SITE SPECIFIC SURFACE INTERACTION OF ELECTRON-DONORS AND ACCEPTORS ON FES2(100) CLEAVAGE PLANES

The interaction of UHV cleaved FeS2(100) surfaces with adsorbed H2O as an electron donor and adsorbed Br2 as an electron acceptor has been studied with LEED, LEISS, UPS, and XPS to simulate semiconductor/electrolyte interfaces in UHV. The (100) cleavage plane is characterized by a c(2 x 2) or p(square-root 2 x square-root 2)R 45-degrees LEED pattern which is interpreted in terms of the unreconstructed FeS2 surface. H2O is molecularly adsorbed at low temperatures (100 K) and desorbs completely at room temperature (RT). LEIS-spectra taken at low coverages (< 0.5 ML) suggest a preferential interaction with the Fe sites. Br2 is ionosorbed at low coverages (< 0.5 ML) as well interacting specifically with Fe-sites. It is molecularly adsorbed at higher coverages. The ionosorbed part does not desorb at RT. The behavior of specific adsorption is related to the electronic nature of the band edges which are derived from Fe d-states.