ENERGY-FILTERING THE THERMAL DIFFUSE BACKGROUND IN ELECTRON-DIFFRACTION

The diffuse background in high-energy electron diffraction is generally attributed to phonon scattering, and referred to as the thermal-diffuse background. We use electron energy loss spectroscopy to show that diffuse scattering may be dominated by energy losses in the 100-1000 eV range caused by electron-electron (Compton) scattering. Although e-e scattering is thoroughly studied, the fact that this process contributes much of the diffuse intensity even in materials with low Debye temperatures is not generally appreciated. The electron-electron and phonon contributions in the high-angle diffuse background in typical CBED patterns are in a 1.5:1, 0.9:1, 0.7:1, 0.15:1 and 0.05:1 ratio for diamond, Al, Si, GaAs and Au, respectively: diffuse scattering does become dominated by phonons for very high Z. The large e-e contribution explains how energy filtering improves the signal-to-background in electron diffraction, and has important implications for the temperature dependence of diffraction patterns and for ''Z-contrast'' microscopy.