Marc D'olieslaeger

Towards Efficient Hybrid Solar Cells Based on Fully Polymer Infiltrated ZnO Nanorod Arrays

L.B. and B.C. contributed equally to this work. The authors thank R. Rieke from Rieke Metals for useful suggestions. This work was financially supported by BOF, UHasselt, the Flemish Odysseus program, and the Interreg project Organext. A. H. is a postdoctoral research fellow of the Research Foundation-Flanders (FWO Vlaanderen).

INVESTIGATION OF THE CVD DIAMOND INTERMEDIATE LAYER STEEL INTERFACE

Abstract An intermediate multilayer structure, based on refractory metals and silver, is used to improve the adhesion of CVD diamond to steel substrates. The diffusion process and recrystallization of the multilayer structure during the diamond deposition and a further thermal annealing are studied by means of secondary ion mass spectrometry, X-ray diffraction and scanning electron microscopy. The stress in the diamond film is investigated by Raman analysis and the adhesion of diamond films to the substrate is examined by indentation tests.

Deposition of aluminium nitride film by magnetron sputtering for diamond-based surface acoustic wave applications

Diamond/piezoelectric material thin film layered structures are expected to be applied to high frequency surface acoustic wave (SAW) devices because of the high acoustic wave velocity of diamond. Aluminium nitride (AlN) has been chosen as piezoelectric material because of its both high phase velocity and high resistivity. AIN thin films have been deposited by DC pulsed magnetron sputtering on Si(100) substrates. Texture and structure of the films have been investigated by X-ray diffraction, cross-section and in-plane view scanning electronic microscopy observation, and atomic force microscopy. One-micron thick, smooth and (002) oriented AlN films have been successfully deposited on freestanding chemical vapour deposition (CVD) diamond layers. The surface acoustic wave characteristics of AlN/diamond structure were investigated.

Effect of oxygen on the electrical characteristics of PPV-LEDs

The presence of oxygen in the surrounding atmosphere exerts an important influence on the electro-optical characteristics and the degradation behaviour of organic electroluminescent Al-PPV-ITO-diodes. Experiments in various gas atmospheres show that the devices possess gas sensing properties. For particular gas compositions the current-voltage (IV)-characteristics feature negative resistance sections in the form of anomalous bumps superimposed on Shockley-like diode characteristics. A new interpretation is provided for the memory switch phenomena related to these anomalous electrical characteristics. The gas sensor like behaviour and the increase in conductivity in an oxygen free ambient is believed to be related to the formation of localized Ohmic paths. The growth of these Ohmic paths is inhibited by oxidation and the paths can melt due to excessive joule heating.

Hexagonal boron nitride nanowalls: physical vapour deposition, 2D/3D morphology and spectroscopic analysis

Hexagonal boron nitride nanowalls were synthesized using reactive radio-frequency magnetron sputtering in combination with a hexagonal BN target. The nanowall formation is purely governed by addition of hydrogen to the nitrogen/argon gas mixture, and leads to a decreased incorporation of carbon and oxygen impurities. The surface morphology is assessed with scanning electron microscopy, while stoichiometry and reduced impurity content of the material was evidenced using Rutherford backscattering spectroscopy. Transmission electron microscopy confirms the hexagonal nature of the nanowalls, whose luminescent properties are studied with cathodoluminescence spectroscopy, shedding more light on the location and nature of the excitonic emission and crystalline quality of the h-BN nanowalls.

Aqueous chemical solution deposition of ultrathin lanthanide oxide dielectric films

Hasselt Univ, Mat Res Inst, Lab Inorgan & Phys Chem, B-3590 Diepenbeek, Belgium. IMEC vzw, Div IMOMEC, B-3590 Diepenbeek, Belgium. IMEC vzw, B-3001 Heverlee, Belgium. Katholieke Univ Leuven, Dept Chem, B-3001 Heverlee, Belgium. XIOS Hogesch Limburg, Dept Ind Sci & Technol IWT, B-3590 Diepenbeek, Belgium.Van Bael, MK, Hasselt Univ, Mat Res Inst, Lab Inorgan & Phys Chem, B-3590 Diepenbeek, Belgium.marlies.vanbael@uhasselt.be jules.mullens@uhasselt.be

Investigation of n-doping in CVD diamond using gap states spectroscopy☆

In-situ doping of CVD diamond with N and Li using N2 and a Li-containing organometallic precursor was investigated. Photothermal deflection spectroscopy (PDS) was used to study optical transitions from localized electronic states in the bandgap of CVD diamond resulting from the presence of extrinsic and intrinsic impurities. The advantage of PDS is its sensitivity, which allows very low defect levels to be investigated even in thin diamond films. The optical absorption coefficient α of N-doped films (100 ppm N2 in the gas phase) shows absorption bands characteristic of Ib diamond. When a Li-containing precursor is used, a deep defect state around 1.5 eV, which has not been reported previously, is observed. Optical transitions due to this defect state are superimposed on the characteristic background absorption present in all CVD diamond films.

Planar helium bubble arrays in nickel

Abstract Annealed nickel samples were thinned for transmission electron microscopy, and pre-implanted with 3 keV helium ions at 300 K to create submicroscopic helium-vacancy clusters. The samples were then irradiated with 95 eV helium ions to a dose of 1 × 10 22 He + /m 2 , again at 300 K. After the second irradiation, which causes no radiation damage since the energy is well below the damage threshold for nickel, planar bubble arrays, lying on (111) planes, were observed in the transmission electron microscope. These aggregates are most probably nucleated at pre-existing He-V clusters created by the 3 keV implantation. This result confirms a preliminary observation reported earlier by Van Veen et al.

Morphology of MDMO-PPV:PCBM bulk heterojunction organic solar cells studied by AFM, KFM, and TEM

The microstructure of MDMO-PPV:PCBM blends as used in bulk hetero-junction organic solar cells was studied by Atomic Force Microscopy (AFM) and Kelvin Force Microscopy (KFM) to image the surface morphology and by means of Transmission Electron Microscopy (TEM) to reveal images of the films interior. By introducing KFM, it was possible to demonstrate that phase separated domains have different local electrical properties than the surrounding matrix. Since blend morphology clearly influences global electrical properties and photovoltaic performance, an attempt to control the morphology by means of casting conditions was undertaken. By using AFM, it has been proven that not only the choice of solvent, but also drying conditions dramatically influence the blend structure. Therefore, the possibility of discovering the blend morphology by AFM, KFM and TEM makes them powerful tools for understanding todays organic photovoltaic performances and for screening new sets of materials.

Study of different chemical methods to prepare ceramic high-temperature superconductors

The preparation of precursors of bulk , and materials by coprecipitation-filtration of hydroxides or oxalates and sol-gel techniques is presented. Their properties are compared with those of products prepared by the conventional solid-state reaction method by means of TGA, FTIR, XRD, SEM, EDX and resistivity measurements.