Surface Modification of Glassy Carbon by Inert Gas Radio-Frequency Discharge Plasmas

Abstract

This investigation on the surface modification of glassy carbon (GC) by radio-frequency (13.56MHz) glow discharge plasmas of inert gases (Ne, Ar and Xe) was conducted with the objective of investigating the effects of plasmas on GC surfaces and the mechanism of the variation with elapsed time of the GC surfaces after the plasma treatment. The contact angles of water to the GC surfaces after the plasma treatment were measured and their change with elapsed time were investigated. Furthermore, the GC surfaces treated by plasmas were analyzed by ESCA and observed by SEM. Also, Raman spectra on the GC surfaces after the plasma treatment were measured. From these results, the following conclusions can be drawn.
The contact angles to the GC surfaces vary with the treatment of Ne (to 34°), Ar (to 15°) and Xe (to 9°) plasma from the contact angle to the untreated GC surface (90°). However, the contact angles are increased from 34° to 70° in the case of Ne plasma treatment, and are increased in the case of Ar (from 15° to 52°) and Xe (from 9° to 35°) plasma treatment in air at room temperature for 24 hours. The values of 0/C on the GC surfaces treated by Ne, Ar and Xe plasma increase. The half-widths of the Raman band at 1360cm^-1 on the treated GC surfaces also increase. In the case that the discharge conditions are the same, effects of the modification become greater with increasing mass of the used gas.
These findings suggest that effects of the inert gas plasma are mainly the formation of the active radical by the ion bombardment and the secession of the surface atoms by the sputtering, and the changes with elapsed time in the contact angles to the GC surfaces after the inert gas plasma treatment would be induced mainly by the decrease in the number of active radicals.