Binding property and structure of aromatic isocyanide self-assembly monolayers on Ag and Au surfaces

Abstract

The binding property of p-biphenyl isocyanide self-assembled monolayers (SAMs) on Au and Ag was investigated by temperature-dependent surface-enhanced Raman spectroscopy (SERS). p-Biphenyl isocyanide was found to desorb on Ag at a low temperature of similar to393 K whereas it appeared to remain enduring at a high temperature of similar to453 K for Au. Structures of p-biphenyl isocyanide SAMs on Au and Ag flat films were checked by means of near-edge x-ray absorption fine structure spectroscopy (NEXAFS) at the two different normal (90degrees) and grazing (20degrees) angles of the incident x-ray beam. Our results suggested that the SAMs prepared by p-biphenyl isocyanide should have a relatively disordered structure even at room temperature on both Au and Ag, as indicated from an insubstantial change in NEXAFS spectra at the two different angles from those of p-biphenyl thiolate and p-biphenyl methanethiolate. The weakness of the isocyanide-metal bond in comparison with the sulphur-metal bond may result in both low surface coverage and orientational disorder. A density functional theory calculation method was employed to attempt to explain the difference in stability for phenyl isocyanide on Ag and Au surfaces. Our calculation result yielded a lower binding energy of phenyl isocyanide on Ag than that on Au, consistent with the temperature-dependent Raman results. Copyright (C) 2005 John Wiley Sons, Ltd.