Limiting crystallite size or lattice strain?Richards, T.L
doi: 10.1107/S0021889870005733pmid: N/A
A scientific controversy as to whether X-ray diffraction line broadening, associated with cold-worked metals, was due to break-up of the metal crystals into minute crystallites or due to lattice strain is recalled, with reference to an abortive attempt by Sir Lawrence Bragg to reconcile the opposing views. Subsequent studies have shown how balanced Sir Lawrence's judgment of the problem was.
X-ray diffraction phenomena in elastically distorted crystalsAndo, Y; Kato, N
doi: 10.1107/S002188987000568Xpmid: N/A
Diffraction phenomena in diametrically compressed single-crystal plates of silicon were systematically studied by topographic methods of the traverse and section types with Cu, Mo and Ag radiations. Black and white contrasts in the traverse topographs depend on the magnitude of the strain gradient, absorption, the sign and the order of the reflection vector, and the crystallographic orientations of the specimens. The results were interpreted in terms of the diffraction theory for a constant strain gradient. The distribution of the strain gradient was calculated under the assumptions of plane stress and isotropic elastic constants. Qualitative agreement was obtained between the theory and experiments. The behaviour of the contrast, including the departure from Friedel's law, is due to Borrmann absorption in distorted crystals. The quantitative discrepancy is explained by anisotropy of the elastic constants. The departure from a constant strain gradient is detectable by the asymmetry of the intensity distribution in section topographs.
An X-ray multiple diffraction study of crystals of arsenic-doped germaniumIsherwood, B.J; Wallace, C.A
doi: 10.1107/S0021889870005666pmid: N/A
An X-ray multiple diffraction technique has been used to investigate the effect on the lattice of single-crystal germanium of the introduction of arsenic at a concentration of approximately 1020 atoms cm-3. Two samples, of similar resistivity, have been examined: one in which arsenic was introduced via the melt during Czochralski growth, and one into which arsenic was diffused after growth. X-ray fluorescence spectroscopy revealed that the latter had an arsenic concentration two or three times that of the `alloy'. The lattice parameter at 25 DegreesC of the Ge-As alloy was found to be 5.65795 A, that of the As-diffused Ge, 5.65820 A, compared with 5.65750 A as determined for pure Ge, the experimental errors being plus or minus0.00003 A. The As-diffused sample was also found to exhibit a considerably higher degree of inhomogeneous strain than the alloy. A brief discussion is given of the possible correlations between arsenic concentration and the observed expansion and strain content of the germanium lattice.
High-voltage transmission scanning electron microscopyCowley, J.M
doi: 10.1107/S0021889870005642pmid: N/A
The use of scanning electron microscopy for the study of thin specimens by transmission has advantages over conventional transmission electron microscopy in terms of simplicity and cheapness, reduction in damage to irradiation-sensitive specimens and convenience for electron diffraction, energy analysis and the electronic measurement and recording of images. These advantages are specially important for microscopes operating in the range 200 kV to 1 MeV. The design of a 600 kV instrument to exploit these advantages is described. The possible modes of operation employing deflexion systems and an energy analyser are discussed with reference to light- and dark-field microscopy, convergent beam diffraction and conventional focused diffraction patterns. The reciprocity principle is invoked to relate both image contrast and instrument design in scanning electron microscopy to that in conventional transmission electron microscopy. Examples are given of light- and dark-field images and diffraction patterns obtained with the instrument.