Influence of O2 exposure on the interaction between CH4 and amorphous AlYB14

Abstract

The influence of surface oxidation on the interaction between CH4 and amorphous AlYB14 (a-AlYB14) has been studied theoretically by using density functional theory and experimentally by ultra-high vacuum atomic force microscopy (UHV-AFM). CH4 mimics the –CH3 termination and aliphatic subunits of a polymer chain. Low-energy ion scattering measurements of magnetron sputtered thin films suggest that the bonding at the surfaces of pristine a-AlYB14 and O2 exposed a-AlYB14 (O2//a-AlYB14) is metal-boron and metal-oxygen dominated, respectively. Based on the ab initio calculations the adsorption energies of CH4 on a-AlYB14 and O2//a-AlYB14 decreases from −0.07 to −0.30eV, respectively. This trend is consistent with experimental data obtained by colloidal probe UHV-AFM studies with a polyethylene sphere, where larger adhesion forces for the O2 exposed surface as compared to the pristine a-AlYB14 surface were measured. No charge transfer takes place between CH4 and the pristine as well as the O2 exposed a-AlYB14. Oxygen chemisorption induces changes in surface bonding. States at the Fermi level are depleted upon oxidation, hence the surface bonding becomes more semiconducting causing a charge redistribution within the adsorbed CH4 molecule. Hence, these data serve as proof of concept for exploring the effect of O2 exposure on the interaction between aliphatic polymers and a-AlYB14 using a correlative experimental and theoretical research approach.