Substrate effect in sputtering of self-assembled monolayers: hexadecanethiol on Au(111) and Ag(111)

Abstract

Sputtering of monolayers of hexadecanethiol (HDT) molecules, CH 3(CH 2) 15SH, self-assembled on Au(111) and Ag(111) substrates has been studied using 800 eV He +-ion bombardment. Sputtering kinetics in the dose range from 1.5×10 12 to 6.5×10 16 cm −2 for HDT/Au and in the range from 8×10 13 to 1.3×10 16 cm −2 for HDT/Ag were monitored by using ion-scattering spectroscopy, X-ray and UV photoelectron spectroscopies, and metastable-induced electron spectroscopy. The effect of immersion time on the structure and sputtering kinetics of the HDT/Au system was checked. The character of the sputtering kinetics was found to depend on the nature of the substrate. A two-stage process that was revealed in sputtering of HDT/Ag could not be clearly distinguished for HDT/Au. In the latter case, the sputtering process in the higher dosage range seems to be dominated by uncovering of a sulfur sublayer and gold atoms due to cleavage of C−S and S–Au bonds with about equal rate. In both systems, ion bombardment induced the formation of CC double bonds. For HDT/Au, the estimated values of the initial sputtering yield of large fragments and of the desorption cross-section of sulfur species are several times larger than for HDT/Ag.