Rodrigo Martins

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.

Today there is a strong interest in the scientific and industrial community concerning the use of biopolymers for electronic applications, driven mainly by low-cost and disposable applications. Adding to this interest, we must recognise the importance of the dream of wireless auto-sustained and low-energy-consumption electronics. This dream can be fulfilled by cellulose paper, the lightest and the cheapest known substrate material, as well as the Earth's major biopolymer and of tremendous global economic importance. Most of the paper used up to now is optimised in terms of the required mechanical and physical properties to be used as the support of inks of different origins. In the future, specific electronic heterogeneous paper sheets should be fabricated aiming to get paper fibers with required bulk and surface functionalities, proper water/vapour barrier, size and diameter/thickness of the fibrils and full paper thickness. This will be the function of components/devices to be incorporated/integrated such as thin-film transistors, complementary metal oxide semiconductor devices, passive electronic components (resistances, inductors and capacitors), memory transistors, electrochromics and thin-film paper batteries. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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 article we review the recent progress in n- and p-type oxide based thin film transistors (TFT), with special emphasis to solution-processed and p-type, and we will summarize the major milestones already achieved with this emerging and very promising technology.

In this paper we report on the fabrication and performance of a portable and low cost optoelectronic platform integrating a double color tuned light emitting diode as light source, an amorphous/nanocrystalline silicon photodetector with a flat spectral response in the wavelength range from 520. nm to 630. nm and integrated electronic for signal acquisition and conditioning constituted by current to voltage converter, a filter and an amplification stage, followed by an analog to digital converter, with appropriate software for full automation to minimize human error. Incorporation of the double color tuned light emitting diode provides for a simple yet innovative solution to signal acquisition independently from the light intensity and/or solution concentration, while considerably decreasing production costs. Detection based on Au-nanoprobes constitutes the biorecognition step and allowed identification of specific sequences of Mycobacterium tuberculosis complex, namely Mycobacterium bovis and M. tuberculosis in biological samples. © 2010 Elsevier B.V.

In order to study the properties of P-doped ZnO films deposited at low temperature substrates, P-doped ZnO films were RF-sputtered on sapphire substrates in the range from RT to 350°C. XRD spectra indicated the growth of the crystallites along the strongest <001> orientation. Further ZnO (002) peak became the weakest when the film was sputtered at 250°C. AFM pictures showed that the surface morphology varied with the deposition temperature. The sample RMS increased with the increase of substrate temperature. XPS spectra showed a clear broad P 2p peak at about 134 eV. Further the film composition varied with the substrate temperature. The average visible transmittance calculated in the wavelength ranging 400-600 nm was more than 60%. The optical band gap calculated from the absorption coefficient was about 3.2 eV. The Hall measurements confirm the n-type conductivity of the films. The carrier concentration in the films decreases with the increase of substrate temperature. The study is helpful for understanding the properties of P-doped ZnO films sputtered at lower substrate temperature and achieving p type ZnO films at lower temperature.

We present a new approach for real-time monitoring of PCR amplification of a specific sequence from the human c-MYC proto-oncogene using a Ta 2O 5 electrolyte-insulator-semiconductor (EIS) sensor. The response of the fabricated EIS sensor to cycle DNA amplification was evaluated and compared to standard SYBR-green fluorescence incorporation, showing it was possible to detect DNA concentration variations with 30mV/μM sensitivity. The sensor's response was then optimized to follow in real-time the PCR amplification of c-MYC sequence from a genomic DNA sample attaining an amplification profile comparable to that of a standard real-time PCR. Owing to the small size, ease of fabrication and low-cost, the developed Ta 2O 5 sensor may be incorporated onto a microfluidic device and then used for real-time PCR. Our approach may circumvent the practical and economical obstacles posed by current platforms that require an external fluorescence detector difficult to miniaturize and incorporate into a lab-on-chip system. © 2011 Elsevier B.V.

Doped zinc oxide with aluminium are attractive alternative material as transparent conducting electrode because they are nontoxic and inexpensive compared with indium tin oxide (ITO) for diffrent applications: solar cells, tft. Transparent aluminumdoped zinc oxide (AZO) thin films were deposited on glass substrates by RF magnetron sputtering at room temperature and 100W from ceramic target ZnO-Al2O3 (98:2 weight percent). The structural, electrical and optical properties of these films were characterized as a function of deposition pressure. AZO films with low resistivity 2.02×10-3 Ωcm and high transmittance (over 80% in vizible range) were thus prepared with a deposition pressure of 3 mTorr.

In this work we present a study aiming to determine the role of Ga2O3-In2O3-ZnO (GIZO) channel layer composition on the electrical performance and stability exhibited by thin-film transistors (TFTs). The GIZO films were obtained by magnetron sputtering using ceramic targets of different compositions (Ga:In:Zn = 2:2:1, 2:2:2, 2:4:1 and 2:4:2 at.). Structural analysis corroborates the fully amorphous character of the GIZO deposited layers. For the target compositional range used we observe a Zn deficiency on the produced films, which affects the In/Ga atomic concentration ratios. Resistivity and mobility are found to show a general trend against the measured In/Ga ratio that reveals the role played by In and Ga cations on the transport mechanisms. Targets with increased In concentrations (2:4:1 and 2:4:2) allow to obtain the best TFT performances with field effect mobilities reaching values of 53.0 and 51.7cm2 V-1 s-1, respectively. In addition, the In-richer GIZO compositions result in considerably more stable TFTs, especially under positive gate bias stress conditions. Finally, it is verified that by using a target with a slightly lower In atomic composition (2:4:2 in comparison to 2:4:1), good stability and mobility can be achieved with potentially lower material costs.© 2011 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.

Nanostructured silicon single junction thin film solar cells were deposited on commercial red clay roof tiles with engobe surfaces and earthenware wall tiles with glazed surfaces, with a test area of 24 mm 2. We studied the influence of the type of substrate tile, back contact, buffer layer and SiO x passivation layer on the optoelectronic performance of the solar cells. Despite the fact that typical micrometre-sized defects on the surfaces of the tiles and the porous nature of the ceramic substrates make deposition of homogeneous thin films on them quite challenging, we have been able to achieve a cell efficiency of 5% and a quantum efficiency of 80% on non-fully optimized cells on commercial tiles. The method is industrially employable utilizing pre-existing plasma-enhanced chemical vapour deposition technologies. The cost-effectiveness and industrial feasibility of the technique are discussed. Our study shows that photovoltaic tiles can combine energy generation with architectural aesthetics leading to significant implications for advancement in building integrated photovoltaics. © 2011 The Royal Society of Chemistry.

A commercial sheet of paper based on natural cellulose fibers acting as permeable membrane with thin film metal cathode (Cu) and anode (Al) layers in each face was used to produce paper batteries that could be interconnected in series and rechargeable using water as electrolyte. Their electrical characteristics and the set of electrochemical reactions that support the experimental behavior observed are described in this paper. A series of integrated batteries able to supply a voltage of about 3 V and a current ranging from 0.7 μA to 25 μA in cells with sizes of 1.2 cm × 3.0 cm for a relative humidity in the range of 50-65% were produced in a single sheet of paper, and successfully applied to control the ON/OFF gate state of paper transistors. © 2010 Elsevier Ltd. All rights reserved.

The present work proposes the development of a bio-battery composed by an ultrathin monolithic structure of an electrospun cellulose acetate membrane, over which was deposited metallic thin film electrodes by thermal evaporation on both surfaces. The electrochemical characterization of the bio-batteries was performed under simulated body fluids like sweat and blood plasma [salt solution - 0.9% (w/w) NaCl]. Reversible electrochemical reactions were detected through the cellulose acetate structure. Thus, a stable electrochemical behavior was achieved for a bio-battery with silver and aluminum thin films as electrodes. This device exhibits the ability to supply a power density higher than 3μWcm-2.Finally, a bio-battery prototype was tested on a sweated skin, demonstrating the potential of applicability of this bio-device as a micropower source. © 2010 Elsevier B.V.

Thin-film transistors (TFTs) were fabricated using a 20-nm-thick indium molybdenum oxide (IMO) semiconductor layer at room temperature. The grazing incidence X-ray diffraction patterns confirmed that the deposited films are amorphous. The average transmittance (400-2500 nm) and the optical band gap are ∼88% and 3.95 eV, respectively. The TFTs fabricated on glass substrates showed a saturation mobility of 4.0 cm2/Vċ s with an I ON/IOFF ratio of 2 × 103 and a threshold voltage of-1.1 V, which are encouraging preliminary results in order to develop IMO as high-performance semiconductor layer. © 2011 IEEE.

Transparent electronics is today one of the most advanced topics for a wide range of device applications, where the key components are wide band gap semiconductors, where oxides of different origin play an important role, not only as passive components but also as active components similar to what we observe in conventional semiconductors. As passive components they include the use of these materials as dielectrics for a wide range of electronic devices and also as transparent electrical conductors for use in several optoelectronic applications, such as liquid crystal displays, organic light emitting diodes, solar cells, optical sensors etc. As active materials, they exploit the use of truly electronic semiconductors where the main emphasis is being put on transparent thin film transistors, light emitting diodes, lasers, ultraviolet sensors and integrated circuits among others. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The 3D scanning electro-optical characteristics of a data acquisition prototype system integrating a 32 linear array of 1D amorphous silicon position sensitive detectors (PSD) were analyzed. The system was mounted on a platform for imaging 3D objects using the triangulation principle with a sheet-of-light laser. New obtained results reveal a minimum possible gap or simulated defect detection of approximately 350 μm. Furthermore, a first study of the angle for 3D scanning was also performed, allowing for a broad range of angles to be used in the process. The relationship between the scanning angle of the incident light onto the object and the image displacement distance on the sensor was determined for the first time in this system setup. Rendering of 3D object profiles was performed at a significantly higher number of frames than in the past and was possible for an incident light angle range of 15 ° to 85 °. © 2012 Optical Society of America.

This work reports the production of ceramic targets based on nanostructured Al-doped ZnO (AZO) powders for sputtering applications. The nanostructured powder is obtained by a new patented process based on the detonation of an emulsion containing both Zn and Al metal precursors in the final proportion of 98:2wt% (ZnO:Al 2O 3), through which the Al contains is highly uniform distributed over ZnO. Due to the nanostructured powder characteristics, the targets can be sintered at substantially lower temperatures (1150-1250°C) by conventional sintering, contributing to production costs reduction of ceramic targets and consequently the costs of photovoltaic and displays industries. Electrical resistivity values around 3.0-7.0×10 -3Ωcm have been obtained depending on final microstructure of the targets. The electro-optical properties of the films produced at room temperature with thicknesses around 360nm, besides being highly uniform exhibit a resistivity of about 1×10 -3Ωcm and a transmittance in the visible range above 90%. © 2012 Elsevier Ltd.

A 32/128 linear array of 1-D amorphous silicon position sensitive detectors (PSD) was integrated into a self constructed suitable and portable data acquisition prototype system. The system is comprised by a commercially available existing electronics module suitable for photodiode data acquisition operations and by another adapter module, which allows for removal and replacement of the 32/128 PSD based sensor. This system is applied for imaging 3-D objects using the triangulation principle with a sheet-of-light laser. The sensor array response obtained from the reflected light of the object was fed into an electronic readout system and the corresponding signals were analyzed using the relevant data algorithm. The obtained results show a sensor nonlinearity of about 4%-7%, a wide sensor/system dynamic range and a 3-D profile spatial resolution supplied by each sensor strip of 339 μm, which can easily be reduced to 8.5 μm and even further with appropriate software modifications. © 2011 IEEE.

This paper addresses a modeling and simulation methodology for analog circuit design with amorphous-GIZO thin-film transistors (TFTs). To reach an effective circuit design flow, with commercially available tools, a TFT model has been first developed with an artificial neural network (ANN). Multilayer perceptron with backpropagation algorithm has been adopted to model the static behavior of the TFT devices, for different aspect ratios. The model was then implemented in Verilog-A, to allow a quick instantiation in circuit. Simulations using Cadence Spectre are performed to validate the model. On a second phase, simulation results of basic analog circuits, with this ANN model, are verified against the actual functional results, namely an adder, subtractor, and current mirror circuit. Results demonstrate not only the ANN model accuracy and compatibility with dc and transient analysis, but also show the a-GIZO TFT capability to perform analog operations. © 2012 IEEE.

Thin films of (Ta 2O 5) 0.85(TiO 2) 0.15 were deposited on quartz and p-Si substrates by DC reactive magnetron sputtering at different substrate temperatures (T s) in the range 303 - 873 K. The films deposited at 303 0K were in the amorphous and it transformed to crystalline at substrate temperatures ≥ 573 0K. The crystallite size was increased from 50 nm to 72 nm with the increase of substrate temperature. The surface morphology was significantly influenced with the substrate temperature. After deposition of the (Ta 2O 5) 0.85(TiO 2) 0.15 films on Si, aluminium (Al) electrode was deposited to fabricate metal/oxide/semiconductor (MOS) capacitors with a configuration of Al/(Ta 2O 5) 0.85(TiO 2) 0.15/Si. A low leakage current of 7.7 × 10 -5 A/cm 2 was obtained from the films deposited at 303 K. The leakage current was decreased to 9.3 × 10 -8 A/cm 2 with the increase of substrate temperature owing to structural changes. The conduction mechanism of the Al/(Ta 2O 5) 0.85(TiO 2) 0.15/Si capacitors was analyzed and compared with mechanisms of Poole-Frenkel and Schottky emissions. The optical band gap (E g) was decreased from 4.45 eV to 4.38 eV with the increase in substrate temperature. © Published under licence by IOP Publishing Ltd.

Indium molybdenum oxide (IMO) thin films were radio-frequency (RF) sputtered at room temperature (RT) and studied as a function of base pressure (BP). The crystallinity of the films is decreased with the increase in BP. A maximum mobility (μ) of 49.6 cm 2 V -1 s -1 was obtained from the IMO films deposited at RT without any post-annealing treatment. The electronic behaviour of the deposited films was investigated by temperature-dependent (100-550 K) Hall measurements. Study on the scattering mechanisms based on the experimental data and theoretical models show that the ionized scattering centres are dominating. The films possess wide work function (4.91 eV) and high transmittance (> 70%) over visible and near infrared (NIR) range. The obtained results, especially the high work function and NIR transmittance, are very promising particularly in applications such as optical detectors and solar cells. Copyright © EPLA, 2012.

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.

This paper deals with high transparent and high conductive oxides based on polycrystalline titanium (Ti) doped (0.5-3 at.%) indium oxide (IO) thin films produced on glass substrates at 400 °C by spray pyrolysis technique. X-ray diffraction analysis confirmed the cubic bixbyite structure of indium oxide. A high mobility of ∼ 97 cm2 V- 1 s- 1, a carrier concentration of ∼ 1.55 × 1020 cm- 3 and a resistivity of ∼ 4.11 × 10- 4 Ω-cm with ∼ 83% of transmittance in the wavelength ranging between 400 and 2500 nm were obtained for 2 at.% Ti doping films, rivalling so to the best known transparent conducting oxide based on indium tin oxide. Moreover, the transmittance in the broad wavelength ranging between 400 and 2500 nm is over 83%, leading so to an increasing carrier generation towards the near infrared region of the spectrum, as required for applications such as solar cells. We also notice that increasing the doping concentration widened the optical band gap and caused a small Burstein-Moss shift, due to mobility decrease, as expected. © 2012 Published by Elsevier B.V.

We have characterized the structure and electrical properties of p-type nanocrystalline silicon films prepared by radio-frequency plasma-enhanced chemical vapor deposition and explored optimization methods of such layers for potential applications in thin-film solar cells. Particular attention was paid to the characterization of very thin (∼20nm) films. The cross-sectional morphology of the layers was studied by fitting the ellipsometry spectra using a multilayer model. The results suggest that the crystallization process in a high-pressure growth regime is mostly realized through a subsurface mechanism in the absence of the incubation layer at the substrate-film interface. Hydrogen plasma treatment of a 22-nm-thick film improved its electrical properties (conductivity increased more than ten times) owing to hydrogen insertion and Si structure rearrangements throughout the entire thickness of the film. © 2012 National Institute for Materials Science.

Titanium oxide (TiO 2) finds potential applications in various fields such as solar cells, optical coatings due to its high refractive index and it also has been widely used in memory devices owing to its high dielectric constant. TiO 2 films have been deposited on p-type silicon (100) substrates by RF magnetron sputtering technique. Thickness, structure and surface morphology of the films were analyzed by using α-step profilometer, Raman spectroscopy and atomic force microscope respectively. Thin film capacitors of the type Al/TiO 2/Si were fabricated by evaporation of Aluminium on to the TiO 2 films. The current - voltage and capacitance - voltage characteristics were carried out to understand the electrical conduction and dielectric properties of the deposited films with a stack of Al/TiO 2/Si. The leakage current density was decreased and capacitance was increased with increase of substrate bias voltage.