Surface and Coatings Technology 173 –174 (2003) 872–876 0257-8972/03/$ - see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0257-8972Ž03.00562-0 Using an afterglow plasma to modify polystyrene surfaces in pulsed radio frequency (RF) argon discharges M. Dhayal , D. Forder , K.L. Parry , R.D. Short , J.W. Bradley * a a b b a, Physics Department, UMIST, PO Box 88, Manchester M60 1QD, UK a Laboratory for Surface and Interface Analysis, Department of Engineering Materials, University of Sheffield, Sheffield S1 3JD, UK b 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 Torr was achieved to decrease the level of impurities in the chamber. The electron temperature (T ) decreases y5 e from 5 eV to less than 0.5 eV in afterglow. The cooling rate of T depends on the pressure, power and duty cycle. By pulsing a e 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 (OyC) 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.  2003 Elsevier Science B.V. All rights reserved. Keywords: Pulsed radio frequency plasma; Polymer surface modification; Tailored plasmas 1. Introduction RF plasma processing is a valuable technique in many different industrial applications, for instance in enhanced chemical vapour deposition, etching and surface modi- fication w1–5x. Pulsing of the RF discharge gives better selectivity in the ion and electron energy on to the surfaces and high etch rates where plasma interacts directly with exposed surface by electrons, ions, free radicals, fast neutral and photons. O. Zabeida et al. w6x measured the time-resolved ion energy distribution function (IEDF) in dual-mode pulsed-microwave yradio frequency plasma and pointed out two approaches to control the ion energy. The first one is the use of pulsed plasma, and the second is dual- mode MWyRF plasma. It was reported that when the MW discharge is pulsed, the characteristics of the plasma are such that the plasma parameters (density, temperature, etc.) and the IEDF vary strongly with the time. *Corresponding author. Tel.: q44-161-200-8702; fax: q44-161- 200-3941. E-mail address: j.w.bradley@umist.ac.uk (J.W. Bradley). Wang and Wendt w7,8x have achieved the control of the IEDF at the substrate using a tailored voltage waveform for substrate bias. They have also described an unmagnetised plasma fluid model based on time- dependent hydrodynamic equations for the ions. A simplified kinetic approach for calculation of IEDF in RF plasma was described by Misakian et al. w9x, Wild and Koidl w10x studied the IEDF in a capacitive coupled plasma and explained the IEDF features by modelling the ion transport through the RF modulated collisional sheaths. One of the main areas of interest in RF plasma is determining the ion energy gained in the RF sheath. When the applied RF period is shorter than the ion transit time across the sheath, the positive ions reach the electrode with the energy equal to the instantaneous potential drop over the sheath region, which may vary from the maximum to the minimum sheath potential drop. This leads to a bi-modal IEDF w1x. However, when the ions transit the sheath over many RF periods, the ions arrive with the average sheath potential. In the current study we pulse a parallel plate capaci- tive coupled radio frequency (RF) discharge, in the