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 substrates for comparative studies of alkanethiol self-assembly. Vapor deposition 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 surface roughness is controlled by the mica substrate temperature during Au evaporation becoming atomically flat at 450-500 degrees C as shown by AFM. Surprisingly the formation of dense blocking self-assembled alkanethiol monolayers (CH3(CH2)(n)SH, n = 9, 11, 13, 15, 17) becomes greatly inhibited as the Au/mica becomes smoother. In comparison, the effect 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 combined with electrochemical potential cycling prior to alkanethiol adsorption yields pinhole-free SAMs while solvent rinse and acidic peroxide pretreatments of Au by themselves fail to do so. In contrast with previous reports, Au surface pretreatment rather than surface roughness plays the more important role in molecular self-assembly.