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Document Server@UHasselt (58.026 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.

Dept. Mathematics-Physics-Informatics (WNI) - Materials Physics

Mostrando recursos 1 - 20 de 598

  1. Current-induced nanogap formation and graphitization in boron-doped diamond films

    Seshan, V.; Arroyo, C.R.; Castellanos-Gomez, A.; Prins, F.; Perrin, M. L.; Janssens, S. D.; HAENEN, Ken; NESLADEK, Milos; Sudhoelter, E. J. R.; de Smet, L. C. P. M.; van der Zant, H. S. J.; Dulic, D.
    A high-current annealing technique is used to fabricate nanogaps and hybrid diamond/graphite structures in boron-doped nanocrystalline diamond films. Nanometer-sized gaps down to similar to 1 nm are produced using a feedback-controlled current annealing procedure. The nanogaps are characterized using scanning electron microscopy and electronic transport measurements. The structural changes produced by the elevated temperature, achieved by Joule heating during current annealing, are characterized using Raman spectroscopy. The formation of hybridized diamond/graphite structure is observed at the point of maximum heat accumulation. (C) 2012 American Institute of Physics. []

  2. Mesoscopic modelling of masonry using weak and strong discontinuities

    Vandoren, Bram; De Proft, Kurt; Simone, Angelo; Sluys, Lambertus Johannes
    A mesocopic masonry model is presented in which joints are modelled by weak and strong discontinuities through the partition of unity property of finite element shape functions. A Drucker-Prager damage model describes joint degradation whereas the bricks remain linear elastic throughout the simulations. Analogies and differences amongst strong and weak discontinuity models are discussed, with special emphasis on kinematic description and implementation. Mesh sensitivity and performance of the presented models are illustrated by two-brick, three-point bending and shear wall tests.

  3. Mesoscopic modelling of masonry using GFEM: a comparison of strong and weak discontinuity models

    Vandoren, Bram; De Proft, Kurt
    Masonry structures are characterised by their low material cost and relatively simple way of constructing. The computational modelling of these structures remains, however, a great challenge. Two major modelling groups exist: macroscale and mesoscale models. The former approach homogenises the masonry constituents, i.e. the bricks and joints, to one orthotropic material whereas the latter approach models the constituents as separate entities. In this contribution, two mesoscopic masonry models are presented and compared: a model in which the joints are represented as strong discontinuities and a model in which weak discontinuities are used to model the joints. The bricks remain linear elastic...

  4. Mesoscopic modelling of masonry using embedded weak discontinuities based on partitions of unity

    Vandoren, Bram; De Proft, Kurt
    The modelling of masonry has been a popular topic within computational mechanics for some years now. Two major groups of modelling approaches exist: macroscopic and mesoscopic models. The macroscopic approach homogenises the mortar joints and bricks creating one orthotropic material, whereas the mesoscopic approach models the joints and bricks as separate entities. In this contribution a two dimensional mesoscopic model will be developed, where mortar joints are modelled by embedded discontinuities using the partition of unity property of the finite element shape functions. Unlike classical mesoscopic models, where joints are modelled using strong discontinuities (i.e. jumps in the displacement field),...

  5. Charge transfer in the weak driving force limit in blends of MDMO-PPV and dithienylthiazolo[5,4-d]thiazoles towards organic photovoltaics with high V-OC

    Nevil, Nissy; Ling, Yun; Van Mierloo, Sarah; Kesters, Jurgen; Piersimoni, Fortunato; Adriaensens, Peter; Lutsen, Laurence; Vanderzande, Dirk; Manca, Jean; Maes, Wouter; Van Doorslaer, Sabine; Goovaerts, Etienne
    A series of three 5'-aryl-2,5-dithienylthiazolo[5,4-d]thiazole (DTTzTz) semiconducting molecules with different aryl substituents has been investigated as alternative acceptor materials in combination with the donor polymer poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) in order to evaluate the photoinduced charge transfer (CT) efficiency in the resulting blends, designed towards possible application in organic photovoltaics. Photoluminescence quenching together with polaron detection by electron paramagnetic resonance and photoinduced absorption (PIA) demonstrate an increasing charge transfer efficiency when the DTTzTz substituents are varied from thien-2-yl to 4-trifluoromethylphenyl and 4-cyanophenyl groups, correlating well with the increasing acceptor strength in this series of molecules. In line with this observation, there...

  6. Mesoscopic modelling of masonry using weak discontinuities in the partition of unity framework

    Vandoren, Bram; Heyens, Koen; De Proft, Kurt
    Modelling of masonry has been a popular topic within computational mechanics for some years now. Three major groups of modelling approaches exist: macroscopic, mesoscopic and microscopic. In this contribution a two dimensional mesoscopic model will be developed, in which mortar joints are modelled by embedded discontinuities using the partition of unity property of the finite element shape functions. Unlike classical mesoscopic models, where joints are modelled using strong discontinuities (i.e. jumps in the displacement field), the model developed in this PhD research uses weak discontinuities. A weak discontinuity introduces a jump in the strain field, allowing for failure to localise...

  7. Time-dependent mesoscopic modelling of masonry using embedded weak discontinuities

    Vandoren, Bram; Heyens, Koen; De Proft, Kurt
    The modelling of masonry has been a popular topic within computational mechanics for some years now. Two major groups of modelling approaches exist: macroscopic and mesoscopic models. In this contribution a two dimensional mesoscopic model (i.e. joints and bricks are modelled as separate entities) will be developed that incorporates time-dependent behaviour. Since in masonry structures the cracks often follow the joints, the potential crack paths are known in advance. Unlike classical mesoscopic models, where joints are modelled using strong discontinuities (i.e. jumps in the displacement field), the model developed in this paper uses embedded weak discontinuities. A weak discontinuity introduces...

  8. Thickness dependent residual stress in sputtered AlN thin films

    Pobedinskas, Paulius; Bolsee, Jean-Christophe; Dexters, Wim; Ruttens, Bart; Mortet, Vincent; D'Haen, Jan; Manca, Jean V.; Haenen, Ken
    Thin aluminium nitride (AIN) films of different thickness are deposited by DC-pulsed magnetron sputtering under identical conditions on sapphire (0001) and silicon (100) substrates. An investigation of the residual stress, morphology and structural properties is carried out. The thickness of the films covers the range from 17 nm to 3.9 μm. A higher compressive residual stress is measured for the thinner films and the presence of a stress gradient is proven. X-ray diffraction (XRD) studies show that all AIN films are achieved with perfect c-axis orientation perpendicular to the film surface and that the films are biaxially strained. XRD rocking...

  9. No additional reduction of mortality or heart failure events with intrathoracic impedance measurements in a context of telemonitoring with structural biofeedback

    GRIETEN, Lars; VERBRUGGE, Frederik; STORMS, Valerie; Verhaert, D.; Rivero-Ayerza, M.; De Vusser, P.; Van Herendael, H.; Vercammen, J.; Jacobs, L.; Rondelez, K.; MULLENS, Wilfried; VANDERVOORT, Pieter
    Our aim was to test if intra-thoracic impedance (ITI) measurements would improve short-term clinical outcome (i.e. all-cause mortality and heart failure hospitalizations) in patients with cardiac resynchronization therapy (CRT) who were followed in a telemonitoring program with structural biofeedback. Methods: CRT patients (n=200; age= 70 +/-14y) were included in a telemonitoring program at Ziekenhuis Oost-Limburg Genk, which comprised daily transmissions through a wireless system installed at their homes. All patients were followed for potential lead/device problems, episodes of anti-tachycardia pacing, device shocks, occurrence of arrhytmias, a decline in biventricular pacing percentage and/or a sudden drop in physical activity. Patients with...

  10. Poly(3-alkylthiophene) nanofibers for photovoltaic energy conversion

    Bertho, Sabine; Oosterbaan, Wibren D.; Vrindts, Veerle; Bolsee, Jean-Christophe; Piersimoni, Fortunato; Spoltore, Donato; D'Haen, Jan; Lutsen, Laurence; Vanderzande, Dirk; Manca, Jean V.
    The use of nanostructured non-conventional semiconductors such as conjugated polymers and metal oxides (e.g. TiO2), opens promising perspectives towards a new generation of solar cells based on the concept of donor:acceptor bulk heterojunctions. In this concept donor material and acceptor material form interpenetrating networks allowing light absorption, charge transfer and charge transport throughout the entire bulk of the thin film. Since nanomorphology is of crucial importance for this type of solar cells, in this contribution the use of nanofibers in bulk heterojunction solar cells is explored in order to obtain highways for charge transport. We investigate in particular the use...

  11. Purity of epitaxial cubic BoronNitride films on (001) Diamond - A prerequisite for their doping

    YIN, Hong; BOYEN, Hans-Gerhard; Ziemann, P.; Dohuard, B.; Houssiau, L.; Renaux, F.; Hecq, M.; Bittencourt, C.
    Phase pure cubic BoronNitride (c-BN) films were epitaxially grown on (001) Diamond substrates at 900 degrees C and analyzed for purity by taking X-ray Photoelectron Spectroscopy (XPS) as well as Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiles. No metallic impurities could be detected within the resolution limit of ToF-SIMS corresponding to some ppm. The films, however, still contain typically 0.5 at. % carbon and 1 at.% oxygen, which both can be traced back to the boron sputter target. All as-prepared c-BN films, with and without additional sputter cleaning of their surface, exhibit a p-type conductivity, which can be attributed...

  12. Parameters affecting the luminescence of nanodiamond particles: Quantum chemical calculations

    Kovalenko, A.; Petrakova, V.; Ashcheulov, P.; Zalis, S.; NESLADEK, Milos; Kraus, I.; Kratochvilova, I.
    In this article, theoretical interpretation and prediction of the optical properties of nanodiamond (ND) particles', containing various luminescence centers, was made. Particularly, nitrogen, and chromium atoms embedded into the diamond crystal lattice were modeled. In the case of nitrogen centers containing ND particles, the effect of various surface terminations (hydrogen and/or oxygen, fluorine) was also studied. To get a qualitative better understanding of the complicated and specific process of ND particles, luminescence using density functional theory, were modeled processes and states influencing the luminescence of ND particles.

  13. Analysis of an optical biosensor based on elastic light scattering from diamond-, glass-, and sapphire microspheres

    MURIB, Mohammed Sharif; Tran, Anh Quang; DE CEUNINCK, Ward; Sch??ning, J.M.; NESLADEK, Milos; Serpeng??zel, Ali; WAGNER, Patrick
    Deoxyribonucleic acid (DNA) and protein recognition are now standard tools in biology. In addition, the special optical properties of microsphere resonators expressed by the high quality factor (Q-factor) of whispering gallery modes (WGMs) or morphology dependent resonances (MDRs) have attracted the attention of the biophotonic community. Microsphere-based biosensors are considered as powerful candidates to achieve label-free recognition of single molecules due to the high sensitivity of their WGMs. When the microsphere surface is modified with biomolecules, the effective refractive index and the effective size of the microsphere change resulting in a resonant wavelength shift. The transverse electric (TE) and the...

  14. Spin-seeding approach for diamond growth on large area silicon-wafer substrates

    Tsigkourakos, Menelaos; Hantschel, Thomas; JANSSENS, Stoffel; HAENEN, Ken; Vandervorst, Wilfried
    The growth of polycrystalline diamond by chemical vapor deposition requires a substrate pre-treatment in order to achieve thin, high-quality, and pore-free diamond layers. Seeding the substrate by immersing it into a nanodiamond (ND) dispersion is most commonly used today, since it yields a high-density seed layer (>1011?cm-2) and leads to a thin closed polycrystalline diamond film. Nevertheless, in a nanoelectronics fabrication facility it would be advantageous to use spinning for seeding the substrate as it is already well established for resist coating and spray etching. Additionally, each wafer would use a fresh and limited amount of seeding dispersion which will...

  15. Excitation of Charge Transfer States and Low-Driving Force Triplet Exciton Dissociation at Planar Donor/Acceptor Interfaces

    PIERSIMONI, Fortunato; Cheyns, David; VANDEWAL, Koen; MANCA, Jean; Rand, Barry P.
    Here, we investigate charge transfer at archetypal planar heterojunction solar cells based, upon phthalocyanines as donors and C-60 or a perylene derivative as acceptors. We demonstrate the ability to measure photocurrent from direct charge transfer state excitation despite the intrinsically small interface area for bilayer systems. We then discuss the implications of triplet versus singlet excitons in these systems, and find that neither the low triplet energy nor low mobility of perylene acceptors with respect to C-60 are responsible for reduced performance, but rather the low exciton diffusion length and unfavorable absorption profile. Furthermore, we show that triplet and singlet...

  16. Grain size tuning of nanocrystalline chemical vapor deposited diamond by continuous electrical bias growth: Experimental and theoretical study

    MORTET, Vincent; Zhang, Liang; Eckert, Maxie; D'HAEN, Jan; Soltani, Ali; Moreau, Myriam; Troadec, David; Neyts, Erik; De Jaeger, Jean-Claude; Verbeeck, Jo; Bogaerts, Annemie; Van Tendeloo, Gustaaf; HAENEN, Ken; WAGNER, Patrick
    In this work, a detailed structural and spectroscopic study of nanocrystalline diamond (NCD) thin films grown by a continuous bias assisted CVD growth technique is reported. This technique allows the tuning of grain size and phase purity in the deposited material. The crystalline properties of the films are characterized by SEM, TEM, EELS, and Raman spectroscopy. A clear improvement of the crystalline structure of the nanograined diamond film is observed for low negative bias voltages, while high bias voltages lead to thin films consisting of diamond grains of only 10 nm nanometer in size, showing remarkable similarities with so-called ultrananocrystalline...

  17. Electrochemical oxidation of ionic liquids at highly boron doped diamond electrodes

    Fabianska, Aleksandra; Ossowski, Tadeusz; Bogdanowicz, Robert; Czupryniak, Justyna; Gnyba, Marcin; Odzga, Tomasz; JANSSENS, Stoffel; HAENEN, Ken; Siedlecka, Ewa M.
    An electrochemical oxidation using a highly boron-doped diamond (BDD) electrode has been tested for the treatment of solutions containing ionic liquids (ILs). The double-sided Si/highly BDD electrodes were synthesized by microwave plasma enhanced chemical vapour deposition (MW PE CVD). Investigation of the electrode surface with scanning electron microscopy (SEM) confirmed that the synthesized layers were continuous and formed densely packed grain structure. The structure of BDD was confirmed by Raman spectra analysis. The effect of IL structure as the kind of electrolyte (Na2SO4 and NaCl) has been investigated. Electrolyses were conducted in an undivided electrolytic cell under galvanostatic conditions. The...

  18. Carrier recombination and diffusivity in microcrystalline CVD-grown and single-crystalline HPHT diamonds

    Scajev, P.; Gudelis, V.; Jarasiunas, K.; Kisialiou, I.; Ivakin, E.; NESLADEK, Milos; HAENEN, Ken
    We report investigation of carrier recombination and diffusivity in bulk diamonds of different crystalline structure microcrystalline (MC) CVD-grown and single crystalline HPHT diamonds. Presence of neutral and positively charged nitrogen and hydrogen defects was determined from NIR and UVIR absorption spectra. Carrier injection into 1-mm thick bulk layers was realized by two-photon absorption at 351?nm wavelength. Carrier lifetimes of 150-330?ns in IIa type HPHT crystals correlated with N density, while the lifetimes in CVD crystal exhibited very fast (80?ps), slower one (38?ns), and mu s-duration thermally-activated (similar to 1.5?eV) decay components. The initial two components correlated with the grain size...

  19. Study of interface properties in CuPc based hybrid inorganic-organic solar cells

    THALLURI, Krishna; SPOLTORE, Donato; PIERSIMONI, Fortunato; Clifford, John N.; Palomares, Emilio; MANCA, Jean
    Metal-substituted phthalocyanine thin films such as copper-phthalocyanine (CuPc) are often used as photo-active and hole transporting layers (HTLs) in fully organic photovoltaic devices. In this work, CuPc is vacuum sublimated on an electron acceptor layer of mesoporous titania (TiO2) for the formation of hybrid TiO2:CuPc solar cell devices. The performance of these hybrid solar cell devices was demonstrated without and with dye sensitization at the TiO2:CuPc interface. The charge separation and photocurrent contribution at the interfaces in these multilayer hybrid devices was studied by using a variety of optoelectrical and photophysical characterization techniques. It is important to understand the fundamental...

  20. MIP-based biomimetic sensor for the electronic detection of serotonin in human blood plasma

    PEETERS, Marloes; Troost, F. J.; VAN GRINSVEN, Bart; HOREMANS, Frederik; ALENUS, Jan; MURIB, Mohammed Sharif; Keszthelyi, D.; ETHIRAJAN, Anitha; THOELEN, Ronald; CLEIJ, Thomas; WAGNER, Patrick
    Serotonin is an important signaling molecule in the human body. The detection of serotonin is commonly performed by high performance liquid chromatography (HPLC), which is costly and time consuming due to extensive sample preparation. We will show that these problems can be overcome by using molecularly imprinted polymers (MIPs) as synthetic receptors in combination with impedance spectroscopy as readout technique. The MIPs were prepared with several blends of the underlying monomers and the best performing MIP material was selected by optical batch-rebinding experiments. MIP microparticles were then integrated in an impedimetric sensor cell and dose-response curves were measured in PBS...

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