Virtual inelastic scattering in high-energy electron diffraction

By the use of convergent-beam and critical-voltage measurements it has become possible to measure the crystal potential to an accuracy of about 10^-3. The possibility that the contribution from virtual inelastic scattering is greater than the errors in these experiments is examined and it is shown that only virtual scattering from single-electron excitations need be considered. Estimates are given for the Fourier coefficients of the virtual inelastic scattering potential for silicon, copper and germanium and these are compared with the errors in the critical-voltage experiments of Hewat & Humphreys [High Voltage Electron Microscopy (1974), edited by P. R. Swann, C. J. Humphreys & M. J. Goringe, pp. 52-56. London and New York: Academic Press]. It is concluded that the virtual inelastic scattering contribution is less than the experimental errors.