High-energy x-ray diffraction study of pure amorphous silicon

Medium and high-energy x-ray diffraction has been used to study the atomic structure of pure amorphous Si prepared by MeV Si implantation into crystal line silicon. Both as-implanted and annealed samples were studied. The inel astically scattered x rays were removed by fitting the energy spectrum for the scattered x rays. The atomic scattering factor of silicon, previously k nown reliably up to 20 Angstrom(-1), has been extended to 55 Angstrom(-1). The radial distribution function of amorphous Si, before and after annealin g, has been determined through an unbiased Fourier transformation of the no rmalized scattering data. Gaussian fits to the first neighbor peak in these functions shows that scattering data out to at least 40 Angstrom(-1) is re quired to reliably determine the radial distribution function. The first-sh ell coordination number increases from 3.79 to 3.88 upon thermal annealing at 600 degrees C, whereas that of crystalline Si determined from similar me asurements on a Si powder analyzed using the same technique is 4.0. Amorpho us Si is therefore under coordinated relative to crystalline Si. Noise in t he distribution function, caused by statistical. variations in the scatteri ng data at high-momentum transfer, has been reduced without affecting the e xperimental resolution through filtering of the interference function after subtracting the contribution of the first-neighbor peak. The difference in duced by thermal annealing in the remainder of the radial distribution func tions, thus revealed, is much smaller than previously believed. [S0163-1829 (99)00943-1].