Direct determination of surface structures from photoelectron diffraction

Abstract
Angle‐resolved photoemission extended fine structure (ARPEFS) is induced by interference between primary and elastically scattered photoelectron waves originating from an adsorbate core level on an ordered surface. Analysis by procedures analogous to those used in surface EXAFS yields absolute surface structures directly. ARPEFS appears capable of yielding bond distances with the same accuracy as EXAFS, and accurate bond angles. The coordination number is unambiguous with ARPEFS. Experiments have been performed with c(2×2)S/Ni(001), along [001] and [011], and p(2×2)S/Cu(001), along [011]. The differential photoelectron cross section in the [011] direction, for example, is modulated by ±50% in ARPEFS, in contrast to the ±2–3% effects observed in surface EXAFS. Single‐scattering theory yields a simple dependence of χ(k)=[I(k)−I0(k)]/I0(k) on the angles αj=cos1(p,pj), βj=cos1(ε, pj), and γ=cos1 (ε,p) relating the primary wave propagation direction p, the direction pj of scattering off atom j, and the photon polarization direction ε.