Downloaded By: [University of Virginia] At: 14:18 12 June 2007 Radiation Effects, 1979, Vol. 45, pp. 119-122 0033-7579/ 79/4501-0119$04.50/ 0 @ 1979 Gordon and Breach Science Publishers, Inc. Printed In United States of America ELECTRON EMISSION FROM INCONEL UNDER ION BOMBARDMENT E. V. ALONSO, R. A. BARAGIOLA, J. FERRON and A. OLIVA-FLORIO Centro Atomic0 Barilochet and Instituto Balseiroz 8400 S.C. de Bariloche, R.N. Argentina (Received March 8, 1979; injinal form July 2, 1979) Electron yields from clean and oxydized Inconel 625 surfaces have been measured for H', H:, Hef, 0' and Ar+ ions at normal incidence in the energy range 1.5-40 keV. These measurements have been made under ultrahigh vacuum and the samples were freed of surface contaminants by bombarding with high doses of either 20 keV Hl or 30 keV Ar+ ions. Differences in yields of oxydized versus clean surfaces are explained in terms of differences in the probability that electrons internally excited escape upon reaching the surface. 1 INTRODUCTION The bombardment of solid surfaces by ion beams produces, inter uliu, electron emission.' The study of this phenomenon, called ion-electron emission (IEE) is important for the understanding of in- elastic ion-surface collisions and gas discharges, for the accurate measurement of small ion currents and for its role in fusion reactors2-' and direct energy converters.'j IEE from surfaces can be explained to result from two distinct processes, potential and kinetic emission. Potential emission occurs through the relaxation of the potential energy of the ion- surface system if the ionization potential of the neutral atom of the ion species exceeds twice the work function of the surface. In kinetic emission, the energy required to liberate target electrons is provided by the kinetic energy of the projectile. Kinetic emission predominates over potential emission (when the latter occurs) for ion velocities larger than 0.4-2 x lo7 cm/s in the case of clean metals' and for ion energies larger than 20-60 eV in the case of gas-covered surface^.^-^ In this work we have measured IEE yields y (defined as the average number of electrons ejected per incident ion) for 1.5-40 keV ions bombarding Inconel targets at normal incidence. The choice of this alloy for our present study was based on the importance which Inconel has being the first-wall t Cornision Nacional de Energia Atornica 1 Universidad Nacional de Cuyo material of the JET (Joint European Torus). Our measurements were performed in UHV for two different surface conditions obtained after bom- bardment with lO1'H; ions/cm2 at 20 keV or with 5 x 1017Arf ions/cm2 at 30 keV. 2 EXPERIMENTAL 2.1 Apparatus The experimental set-up was described in detail previously" so only a summary will be given here. The ion beams were produced with a conventional ion accelerator equipped with a radio-frequency ion source. After mass-analysis the beam passes through two stages of differential pumping and into the ultrahigh vacuum chamber. The operating pressure in this chamber with the ion beam on was always kept in the lO-"-Torr range. Total errors in the measurements of the yields were +_ 5 %. This number includes statistical un- certainties and systematic errors due to the presence of fast charge-transfer neutrals in the beam, and the emission of secondary ions (sput- tered and backscattered) from the target. The accuracy of the measurements of ion energy was +(0.1% + 30 eV). An evaluation of the surface cleaning methods discussed below were made in a different UHV system using Auger electron spectroscopy (AES) combined with H: and Ar' ion bombardment with a 10 kV ion gun. 119