Platinum nanoparticle interaction with chemically modified highly oriented pyrolytic graphite surfaces

Ar, N-2, O-2, and H2O radio frequency (13.56 MHz) plasma treatments have been carried out on insulator-Supported samples of highly oriented pyrolytic graphite (HOPG). The HOPG surface was found to be minimally damaged by all the plasma treatments, which break C-C bonds and form free radicals in the outermost few layers. These free radicals subsequently react, on exposure to air, forming various oxidation products; both XPS and photoacoustic FTIR indicate that these include C-OH, C=O, and -COOH. Pt was deposited onto these samples by evaporation, forming nanoparticles. After plasma treatment, the dimensions of the Pt nanoparticles were similar to 3.5-4 nm, compared to similar to 6 nm on untreated HOPG, and they no longer diffused laterally; this indicates enhanced interfacial adhesion for all these plasma treatments. The occurrence of oxidation products strongly suggests that the increased Pt nanoparticle adhesion to the treated HOPG surface is due to their presence.