Scattering from amorphous material

Neutron Scattering from Amorphous Materials 3.2.1 Overview... 

Scattered waves from neighbouring atoms interfere in exactly the same way and unless the atoms are ordered as in a crystal, the total diffraction pattern is a function of the radial distribution of scattering density (atoms) only. This is the mechanism whereby diffraction patterns arise during gas-phase electron diffraction, scattering by amorphous materials, and diffraction... 

Diffraction patterns from amorphous materials consist of a few vague halos. Accurate measurement of the intensity distributions of these halos in reciprocal space provides information about the distribution of atoms in real space. Reviews of the experimental methods and data handling techniques for X-ray-, electron-, and neutron-scattering is given in the literature The mathematical tool which is used to relate the... 

The Phenomenon. In existing materials the electron density is not even constant inside a single phase. This is obvious for the liquid structure of amorphous regions. Nevertheless, even in crystalline phases lattice distortions and grain boundaries result in variations of the electron density about its mean value. In analogy to the sunlight scattered from the fluctuations of air density, X-rays are scattered from the fluctuations of electron density. 

The experimental techniques most commonly used to measure the phonon distributions are IR absorption, Raman scattering and neutron scattering. The IR and Raman spectra of crystalline silicon reflect the selection rules for optical transitions and are very different from the phonon density of states. The momentum selection rules are relaxed in the amorphous material so that all the phonons contribute to the spectrum. 

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