EFFECT OF GOLD TOPOGRAPHY AND SURFACE PRETREATMENT ON THE SELF-ASSEMBLY OF ALKANETHIOL MONOLAYERS

Thin films of vapor deposited and sputtered Au are prepared as substra tes for comparative studies of alkanethiol self-assembly. Vapor deposi tion of Au is carried out on freshly cleaved heated mica substrates in ultrahigh vacuum at 25, 150, 300, 450, and 500 degrees C. The Au surf ace roughness is controlled by the mica substrate temperature during A u evaporation becoming atomically flat at 450-500 degrees C as shown b y AFM. Surprisingly the formation of dense blocking self-assembled alk anethiol monolayers (CH3(CH2)(n)SH, n = 9, 11, 13, 15, 17) becomes gre atly inhibited as the Au/mica becomes smoother. In comparison, the eff ect of surface pretreatment of microscopically rougher Au substrates, prepared by sputtering onto Si[100] substrates, was also investigated. Pretreatment of Au/Si with a brief exposure to acidic peroxide combin ed with electrochemical potential cycling prior to alkanethiol adsorpt ion yields pinhole-free SAMs while solvent rinse and acidic peroxide p retreatments of Au by themselves fail to do so. In contrast with previ ous reports, Au surface pretreatment rather than surface roughness pla ys the more important role in molecular self-assembly.