Structure sensitive adsorption of DMSO on Au surfaces

Using a variable temperature STM, we have observed the adsorption of DMSO o n Au(100) and Au(111) surfaces at temperatures below 215 K. For DMSO on Au( 100), the molecules are trapped on the terraces at high points on the hex r econstruction giving rise to an ordered low coverage phase. Consistent with data from previous temperature programmed desorption (TPD) measurements, t his phase coexists with a higher coverage "striped" phase formed when the D MSO molecules associate with each other. On Au(111), the DMSO molecules nuc leate, order, and grow only from step edges; the steps are the only appropr iately electropositive sites on this surface.