Radial distribution functions from diffracted electron intensities

Abstract

Many previous studies have shown the benefits of electronically recorded intensity profiles of electron diffraction patterns obtained with a transmission electron microscope (TEM). The technique, which is based on the scanning diffraction method developed by Grigson et al., avoids the complex procedures involved in making densitometer traces from film, greatly expands the dynamic range, and allows energy filtering to remove inelastically scattered electrons that have lost more than a few eV. Early applications to amorphous materials employed TEMs fitted with scanning systems and electrostatic filters below the projector lens. The main emphasis of the work of Graczyk et al. was on structural models for amorphous semiconductors such as silicon and germanium. However, a treatment for binary materials was developed and measurements were made for SiO2 and Ge-Te alloys. Cockayne et al. have recently extended these early techniques to modern 100 and 300 kV analytical electron microscopes, which when equipped with energy loss spectrometers and energy-dispersive x-ray analysis systems, do not require further major modification. Applications for which radial distribution functions have been determined from online measurements of energy-filtered selected area electron diffraction pattern intensity profiles have included amorphous thin films of carbon (a-C), germanium (a-Ge), boron nitride (a-BN), hydrogenated silicon (a-Si:H), silicon-carbon (a-Si1-xCx:H), and phosphorus- and boron-doped hydrogenated silicon.