Adenine adlayers on Cu(111): XPS and NEXAFS study.

The adsorption of adenine on Cu(111) was studied by photoelectron and near edge x-ray absorption fine structure spectroscopy. Disordered molecular films were deposited by means of physical vapor deposition on the substrate at room temperature. Adenine chemisorbs on the Cu(111) surface with strong rehybridization of the molecular orbitals and the Cu 3d states. Annealing at 150 °C caused the desorption of weakly bonded molecules accompanied by formation of a short-range ordered molecular adlayer. The interface is characterized by the formation of new states in the valence band at 1.5, 7, and 9 eV. The present work complements and refines existing knowledge of adenine interaction with this surface. The coverage is not the main parameter that defines the adenine geometry and adsorption properties on Cu(111). Excess thermal energy can further rearrange the molecular adlayer and, independent of the initial coverage, the flat lying stable molecular adlayer is formed.