Geometrical characterization of pyrimidine base molecules adsorbed on Cu(1 1 0) surfaces: XPS and NEXAFS studies

The structures of pyrimidine base molecules of thymine and cytosine adsorbed onto Cu(110) surfaces (θ≪1.0 ML and ≫1.0 ML) have been discussed based on the results of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The NEXAFS analysis for azimuthal orientation of molecules on surfaces indicates that the adsorbed molecules are in an upright configuration with their π plane parallel to the row structure ([1 1̄ 0] direction), well below saturation coverage (θ ∼ 0.2 ML). Based on the chemical shifts observed in XP spectra (N1s, O1s region), the molecules have been determined to interact with surfaces through their nitrogen atom (lone-pair) next to the carbonyl group (C=O).