Rodrigo Martins

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.

Where a-Si:H pin devices are concerned, one of the main obstacles regarding improved performance is device stability, usually attributed to adverse behaviour at various interfaces within the device. Several attempts have been made to overcome this problem, such as the use of blocking layers at the interfaces. Although these have led to some improvements in device performance, most of the problems associated with device stability remain. This is mainly due to the defects at the interfaces, since the blocking layers (silicon alloys with carbon, nitrogen or oxygen) usually have a high density of bulk states, in comparison to intrinsic a-Si:H films. In this paper, we present a method that seems to be capable of improving device stability. It consists of performing a controlled removal of oxide interlayers at the interfaces, by an appropriate etching process. This enables the production of highly smoothed interfaces, and reduces possible cross-contamination of the i-layer from the adjacent doped layers. This amounts to a new design of typical pin devices, in which thin absorber layers are placed at the p/i and i/n interfaces. Their purpose is to trap most of the impurity atoms diffused from the doped layers, after which they are removed by appropriate etching. The fabrication of the absorbers (sacrificial layers), the nature of the etching and the tailoring of the defect profile at the interfaces will be discussed, including the performance exhibited by the resulting devices. © 2002 Elsevier Science B.V. All rights reserved.

One of the main problems in producing large area amorphous silicon devices concerns films uniformity. In this paper we present data concerning the role of reactor geometry and design and on the film performances as well as the problems related to mechanical mismatches in scaling up the reactor size. © 1991 Elsevier Science Publishers B.V. All rights reserved.

This paper deals with the engineering aspects related to the rf energy coupling in Plasma Enhanced Chemical Vapour Deposition (PECVD) processes, in a diode-type unit in which an extra grid is used. The main emphasis is given in the determination of the real power delivered to the gas and comparing it with the total power losses, besides determining the best way to control the powder formed during the process. © 1994.

In this paper, we report the environmental, optical, and gate bias stress stability of amorphous zinc-tin-oxide (ZTO) thin-film transistors (TFTs) fabricated by sol-gel spin-coating method. The ZTO TFTs showed excellent environmental and optical stability. The threshold voltage stability of ZTO TFTs was sensitive to both positive and negative gate bias stress. Maximum threshold voltage shifting of +1.9 and -3.2 V was observed under a gate bias stress of +10 and -10 V, respectively, with no significant change to subthreshold swing value. © 2006 IEEE.

In this work, we show the possibility to use undoped porous silicon (PS) thin films produced by hot wire chemical vapour deposition technique (HW-CVD) as ethanol detector. Silicon thins films produced by HW-CVD technique, under certain deposition conditions, have a porous structure [Vacuum 52 (1999) 147]. Therefore, in the presence of an alcohol, the OH group is adsorbed by the uncompensated bonds behaving as donor-like carriers leading to an increase in the current flowing through the material. This current enhancement is bias dependent in glass/ITO/i-a-Si:H/Al sensor and increases as the ethanol vapour pressure increases from 10-1mbar to atmospheric pressure. The response time of the current of the sensor and its recovery time are in the range of 10-50s at room temperature. Ethanol quantities above 50ppm can be detected. © Published by Elsevier B.V.

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.

We present the results obtained with an extended-gate ISFET totally based on amorphous oxides (GIZO as the semiconductor, +{\hbox{Ta}}-{2}{\hbox{O}}-{5}{\ hbox{:SiO}}-inf2-inf as the dielectric and +{\hbox{Ta}}-{2}{\hbox{O}}-inf5-inf as the sensitive layer). A full characterization of the device was performed with constant ionic strength pH buffer solutions, revealing a sensitivity of 40 mV/pH with small hysteresis, and good linearity in the pH 4-pH 10 range buffer solutions. These results clearly show that it is possible to produce room-temperature disposable and low cost bio-sensors. © 2005-2012 IEEE.

This work refers to the fabrication of hybrid solar cells based on porous silicon (PS) filled with copper phthalocyanine (CuPc) to form GZO/CuPc-PS/Si/Al structure. We used n-type Si since photoinduced charge transfer from CuPc to Si is observed only for n-type Si. The characteristic 100% peak at 6.8°2θ from XRD confirms that the CuPc coating on PS exists in α-CuPc polymorph. The systematic increase in FWHM of XRD peak at 69.1°2θ and red-shift of LO phonon Raman spectra indicate a progressive reduction of Si nanocrystallites size with increasing etching time and the estimated size agrees well with atomic force microscopic images. The FTIR results confirm the formation of α-CuPc polymorph and it is also corroborated well with XRD and Raman results. © 2008.

This work presents a fast method to determine qualitatively the uniformity and the thickness of transparent or semitransparent thin films in the visible to near-infrared region. The method proposed is based on the information recorded by a colour scanner in the form of coloured regions, due to the constructive interferences caused by multibeam wavelength light sources as function of the film thickness and refractive index. The method is well applied in transparent films, where the uniformity cannot be seen by visual inspection. This paper shows that the results obtained for ZrO2 films are satisfactory enabling the application of this technique to determine the films uniformity in fast and cheap way.

Flexible and large area (5 mm × 80 mm with an active length of 70 mm) position-sensitive detectors (PSDs) deposited onto polymeric substrates (polyimide - Kapton VN) have been fabricated. The optimized structure presented is based on a heterojunction of amorphous silicon (a-Si: H)/ZnO: Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity, and position detection measurements. The set of data obtained on one-dimensional PSDs based on the heterojunction show excellent performances with a maximum spectral response of 0.12 A/W at 500 nm and a nonlinearity of ±10% over 70-mm length. The produced sensors present a nonlinearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the a-Si: H film. In order to prove this behavior, it was measured the defect density obtained by the constant photocurrent method on a-Si: H thin films deposited on polymeric substrates and bent with different radii of curvature. © 2005 IEEE.

Large area thin film position sensitive detectors based on amorphous silicon technology have been prepared on polyimide substrates using the conventional plasma-enhanced chemical vapour deposition. The sensors have been characterized by spectral response, light intensity dependence and linearity measurements in a bent state in order to evaluate the properties in real working conditions. The obtained one-dimensional (1D) position sensors with 10 mm width and 20 mm length present a non-linearity of ±1% which are comparable to the ones produced on glass substrates.

This work describes the fabrication and characterization of an improved version of large area (5mm×80mm with an active length of 70mm) flexible position sensitive detectors deposited onto polymeric substrates (polyimide-Kapton® VN). The new configuration presented by the sensor is based on a heterostructure of a-Si:H/ZnO:Al. The sensors were characterized by spectral response, photocurrent dependence as a function of light intensity and position detection measurements. The set of data obtained on one-dimensional position sensitive detectors based on the heterostructure show excellent performances with a maximum spectral response of 0.12A/W at 500nm and a non-linearity of ±10% over 70mm length. The produced sensors present a non-linearity higher than those ones produced on glass substrates, due to the different thermal coefficients exhibited by the polymer and the amorphous silicon film. In order to prove this behaviour, it was measured the defect density obtained by the constant photocurrent method on amorphous silicon deposited on polymeric substrates bended with different radius of curvature. © 2004 Elsevier B.V. All rights reserved.

The special Professor Walter E. Spear commemoration issue of the Philosophical Magazine, published in October 2009, contains papers which cover the numerous relevant issues, driven by commercial applications, primarily solar energy and displays. Kocka reviews the complex microstructure of crystallites embedded in the amorphous silicon tissue, the transport mechanism is determined by the conductive grains and influenced by the passivation through H at the grain boundaries. Hugger and co-researchers report on transient photocapacitance spectroscopy and drive-level capacitance profiling as a way of elucidating the fundamental electronic properties of hydrogenated ncSi. Tawada recounts the history of a-Si:H pin heterojunction solar cells, emphasizing the role of the p-type silicon carbide layer in the improvement of the device. Schubert and colleagues focus their work on the production of flexible PV modules with many applications in the architectural arena or integrated into clothing.

Doped a/μc-Si:H films were produced in different starting deposition conditions by the hot wire chemical vapor deposition technique. In this paper, we show that by changing the initial onset deposition conditions of the process and maintaining the overall pressure, hydrogen dilution and filament temperature, it is possible to control the compactness of the films. As the films nucleation is the key parameter to produce compact films, we show that starting the process with hydrogen and progressively introducing the process gas enhances the compactness and improve the electrical properties of the films produced. © 2002 Elsevier Science B.V. All rights reserved.

The possibility of fabricating high-mobility ZnO thin-film transistors (ZnO-TFT) at room temperature by rf magnetron sputtering was discussed. It was found that the films were nanocrystalline with a hexagonal structure and exhibited a preferred orientation with the c-axis perpendicular to the substrate. The undoped ZnO films exhibited improved crystallinity fraction of the nanocrystals and low oxygen vacancies. Analysis shows that the exposure of the ZnO-TFTs to the ambient light has no effect on the current voltage characteristics.

During the last years, oxide semiconductors have shown that they will have a key role in the future of electronics. In fact, several research groups have already presented working devices with remarkable electrical and optical properties based on these materials, mainly thin-film transistors (TFTs). Most of these TFTs use indium-tin oxide (ITO) as the material for source/drain electrodes. This paper focuses on the investigation of different materials to replace ITO in inverted-staggered TFTs based on gallium-indium-zinc oxide (GIZO) semiconductor. The analyzed electrode materials were indium-zinc oxide, Ti, Al, Mo, and Ti/Au, with each of these materials used in two different kinds of devices: one was annealed after GIZO channel deposition but prior to source/drain deposition, and the other was annealed at the end of device production. The results show an improvement on the electrical properties when the annealing is performed at the end (for instance, with Ti/Au electrodes, mobility rises from 19 to 25 cm2/V · s, and turn-on voltage drops from 4 to 2 V). Using time-of-flight secondary ion mass spectrometry (TOF-SIMS), we could confirm that some diffusion exists in the source/drain electrodes/ semiconductor interface, which is in close agreement with the obtained electrical properties. In addition to TOF-SIMS results for relevant elements, electrical characterization is presented for each kind of device, including the extraction of source/drain series resistances and TFT intrinsic parameters, such as VTi (intrinsic threshold voltage). © 2008 IEEE.

A quantitative study of the dynamics of threshold-voltage shifts with time in gallium-indium zinc oxide amorphous thin-film transistors is presented using standard analysis based on the stretched exponential relaxation. For devices using thermal silicon oxide as gate dielectric, the relaxation time is 3× 105 s at room temperature with activation energy of 0.68 eV. These transistors approach the stability of the amorphous silicon transistors. The threshold voltage shift is faster after water vapor exposure suggesting that the origin of this instability is charge trapping at residual-water-related trap sites. © 2009 American Institute of Physics.

The present work is focused on gelatin-based electrolytes doped with a range of concentration of zinc triflate (Zn(CF3SO3)2). The transparent-thin-film samples have been represented by the notation GelatinnZn(CF3SO3)2, where n represents the zinc triflate salt concentration in the electrolyte membranes from 0.00 wt% to 10.93 wt% The samples have been characterized by conductivity measurements, thermal analysis, cyclic voltammetry, X-ray diffraction (XRD), polarized optical microscopy (POM) and scanning electron microscopy (SEM). The gelatin-based electrolytes were also tested as ionic conductors in electrochromic devices with the glass/ITO/WO3/gelatin-based electrolyte/CeO2-TiO2/ITO/glass configuration. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tuberculosis (TB) remains one of the most serious infectious diseases in the world and the rate of new cases continues to increase. The development of cheap and simple methodologies capable of identifying TB causing agents belonging to the Mycobacterium tuberculosis Complex (MTBC), at point-of-need, in particular in resource-poor countries where the main TB epidemics are observed, is of paramount relevance for the timely and effective diagnosis and management of patients. TB molecular diagnostics, aimed at reducing the time of laboratory diagnostics from weeks to days, still require specialised technical personnel and labour intensive methods. Recent nanotechnology-based systems have been proposed to circumvent these limitations. Here, we report on a paper-based platform capable of integrating a previously developed Au-nanoprobe based MTBC detection assay - we call it "Gold on Paper". The Au-nanoprobe assay is processed and developed on a wax-printed microplate paper platform, allowing unequivocal identification of MTBC members and can be performed without specialised laboratory equipment. Upon integration of this Au-nanoprobe colorimetric assay onto the 384-microplate, differential colour scrutiny may be captured and analysed with a generic "smartphone" device. This strategy uses the mobile device to digitalise the intensity of the colour associated with each colorimetric assay, perform a Red Green Blue (RGB) analysis and transfer relevant information to an off-site lab, thus allowing for efficient diagnostics. Integration of the GPS location metadata of every test image may add a new dimension of information, allowing for real-time epidemiologic data on MTBC identification. © 2012 The Royal Society of Chemistry.

The model presented is based on the heat transfer and energy balance equations that rule the set of physical and chemical interactions that take place on the gas phase of a growth process, assuming that the deposition process occurs under laminar dynamic flow conditions (Knudsen number below 1). In these conditions, the chemistry and physics of the process involved in the growth mechanism of silicon thin films produced by the hot wire or the hot-wire plasma assisted technique can be proper derived by balance equations that supply information about how the plasma density, the gas dilution and the gas temperature influence the growth mechanism and the equilibrium of the concentration of species presented on the growth surface. The model developed establishes a relation between the abundance species formed and the parameters initiators of the process such as the filament temperature and the rf power density used.

This paper aims to characterize the growth process of polymorphous/ nanocrystalline silicon (pm-Si:H) films produced by PECVD at 13.56 MHz. The emphasis is in determining the plasma parameters that allow to control the conditions where pm/nc-Si:H can be obtained under high hydrogen dilution, where the only varied parameter is the silane gas flow, fixing rf power, deposition pressure and substrate temperature. The data achieved show that good pm/nc-Si:H films are produced at 240 Pa using a silane gas flow of 5sccm (dilution 1:70) to which it corresponds films with photosensitivities exceeding 106, optical gaps close to 1.80 eV and 18 at% hydrogen contents. The data also show that under certain deposition conditions the pm-Si:H films peel-off.