Publications

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2016
Kardarian, K., D. Nunes, P. {Maria Sberna}, A. Ginsburg, D. A. Keller, J. {Vaz Pinto}, J. Deuermeier, A. Y. Anderson, A. Zaban, R. Martins, and E. Fortunato, "{Effect of Mg doping on Cu2O thin films and their behavior on the TiO2/Cu2O heterojunction solar cells}", Solar Energy Materials and Solar Cells, vol. 147, pp. 27–36, apr, 2016. AbstractWebsite

Abstract The present work shows the effect of magnesium doping on structural, optoelectrical and electrical properties of Cu2O thin films prepared by spray pyrolysis. The variation in the concentration of Mg shows significant impact on the final thin film properties, whereas the film doped with 0.5 at{%} of Mg exhibited major property improvements in comparison with the undoped thin film and among the other concentrations tested. This condition was further applied for the deposition of an absorber layer in a heterojunction solar cell array with a gradient in thicknesses of active layers to investigate the impact of changing thicknesses on the PV parameters of the solar cell. TiO2 was used as a window layer and the 0.5 at{%} Cu2O doped film as an absorber layer. The produced heterojunction solar cell array was further exposed to a rapid thermal annealing treatment. The I–V measurements show an open circuit voltage of up to 365 mV and a short circuit current density, which is dependent on absorber layer thickness, and reaches to a maximum value of 0.9 mA/cm2.

Gonçalves, A., J. Resende, A. C. Marques, J. V. Pinto, D. Nunes, A. Marie, R. Gonçalves, L. Pereira, R. Martins, and E. Fortunato, "Smart optically active VO nanostructured layers applied in roof-type ceramic tiles for energy efficiency", Solar Energy Materials & Solar Cells, vol. 150, pp. 1-9, 2016.
2015
Morais, A. R. C., J. V. Pinto, D. Nunes, L. B. Roseiro, M. C. Oliveira, E. Fortunato, and R. Bogel-Łukasik, "{Imidazole: Prospect Solvent for Lignocellulosic Biomass Fractionation and Delignification}", ACS Sustainable Chemistry {&} Engineering: American Chemical Society, dec, 2015. AbstractWebsite
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Nunes, D., A. Pimentel, J. V. Pinto, T. R. Calmeiro, S. Nandy, P. Barquinha, L. Pereira, P. A. Carvalho, E. Fortunato, and R. Martins, "Photocatalytic behavior of TiO2 films synthesized by microwave irradiation", Catalysis Today, 2015. AbstractWebsite

Titanium dioxide was synthesized on glass substrates from titanium (IV)isopropoxide and hydrochloride acid aqueous solutions through microwave irradiation using as seed layer either fluorine-doped crystalline tin oxide (SnO2:F) or amorphous tin oxide (a-SnOx). Three routes have been followed with distinct outcome: (i) equimolar hydrochloride acid/water proportions (1HCl:1water) resulted in nanorod arrays for both seed layers; (ii) higher water proportion (1HCl:3water) originated denser films with growth yield dependent on the seed layer employed; while (iii) higher acid proportion (3HCl:1water) hindered the formation of TiO2. X-ray diffraction (XRD) showed that the materials crystallized with the rutile structure, possibly with minute fractions of brookite and/or anatase. XRD peak inversions observed for the materials synthesized on crystalline seeds pointed to preferred crystallographic orientation. Electron diffraction showed that the especially strong XRD peak inversions observed for TiO2 grown from the 1HCl:3water solution on SnO2:F originated from a [001] fiber texture. Transmittance spectrophotometry showed that the materials with finer structure exhibited significantly higher optical band gaps. Photocatalytic activity was assessed from methylene blue degradation, with the 1HCl:3water SnO2:F material showing remarkable degradability performance, attributed to a higher exposure of (001) facets, together with stability and reusability.

Nunes, D., L. Santos, P. Duarte, A. Pimentel, J. V. Pinto, P. Barquinha, P. A. Carvalho, E. Fortunato, and R. Martins, "Room Temperature Synthesis of Cu2O Nanospheres: Optical Properties and Thermal Behavior", Microscopy and Microanalysis, vol. 21, issue 01, pp. 11, 2015. Abstract

The present work reports a simple and easy wet chemistry synthesis of cuprous oxide (Cu2O) nanospheres at room temperature without surfactants and using different precursors. Structural characterization was carried out by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy coupled with focused ion beam and energy-dispersive X-ray spectroscopy. The optical band gaps were determined from diffuse reflectance spectroscopy. The photoluminescence behavior of the as-synthesized nanospheres showed significant differences depending on the precursors used. The Cu2O nanospheres were constituted by aggregates of nanocrystals, in which an on/off emission behavior of each individual nanocrystal was identified during transmission electron microscopy observations. The thermal behavior of the Cu2O nanospheres was investigated with in situ X-ray diffraction and differential scanning calorimetry experiments. Remarkable structural differences were observed for the nanospheres annealed in air, which turned into hollow spherical structures surrounded by outsized nanocrystals. FAU - Nunes, Daniela

Santos, L., P. Wojcik, J. V. Pinto, E. Elangovan, J. Viegas, L. Í. Pereira, R. Martins, and E. Fortunato, "Structure and Morphologic Influence of WO3 Nanoparticles on the Electrochromic Performance of Dual-Phase a-WO3/WO3 Inkjet Printed Films", Advanced Electronic Materials, pp. n/a-n/a, 2015. AbstractWebsite

The optimization of tungsten trioxide (WO3) nanoparticles produced via hydrothermal synthesis for application in electrochromic (EC) devices is reported. The structure and morphology of the nanoparticles are controlled by changing the acidity of the aqueous solvent added to the sol-gel precursor (peroxopolytungstic acid) during synthesis. Orthorhombic hydrated WO3 nanorods or monoclinic WO3 nanoslabs are obtained when HCl is added, while synthesis only in aqueous medium results in a mixture of both types of polymorphs. Dual-phase thin films are processed by inkjet printing deposition of the nanoparticles in flexible polyethylene terephthalate substrate with indium tin oxide coating (ITO PET) followed by the deposition of the precursor solution. When compared with purely amorphous tungsten oxide films, the dual phase ones present higher optical densities and improved capacity, and cyclability stability. The best results, obtained for orthorhombic hydrated nanoparticles (ortho-WO3·0.33H2O), are due to its high surface area and improved conductivity. Additionally, the ex situ X-ray diffraction (XRD) lithiation studies show evidence of a higher distortion of the monoclinic when compared with the orthorhombic crystallographic structure, which contribute to the inferior EC performance. These results validate the use of inkjet printing deposition with low processing temperatures for EC dual-phase thin films containing optimized nanoparticles which are compatible with low-cost substrates.

Nunes, D., T. R. Calmeiro, S. Nandy, J. V. Pinto, A. Pimentel, P. Barquinha, P. A. Carvalho, J. C. Walmsley, E. Fortunato, and R. Martins, "{Charging effects and surface potential variations of Cu-based nanowires}", Thin Solid Films: Elsevier B.V., pp. 1–9, 2015. AbstractWebsite

The presentwork reports charging effects and surface potential variations in pure copper, cuprous oxide and cu- pric oxide nanowires observed by electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM). The copper nanowires were produced by wet synthesis, oxidation into cuprous oxide nanowires was achieved throughmicrowave irradiation and cupric oxide nanowireswere obtained via furnace annealing in at- mospheric conditions. Structural characterization of the nanowireswas carried out byX-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. During the EFM experiments the electrostatic field of the positive probe charged negatively the Cu-based nanowires, which in turn polarized the SiO2 dielectric substrate. Both the probe/nanowire capacitance as well as the sub- strate polarization increased with the applied bias. Cu2O and CuO nanowires behaved distinctively during the EFMmeasurements in accordancewith their band gap energies. Thework functions(WF) of the Cu-based nano- wires, obtained by KPFM measurements, yieldedWFCuO N WFCu N WFCu2O

Kiazadeh, A., D. Salgueiro, R. Branquinho, J. Pinto, H. L. Gomes, P. Barquinha, R. Martins, and E. Fortunato, "{Operational stability of solution based zinc tin oxide/SiO2 thin film transistors under gate bias stress}", APL Materials, vol. 3, no. 6, pp. 062804, 2015. AbstractWebsite

In this study, we report solution-processed amorphous zinc tin oxide transistors exhibiting high operational stability under positive gate bias stress, translated by a recoverable threshold voltage shift of about 20{%} of total applied stress voltage. Under vacuum condition, the threshold voltage shift saturates showing that the gate-bias stress is limited by trap exhaustion or balance between trap filling and emptying mechanism. In ambient atmosphere, the threshold voltage shift no longer saturates, stability is degraded and the recovering process is impeded. We suggest that the trapping time during the stress and detrapping time in recovering are affected by oxygen adsorption/desorption processes. The time constants extracted from stretched exponential fitting curves are ≈106 s and 105 s in vacuum and air, respectively.

Nunes, D., A. Pimentel, J. V. Pinto, T. R. Calmeiro, S. Nandy, P. Barquinha, L. Pereira, P. A. Carvalho, E. Fortunato, and R. Martins, "{Photocatalytic behavior of TiO2 films synthesized by microwave irradiation}", Catalysis Today: Elsevier B.V., 2015. AbstractWebsite
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2014
Miguel, C., J. V. Pinto, M. Clarke, and M. J. Melo, "The alchemy of red mercury sulphide: The production of vermilion for medieval art", Dyes and Pigments, vol. 102, pp. 210-217, 2014. AbstractWebsite

Vermilion red, mercury sulphide (α-HgS), was one of the most important reds in art and its use as a pigment dates back to Antiquity. In medieval Europe, it could be mined as cinnabar, or produced as vermilion by heating mercury with sulphur. This work aims to study the production of synthetic vermilion as a medieval pigment and to confirm which was the source (mineral or artificial) of the reds used in Portuguese medieval illuminations. The production of synthetic vermilion was based on the process described in the Judaeo-Portuguese medieval treatise “The book on how to make colours”, using materials and technologies as close as possible to the medieval ones. The reaction mechanism was studied by following the heating process by X-ray diffraction, and it was possible to conclude that the transformation from black cubic β-HgS into red hexagonal α-HgS is a solid-state phase transition, occurring at 235 °C. This result is contrary to what published in technical art literature, in which this process is described as a sublimation. Moreover, Scanning Electron Microscopy evidenced a sinterization effect on the artificial vermilion, not found in medieval original samples nor in paints prepared with mineral cinnabar from Almadén (Spain). Red mercury sulphide, natural and synthetic, was then prepared as a parchment-glue paint and compared to proteinaceous red paints from 12th–13th century miniatures produced in important medieval monasteries, previously fully characterized by a multi-analytical approach (μ-Energy dispersive X-ray fluorescence, μ-Fourier Transform Infrared Spectroscopy, Raman microscopy). A comparative Electron probe microanalysis of the red paints point to a mineral provenance for medieval vermilion found in Portuguese illuminations.

Pereira, S., A. Gonçalves, N. Correia, J. Pinto, L. Í. Pereira, R. Martins, and E. Fortunato, "Electrochromic behavior of NiO thin films deposited by e-beam evaporation at room temperature", Solar Energy Materials and Solar Cells, vol. 120, Part A, pp. 109-115, 2014. AbstractWebsite

In this work we report the role of thickness on electrochromic behavior of nickel oxide (NiO) films deposited by e-beam evaporation at room temperature on ITO-coated glass. The structure and morphology of films with thicknesses between 100 and 500 nm were analyzed and then correlated with electrochemical response and transmittance modulation when immersed in 0.5 M LiClO4–PC electrolyte. The NiO exhibits an anodic coloration, reaching for the thickest film a transmittance modulation of 66% between colored and bleached state, at 630 nm, with a color efficiency of 55 cm2 C−1. Very fast switch between states was obtained, where coloration and bleaching times are 3.6 s cm−2 and 1.4 s cm−2, respectively.

Veigas, B., R. Branquinho, J. V. Pinto, P. J. Wojcik, R. Martins, E. Fortunato, and P. V. Baptista, "Ion sensing (EIS) real-time quantitative monitorization of isothermal DNA amplification", Biosensors and Bioelectronics, 2014. Abstract
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Ceia, T. F., A. G. Silva, C. S. Ribeiro, J. V. Pinto, M. H. Casimiro, A. M. Ramos, and J. Vital, "PVA composite catalytic membranes for hyacinth flavour synthesis in a pervaporation membrane reactor", Catalysis Today, vol. 236, pp. 98-107, 2014. Abstract
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2013
Nandy, S., G. Goncalves, J. V. Pinto, T. Busani, V. Figueiredo, L. Pereira, R. F. Paiva Martins, and E. Fortunato, "Current transport mechanism at metal-semiconductor nanoscale interfaces based on ultrahigh density arrays of p-type NiO nano-pillars", Nanoscale, vol. 5, issue 23, pp. 11699-11709, 2013. AbstractWebsite

The present work focuses on a qualitative analysis of localised I-V characteristics based on the nanostructure morphology of highly dense arrays of p-type NiO nano-pillars (NiO-NPs). Vertically aligned NiO-NPs have been grown on different substrates by using a glancing angle deposition (GLAD) technique. The preferred orientation of as grown NiO-NPs was controlled by the deposition pressure. The NiO-NPs displayed a polar surface with a microscopic dipole moment along the (111) plane (Tasker's type III). Consequently, the crystal plane dependent surface electron accumulation layer and the lattice disorder at the grain boundary interface showed a non-uniform current distribution throughout the sample surface, demonstrated by a conducting AFM technique (c-AFM). The variation in I-V for different points in a single current distribution grain (CD-grain) has been attributed to the variation of Schottky barrier height (SBH) at the metal-semiconductor (M-S) interface. Furthermore, we observed that the strain produced during the NiO-NPs growth can modulate the SBH. Inbound strain acts as an external field to influence the local electric field at the M-S interface causing a variation in SBH with the NPs orientation. This paper shows that vertical arrays of NiO-NPs are potential candidates for nanoscale devices because they have a great impact on the local current transport mechanism due to its nanostructure morphology.

Pinto, J. V., R. Branquinho, P. Barquinha, E. Alves, R. Martins, and E. Fortunato, "Extended-Gate ISFETs Based on Sputtered Amorphous Oxides", Journal of Display Technology, vol. 9, issue 9, pp. 729-734, 2013. AbstractWebsite
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Figueiredo, V., J. V. Pinto, J. Deuermeier, R. Barros, E. Alves, R. Martins, and E. Fortunato, "p-Type CuxO Thin-Film Transistors Produced by Thermal Oxidation", Journal of Display Technology, vol. 9, issue 9, pp. 6, 2013. AbstractWebsite
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Branquinho, R., J. V. Pinto, T. Busani, P. Barquinha, L. Pereira, P. Viana Baptista, R. Martins, and E. Fortunato, "Plastic Compatible Sputtered Ta2O5 Sensitive Layer for Oxide Semiconductor TFT Sensors", Display Technology, Journal of, vol. 9, issue 9, pp. 723-728, 2013. Abstract

The effect of post-deposition annealing temperature on the pH sensitivity of room temperature RF sputtered Ta2O5 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 °C and crystallize at 700 °C in an orthorhombic phase. Electrolyte-insulator-semiconductor (EIS) field effect based sensors with an amorphous Ta2O5 sensing layer showed pH sensitivity above 50 mV/pH. For sensors annealed above 200 °C pH sensitivity decreased with increasing temperature. Stabilized sensor response and maximum pH sensitivity was achieved after low temperature annealing at 200 °C, which is compatible with the use of polymeric substrates and application as sensitive layer in oxides TFT-based sensors.

Santos, R., J. Loureiro, A. Nogueira, E. Elangovan, J. V. Pinto, J. P. Veiga, T. Busani, E. Fortunato, R. Martins, and I. Ferreira, "Thermoelectric properties of V2O5 thin films deposited by thermal evaporation", Applied Surface Science, vol. 282, pp. 590-594, 2013. AbstractWebsite
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Cruz, M. M., R. C. Silva, J. V. Pinto, R. P. Borges, N. Franco, and A. Casaca, "{Formation of oriented nickel aggregates in rutile single crystals by Ni implantation}", Journal of Magnetism and Magnetic Materials, vol. 340: Elsevier, pp. 102–108, 2013. AbstractWebsite

The magnetic and electrical properties of Ni implanted single crystalline TiO2 rutile were studied for nominal implanted fluences between 0.5?1017 cm−2 and 2.0?1017 cm−2 with 150 keV energy, corre- sponding to maximum atomic concentrations between 9 at{%} and 27 at{%} at 65 nm depth, in order to study the formation of metallic oriented aggregates. The results indicate that the as implanted crystals exhibit superparamagnetic behavior for the two higher fluences, which is attributed to the formation of nanosized nickel clusters with an average size related with the implanted concentration, while only paramagnetic behavior is observed for the lowest fluence. Annealing at 1073 K induces the aggregation of the implanted nickel and enhances the magnetization in all samples. The associated anisotropic behavior indicates preferred orientations of the nickel aggregates in the rutile lattice consistent with Rutherford backscattering spectrometry—channelling results. Electrical conductivity displays anisotropic behavior but no magnetoresistive effects were detected.

Figueiredo, V., J. V. Pinto, J. Deuermeier, R. Barros, E. Alves, R. Martins, and E. Fortunato, "{p-Type Cu O Thin-Film Transistors Produced by Thermal Oxidation}", Journal of Display Technology, vol. 9, no. 9, pp. 735–740, 2013. Abstract

Thin-films of copper oxide Cu O were produced by thermal oxidation of metallic copper (Cu) at different tempera- tures (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 Cand its conversion toCuO starts at 250 C. For lower thick- nesses 40 nm, the films oxidized at 250 Cshowed 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.

Branquinho, R., J. V. Pinto, T. Busani, P. Barquinha, L. Pereira, P. V. Baptista, R. Martins, and E. Fortunato, "{Plastic Compatible Sputtered Ta O Sensitive Layer for Oxide Semiconductor TFT Sensors}", Journal of Display Technology, vol. 9, no. 9, pp. 723–728, 2013. Abstract

The effect of post-deposition annealing temperature on the pH sensitivity of room temperature RF sputtered Ta O was investigated. Structural and morphological features of these films were analyzed before and after annealing at various tem- peratures. The deposited films are amorphous up to 600 Cand crystallize at 700 C in an orthorhombic phase. Electrolyte-insu- lator-semiconductor (EIS) field effect based sensors with an amor- phousTa O sensing layer showed pHsensitivity above 50 mV/pH. For sensors annealed above 200 C pH sensitivity decreased with increasing temperature. Stabilized sensor response andmaximum pHsensitivitywas achieved after low temperature annealing at 200 C, which is compatible with the use of polymeric substrates and application as sensitive layer in oxides TFT-based sensors

2012
Casimiro, M. H., A. G. Silva, J. V. Pinto, A. M. Ramos, J. Vital, and L. M. Ferreira, "Catalytic poly(vinyl alcohol) functionalized membranes obtained by gamma irradiation", Radiation Physics and Chemistry, vol. 81, issue 9, pp. 1314-1318, 2012. Abstract
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Duarte, P., D. P. Ferreira, T. F. Lopes, J. V. Pinto, I. M. Fonseca, I. Ferreira Machado, and L. F. Vieira Ferreira, "DSM as a probe for the characterization of modified mesoporous silicas", Microporous and Mesoporous Materials, vol. 161, pp. 139-147, 2012. Abstract
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Figueiredo, V., E. Elangovan, R. Barros, J. V. Pinto, T. Busani, R. Martins, and E. Fortunato, "{p-Type Cu x O Films Deposited at Room Temperature for Thin-Film Transistors}", Journal of Display Technology, vol. 8, no. 1, pp. 41–47, 2012. Abstract

Thin-films of copper oxide @Cu OA were sputtered from a metallic copper (Cu) target and studied as a function of oxygen partial pressure @O??A. A metallic Cu film with cubic structure obtained from 0{%} O?? has been transformed to cubic CuPO phase for the increase in O?? to 9{%} but then changed to monoclinic CuO phase (for O?? PS7). The variation in crystallite size (calculated from x-ray diffraction data) was further substantiated by the variation in grain size (surface microstruc- tures). The Cu O films produced with O?? ranging between 9{%} and 75{%} showed p-type behavior, which were successfully applied to produce thin-film transistors.

2011
Nayak, P. K., J. V. Pinto, G. Goncalves, R. Martins, and E. Fortunato, "Environmental, Optical, and Electrical Stability Study of Solution-Processed Zinc-Tin-Oxide Thin-Film Transistors", Journal of Display Technology, vol. 7, issue 12, pp. 640-643, 2011. Abstract
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