SURFACE-CHEMISTRY AND MOLECULAR REACTIONS ON KNBO3 SINGLE-CRYSTAL SURFACES

We have exposed the surface of KNbO3 single crystals, cleaned in UHV by scraping, to a variety of simple molecules (H-2, O2, N2, CO, CO2, H2O, NH3, NO3, C2H4, and (CH3)2CO). From photoemission and work function measurements we derive that out of these molecules only CO2 and acetone ((CH3)2CO) react with- the surface. Initially CO2 reacts with the regions of the (100) surface terminated by fragments of the KO(100) bulk plane, forming a surface carbonate. At high exposures, after the KO facets are saturated, CO2 dissociates at the NbO2 terminated surface regions into O and CO. The oxygen atoms react with the Nb atoms restoring the full bulk octahedral oxygen coordination of these atoms, while the CO fragments are desorbing.