XSW study of oxygen/alkali metal/Si(111) interfaces

The X-ray standing wave technique has been applied to investigate the local ization of oxygen adsorbed on clean Si(1 1 1)7 x 7 and Si(1 1 1) partly cov ered by alkali metal (Na, K) atoms. To this end we scanned over the Si(1 1 1) Bragg reflection excited with 3.3 keV photons while detecting the O 1s c ore level. O 1s photoelectrons with similar to2.7 keV kinetic energy where detected with a resolution high enough to resolve chemically shifted compon ents in the O 1s core level separated by similar to1 eV. This allows to per form a chemical-state-resolved X-ray standing-wave analysis. The possibilit y of detecting low Z elements opens a new field to the use of the X-ray sta nding-wave technique. (C) 2001 Elsevier Science B.V. All rights reserved.