Differences between effects of ions in plasma on the edge surface of carbon material and those on the basal surface

Abstract

We studied the effects of argon (Ar) plasma treatment of different surfaces of pyrolytic graphite (PG), which is an anisotropic material, on the PG surface structure, at various sheath voltages but keeping the other plasma parameters constant. We call a surface parallel to the substrate surface a basal surface, and one orthogonal to the substrate surface an edge surface. The experiment revealed that the Ar plasma treatment induces various effects depending on the carbon structure. The contact angle with water on the PG surfaces was decreased by the Ar plasma treatment. Also, X-ray photoelectron spectroscopy (XPS) analysis of the PG surfaces after the Ar plasma treatment revealed that oxygen-containing functional groups had been introduced onto the PG surfaces. The modification effect was greater for the edge surfaces than for the basal surfaces of the PG. Based on these results, we developed a model of ion effects on the basal and edge surfaces of the carbon surface structure.