MEM analysis of electron-density distributions for silicon and diamond using short-wavelength X-rays (W K alpha(1))

Short-wavelength X-rays (W K alpha(1): lambda = 0.209 Angstrom) have been used to collect higher-order reflections for studies of the electron-density distributions of silicon and diamond with high resolution. The sp(3) bonding electron-density distributions of these materials are visible in the total electron-density maps synthesized by the maximum-entropy method (MEM) and also in the difference MEM maps synthesized by Fourier summation of F-mem(h) - F-core(h), where F-mem(h) is the structure factor calculated from the MEM map and F-core(h) is the structure factor calculated from Si-core and C-core models, if very extensive data sets with higher-order reflections are used. These maps are more informative than the conventional difference Fourier map synthesized by Fourier summation of F-obs(h) - F-core(h) using the observed structure factor F-obs(h) instead of F-mem(h). The present maps can be compared with certain band-theory calculations.