Core-level photoemission spectra from a W(111) surface using synchrotron radiation are presented. These core-level spectra are shown to be composed of four components with the same peak shape: one from bulk atoms and three from different crystallographic sites in the selvedge.The selvedge peaks comprise a peak from the topmost surface atoms (shifted by -0.45~0.01 eV) and two different underlayer sites (shifted by -0.30~0.02 eV and -0.11~0.002 eV from the bulk peak). This contrasts with a previous model, proposed by Wertheim, Citrin, and van der Veen, which used only two surface components: a broadened surface atom peak and one underlayer peak. The data presented can be fitted with three peaks, yielding good agreement with the peak energies obtained by these authors; however, we show that the four-peak model gives a better fit to the experimental spectra. The use of two underlayer peaks is in good agreement both with intuitive arguments based on the coordination number of atoms in the selvedge and with two previous theoretical calculations of the surface core-level shift. The values determined from the fitting parameters for the core-level line shape are also in good agreement with values calculated by other workers.

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The polarization dependence of the Cl K-edge 'white-line' has been measured from Si(111)7*7-Cl and Si(100)2*1-Cl. In both cases it has the form expected on the basis of a pseudo-intramolecular sigma *-resonance model. This suggests that the near-edge X-ray absorption fine structure (NEXAFS) could provide a simple, incisive monitor of the surface structure for atomic adsorbates on semiconductors. Together with the corresponding surface extended X-ray adsorption fine structure (SEXAFS), the Si(100)2*1-Cl NEXAFS indicates that Cl bonds atop a buckled dimer with a Cl-Si bond length of 2.00+or-0.02 AA.

We have determined the molecular orientation of CO adsorbed on the Cu(ll0) surface at 150 K as being within 20' of the surface normal, using x-ray absorption spectroscopy in the nearedge region. Measurements were carried out in the [ O l l ] azimuth, using Auger yield detection. We discuss the difficulties of using NEXAPS spectroscopy whilst performing Auger yield meaEupement5 with a fixed electron energy analyser.

A vertically dispersing high-energy spherical grating monochromator (HESGM) has been installed on the synchrotron radiation source (SRS) at the Daresbury Laboratory. The instrument has no entrance slit and provides a high intensity source of x rays of energy 250–1400 eV focused into a small spot suitable for surface spectroscopy. Photoabsorption features of 240 meV have been resolved, but the resolution of the instrument is dependent on the SRS stored beam current. The degree of linear polarization has been measured at the carbon K edge to be 0.80.