A LOW-ENERGY HELIUM ATOM DIFFRACTION STUDY OF DECANETHIOL SELF-ASSEMBLED ON AU(111)

We report the results of low energy helium atom diffraction studies of the surface of decanethiol self-assembled on the (111) face of single crystal gold. Our survey of 13 separate samples indicates that for de canethiol the standard self-assembly methodology results in monolayers of widely varying quality. We observe that surface order is generally enhanced by preparing monolayers in micromolar solution as compared t o the usual millimolar preparation [M.D. Porter et al., J. Am. Chem. S ec. 109 (1987) 3559; C.D. Bain et al., J. Am. Chem. Sec. 111 (1989) 32 1]. This result is in agreement with a parallel study conducted using grazing-incidence X-ray diffraction (GIXD). Particular attention is fo cused on two exceptionally high-quality samples which show more clearl y than ever before the c(4 root 3 x 2 root 3)R30 degrees diffraction p attern first observed for octadecanethiol monolayers [N. Camillone III et at, J. Chem. Phys. 98 (1993) 3503]. The diffraction patterns obser ved for these samples and their structural implications are discussed in light of recent advances made in other laboratories. We also discus s the results of thermal annealing experiments. (C) 1997 Elsevier Scie nce B.V.