Using an afterglow plasma to modify polystyrene surfaces in pulsed radio frequency (RF) argon discharges

Abstract

A systematic study has been made to characterise a pulsed RF discharge used for the plasma treatment of polymers. Using a time-resolved Langmuir probe and a time-resolved retarding field energy analyser (RFA) the electron temperature and density, plasma potential, ion energy distribution function (IEDF) and electron energy distribution function (EEDF) has been measured. The source was pulsed for a range of frequencies from 100 Hz to 1 KHz at various duty cycles from 20 to 80%. A base pressure less than 10 −5 Torr was achieved to decrease the level of impurities in the chamber. The electron temperature ( T e ) decreases from 5 eV to less than 0.5 eV in afterglow. The cooling rate of T e depends on the pressure, power and duty cycle. By pulsing a biased grid synchronously with the pulsed RF, ions are selected from different time of the plasma and allowed to impinge on a polymer surface. Modified oxygen to carbon (O/C) ratio in the upper layer of polystyrene has been measured by X-ray photon emission spectroscopy (XPS) for different energy and flux of plasma ions. These results show that the treatment is either insensitive to ion energy or dominated by the UV in the discharge.