SOURCE-WAVE ANGULAR-MOMENTUM EFFECTS ON ELECTRON-DIFFRACTION PATTERNS

We use a simple model to predict when electron-emission diffraction patterns from surfaces will have peaks or dips along internuclear axes. A high angular-momentum electron wave emitted from an atom acts like an s wave (l = 0) in an extra centrifugal potential. This extra potential changes the electron's effective wave number and phase shift, altering the conditions for constructive interference when this wave scatters from nearby atoms. We demonstrate that the difference in source-wave angular momentum between Cu M2,3M4,5M4,5 Auger and Cu 3p photoelectrons explains the difference between their emission angular distributions from surfaces: the Auger-electron emission has a predominantly f-like source wave (l = 3) and destructive interference in the forward electron-scattering direction ("silhouette") while the photoelectron has lower angular momentum and constructive interference ("peak"). As long as this effect is considered, Auger-electron emission patterns can be used to determine surface structures. The unusual Auger-electron emission patterns observed by Frank et al. [Science 247, 182 (1990)] can be explained as due to high source-wave angular momentum and low electron energy.