Kikuchi Electron Research Articles

ELECTRON BEAM CHANNELING IN SINGLE-CRYSTAL SILICON BY SCANNING ELECTRON MICROSCOPY

An annular semiconductor diode detector was used in a Cambridge Stereoscan electron microscope to resolve beam-orientation-dependent backscattered electron images not only as bands but also as extremely complicated defect and excess line patterns with angular resolution ≤ 5 × 10−4 rad. The resultant patterns are similar in appearance to transmission and reflection Kikuchi electron diffraction patterns.

Investigation of relative interfacial free energies in 304 stainless steel by electron transmission and diffraction microscopy

Coherent twin-grain boundary intersections in thin films of annealed 304 stainless steel were examined by transmission and diffraction electron microscopy. Standard electron diffraction and Kikuchi line techniques were combined with electron transmission image data in a computer program to obtain twin—grain boundary energy ratios. It is shown that a three-dimensional analysis of twin-grain boundary intersections yields a greatly reduced spread of individual energy ratio values when compared with 2-dimensional or optical data. It is further shown that negative values of the twin—grain boundary energy ratio obtained by optical measurement of boundary surface traces are invalid, and simply reflect the errors inherent in a two-dimensional approximation of the intersection of boundary planes in threedimensions. The mean twin-grain boundary energy ratio computed for stainless steel for a rigorous Kikuchi electron diffraction analysis was 0.034. An attempt was also made to further minimize measurement error by insuring that the specimen surface plane was normal to the electron beam, and therefore coincident with the crystallographic surface plane determined by selected area electron diffraction. The technique applied here consisted of a check of specimen surface orientations by the analysis of angles between the surface traces of coherent {111} twin boundary planes and {111} dislocation slip planes. Twin—grain intersections admitted as acceptable examples for detailed three-dimensional analysis were then determined on the basis of angular deviations between surface traces not exceeding three degrees from the value expected when the specimen surface plane is normal to the electron beam. Of the 87 twin-grain intersections of this type analyzed in stainless steel, only 35 fulfilled the above criterion. Computer analysis of these 35 electron transmission images gave twin-grain boundary energy ratios ranging from 0.002 to 0.07 with a mean energy ratio of 0.022 compared to the earlier result of 0.034 obtained for identical stainless steel samples where errors of specimen surface orientation were neglected.

On the four‐axis hexagonal reciprocal lattice and its use in the indexing of transmission electron diffraction patterns

AbstractA four‐axis hexagonal reference basis can be constructed in the reciprocal space of hexagonal crystals in such a way that the resulting lattice contains as a subset all the points of the conventional reciprocal lattice. All other points not belonging to this subset have no physical significance since they have non‐integral indices and hence cannot represent real crystal planes. Since these points cannot register as spots in an actual diffraction pattern, the four‐axis hexagonal lattice and the conventional reciprocal lattice are physically indistinguishable. _ The interpretation of diffraction patterns of hexagonal crystals is easier when indexing is referred to the four‐axis basis. The necessary crystallographic relationships can be obtained directly in terms of Miller‐Bravais indices using elementary vector analysis and when applied to Kikuchi electron diffraction maps, the problem of determining the foil orientation becomes especially simple.

Structure and mechanical properties of Ta-Mo alloy single crystals

High purity single crystals of the Ta-Mo alloy series were grown near 10 at. % increments by electron beam zone refining. The methods of investigation of the prepared crystals included: specific resistivity at 273°K, 77°K and 4.2°K, critical resolved shear stress for plastic flow or cleavage at 273°K, lattice parameter determinations, transmission electron microscopy and diffraction and quantitative X-ray diffracted intensity measurements of {200} and {220} reflections. It was found that alloys of compositions between Mo-19 Ta and Mo-58 Ta cleaved on the {100} planes. Lattice parameter measurements and electron microscopy showed that the alloy series is b.c.c. with no long range order, coherent over dimensions greater than 300 Å, nor intermediate phases. Kikuchi electron diffraction proved that there exist deviations from random solid solution in the brittle crystals. This result was confirmed by X-ray intensity measurements of 200 and 220 lines. The ratio of constituent atoms on {100} and {110} differ from the ratio of atoms corresponding to the total composition of the crystal in such a way as to generate quasi-cubic domains for {100} and quasi-dodecahedral domains for {110} deviations. It is suggested that the increase in critical resolved shear stress for plastic flow with alloy composition results from a corresponding increase in the Peierls-Nabarro friction of dislocations produced by alloying, composition deviations and concomitant changes in the elastic coefficients in a local region of the crystal. Both Mo and Ta are anisotropic and have very different elastic constants. Alloying and the existence of composition deviations change the elastic coefficients, in the range of alloys which cleave, to values which marginally fulfill the strain energy restrictions. The presence of a critical density of dislocations in a local region can change the values of the elastic coefficients such that the crystal is locally energetically unstable. The crystal then cleaves on a {100} plane which relieves the maximum strain energy. By analogy, other solid solutions are expected to become brittle when the components have widely differing and anisotropic elastic constants. Marked changes in the slope of ( ρ273°K minus ρ4.2°K) versus alloy composition at Mo-20 Ta, Mo-50 Ta and Ta-12 Mo indicate that there is a relatively large change occurring in the density of states in the d and s bands and/or marked changes in the elastic coefficients at these compositions.

Further Applications of Kikuchi Diffraction Patterns; Kikuchi Maps

Composite Kikuchi electron diffraction patterns have been obtained which map out reciprocal space for silicon over the 〈001–011–111〉 stereographic triangle. These maps enable unknown diffraction patterns to be quickly solved even when they do not contain any Kikuchi poles. Unlike spot patterns, the Kikuchi patterns and maps uniquely represent the crystal symmetry. Some applications of these maps in crystallographic and electron microscopy investigations are discussed.