III. Energy spectra for copper

Abstract

Abstract In Cu results generally similar to those for Au are found, but with a reduction of all focusing energies. Ejection in a direction away from a focusing or channelling axis, gave a spectrum that fitted extremely well to the random cascade model. Near the ⟨110⟩ direction the spectra can again be understood in terms of random cascades plus focused collision sequences, though the energy loss characteristics of the sequences evidently differ from the case of ⟨110⟩ focusing in Au. The ⟨110⟩ focusing energy is found to be 50±10 ev, in fair agreement with predictions of Gibson, Goland, Milgram and Vineyard (1960). The apparent focusing energy increases as one moves away from the focusing axis, reaching 90 ev at 10° from ⟨110⟩. This shows how defocused sequences propagate above the focusing energy. In changing from A+ to Xe+ ions at 43 kev the apparent focusing energy remains unaltered though the ratio of contributions from random and focused ejection is decreased. This confirms that the features of the spectrum attributed to focusing are not a function of the bombarding ion. In the ⟨100⟩ direction the spectrum again shows the effect of random cascades plus focused collision sequences with a propagation limit of 320±50 ev.