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Brief Reports are accounts of completed research which, while meeting the usual Physical Review standards of scientiftc quaiity, do not warrant regular articles A. Brief Report may be no longer than four printed pages and must be accompanied by an abstract T. he same publication schedule as for regular articles is followed, and page proofs are sent to authors Empty electronic states of gadolinium silicides (Gd3Si, and Gd5Si3) are investigated by means of inverse photoemission in the ultraviolet photon range. Isochromat spectra taken at different photon energies (11 -2S eV) are presented. The results are discussed in terms of bond formation between metal and silicon orbitals, in analogy with silicides of other low-d-occupancy metals (Ca silicides).The valence electronic states and the chemical bond in transition-metal silicides have been widely studied in recent years these studies have been largely motivated by the interest in connecting silicides properties with those of reactive silicon-metal interfaces. More recently rare-earth -silicon interfaces have attracted increasing attention because of their peculiar properties. However, up to now only few spectroscopic investigations on the rare-earth bulk silicides have been reported. ' This is due to the difficulty in the investigation of valence states because of the overlap with strong spectral features of the 4f states. This problem is common both to direct photoemission (PE) and to inverse-photoemission (IPE) spectroscopy.However, Gd is a favorable case since the 4f signal in PE is about 7 eV below the Fermi level EF, thus leaving an energy windo~to observe valence states near EF.This attractive situation has been already exploited to investigate occupied valence states via PE spectroscopy for the whole Gd-silicide family as well as for the Gd/Si interface.The purpose of the present work is to give an insight into the empty valence counterpart of these systems by means of inverse photoemission in the ultraviolet (uv) region. This is done by measuring isochromat spectra for the two extreme stoichiometries of Gd-Si phase diagram (Gd3Si5 and GdsSi3) at low enough energies so that the 4f signal is negligible.In studying chemical bonds in silicides, a simple picture based on a two-level model (Si p and metal d states) has been developed. ' Though very useful at a first approach, at least for near-noble-metal silicides, this model is subject to some criticism. ' In particular it is expected to fail in the case of alkaline-earth and rare-earth silicides, where the metal atoms have a d-atomic occupancy close to zero. Detailed calculations as well as experimental results on the occupied" and empty' electronic states in Ca silicides confirming this expectation have been presented recently. To some extent the results on the SiCa system can be used as a guideline to interpret the related data on Gd silicides. Auger line-shape analysis has indeed been performed on both Ca and Gd silicides, ' ' using the same interpretation scheme. In this connection the present investigatio...

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