Scattering of 0.06–2.5-eV Neon and Argon Atoms from a Silver (111) Crystal

Abstract

Reflected density distributions of argon and neon scattered from the (111) plane of a silver crystal have been examined at incident energies from 0.06 to 2.5 eV. Two regimes of scattering were detected in which the characteristic properties of the reflected distribution, direction and width, reverse their behavior as a function of incident energy. This confirms the recent theoretical work of Oman, wherein he characterizes the two regimes as thermal scattering and structure scattering. The data suggest that, for scattering at incident energy $E_i$ and angle ${\theta }_i$ , the transition from one type of interaction to the other is characterized by one critical value of $E_i\cos {\theta }_i$ . For argon, this critical value is near 0.21 eV and for neon 0.108 eV. At these critical energies the velocities of argon and neon are nearly identical. At a given incident angle, a maximum degree of supraspecular scattering exists, which is less for neon than for argon.