Electrostatic charging eects in fast H interactions with thin Ar ®lms

We have studied electron emission, luminescence and sputtering from thin Ar ®lms excited by 2 MeV protons. We varied the voltage, Va, of the anode surrounding the target, which extracts electrons from the ®lm and results in unbalanced positive charges. The resulting large internal electric ®elds alter sputtering and luminescence. At the beginning of irradiation of a freshly deposited ®lm, we observe that a positive anode voltage of a few hundred volts produces a large, catastrophic increase in sputtering which gradually disappears as irradiation progresses. We discuss the results in terms of dielectric breakdown induced by macroscopic charging associated with deep charged defect sites. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 79.20.Rf; 34.50.Dy; 77.22.Jp