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Martins R.,New University of Lisbon | Figueiredo V.,New University of Lisbon | Barros R.,New University of Lisbon | Barros R.,Materiais Avancados SA | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

P-type thin-film transistors (TFTs) using room temperature sputtered tin and copper oxide as a transparent oxide semiconductor have been produced on rigid and paper substrates. The SnO x films shows p-type conduction presenting a polycrystalline structure composed with a mixture of tetragonal β-Sn and α-SnO x phases, after annealing at 200°C. These films exhibit a hole carrier concentration in the range of ≈ 10 16-10 18 cm -3, electrical resistivity between 101-102 Ωcm, Hall mobility of 4.8 cm 2/Vs, optical band gap of 2.8 eV and average transmittance ≈ 85 % (400 to 2000 nm). Concerning copper oxide Cu xO thin films they exhibit a polycrystalline structure with a strongest orientation along (111) plane. The Cu xO films produced between an oxygen partial pressure of 9 to 75% showed p-type behavior, as it was measured by Hall effect and Seebeck measurements. The bottom gate p-type SnO x TFTs present field-effect mobility above 1.24 cm 2/Vs (including the paper p-type oxide TFT) and an on/off modulation ratio of 10 3 while the Cu xO TFTs exhibit a field-effect mobility of 1.3×10 -3 cm 2/Vs and an on/off ratio of 2×10 2. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE). Source


Loureiro J.,CENIMAT I3N | Neves N.,Materiais Avancados SA | Barros R.,CENIMAT I3N | Mateus T.,CENIMAT I3N | And 9 more authors.
Journal of Materials Chemistry A | Year: 2014

Improved thermoelectric properties of Aluminum Zinc Oxide (AZO) thin films deposited by radio frequency (RF) and pulsed Direct Current (DC) magnetron sputtering at room temperature are reported. In both techniques films were deposited using sintered and non-sintered targets produced from nano-powders. It is confirmed that both the Al doping concentration and film thickness control the thermoelectric, optical and structural properties of these films. Seebeck coefficients up to -134 μV K-1 and electrical conductivities up to 4 × 104 (Ω m)-1 lead to power factors up to 4 × 10-4 W mK-2, which is above the state-of-the-art for similar materials, almost by a factor of three. The thermoelectric I-V response of an optimized AZO element with a planar geometry was measured and a maximum power output of 2.3 nW, for a temperature gradient of 20 K near room temperature, was obtained. Moreover, the low thermal conductivity (<1.19 W mK-1) yields a ZT value above 0.1. This is an important result as it is at least three times higher than the ZT found in the literature for AZO, at room temperature, opening new doors for applications of this inexpensive, abundant and environmental friendly material, in a new era of thermoelectric devices. This journal is © the Partner Organisations 2014. Source


Neves N.,Materiais Avancados SA | Neves N.,New University of Lisbon | Lagoa A.,Materiais Avancados SA | Calado J.,Materiais Avancados SA | And 4 more authors.
Journal of the European Ceramic Society | Year: 2014

Emulsion detonation synthesis method was used to produce undoped and Al-doped ZnO nanostructured powders (0.5-2.0wt.% Al2O3). The synthesized powders present a controlled composition and a morphology which is independent on the doping level. The XRD results indicate wurtzite as the single phase for undoped ZnO and the presence of gahnite as secondary phase for Al-doped ZnO powders. The sintering behavior of each powder was studied based on their linear shrinkage and shrinkage rate curves, showing the high sinterability of the powders. Activation energies for densification in the earlier stage were calculated for all compositions and possible sintering mechanisms are suggested depending on the doping level. The high chemical homogeneity and sinterability and the lower electrical resistivity of the bulk Al-doped sintered samples demonstrates the feasibility of emulsion detonation synthesis for the production of high quality Al-doped ZnO powders to be used in ceramic sputtering targets manufacture. © 2014 Elsevier Ltd. Source


Neves N.,Materiais Avancados SA | Neves N.,New University of Lisbon | Barros R.,Materiais Avancados SA | Barros R.,New University of Lisbon | And 5 more authors.
Journal of the European Ceramic Society | Year: 2012

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. Source

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