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on the occasion of his 80th birthday A normal coordinate analysis of the vibration spectrum of crystalline V20, is carried out in the assumption of a Urey-Bradley force field. The calculated frequencies are adjusted to 29 experimental infrared and Raman frequencies by an automatic force constant refinemeat program. Analysis of the potential energy distribution and the atomic displacements allows the classification of the modes into nine types of oxygen vibrations and three types of chain modes. A discussion is given of effective charges and infrared intensities. An assignment of the infrared spectrum of polycrystalline V,O, is added. The inErared (IR) spectrum of V,O,, and to a lesser extent the Raman spectrum, have been the subject of several papers [l to 111. Due to the complicated lattice structure and the high number of fundamentals, the assignment of experimental frequencies without normal-mode calculations has necessarily been restricted t o a few bands in the higher-frequency range. A thorough understanding of the vibration spectrum is however of both academic and practical importance. The latter is illustrated by the frequent use of the TR spectrum of V,O, catalysts as a monitor for bond changes which occur a t different stages of the reaction.Some years ago, Gilson et al. [8] have published an extended list of IR and Raman frequencies of V,O,, together with calculated frequencies and bond assignments. As we have already shown in a previous paper [lo], the experimental frequencies as determined by Gilson et al. deviate substantially from the correct values. We have therefore carried out new normal-mode calculations starting from our own IR and Raman data. The calculated frequencies are fitted to the experimental ones by adjusting the force constants in an automatic least-squares fitting program. We found that a simple valence force field is inadequate for a reasonable fit to some of the important bands. The fit was markedly improved by allowance for repulsive action between non-bonded atoms (UB force field).

Complementary infrared and transmission electron microscopy studies of the effect of high temperature-high pressure treatments on oxygen-related defects in irradiated silicon Infrared absorption spectra of polyhedral and platelet oxygen precipitates in silicon are analyzed using a modified Day-Thorpe approach ͓J. Phys.: Condens. Matter 11, 2551 ͑1999͔͒. The aspect ratio of the precipitates is determined by transmission electron microscopy analysis. The reduced spectral function and the stoichiometry of the precipitate are extracted from the absorption spectra and the amount of precipitated interstitial oxygen. The experimental absorption spectra can be divided in a set with a Fröhlich frequency of around 1100 cm Ϫ1 and in a set with a Fröhlich frequency between 1110 and 1120 cm Ϫ1 . It is shown that the shift in the Fröhlich frequency is not due to a differing stoichiometry, but to the detailed structure of the reduced spectral function. Inverse modeling of the spectra suggests that the oxide precipitates consist of substoichiometric SiO ␥ with ␥ϭ1.17Ϯ0.14.

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Deep level transient spectroscopy of electron irradiated p-type silicon reveals a defect level at Ev+0.19 eV, which during anneal treatments at 200 °C gradually transforms into a band with Ev+0.24 eV. Both energy levels however, are reported in literature to be the donor level of the divacancy. In the present study it is proposed that during the low-temperature anneal the divacancy interacts with oxygen, forming a V2O complex. During heat treatments at temperatures in the range between 250 and 450 °C a further shift of the deep level to higher energy positions is observed which might be related with other vacancy-oxygen complexes.