Advanced Materials Forum III

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Authors: Elvira Fortunato, Alexandra Gonçalves, António Marques, Ana Pimentel, Pedro Barquinha, Hugo Águas, Luís Pereira, Leandro Raniero, Gonçalo Gonçalves, Isabel Ferreira, Rodrigo Martins
Abstract: In this paper we report some of the recent advances in transparent thin film oxide semiconductors, specifically zinc oxide (ZnO), produced by rf magnetron sputtering at room temperature with multifunctional properties. By controlling the deposition parameters it is possible to produce undoped material with electronic semiconductor properties or by doping it to get either n-type or p-type semiconductor behavior. In this work we refer our experience in producing n-type doping ZnO as transparent electrode to be used in optoelectronic applications such as solar cells and position sensitive detectors while the undoped ZnO can be used as UV photodetector or ozone gas sensor or even as active layer of fully transparent thin film transistors.
Authors: Hugh D. Burrows, Ricardo Castro, M. Alexandra Esteves, Barbara Gigante, Luísa Leitão, Ana Pauleta
Abstract: Five novel triarylamines based on the bulky dehydroabietic acid unit have been synthesised, and their potential as hole transport layers tested. This bulky group facilitates film preparation and stability without significantly affecting the chemical or materials properties. Three of these systems present excellent stability, and show considerable potential for device applications.
Authors: Rodrigo Martins, Daniel Costa, Hugo Águas, Fernanda Soares, António Marques, Isabel Ferreira, P.M.R. Borges, Sergio Pereira, Leandro Raniero, Elvira Fortunato
Abstract: This work aims to report results of the spatial and frequency optical detection limits of integrated arrays of 32 one-dimensional amorphous silicon thin film position sensitive detectors with nip or MIS structure, under continuous and pulsed laser operation conditions. The arrays occupy a total active area of 45 mm2 and have a plane image resolution better than 15 m with a cut-off frequency of about 6.8 kHz. The non-linearity of the array components varies with the frequency, being about 1.6% for 200 Hz and about 4% for the cut-off frequency (6.8 kHz).
Authors: Shibin Zhang, Z. Hu, Leandro Raniero, X. Liao, Isabel Ferreira, Elvira Fortunato, Paula M. Vilarinho, Luís Pereira, Rodrigo Martins
Abstract: A series of amorphous silicon carbide films were prepared by plasma enhanced chemical vapor deposition technique on (100) silicon wafers by using methane, silane, and hydrogen as reactive resources. A very thin (around 15 Å) gold film was evaporated on the half area of the a- SiC:H films to investigate the metal induced crystallization effect. Then the a-SiC:H films were annealed at 1100 0C for 1 hour in the nitrogen atmosphere. Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to analyze the microstructure, composition and surface morphology of the films. The influences of the high temperature annealing on the microstructure of a-SiC:H film and the metal induced metallization were investigated.
Authors: V. Thaiyalnayaki, M.Fátima Cerqueira, Francisco Macedo, João Alves Ferreira
Abstract: Amorphous and nanocrystalline silicon thin films have been produced by reactive r.f. sputtering and their microstructure, optical and thermal properties were evaluated. A good correlation was found between the microstructure determined by Raman spectroscopy and X- ray diffraction and the thermal transport parameters.
Authors: Luís Pereira, Pedro Barquinha, Elvira Fortunato, Rodrigo Martins
Abstract: In this work metal induced crystallization (MIC) using nickel (Ni) was employed to obtain poly-Si by crystallization of amorphous films for application as active layer in TFTs. Ni layers with thicknesses of 0.5 nm, 1 nm and 2 nm were used to crystallize the silicon. The TFTs were produced with a bottom gate configuration using a multi-layer Al2O3/TiO2 insulator produced by atomic layer deposition (ALD) as gate dielectric. The best performances of the TFT produced were obtained when using very thin Ni layers for the crystallization. This is attributed to a lower metal contamination and to the enhancement of grain size, as a result of the lower nucleation density achieved, when using the thinnest Ni layer. Devices that exhibit effective mobility of 45.5 cm2V-1s-1 and an on/off ratio of 5.55×104 were produced using a 0.5 nm Ni layer to crystallize the active channel area.
Authors: Henrique Leonel Gomes, Peter Stallinga, D.M. de Leeuw
Abstract: Field effect transistors based on several conjugated organic materials were fabricated and assesed in terms of electrical stability. The device characteristics were studied using steady state measurements as well as techniques for addressing trap states. Temperature-dependent measurements show clear evidence for an electrical instability occurring above 200 K that is caused by an electronic trapping process. It is suggested that the trapping sites are created by a change in the organic conjugated chain, a process similar to a phase transition.
Authors: Sergio Pereira, M.R. Correia, Eduardo Alves
Abstract: This paper concerns the structural and optical properties of the group III-V semiconductor alloy, indium gallium nitride (InGaN). We focus on the reasons of interest to study InGaN. Recent advances regarding the basic understanding (ex. accurate composition determination) and some yet unclear issues (ex. phase separation) regarding this material system, are also briefly discussed. Illustrative results on the light emitting and structural properties are presented.
Authors: Gonçalo Gonçalves, Elvira Fortunato, J.I. Martins, Rodrigo Martins
Abstract: In this work, the relation between oxidant/monomer ratio and the electrical conductivity of polypyrrole was studied using different ratios. We achieved a maximum value for electrical conductivity of 7.5 S/cm for a ratio of 2:1. We also developed a chemical dip-coating process to produce the cathode layer in tantalum capacitors. We obtained capacitances of about 80 µF after 8 cycles using the sequence Monomer/Oxidant.
Authors: Joana Catarina Madaleno, Luiz Pereira
Abstract: In this work we present an equipotential surface map with a resolution higher than 100 nm, resulting from conductive atomic force microscopy (AFM). The images, obtained in polycrystalline MPCVD (Microwave Plasma Assisted Chemical Vapor Deposition) diamond devices, are clearly structure dependent. Diamond and non-diamond phases were identified by micro-Raman spectroscopy and correlated with the electrical conduction map. The application of the non-homogeneous contact theory lead to the extraction of two Schottky Barrier Heights (SBH), one close to 0.6 V with dispersion ~ 0.1 V, attributed to the diamond / metal interface, and the other close to 0.4 V with dispersion ~ 0.04 V, due to the non-diamond phases / metal interface. The diamond / non-diamond phase ratio is about 85:15, taken from the micro-Raman spectra. Combining these results with the electrical conduction map, a general model to predict the macroscopic electrical behavior of polycrystalline diamond based devices is proposed.

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