Effect of oxygen gas on polycarbonate surface in keV energy Ar+ ion irradiation

Ar+ ion irradiation on a polycarbonate (PC) surface was carried out in an oxygen environment in order to investigate the effects of surface chemical reaction, surface morphology, and surface energy on wettability of PC. Doses of Ar+ ion were changed from 5 X 10(14) to 5 X 10(16) at 1 keV ion beam energy by a broad ion beam source. Contact angle of PC was not reduced much by Ar+ ion irradiation without flowing oxygen gas, but decreased significantly as Ar+ ion was irradiated with flowing 4 sccm (ml/min) oxygen gas and showed a minimum of 12 degrees to water and 5 degrees to formamide. A newly formed polar group was observed on the modified PC surface by Ar+ ion irradiation with flowing oxygen gas, and it increased the PC surface energy. On the basis of x-ray photoelectron spectroscopy analysis, the formed polar group was identified as a hydrophilic C=O bond (carbonyl group). In atomic force microscopy (AFM) study, the root mean square of surface roughness was changed from 14 Angstrom to 22-27 Angstrom by Ar+ ion irradiation without flowing oxygen gas and 26-30 Angstrom by Ar+ ion irradiation with flowing 4 seem oxygen gas. It was found that wettability of the modified PC surface was not greatly dependent on the surface morphology, but on an amount of hydrophilic group formed on the surface in the ion beam process.