Energy spectra of particles bombarding the cathode in glow discharges

The energy distributions of ions hitting the cathode in DC glow discharges have been measured for an argon plasma, using a pressure range of 0.14-1.0 mbar and a voltage range of 240-350 V, with plasma currents of 4 x 10(-3)-0.26 mA/cm(2). The measurements were performed with a commercial energy analyser and mass spectrometer mounted in a differentially pumped system, allowing logarithmic measurement sensitivity of the ion distributions. A simple ion-neutral collisional model was used to interpret the measured Ar+ energy distributions and extract the ratio LII between the sheath thickness L and the mean free path lambda for ion-neutral collisions. The extracted values, in conjunction with the measured plasma current, voltage and pressure, are seen to be in agreement with the Child law equilibrium condition for a collisional sheath. Furthermore, the symmetrical charge transfer cross-section for argon ions, sigma, was extracted from the data and found to be in good agreement with reported values. (C) 2000 Elsevier Science Ltd. All rights reserved.