so disorder does not affect so strongly the mobility as it happens in covalent semiconductors. The electrical properties of the oxide films (resistivity, carrier concentration, and mobility) are highly dependent on the oxygen vacancies (source of free carriers), which can be controlled by changing the oxygen partial pressure during the deposition process and/or by adding other metal ions to the matrix. In this case, we make the oxide matrix less sensitive to the presence of oxygen, widening the range of oxygen partial pressures that can be used and thus improving the process control of the film resistivity. The results obtained in fully transparent TFT using polycrystalline ZnO or amorphous indium zinc oxide (IZO) as channel layers and highly conductive poly/nanocrystalline ZGO films or amorphous IZO as drain/source layers show that both devices work in the enhancement mode, but the TFT with the highest electronic saturation mobility and on/off ratio 49.9 cm2 V s and 4.3× 108, respectively, are the ones in which the active and passive layers are amorphous. The ZnO TFT whose channel is based on polycrystalline ZnO, the mobility and on/off ratio are, respectively, 26 cm2 V s and 3× 106. This behavior is attributed to the fact that the electronic transport is governed by the s -like metal cation conduction bands, not significantly affected by any type of angular disorder promoted by the 2p O states related to the valence band, or small amounts of incorporated metal impurities that lead to a better control of vacancies and of the TFT off current. © 2007 American Institute of Physics.

This paper presents results of the spatial and frequency detection limits of an integrated array of 32 one-dimensional amorphous silicon thin film position sensitive detectors with a nip structure, under continuous and pulsed laser operation conditions. The data obtained show that 0.45×0.06 cm arrays, occupying a total active area of about 1 cm2 have a spatial resolution better than 10 μm (modulation transfer function of about 0.2), with a cut-off frequency of about 6.8 KHz. Besides that, under pulsed laser conditions the device non-linearity has its minimum (about 1.6%), for a frequency of about 200Hz. Up to the limits of the cut-off frequency, the device non-linearity increases to values above 4%.

This paper deals with the structure, composition and electro-optical characteristics of n-type amorphous and microcrystalline silicon thin films produced by plasma-enhanced chemical vapour deposition in a hydrogenhelium mixture. In addition, special emphasis is given to the role that hydrogen incorporation plays in the film's properties and in the characteristics of n-type microcrystalline films presenting simultaneously optical gaps of about 2·3 eV (controlled by the hydrogen content in the film), a dark conductivity of 6-5S cm-1 and a Hall mobility of about 0·86 cm2 V-1 s-1, the highest combined values for n-type microcrystalline silicon films, as far as we know.

The aim of this work is to provide the basis for the interpretation of the lateral photoeffect in p-i-n a-Si:H one-dimensional thin-film position-sensitive detectors (1D TFPSDs) under steady state, through an analytical model. The experimental data recorded in 1D TFPSD devices with different characteristics are compared with the predicted curves and the obtained correlations are discussed. © 1996.

The aim of this work is to present an analytical model able to interpret the experimental data of the dependence of film's uniformity on the discharge pressure, gas flow and temperature used during the production of thin films by the plasma enhancement chemical vapour deposition technique, under optimised electrode's geometry and electric field distribution. To do so, the gas flow is considered to be quasi-incompressible and inviscous leading to the establishment of the electro-fluid-mechanics equations able to interpret the film's uniformity over the substrate area, when the discharge process takes place in the low power regime.

The electrosynthesis of polypyrrole (PPy) has been achieved on aluminium in aqueous medium of tartaric acid by means of cyclic voltammetry, potentiostatic and galvanostatic techniques. Scanning electron microscopy (SEM) and X-ray microanalysis by energy spectroscopy dispersion (EDS) applying on surfaces show that the PPy coating is developed from the metal surface through the cracks of the initial Al2O3 layer. A mechanism involving the participation of the supporting electrolyte and the pyrrole (Py) in distinct active sites was proposed based on the linear sweep voltammetry. It is observed for all applied electrochemical techniques that the pyrrole concentration has to be higher than 0.1 M to allow the polypyrrole electrodeposition in acid medium. Scanning electron microscopy, secondary electrons (SE) and backscattering electrons (BE), shows that the PPy coating obtained in galvanostatic and potentiostatic modes starts with small islands at weak applied potentials or current densities. Moreover, EDS reveals a good homogeneity and compactness of the film achieved in galvanostatic method. The corrosion results in 3% NaCl medium show that the PPy coating decreases the corrosion behaviour of the aluminium. The bilayer Al2O3/PPy shows a capacitor with future applications. © 2006 Elsevier Ltd. All rights reserved.

This paper deals with the interpretation of transport properties of amorphous silicon hydrogenated films (a-Si:H) through dark conductivity, photoconductivity and pulse controlled capacitance-voltage measurements. a-Si:H films were produced by rf glow discharge coupled either inductively or capacitively to a 3% SiH4/Ar mixture at different crossed electromagnetic static fields. The data concerned with the dark activation energy, photoactivation energy, variation of the density of localized states and photosensitivity, (σph/σd)25°C, of a-Si:H films can account for their optoelectronic properties which are strongly dependent on the deposition parameters. We also observed that crossed electromagnetic static fields applied during film formation influences hydrogen incorporation in a different manner than previously proposed. © 1983.

The aim of this work is to provide the basis for the interpretation, under steady state conditions, of the lateral photoeffect in p-i-n a-Si:H one-dimensional thin-film position-sensitive detectors (1D TFPSD) and the determination of its linear spatial detection limits, function of the device, and light spot source characteristics. This leads to the development of a model, based on the application of the Poisson, continuity, and current density equations in the p-i-n junction, where two thin resistive layers, as equipotentials, are considered on both sides of the doped layers. The experimental data recorded in 1D TFPSD devices with different performances are compared with the predicted curves and the obtained correlations discussed. © 1995 American Institute of Physics.

A linear array thin film position sensitive detector (LTFPSD) based on hydrogenated amorphous silicon (a-Si:H) is proposed for the first time, taking advantage of the optical properties presented by a-Si:H devices we have developed a LTFPSD with 128 integrated elements able to be used in 3-D inspections/measurements. Each element consists on a one-dimensional LTFPSD, based on a p.i.n. diode produced in a conventional PECVD system, where the doped layers are coated with thin resistive layers to establish the required device equipotentials. By proper incorporation of the LTFPSD into an optical inspection camera it is possible to acquire information about an object/surface, through the optical cross-section method. The main advantages of this system, when compared with the conventional CCDs, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).

This paper deals with the determination of plasma impedance and ion density in r.f. plasmas using different mixtures of silane with methane or ethylene and r.f. powers. The aim is to correlate these parameters with carbon and hydrogen contents of the films produced. The data achieved show that the best carbon incorporation is achieved using ethylene gas mixtures, under low gas mixture concentration, where the substrate also sustains a low ion bombardment. The data also show that particulates in the plasma can be more easily formed in the ethylene-based processes. © 2001 Published by Elsevier Science B.V.

Amorphous/nanocrystalline silicon p i′ i i′ n devices fabricated on micromachined glass substrates are integrated with oligonucleotide-derivatized gold nanoparticles for a colorimetric detection method. The method enables the specific detection and quantification of unamplified nucleic acid sequences (DNA and RNA) without the need to functionalize the glass surface, allowing for resolution of single nucleotide differences between DNA and RNA sequences-single nucleotide polymorphism and mutation detection. The detector's substrate is glass and the sample is directly applied on the back side of the biosensor, ensuring a direct optical coupling of the assays with a concomitant maximum photon capture and the possibility to reuse the sensor. © 2007 American Institute of Physics.

This paper deals with a new process to improve the stability of a-Si:H pin solar cells deposited in a single batch process by proper passivation of the interfaces. The process consists in removing partially a deposited sacrificial oxide layer grown between the p/i or i/n interfaces by SF6 etching. This layer is an absorber of defects and impurities that are introduced in the interfaces, mainly from the chamber walls and the substrate surface. The results achieved in laboratory samples lead to devices in which the fill factor and short circuit current density were improved respectively towards 75% and 16.5 mA cm-2, with a final working efficiency of about 9.5%. © 2001 Elsevier Science Ltd. All rights reserved.

This work reports on the performances of undoped and doped amorphous/nanocrystalline silicon films grown by hot wire plasma assisted technique. The structure (including the presence of several nanoparticles with sizes ranging from 5 nm to 50 nm), composition (oxygen and hydrogen content) and transport properties of the films are highly dependent on the temperature of the filament and on the hydrogen dilution. The undoped films grown under low r.f. power (≈4mWcm-2) and filament temperatures around 1850 K present dark conductivities below 10-10 Scm-1, optical gaps of about 1.6 eV and photosensitivities above 105, (under AM 1.5 light intensities), with almost no traces of oxygen content. For the n- and the p-doped silicon films also fabricated under the same conditions the conductivities obtained are of about 10-2Scm-1 and 10-5Scm-1, respectively. © 1998 Elsevier Science Ltd. All rights reserved.