Scanning tunneling microscopy and X-ray photoelectron spectroscopy of silver deposited octanethiol self-assembled monolayers

Ag deposited self-assembled monolayers (SAMs) of octanethiol (CH3(CH2)(7)SH ) have been studied using scanning tunneling microscopy and X-ray photoelec tron spectroscopy (XPS). At the initial stage of Ag deposition, monatomic h eight islands, similar to7 x 10(11) cm(-2) in density, grow at the SAMs/Au( 1 1 1) interface and become larger as more Ag atoms are deposited up to a f ull monolayer coverage of Ag. The differences of the nucleation density and the growth property between Ag and Au islands can be attributed to the hig her mobility of Ag atoms and the difference of the molecular packing on the se islands. XPS analysis of this structure (SAMs/Ag monolayer/Au) shows tha t the Ag 3d(5/2) binding energy is shifted -0.3 eV with respect to bulk Ag, the C 1s binding energy is similar to0.3 eV higher than that before Ag dep osition, and the S 2p(3/2) binding energy exhibits little shift before and after deposition. The origin of the shift can be explained by the change of the dipole at the interface and the electrical isolation of alkyl chains f rom the surroundings. (C) 2001 Elsevier Science B.V. All rights reserved.