We have studied the dependence of electron yields $\gamma$ from clean Cu and Au surfaces on the incidence angle $\theta$ of 5-50-keV ${\mathrm{He}}^{+}$, ${\mathrm{Ar}}^{+}$, and ${\mathrm{Xe}}^{+}$ projectiles, in the angular range 0°-80°, and under ultrahigh-vacuum conditions. We have found that, at small angles, $\gamma \propto {sec}^f\theta$, with $f$ generally different from unity. For ${\mathrm{Xe}}^{+}$ on Cu, $\gamma \left(\theta \right)$ presents an energy-dependent maximum, similar to that obtained for sputtering. The results are explained in terms of the anisotropy of the electron cascade in the solid, and the depth distribution of the inelastic energy deposited by the projectile, and by rapidly recoiling target atoms in the near-surface region of the solid.

• Received 9 February 1981

DOI:https://doi.org/10.1103/PhysRevB.24.4412