Effects of bombarded ion mass on electrical resistivity and wettability of carbon films

A study has been made of electrical properties and wettability of ion-bombarded PVD carbon thin films. Carbon thin films were prepared on glass plates by vacuum deposition by electron-beam (EB) evaporation. Ion bombardment of He, Ne, Ar and Kr-ions was carried out with a fluence of 1 × 10 ¹⁶ ions/cm ² at 150 keV at room temperature. The beam current density was as low as 0.5 μA/cm ² to prevent the specimen from heating. Sheet resistivity of carbon thin films was measured by using a four point probe method. Wettability of the specimens was investigated by the contact angle of water. Laser Raman spectroscopy was employed for estimating the structure of bombarded layers. It was found that ion bombardment causes the sheet resistivity to be lower, as the bombarded ions are lighter. The contact angle of water is lower as the heavier ions are bombarded. Raman spectra show that the structure of He-bombarded carbon thin film is graphite-like and that of Kr-bombarded one is amorphous-like. The change in resistivity and wettability will be discussed with respect to carbon structures formed due to elastic and inelastic collisions.