PNNL

Abstract

X-ray absorption spectroscopy and X-ray photoemission spectroscopy have been used to examine sulfur-gold bond formation in self-assembled monolayers derived from a dithiol monomer and disulfide-containing polyamide. These compounds were designed to allow the molecules to adsorb to gold through two terminal sulfurs, forming surface-attached loops. Element and site-specific density of unoccupied electronic states was probed by x-ray absorption spectroscopy at the C1s, N1s, O1s (K-edge) and S 2p (L2,3-edge) absorption edges. Photoemission measurements of the C1s, N1s, O1s and S 2p core lines were also used to estimate relative coverage, confirm layer formation and evaluate chemical bonding of the monomer and polymer to the Au coated substrates. In case of the dithiol monomer SAM, the spectroscopic evidence clearly shows that most of the molecules adsorb through only one sulfur. The disulfide-containing polymer, in contrast to the monomer, attaches to the surface through both sulfurs to form the anticipated surface-attached loop.