ADSORBATE STRUCTURE DETERMINATION ON SURFACES USING PHOTOELECTRON DIFFRACTION

Photoelectron diffraction is the name given to the phenomenon resultin g from the coherent interference of the directly emitted component of an electron wavefield, emerging from an atom as a result of core level photoemission, with other components elastically scattered by surroun ding atoms. Experimental characterization of this effect provides info rmation which can be used to provide quantitative determinations of th e structure of surfaces, and particularly of adsorbed species on surfa ces, in an element-specific fashion. Since the initial demonstration o f the phenomenon in the late 1970s, an extensive methodology for surfa ce structure determination has been developed. In this review the back ground physics of the process, and the development of the technique is described. A brief discussion of the high energy forward scattering v ersion of the technique (x-ray Photoelectron Diffraction-XPD), which u tilizes zero-order diffraction effects, is included, but the most of t he review is concerned with the lower energy backscattering method mor e relevant to the determination of detailed adsorption sites on surfac es. In addition to the general theoretical, experimental and methodolo gy background, a number of the more recent developments are described including use of 'direct inversion' methods for (approximate) structur e determination, including a survey of photoelectron holography, and t he realization of chemical shift photoelectron diffraction to allow st ructure determinations of surfaces including atoms of one element in m ore than one inequivalent site. All of the developments are illustrate d with specific examples, mainly of molecular and atomic adsorbates on metal surfaces.