PNNL

Abstract

Well-ordered FeO(111) thin films are epitaxially grown on a Pt(111) substrate. A series of molecules including CH4, CH3Cl, CH2Cl2, CHCl3, and CCl4 are used as probes to test the chemical reactivity of the FeO(111) surface. The temperature programmed desorption spectra show no evidence of dissociative adsorption or chemical reaction between the substrate and the adsorbates. The desorption kinetics studies reveal that all the molecules are physisorbed and have desorption kinetics with an order between 0 and 1. Kinetic analysis is conducted, assuming both zero and first order desorption, and shows that an uncertainty in the desorption order introduces an error in determination of the terrace site desorption energies (? = 0.5 ML) of only ~ 2%. The desorption energies for the series of molecules increase with the number of chlorine atoms in the molecule. The increase of desorption energies is not linear with the molecular polarizability and the deviations from linearity are attributed to the permanent dipole in some of the molecules. We conclude that the oxygen terminated FeO(111) surface is in general unreactive toward both C-H and C-Cl bonds.