DE-WETTING OF Fe OXIDE FROM CLEAN AND SULFUR-COVERED Fe METAL SUBSTRATES

摘要

Studies performed in UHV on Fe/Fe-oxide interfaces suggest a mechanism for S-inducedrnthermal instability of the interface. In the absence of sulfur, oxide debonding is initiated byrnthe diffusion of oxygen into the bulk from an Fe-O interfacial "glue" layer. Once diffusionrnoccurs, the polar oxide dewets from the nonpolar metal substrate. In the presence of S, thernformation of the FeO layer is inhibited due to site competition between S and O atoms atrnthe interface. Upon heating, S reacts with existing interfacial oxide sites to produce SO_2,rnand destroying interfacial oxide-metal bonds at a lower temperature (640 K) than that atrnwhich oxygen diffusion from the FeO layer occurs (～900 K). At this point there is norninterfacial bonding between the polar oxide and the non-polar S-modified substrate, andrnoxide dewetting occurs. Due to lower Fe coordination at the surface, Fe-S bonds are largelyrncovalent, and therefore the S-modified surface is still nonpolar.