Bombardment-induced photon emission from Al and Al 2O 3 targets

Abstract

Ion impact on Al has been described by several authors as leading to the ejection of excited neutral Al atoms which in turn decay with the emission of photons. We have undertaken a study of these photons as arising from 10 keV Ne bombardment of Al and Al 2O 3. One group of experiments involved measuring photon intensities under conditions of equilibrium. By increasing either the current or the oxygen pressure, the intensities approached a well-defined limit such as would be expected if the intensities were proportional to the steady-state oxygen coverage. Remarkable here is that a good description of the experimental results was obtained using a model in which photons are assumed to arise only in the presence of oxygen. A second group of experiments involved the measurement of photon transients. Beam interruption led, when bombardment was resumed, to a transient with a half-time of ~ 3 sec and which was attributed to the amount of oxygen adsorbed on the surface having increased. Changing the current or pressure caused a transient which was about 8 times longer and which was attributed to the amount of recoil-implanted oxygen having changed. There is a close parallel, in the case of bombarded Al, between photon and ion yields; thus, the yields of Al + and Al ++ but not Al +++ are known to depend on the presence of oxygen. The role played by adsorbed or recoil-implanted oxygen is shown to be consistent with the band structures of Al and Al 2O 3 provided the electron affinity of Al 2O 3 is ⩽ 0.8 eV.