The secondary electron ejection coefficient has been measured for the three low-index planes of copper single crystals using a sputtering technique to maintain monatomically clean surfaces. The ion used was ${\mathrm{Ar}}^{+}$ in the energy range 0.5 to 10.0 keV. The planes investigated were the (100), (110), and the (111) planes. A simple geometrical model based on the opacity of the lattice in different crystallographic directions is found to agree reasonably well with the experimental results at higher energies.

• Received 3 October 1962

DOI:https://doi.org/10.1103/PhysRev.129.2409