The adsorption of 5-Fluorouracil (5FU) on Au(111) and Cu(111) surfaces as a function of molecular coverage and temperature has been studied, using x-ray photoelectron spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. The nature of 5-Fluorouracil bonding with the two substrates is remarkably different. The Cu substrate forms a chemisorbed complex with 5-FU while the Au substrate shows only physisorption. NEXAFS data at the C, N and O K-edge show a strong angular dependence, indicating that 5-FU lies nearly parallel on the inert Au(111) surface, and at a steep angle on the Cu(111) surface. 5-FU is a biomolecule used for cancer treatment and the results are relevant for those using metal surfaces to prepare 5-FU for applications such as drug delivery.
