Rodrigo Martins

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.

Thin-films of copper oxide Cu O were produced by thermal oxidation of metallic copper (Cu) at different temperatures (150-450 C). The films produced at temperatures of 200, 250 and 300 C showed high Hall motilities of 2.2, 1.9 and 1.6 cm V s , respectively. Single Cu O phases were obtained at 200 C and its conversion to CuO starts at 250 C. For lower thicknesses 40 nm, the films oxidized at 250 C showed a complete conversion to CuO phase. Successful thin-film transistors (TFTs) were produce by thermal oxidation of a 20 nm Cu film, obtaining p-type Cu O (at 200 C) and CuO (at 250 C) with On/Off ratios of 6 10 and 1 10 , respectively. © 2005-2012 IEEE.

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.

In this work, we report results concerning the performances of thin-film transistors (TFTs) where the channel layer is based on microcrystalline zinc tin oxide (ZTO) processed by spray pyrolysis technique. TFTs made with 30 nm thick ZTO channel layer deposited at a substrate temperature of 400 C and 300 Cexhibited, respectively, a saturation mobility of 2.9 cm V s and 1.45 cm V s ; voltage of 0.15 V, and 0.2 V; a sub-threshold swing of 400 mV/dec and 500 mV/dec; ON/OFF ratio at the onset of hard saturation current of 3.5 10 and 6 10 , for a drain to source voltage of 10 V (close to or below the gate to source voltage). This indicates that the substrate temperature is relevant in determining the devices' electronic performances. © 2013 IEEE.

The effect of post-deposition annealing temperature on the pH sensitivity of room temperature RF sputtered +{\hbox{Ta}}-{2}{\hbox{O}}5 was investigated. Structural and morphological features of these films were analyzed before and after annealing at various temperatures. The deposited films are amorphous up to 600 +^{\circ}{\hbox{C}}+ and crystallize at 700 +^{\circ}{\hbox{C}}+ in an orthorhombic phase. Electrolyte-insulator- semiconductor (EIS) field effect based sensors with an amorphous +{\hbox{Ta}}-{2}{\hbox{O}}5 sensing layer showed pH sensitivity above 50 mV/pH. For sensors annealed above 200 +^{\circ}{\hbox{C}}+ pH sensitivity decreased with increasing temperature. Stabilized sensor response and maximum pH sensitivity was achieved after low temperature annealing at 200 +^{\circ}{\hbox{C}}+ , which is compatible with the use of polymeric substrates and application as sensitive layer in oxides TFT-based sensors. © 2005-2012 IEEE.

In this work Laponite was combined with a modified abundant natural polymer, (caboxymethyl cellulose), acrylic sodium salt polymer and lithium perchlorate aiming to produce inexpensive and sustainable nanocomposite electrolytes for functional electrochemical devices. Optical, electrochemical, structural, morphological and rheological characterization was performed in order to evaluate their properties and potential advantages as electrolyte. It was verified that the addition of Laponite led to an ionic conductivity at room temperature (25 C) in the range of 6 to 9 × 10- 5 Scm - 1 this value being then determined by the composition of the nanocomposite. These electrolytes were applied to electrochromic devices using evaporated nickel oxide thin film as the electrochromic layer. The devices exhibited a significant transmittance modulation that exceeds 45 % at 600 nm. © 2013 Elsevier B.V.

The ability to process and dimensionally scale field-effect transistors with and on paper and to integrate them as a core component for low-power-consumption analog and digital circuits is demonstrated. Low-temperature-processed p- and n-channel integrated oxide thin-film transistors in the complementary metal oxide semiconductor (CMOS) inverter architecture are seamlessly layered on mechanically flexible, low-cost, recyclable paper substrates. The possibility of building these circuits using low-temperature processes opens the door to new applications ranging from smart labels and sensors on clothing and packaging to electronic displays printed on paper pages for use in newspapers, magazines, books, signs, and advertising billboards. Because the CMOS circuits reported constitute fundamental building blocks for analog and digital electronics, this development creates the potential to have flexible form factor computers seamlessly layered onto paper. The holistic approach of merging low-power circuitry with a recyclable substrate is an important step towards greener electronics. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

We report the effect of a disperse carbon interlayer between the n-a-Si:H layer and an aluminium zinc oxide (AZO) back contact on the performance of amorphous silicon solar cells. Carbon was incorporated to the AZO film as revealed by x-ray photoelectron spectroscopy and energy-dispersive x-ray analysis. Solar cells fabricated on glass substrates using AZO in the back contact performed better when a disperse carbon interlayer was present in their structure. They exhibited an initial efficiency of 11%, open-circuit voltage Voc = 1.6 V, short-circuit current JSC = 11 mA cm -2 and a filling factor of 63%, that is, a 10% increase in the J SC and 20% increase in the efficiency compared to a standard solar cell. © 2013 National Institute for Materials Science.

Electrospun fibers of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2) with exceptional electro-optical performance are obtained. The I/T characteristics measured in fibers with 7-15 μm diameter and 1 mm length show a semiconductor behavior; their thermal activation energy is 0.5 eV and the dark conductivity at RT is 5 × 10-9 (Ω cm)-1. Besides exhibiting a photosensitivity of about 60 under white light illumination with a light power intensity of 25 mW · cm-2, the fibers also attain RT photoluminescence in the cyan, yellow, and red wavelength range under ultraviolet, blue, and green light excitation, respectively. Optical microscope images of F8T2 reveal homogeneous electrospun fibers, which are in good agreement with the uniformly radial fluorescence observed. The production of electrospun fibers from poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-bithiophene] (F8T2) obtained without a carrier polymer is reported. The obtained fibers are shown to have properties suitable for organic fiber photovoltaic and sensors applications. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In the present work one host natural matrix - agar - has been doped with magnesium triflate (Mg(CF3SO3)2) with the goal of developing electrolytes for the fabrication of solid-state devices. The resulting samples have been represented by the notation Agar nMg(CF3SO3)2, where n represents the percentage of the magnesium triflate salt proportion in the electrolyte samples. The samples investigated, with n between 0.00% and 37.56%, have been obtained as transparent and thin films. The samples have been characterized by conductivity measurements, thermal analysis, cyclic voltammetry, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The agar-based electrolytes were also tested as ionic conductor in an electrochromic device with the following configuration: glass/indium tin oxide (ITO)/WO 3/agar-based electrolyte/CeO2-TiO2/ITO/glass. © 2013 Copyright Taylor and Francis Group, LLC.

This work reports the structural, optical, electrical and thermoelectric properties of vanadium pentoxide (V2O5) thin films deposited at room temperature by thermal evaporation on Corning glass substrates. A post-deposition thermal treatment up to 973 K under atmospheric conditions induces the crystallization of the as-deposited amorphous films with an orthorhombic V2O5 phase with grain sizes around 26 nm. As the annealing temperature rises up to 773 K the electrical conductivity increases. The films exhibit thermoelectric properties with a maximum Seebeck coefficient of -218 μV/K and electrical conductivity of 5.5 (Ω m) -1. All the films show NIR-Vis optical transmittance above 60% and optical band gap of 2.8 eV. © 2013 Elsevier B.V. All rights reserved.

This paper characterizes transparent current mirrors with n-type amorphous gallium-indium-zinc-oxide (a-GIZO) thin-film transistors (TFTs). Two-TFT current mirrors with different mirroring ratios and a cascode topology are considered. A neural model is developed based on the measured data of the TFTs and is implemented in Verilog-A; then it is used to simulate the circuits with Cadence Virtuoso Spectre simulator. The simulation outcomes are validated with the fabricated circuit response. These results show that the neural network can model TFT accurately, as well as the current mirroring ability of the TFTs. © 2005-2012 IEEE.

In obtaining uniform array of ZnO 1D nanostructures, especially using solution based methods, the thickness and the morphology of the epitaxial seeds layer are very important. The paper presents the effect of the thickness and the morphology of the Al:ZnO seeds layer on the morphology and properties of ZnO nanowires array grown by hydrothermal method. Compact and vertically aligned ZnO 1D nanostructures were obtained. Concentration of 0.02 M of zinc nitrate was found to be optimal for growing nanowires with diameters up to 50 nm and lengths between 1.5 and 2.5 microns. Using 0.04 M solution, nanorods with diameter between 50 and 100 nm were obtained. The correlation between the crystal structure and optical properties of ZnO nanowires is discussed. From electrical measurements on single nanowire, resistivity value of 9×10?2 cm was obtained. The I-V curves of single ZnO NWs show quasi diode characteristic when an e-beam is irradiating the NWs, and a typical semiconductive behaviour when the e-beam is turned off. Copyright © 2013 American Scientific Publishers.

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.

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 microstructural aspects related to crystalline or amorphous structure of as-deposited and annealed films of sol-gel-derived WO 3 are shown in the literature to be critical for electrochromic (EC) performance. In consideration of ion insertion materials, there is a need for developing light and at the same time nanocrystalline structures to improve both coloration efficiency and switching kinetics. By controlling microstructure and morphology, one could design a material with optimal EC performance. This report compares the microstructural and morphological characteristics of standard WO 3 wet deposition techniques versus inkjet printing technology (IPT), correlating these features with their optical and electrochemical performances, emphasizing the importance of the dual-phase a-WO 3/TiO 2/WO X film composition proposed in this work for high-performance EC applications. The effect of the type and content of metal oxide nanoparticles in the precursor sols formulated in various peroxopolytungstic acid (PTA) and oxalic acid (OAD) proportions on film properties is comprehensively studied using multi-factorial design of experiment (DOE). To the authors' knowledge, no other report on sol-gel deposition of inorganic EC materials via the inkjet printing technique exists, in which furthermore the film crystallinity can be controlled under low-temperature process conditions. The proposed method enables development of EC films which irrespective of their composition (a-WO 3, a-WO 3/TiO 2 or a-WO 3/TiO 2/WO X) outperform their amorphous or nanocrystalline analogues presented as the state-of-the-art due to their superior chemical and physical properties. © 2012 The Royal Society of Chemistry.