Highly Ordered Self-Assembled Monolayers of Carboxy- and Ester-Terminated Alkanethiols on Au(111): Infrared Absorption and Hyperthermal-Deposition Experiments with Cr(benzene)2 Ions

Abstract

The physical and chemical properties of carboxy- and ester-terminated alkanethiolate self-assembled monolayers (SAMs) on a gold (Au) substrate (Au(111)), which were prepared in a one-pot reaction, were investigated by means of infrared reflection absorption spectroscopy (IRAS) and hyperthermal-deposition experiments with Cr(benzene)2 ions. IRAS spectra showed that the vibrational modes of hydrogen-bonded COOH and CH2 wagging are sensitive to the flatness and cleanness of Au substrates for COOH-SAM and COOMe-/COOEt-SAM, respectively. The intensities of CH2 wagging modes are temperature dependent, which is relevant to the alkyl chain ordering in the highly ordered SAM. The terminal groups of the highly ordered SAM are dissociated by hyperthermal collision events of gas-phase-synthesized Cr(benzene)2 sandwich complex ions, and the adsorption properties of deposited Cr(benzene)2 are discussed in relation to IRAS and temperature-programmed desorption (TPD) measurements.