Ion-induced erosion of organic self-assembled monolayers

Laser post-ionization mass spectrometry combined with Scanning Tunneling Microscopy (STM) has been used to investigate processes of ion-stimulated erosion of self-assembled monolayers (SAM) of phenethyl mercaptan C6H5CH2CH2S (PEM) deposited on gold. Results indicate that only PEM fragments are emitted from the surface. Most of the PEM fragments (predominantly C6H5CH2CH3 with m/z = 106) are emitted with thermal kinetic energies. STM images collected on 8 keV H-2(-)-irradiated surfaces with a system tuned to probe electronic states of sulfur atoms show no additional damage induced by irradiation. This indicates that sulfur atoms are not removed from the surface during hydrogen bombardment. It is proposed that the emission of SAM molecules is initiated by chemical reactions which gently break C-S bonds. (C) 1999 Elsevier Science B.V. All rights reserved.