Papers by Author: António Marques

Abstract: Total hip replacement is a common practice in every day clinical work. Artificial hip implants consist of a femoral component and an acetabular component. Nowadays the acetabular component is composed of a polymeric cup and a metallic shell. This study focuses the development of an innovative acetabular component substituting the metallic shell by a multilayer coating on the acetabular cup. A titanium coating was deposited onto ultra-high molecular weight polyethylene (UHMWPE) samples by physical vapour deposition (PVD), having an in situ pretreatment with argon ion bombardment in order to optimize the adhesive strength by surface modification, followed by the deposition of a thin film of hydroxyapatite (HA) using rf magnetron sputtering technique, at room temperature. Results obtained seem to indicate that these multilayer coatings can be a viable alternative to the metallic shell, leading to the substitution of a two part for a one part acetabular component.

Abstract: Electrochromic materials have attracted considerable attention during the last two decades as a consequence of their potential application in several different types of optical devices. Examples of these devices include intelligent windows and time labels. In this paper the authors describe results obtained with thin tungsten oxide films produced at room temperature by rf magnetron sputtering under an argon and oxygen atmosphere on transparent conductive oxide coated glass substrates. To protect the surface of the electrochromic film, prevent water absorption and obtain a good memory effect under open circuit voltages, a layer of Ta2O5 was deposited over the WO3 films. In this study, the effect of different electrolyte compositions on the open circuit memory of optical devices has been characterized. The best results were obtained for electrochromic devices with polymer gel p(TMC)3LiClO4 and p(TMC)8LiClO4 electrolytes. These prototype devices present an overall transmittance of ~75% in their bleached state and after coloration 40.5 and 52.5% respectively. These devices also show memory effect and an optical density considered satisfactory for some electrochromic applications.

Abstract: The purpose of this work is to present in-depth electrical characterization on transparent TFTs, using zinc oxide produced at room temperature as the semiconductor material. Some of the studied aspects were the relation between the output conductance in the post-pinch-off regime and width-to-length ratios, the gate leakage current, the semiconductor/insulator interface traps density and its relation with threshold voltage. The main point of the analysis was focused on channel mobility. Values extracted using different methodologies, like effective, saturation and average mobility, are presented and discussed regarding their significance and validity. The evolution of the different types of mobility with the applied gate voltage was investigated and the obtained results are somehow in disagreement with the typical behavior found on classical silicon based MOSFETs, which is mainly attributed to the completely different structures of the semiconductor materials used in the two situations: while in MOSFETS we have monocrystalline silicon, our transparent TFTs use poly/nanocrystalline zinc oxide with grain sizes of about 10 nm.

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).

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.