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

Sputtering of monolayers of hexadecanethiol (HDT) molecules, CH3(CH2)(15)SH, self-assembled on Au(lll) and Ag(lll) substrates has been studied using 800 eV He+-ion bombardment. Sputtering kinetics in the dose range from 1.5 x 10(12) to 6.5 x 10(16) cm(-2) for HDT/Au and in the range from 8 x 10(13) to 1.3 x 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 ro 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. (C) 1999 Elsevier Science B.V. All rights reserved.