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 b een used to collect higher-order reflections for studies of the electr on-density distributions of silicon and diamond with high resolution. The sp(3) bonding electron-density distributions of these materials ar e visible in the total electron-density maps synthesized by the maximu m-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 s tructure factor calculated from the MEM map and F-core(h) is the struc ture factor calculated from Si-core and C-core models, if very extensi ve data sets with higher-order reflections are used. These maps are mo re informative than the conventional difference Fourier map synthesize d by Fourier summation of F-obs(h) - F-core(h) using the observed stru cture factor F-obs(h) instead of F-mem(h). The present maps can be com pared with certain band-theory calculations.