PHOTOEMISSION EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE (PEXAFS) - A NEW APPROACH TO PROBE SURFACE AND INTERFACE ATOMIC GEOMETRY

Photoemission extended x-ray absorption fine structure (PEXAFS) is a n ew variation of photoelectron-detection EXAFS. The PEXAFS technique pr obes short-range order of atoms in the top-most surface atomic layers by measuring adsorbate and/or substrate complex interatomic bond lengt hs. Major advantages of this new technique include i) a very high surf ace sensitivity, ii) an improved signal/noise ratio allowing very shor t data collection times, iii) the unique feature to double-check inter atomic distances. In addition, PEXAFS experiments could be performed i n combination with core level and valence band photoemission spectrosc opies (XPS) using synchrotron radiation on the same experimental syste m at the same soft x-ray storage ring. This provides the unique abilit y to probe at the same time, on the same surface and at the same cover age both atomic geometry and electronic structure of the investigated system. It gives access to such important informations as i) surface r econstruction and/or relaxation, ii) bonding nature, iii) adsorption s ite and, iv) initial interface formation. These interesting features a re used to understand some prototypical systems of strong current inte rest including various metal-semiconductor interfaces and the effect o f an Ar+ ion beam on the atomic surface structure.