Adsorption of polar molecules on diamond-like carbon films with different trapped charge densities

Abstract

This work investigates the effect of trapped charge densities present in diamond-like carbon films (DLC) on adsorption of polar molecules on the film surface. Hydrogen-free and hydrogenated DLC films with different hydrogen/carbon contents were produced using filtered-cathodic arc sputtering (FCA-sputtering) and radio-frequency plasma enhanced chemical vapor deposition (RF-PECVD) techniques, respectively. After treating the as-prepared films in a dilute solution of dipropylene glycol monomethyl ether, adsorption of such molecules was found throughout the film surface. Capacitance–voltage (C–V) measurements have shown that the DLC films with lower hydrogen/carbon content inherently have larger trapped charge accumulations within their structures. A charge density of 1600nC/cm2 was measured in a DLC film with a lower hydrogen/carbon content (produced from C2H4 and Ar precursors), while a much smaller charge density of 64nC/cm2 was measured in a DLC film with a higher hydrogen/carbon content (produced from 10% CH4 and 90% H2 precursors). A correlation between charge densities and the degree of polar molecule adsorption was observed. Films with higher charge densities appeared to be more prone to polar molecule adsorption.