Abstract: The tetravalent and hexavalent selenium content of water samples can be determined by conventional energy-dispersive X-ray fluorescence after different preconcentration steps. Selenium values of nearly three-hundred different environmental and drinking water samples in Belgium are reported. The results are quite low, ranging from the detection limits up to 1 μg l−1. The concentration levels are compared to literature data and the speciation is discussed. The contribution of drinking water to the daily intake of selenium in Belgium ranges from less than 0.2 to 5%.

Abstract: In this work, photoelectric yield and electrical properties of several types of epitaxial erbium silicide on silicon Schottky diodes are studied, Different preparation conditions are used simultaneously on n- and p-Si(111) substrates for the 200 Angstrom thick silicide films. A last type of sample consists in 1.3 monolayer of epitaxial silicide with root 3 X root 3 superstructure on the Si substrate and covered by silver on the top. Photocurrent measurements are done as a function of photon energy at several temperatures. All these samples show barrier heights near 1 eV on p-type Si, even for the interface comprising only 1.3 monolayer of silicide whereas barrier heights on n-rype Si span the range from 0.28 to 0.67 eV for this last kind of sample, the sum of the barriers always exceeding the silicon band gap, These photoelectric results are confirmed by electrical characterisations, All these results show that the Fermi level is pinned 0.1 eV below the conduction band edge on p-type Si but shifts to various positions lower within the band gap on n-type Si. This fact leads to the hypothesis of a density of -7 interface states close to the charge change in the Si depletion zone from p- to n-type, namely 10(12) eV(-1) cm(-2). Although some inhomogeneities and defects at the interface are detected by electron microscopy for samples annealed at 750 degrees C, Fermi level position seems rather insensitive to the structural details of the interface while the silicide thickness plays a role on n-type Si.

Abstract: We analyzed ultra-thin ZrO2/SiO2/Si gate dielectrics under post-deposition anneals in dry O-2 at temperatures from 500 to 700 degreesC. TOF-SIMS profiling of ZrO2/SiO2/Si stacks is hampered by many sputter induced artifacts. The depletion of oxygen leads to a decrease in SIMS intensities. However, preferential sputtering is accompanied by transport of the depleted species towards the surface. Due to recoil implantation oxygen gets piled-up near the ZrO2/SiO2 interface. Either normal or radiation-enhanced diffusion transports oxygen back to the surface. Simultaneously also segregation of zirconium towards and through the interface is observed, resulting in a large zirconium tail in the underlying silicon substrate. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: A far-infrared absorption study of electrons in lightly-doped GaAs/Al0.3Ga0.7As superlattices is presented. Both weakly and strongly coupled superlattices are investigated, and the difference between intersubband transitions and transitions between extended minibands is demonstrated. At low temperatures, the absorption spectra are dominated by donor transitions. The 1s-2p(z) transition, which is intimately related to the intersubband transition, is observed. All experimental data are compared to an envelope function calculation for the miniband structure and a variational calculation for the donor energies. Excellent agreement between experiment and theory is achieved.

Abstract: The main results and conclusions are presented of a round robin study of silicon oxide on silicon reference samples for ellipsometry. The oxide films with nominal thicknesses of 10, 50 and 120 nm are grown by thermal oxidation. The oxide film thicknesses have been determined by single wavelength ellipsometry (SWE), by spectroscopic ellipsometry (SE) and by cross-sectional conventional and high-resolution transmission electron microscopy (TEM and HREM) in different laboratories. The main conclusions are that special precautions have to be taken in order to use TEM as a reliable thickness measurement technique; that single wavelength ellipsometry can be used with great accuracy and reproducibility for the 50 and 120 nm film thicknesses but that it shows some inherent problems for the 10 nm films; and that spectroscopic ellipsometry showed for all film thicknesses an accuracy and reproducibility which is clearly superior to that of SWE.

Abstract: Shallow trench isolation (STI) is a promising technology for the isolation structures of the new generation of ULSI devices with dimensions below 0.18 mum. The various processing steps cause stress fields in STI structures, which can lead to defect formation in the silicon substrate. In their turn, stress fields affect the electrical parameters and the reliability of devices. Convergent beam electron diffraction (CBED) is used in this study to examine the influence of a wet and a dry pre-gate oxidation on the stress distribution around STI structures. The measurements are performed on STI structures with different width and spacing. CBED analysis is compared with bright-field TEM images. Defects are observed in high-strain areas of small isolated structures. (C) 2001 Elsevier Science Ltd. All rights reserved.