Characterization of COOH-Terminated Self-Assembled Monolayers and Adsorption Efficiency of DNA Molecules Studied by X-ray Photoelectron Spectroscopy and Near-Edge X-ray Absorption Fine Structure Spectroscopy

Abstract

Self-assembled monolayers (SAMs) of three thiol derivatives with a COOH group at the terminus of the molecule were prepared on Au(111) substrates as templates for immobilization of DNA molecules. The adsorption states and the structures were examined by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. S 2p XPS results showed that these molecules are mostly chemisorbed on the Au(111) surface through S–Au bonds. The molecular orientation in these SAMs was elucidated using the polarization dependence of the C K-edge NEXAFS spectra. These results suggested that the film structure and the molecular packing differ among these SAMs. We compared the amounts of the amino-terminated DNA molecules adsorbed on these SAMs estimated from the peak intensity of the N 1s XP spectra. These results show that the adsorption efficiency of the DNA molecules depends on the structures of the COOH-terminated SAMs.