Document Server@UHasselt
(3.246 recursos)
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 40
1.
Fretting wear rate of sulphur deficient MoSx coatings based on dissipated energy - Xiaoling Zhang, W.; LAUWERENS, Walter; STALS, Lambert; He, J.; Celis, J-P
The fretting wear of sulphur-deficient MoSx coatings with different crystallographic orientations has been investigated in ambient air of controlled relative humidity. The coefficient of friction and the wear rate of MoSx coatings sliding against corundum depend not only on fretting parameters like contact stress, fretting frequency, and relative humidity, but also strongly on the crystallographic orientation of the coatings. For randomly oriented MoSx coatings, the coefficient of friction and the wear rate increased significantly with increasing relative humidity. In contrast, basal-oriented MoSx coatings were less sensitive to relative humidity. The coefficient of friction of both types of MoSx coatings decreased...
2.
Phosphorous doping of microcrystalline CVD diamond using modified conditions - HAENEN, Ken; LAZEA, Andrada; MORTET, Vincent; D'HAEN, Jan; Geithner, P; Ristein, J
Phosphorous-doping of predominantly (110) oriented polycrystalline CVD diamond films is presented. Incorporation of phosphorous into the diamond grains was accomplished by using novel microwave plasma enhanced chemical vapor deposition (MW PE CVD) growth conditions. The substitutional nature of the phosphorous atom was confirmed by applying the quasi-steady-state photocurrent technique (PC) and cathodoluminescence (CL) measurements at low temperature. Topographical information and the relation between substrate and P-doped film grain orientation;vas obtained with scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). The optimized growth parameters for P-doped layers on (110) oriented polycrystalline diamond differ substantially from the standard conditions reported in...
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The influence of different surface terminations on electrical transport and emission properties for freestanding single crystalline (100) CVD diamond samples - DEFERME, Wim; BOGDAN, Anna; HAENEN, Ken; DE CEUNINCK, Ward; Flipse, K.; NESLADEK, Milos
The surface density of states of hydrogen and oxygen terminated diamond is an important parameter from the point of view of electrical transport properties at the surface. In addition, the presence of surface states has a detrimental influence on the electrical contact properties. Therefore it is of great importance that the influence of different species on the surface-related properties of the diamond layer is well understood. In this work (100)-oriented CVD diamond films are terminated using a hydrogen plasma with and without small additions of oxygen (1 to 4%). XPS and UPS measurements are performed to look at the influence...
4.
Surface characterisation of silicon substrates seeded with diamond nanoparticles under UHV annealing - Arnault, J. C.; Saada, S.; WILLIAMS, Oliver; HAENEN, Ken; Bergonzo, P.; NESLADEK, Milos; Polini, R.; Osawa, E.
The thermal stability of Ultra Dispersed Diamond on silicon surfaces has been investigated. Samples have been annealed under Ultra-High Vacuum conditions. The evolution of the carbon binding states at the surface has been monitored sequentially by XPS and XEELS. After annealing at 1173 K, sp(3) seeds present initially have been significantly modified. Contrary to lower temperature, no diamond has been detected either by XPS or by FEG-SEM after a short growth step. XPS spectra indicate the formation of silicon carbide. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
5.
Penicillin detection with nanocrystalline-diamond field-effect sensor - Abouzar, Maryam H.; Poghossian, Arshak; Razavi, Arash; Besmehn, Astrid; BIJNENS, Nathalie; WILLIAMS, Oliver; HAENEN, Ken; WAGNER, Patrick; Schoening, Michael J.
Nanocrystalline-diamond (NCD) films have been utilised for the detection of penicillin G for the first time. The developed penicillin-sensitive biosensor consists of a field-effect capacitive electrolyte-diamond-insulator-semiconductor (EDIS) structure with an immobilised enzyme layer that covers the gate region of the sensor. Undoped NCD thin films of about 100 nm thickness were grown on a p-Si-SiO2 (50 nm thermally grown SiO2) structure by microwave plasma-enhanced chemical vapour deposition. The enzyme penicillinase has been adsorptively immobilised directly onto the O-terminated NCD surface. The EDIS biosensors have been characterised in buffer solutions with different content of penicillin G by means of capacitance-voltage and...
6.
Optical properties of heavily boron-doped nanocrystalline diamond films studied by spectroscopic ellipsometry - Zimmer, A.; WILLIAMS, Oliver; HAENEN, Ken; Terryn, H.
The optical properties of heavily boron-doped nanocrystalline diamond films grown by microwave plasma enhanced chemical vapor deposition on silicon substrates are presented. The diamond films are characterized by spectroscopic ellipsometry within the midinfrared, visible, and near-ultraviolet regions. The ellipsometric spectra are also found to be best described by a four-phase model yielding access to the optical constants, which are found distinct from previous nanocrystalline diamond literature values. The presence of a subgap absorption yielding high extinction coefficient values defined clearly the boron incorporated films in comparison to both undoped and composite films, while refractive index values are relatively comparable. (C)...
7.
Electronic and optical properties of boron-doped nanocrystalline diamond films - Gajewski, W.; Achatz, P.; Williams, Oliver; Haenen, Ken; Bustarret, E.; Stutzmann, M.; Garrido, J. A.
We report on the electronic and optical properties of boron-doped nanocrystalline diamond (NCD) thin films grown on quartz substrates by CH4/H-2 plasma chemical vapor deposition. Diamond thin films with a thickness below 350 nm and with boron concentration ranging from 10(17) to 10(21) cm(-3) have been investigated. UV Raman spectroscopy and atomic force microscopy have been used to assess the quality and morphology of the diamond films. Hall-effect measurements confirmed the expected p-type conductivity. At room temperature, the conductivity varies from 1.5x10(-8) Omega(-1) cm(-1) for a nonintentionally doped film up to 76 Omega(-1) cm(-1) for a heavily B-doped film. Increasing...
8.
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.
9.
The relation between open-circuit voltage and the onset of photocurrent generation by charge-transfer absorption in polymer: Fullerene bulk heterojunction solar cells - VANDEWAL, Koen; GADISA DINKU, Abay; OOSTERBAAN, Wibren; BERTHO, Sabine; BANISHOEIB, Fateme; VAN SEVEREN, Ineke; LUTSEN, Laurence; CLEIJ, Thomas; VANDERZANDE, Dirk; MANCA, Jean
Photocurrent generation by charge-transfer (CT) absorption is detected in a range of conjugated polymer-[6,61-phenyl C61 butyric acid methyl ester (PCBM) based solar cells. The low intensity CT absorption bands are observed using a highly sensitive measurement of the external quantum efficiency (EQE) spectrum by means of Fourier-transform photocurrent spectroscopy (FrPS). The presence of these CT bands implies the formation of weak ground-state charge-transfer complexes in the studied polymer-fullerene blends. The effective band gap (Eg) of the material blends used in these photovoltaic devices is determined from the energetic onset of the photocurrent generated by CT absorption. It is shown that...
10.
Fourier-Transform Photocurrent Spectroscopy for a fast and highly sensitive spectral characterization of organic and hybrid solar cells - VANDEWAL, Koen; GORIS, Ludwig; HAELDERMANS, Ilse; NESLADEK, Milos; HAENEN, Ken; WAGNER, Patrick; MANCA, Jean
Two modes of Fourier-Transform Photocurrent Spectroscopy (FTPS) are presented for a fast and sensitive determination of photocurrent spectra of organic and dye sensitized solar cells. Furthermore, FTPS allows to spectrally resolve sub-bandgap absorption phenomena in P3HT, in organic P3HT:PCBM bulk heterojunctions and in hybrid P3HT/TiO2 solar cells. The sub-bandgap absorption in the P3HT:PCBM blend is dominated by a band due to the formation of a ground-state charge-transfer complex between the polymer and PCBM. In P3HT/TiO2 junctions such a charge-transfer complex band is not observed. Long-lived light induced sub-bandgap states appear in pure P3HT and in P3HT/TiO2 junctions after irradiation with...
12.
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.
16.
Substrate influence in Young's modulus determination of thin films by indentation methods: Cubic boron nitride as an example - Richter, F.; Herrmann, M.; Molnar, F.; Chudoba, T.; Schwarzer, N.; Keunecke, M.; Bewilogua, K.; Zhang, X. W.; BOYEN, Hans-Gerhard; Ziemann, P.
This paper deals with the determination of Young's modulus of thin films by indentation methods using cubic boron nitride (c-BN) as an example. This is a non-trivial task because the Young's modulus of this material comes close to that of the diamond indenter. An analysis of results from literature revealed that Young's moduli of c-BN thin films are generally distinctly smaller than bulk material values. We give reasons that this is at least to a large extent due to measuring problems, in particular the absence of a proper correction of substrate influence. In the experimental part we have used nanoindentation...
17.
The contribution of activity-based transport models to air quality modelling: A validation of the ALBATROSS-AURORA model chain - Beckx, C.; INT PANIS, Luc; Van De Vel, Karen; Arentze, Theo; Lefebvre, Wouter; JANSSENS, Davy; WETS, Geert
The potential advantages of using activity-based transport models for air quality purposes have been recognized for a long time but models that have been developed along these lines are still scarce. In this paper we demonstrate that an activity-based model provides useful information for predicting hourly ambient pollutant concentrations. For this purpose, the traffic emissions obtained in a previous application of the activity-based model ALBATROSS were used as input for the AURORA air quality model to predict hourly concentrations of NO2, PM10 and O-3 in the Netherlands. Predicted concentrations were compared with measured concentrations at 37 monitoring stations from the...
18.
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.
19.
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...
20.
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...
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