Document Server@UHasselt
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Repository of the University of Hasselt containing publications in the fields of statistics, computer science, information strategies and material from the Institute for behavioural sciences.
Mostrando recursos 1 - 20 de 36
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Electrical activity of intragrain defects in polycrystalline silicon layers obtained by aluminum-induced crystallization and epitaxy - Van Gestel, D.; Romero, M. J.; Gordon, I.; Carnel, L.; D'HAEN, Jan; Beaucarne, G.; Al-Jassim, M.; Poortmans, J.
Defect etching revealed a very large density (similar to 10(9) cm(-2)) of intragrain defects in polycrystalline silicon (pc-Si) layers obtained through aluminum-induced crystallization of amorphous Si and epitaxy. Electron-beam-induced current measurements showed a strong recombination activity at these defects. Cathodoluminescence measurements showed the presence of two deep-level radiative transitions (0.85 and 0.93 eV) with a relative intensity varying from grain to grain. These results indicate that the unexpected quasi-independence on the grain size of the open-circuit voltage of these pc-Si solar cells is due to the presence of numerous electrically active intragrain defects. (c) 2007 American Institute of Physics.
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Biological applications of nanocrystalline diamond - WILLIAMS, Oliver; DAENEN, Michael; HAENEN, Ken
Nanocrystalline diamond films have generated substantial interest in recent years due to their low cost, extreme properties and wide application arena. Diamond is chemically inert, has a wide electrochemical window and is stable in numerous harsh environments. Nanocrystalline diamond has the advantage of being readily grown on a variety of substrates at very low thickness, resulting in smooth conformal coatings with high transparency. These films can be doped from highly insulating to metallically conductive and at very high concentrations become superconducting.
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Crystallization resistance of barium titanate zirconate ultrathin films from aqueous CSD: a study of cause and effect - HARDY, An; Van Elshocht, Sven; Knaepen, Werner; D'HAEN, Jan; Conard, Thierry; Brijs, Bert; Vandervorst, Wilfred; Pourtois, Geoffrey; Kittl, Jorge; Detavernier, Christophe; Heyns, Marc; VAN BAEL, Marlies; VAN DEN RUL, Heidi; MULLENS, Jules
Ultrathin BaZr0.8Ti0.2O3 films (t < 30 nm) on SiOx/Si substrates were obtained by means of aqueous chemical solution deposition (CSD). Though the precursor crystallized into cubic perovskite powder at 600 degrees C, ultrathin films only crystallized at 950 to 1000 degrees C, even after addition of excess Ba to compensate for loss of Ba. Films with thickness above 100 nm, on the other hand, crystallized readily around 650 degrees C. The crystallization is related to film thickness, affecting the crystallization activation energy, and to silicate formation by reaction with the substrate, exerting its largest influence in ultrathin films. Barium deficiency,...
8.
Morphology of water-based chemical solution deposition (CSD) lead titanate films on different substrates: Towards island formation - DE DOBBELAERE, Christopher; HARDY, An; D'HAEN, Jan; VAN DEN RUL, Heidi; VAN BAEL, Marlies; MULLENS, Jules
This study aims at the deposition of PbTiO3 (PT) islands prepared by a water-based chemical solution deposition (CSD). Two aqueous citrato-based PbTiO3 precursor solutions, either with or without peroxide, are deposited by spin coating. The effect of different substrates on the formation of separated grains or islands is examined. It is observed that spin coating of a 0.6 M precursor solution on a Pt(1 1 1)/IrO2/Ir/SiO2/Si substrate gives the best results towards island formation. For this substrate, crystallizations are carried out between 600 degrees C and 900 degrees C. A final crystallization at 800 degrees C results in the highest...
9.
Thermal behaviour of arsenic trioxide adsorbed on activated carbon - Cuypers, Frederic; DE DOBBELAERE, Christopher; HARDY, An; VAN BAEL, Marlies; Helsen, Lieve
The thermal stability and desorption of arsenic trioxide (As2O3) adsorbed on activated carbon (AC) was investigated as this phenomenon is expected to influence the arsenic release during low temperature pyrolysis of chromated copper arsenate (CCA) wood waste. Firstly, a thermogravimetric (TG) experiment with arsenolite, an allotropic form of As2O3, was performed. The sample starts to sublime at temperatures lower than 200,C with a sublimation peak temperature of 271 degrees C. Subsequently, TG experiments with samples of As2O3 adsorbed on AC revealed that only very little (max. 6 +/- 3 wt%) As2O3 was volatilised at temperatures below 280 degrees C, while...
10.
Study of bio-oils and solids from flash pyrolysis of sewage sludges - Pokorna, E.; POSTELMANS, Niels; Jenicek, P.; SCHREURS, Sonja; CARLEER, Robert; YPERMAN, Jan
The aim of this study was to evaluate the production of pyrolysis oil from three types of sewage sludges. The flash pyrolysis was performed at 500 degrees C, the maximum oil yield was 43.1%, and the water content in bio-oils obtained from secondary sludges was relatively low - 10.3% and 17.0%. GC-MS results showed that pyrolytic bio-oils of studied sludges dominantly contained fatty acids and nitrogenous compounds with potential added value. Obtained solids had high ash content and low calorific value which make them unattractive for use in incineration. FT-IR results showed that solids gave similar IR features as notified...
11.
Fast pyrolysis of heavy metal contaminated willow: Influence of the plant part - LIEVENS, Caroline; CARLEER, Robert; CORNELISSEN, Tom; YPERMAN, Jan
Fast pyrolysis of heavy metal contaminated willow, with high concentrations of Cd, Cu, Pb and Zn, resulting from phytoremediation, is investigated. The distribution of the heavy metals depends on the plant part (leaves and branches). Nevertheless, their individual pyrolysis fractions (at an operational temperature of 623 K), i.e., bio-oil/tar and gas, are both heavy metal free. Some small differences in the kind and amounts of the organic compounds are found in the bio-oil and gaseous fraction. In view of practical considerations leaves and branches should nevertheless be pyrolysed simultaneously. The use of hyphenated thermal analytical techniques allows obtaining more detailed...
12.
The infrared optical absorption spectra of the functionalized nanocrystalline diamond surface - Remes, Z.; Kromka, A.; Kozak, H.; Vanecek, M.; HAENEN, Ken; WENMACKERS, Sylvia
We propose a new method of detecting the functional groups at the NCD surface based on the interfrence-free infrared reflection absorption spectroscopy of p-polarized IR light at Brewster's angle of incidence (BA-IRRAS). We report IR absorbance spectra of a linker molecule monolayer (10-undecenoic acid) covalently bonded to the NCD surface with and without DNA fragments coupled to it, and IR spectra of organosilane polymer coatings deposited on NCD surface by the spin coating technology. The homogeneity of the surface coatings was monitored by fluorescence microscopy. (C) 2008 Elsevier B.V. All rights reserved.
13.
Recent developments of wide-bandgap semiconductor based UV sensors - BenMoussa, A.; Soltani, A.; Schuehle, U.; HAENEN, Ken; Chong, Y. M.; Zhang, W. J.; Dahal, R.; Lin, J. Y.; Jiang, H. X.; Barkad, H. A.; BENMOUSSA, Boumediene; Bolsee, D.; Hermans, C.; Kroth, U.; Laubis, C.; MORTET, Vincent; De Jaeger, J. C.; Giordanengo, B.; Richter, M.; Scholze, F.; Hochedez, J. F.
Future missions for space astronomy and solar research require innovative vacuum ultraviolet (VUV) photodetectors. Present UV and VUV detectors exhibit serious limitations in performance, technology complexity and lifetime stability. New developments of metal-semiconductor-metal (MSM) solar-blind photodetectors based on diamond, cubic boron nitride (c-BN), and wurtzite aluminum nitride (AlN) are reported. In the wavelength range of interest. the characteristics of the MSM photodetectors present extremely low dark current. high breakdown voltage. and good responsivity. Diamond, c-BN, and AlN MSM photodetectors are sensitive and stable under UV irradiation. They show a 200 nm to 400 nm rejection ratio of more than four...
14.
Diamond nano-wires, a new approach towards next generation electrochemical gene sensor platforms - Nebel, C. E.; Yang, N.; Uetsuka, H.; Osawa, E.; Tokuda, N.; WILLIAMS, Oliver
A novel bio-sensing platform is introduced by combination of a) geometrically controlled DNA bonding using vertically aligned diamond nano-wires and b) the superior electrochemical sensing properties of diamond as transducer material. Ultra-hard vertically aligned diamond nano-wires are electrochemically modified to bond phenyl linker-molecules to their tips which provide mesospacing for DNA molecules on the transducer. The nano-wires are generated by reactive ion etching of metallically boron doped atomically smooth single crystalline CVD diamond. Surface properties are characterized by atomic force, scanning electron and scanning tunneling microcopy. Electro- and bio-chemical sensor properties are investigated using cyclic and differential pulse voltammetry as...
15.
Differences in metal sequestration between zebra mussels from clean and polluted field locations - Voets, Judith; STEEN REDEKER, Erik; Blust, Ronny; Bervoets, Lieven
Organisms are able to detoxify accumulated metals by, e.g. binding them to metallothionein (MT) and/or sequestering them in metal-rich granules (MRG). The different factors involved in determining the capacity or efficiency with which metals are detoxified are not yet known. In this work we studied how the sub-cellular distribution pattern of cadmium, copper and zinc in whole tissue of zebra mussels from clean and polluted surface waters is influenced by the total accumulated metal concentration and by its physiological condition. Additionally we measured the metallothionein concentration in the mussel tissue. Metal concentration increased gradually in the metal-sensitive and detoxified sub-cellular...
16.
Thermionic electron emission from low work-function phosphorus doped diamond films - Koeck, Franz A. M.; Nemanich, Robert J.; LAZEA, Andrada; HAENEN, Ken
Thermionic electron emitters are a key component in applications ranging from travelling wave tubes for communications, space propulsion and direct energy conversion. As the conventional approach based on metallic emitters requires high operating temperatures the negative electron affinity (NEA) characteristic of diamond surfaces in conjunction with suitable donors would allow an electronic structure corresponding to a low effective work function. We have thus prepared phosphorus-doped polycrystalline diamond films on metallic substrates by plasma assisted chemical vapor deposition where an NEA surface characteristics was induced by exposure of the film surface to a hydrogen plasma. Thermionic electron emission measurements in an...
17.
Low-temperature transport in highly boron-doped nanocrystalline diamond - Achatz, P.; Gajewski, W.; Bustarret, E.; Marcenat, C.; Piquerel, R.; Chapelier, C.; Dubouchet, T.; WILLIAMS, Oliver; HAENEN, Ken; Garrido, J. A.; Stutzmann, M.
We studied the transport properties of highly boron-doped nanocrystalline diamond thin films at temperatures down to 50 mK. The system undergoes a doping-induced metal-insulator transition with an interplay between intergranular conductance g and intragranular conductance g(0), as expected for a granular system. The conduction mechanism in the case of the low-conductivity films close to the metal-insulator transition has a temperature dependence similar to Efros-Shklovskii type of hopping. On the metallic side of the transition, in the normal state, a logarithmic temperature dependence of the conductivity is observed, as expected for a metallic granular system. Metallic samples far away from the...
18.
Thin film magnetoelectric composites near spin reorientation transition - Tiercelin, N.; Preobrazhensky, V.; MORTET, Vincent; Talbi, A.; Soltani, Ali; HAENEN, Ken; Pernod, D.
We report the use of a magnetic instability of the spin reorientation transition type to enhance the magnetoelectric sensitivity in magnetostrictive-piezoelectric structures. We present the theoretical study of a clamped beam resonant actuator composed of a piezoelectric element on a passive substrate actuated by a magnetostrictive nanostructured layer. The experiments were made on a polished 150 mm thick 18 x 3 mm(2) lead zirconate titanate (PZT) plate glued to a 50 mm thick silicon plate and coated with a giant magnetostrictive nanostructured Nx(TbCo2 5nm/FeCo5nm) layer. A second set of experiments was done with magnetostrictive layer deposited on PZT plate. Finally,...
19.
The Diamond Nano-Balance - WILLIAMS, Oliver; MORTET, Vincent; DAENEN, Michael; HAENEN, Ken
Detecting nano-gram quantities of analyte in the liquid or gas phase is crucial for pathogen detection, antigen/DNA detection, water monitoring, electrochemical analysis, and many other bioelectrochemical applications. The quartz crystal microbalance (QCM) has become a significant sensor for both liquid and gas phase graviometry due to its high sensitivity, robustness, ease of use and simultaneous electrochemistry capabilities. One key factor plaguing the QCM in most sensor applications is the stability of the surface functionalisation. Diamond offers the most stable surface for functionalisation, the widest electrochemical window and the lowest noise floor. Unfortunately the growth of diamond on QCMs is problematic...
20.
Optical spectroscopic study of n-type diamond - NESLADEK, Milos; MEYKENS, Kristien; HAENEN, Ken; STALS, Lambert; KOIZUMI, Satoshi; TERAJI, Tokuyuki
Preparation of n-type diamond has been one of the challenges in the diamond field, not successful in the past. Recently the group at NIRIM has succeeded in deposition of thin n-type P-doped CVD diamond films. Hall effect measurements confirmed n-type conductivity with the activation energy of the carrier concentration of 0.40-0.60 eV. Here, we present the first spectroscopic study of the phosphorus optical activity in diamond, using the constant photocurrent method [3] (CPM) and an optical absorption technique - photothermal deflection spectroscopy (PDS) [4]. Two new optically active defects are detected in the gap of P-doped CVD diamond: the first...
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