Characteristic energy losses of low-energy electrons reflected from aluminium and copper

Abstract

The characteristic energy loss spectra of electrons reflected from freshly evaporated Al and Cu specimens have been measured for various primary electron energies in the range 9-265 ev. Contrary to expectation the ratio of the intensity of the 10 ev surface plasma loss to that of the 15 ev volume loss in Al, for electrons scattered through 90°, is found to decrease with decreasing primary energy in the range from about 240 ev to 80 ev. This appears to be due to the behaviour of the surface loss, which decreases rapidly in intensity with decreasing primary energy. Both the surface and volume plasma losses of Al cease to be excited when the primary energy is less than about 26-29 ev, the surface loss cutting off at a slightly lower primary energy than the volume loss. The modified surface loss of Al resulting from oxidation of the specimen surface is observed at 7.1 ev, and the half-width of the 10 ev surface loss increases from 3.8 ev to 5.3 ev with increasing surface oxidation, indicating that the surface plasma oscillations are damped by the contamination. The energy losses of Cu have been investigated by observing their intensity dependence on (i) the primary electron energy for a fixed scattering angle of 90° and (ii) the electron scattering angle for various fixed primary energies, scattering angles of 90° and 20° being employed. The results indicate that a loss observed at 3.5 ev is possibly due to excitation of surface plasma oscillations.