Structure of Prototypical Semiconductor Surfaces and Interfaces Investigated by Photoemission Extended X-Ray Absorption Fine Structure (PEXAFS)

Extended X-ray absorption fine structure (EXAFS) has been known for half a century. However, using synchrotron radiation, it has developed into a powerful tool for determining the atomic structure of a wide variety of surfaces and interfaces. The power of this technique lies in its sensitivity to the local environment of a particular element. Photoemission extended X-ray absorption fine structure (PEXAFS) is a new variation of electron detection surface EXAFS (SEXAFS) using photoemission spectroscopy in the constant initial state mode, Due to small escape depths, a very high surface sensitivity is achieved. Other major advantages of this new technique include (i) an improved signal/noise ratio allowing very short data collection times, which is an especially useful feature for short lifetime surfaces, and (ii) double-checking interatomic distances. Combined with core level and valence band photoemission spectroscopies. PEXAFS provides the exceptional ability to probe the atomic geometry and the electronic structure at the same time and for the same surface. It thus gives access to important issues, such as (i) surface reconstruction and/or relaxation, (ii) bonding nature, (iii) adsorption site and (iv) initial interface formation. Furthermore, it could be used to clarify photoemission core level shift origin by allowing one to discriminate structural changes from other causes as initial or final state effects. This article reviews the latest PEXAFS investigations for model elemental (silicon) and compound (indium phosphide) semiconductor surfaces and their interfaces with alkali metals, antimony, aluminum, bismuth and silver.