Interaction of sodium overlayers with the PbS(100) (galena) surface: evidence for a Na↔Pb exchange reaction

Abstract

X-ray standing wave (XSW) and core level photoemission methods were used to study the atomic and electronic structure of sodium overlayers on cleaved (100) surfaces of the mineral galena (PbS). Both techniques provide clear evidence of an exchange reaction in which, at least, a portion of the surface lead ions (Pb2+) is replaced by sodium ions (Na+). The replacement results in a new component in the photoemission spectra associated with reduced lead, while a direct change in the lead surface atom position relative to the 200 bulk diffraction planes is observed in the XSW signa. Changes in the surface geometry of sulfur ions are smaller. The interface of the reacted PbS surface is strongly disordered, as indicated by a small coherent fraction (0.37–0.48) for sodium and rapid quenching of the substrate (1×1) low energy electron diffraction pattern.