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Convergent beam electron diffraction

Published online by Cambridge University Press:  05 July 2018

P. E. Champness
P. E. Champness*
Affiliation:
Department of Geology, University of Manchester, Manchester M13 9PL
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Abstract

In convergent-beam electron diffraction (CBED) a highly convergent electron beam is focussed on to a small (⩽50 nm) area of the sample. Instead of the diffraction spots that are obtained in the back focal plane of the objective lens with parallel illumination in conventional selected-area electron diffraction, CBED produces discs of intensity. The point group can be determined uniquely from the symmetry within the individual discs and the overall pattern. In order to determine the point group, it is usually necessary to record a number of CBED patterns with the electron beam aligned along different zone axes, but sometimes only one, high-symmetry pattern is required. The positions of reflections in higher-order Laue zones can be used to identify the crystal system and lattice type and to detect the presence of certain glide planes. The repeat along the zone axis that is parallel to the beam can be calculated from the diameters of the Laue zones. Hence the presence ofpolymorphs can be detected. Doubly-diffracted discs in CBED often contain a ‘line of dynamic absence’, the orientation of this line with respect to the symmetry seen in the bright field disc allows the symmetry element responsible for it (glide plane or screw diad) to be identified. This allows 191 of the 230 space groups to be uniquely identified. The measurement of specimen thickness, extinction distance and cell parameters are also briefly discussed.

Keywords

convergent beam electron diffractionelectron microscopyelectron diffraction.
Type
Electron Microscopy in Mineralogy and Petrology
Information
Mineralogical Magazine , Volume 51 , Issue 359 , March 1987 , pp. 33 - 48
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1987

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References

Akizuki, M., Hampar, M.S. and Zussman, J. (1979) Mineral. Mag., 43, 237.CrossRefGoogle Scholar
Allen, F.M., Buseck, P.R. and Rossman, G.R. (1986) Geol. Soc. Am. Abst. with Program 18, 525.Google Scholar
Allen, S.M. (1981) Phil. Mag. A43, 325 CrossRefGoogle Scholar
Allen, S.M. and Hall, E.L. (1982) Ibid. 46, 243.Google Scholar
Bannister, F.A., Hey, M.A. and Stadler, H.P. (1947) Mineral Mag., 28, 129.Google Scholar
Buxton, B.F., Eades, J.A., Steeds, J.W. and Rackham, G.M. (1976) Phil. Trans. Roy. Soc. 281A, 171 Google Scholar
Castro-Fernandes, F.R., Sellars, C.M. and Whiteman, J.A. (1985) Phil. Mag. A52, 289 CrossRefGoogle Scholar
Cliff, G. and Kenway, P.B. (1982) Proc. Microbeam Anal. Soc. 107.Google Scholar
De Cooman, B.C. and Carter, C.B. (1985) Phil. Mag. A51, 175 CrossRefGoogle Scholar
Eades, J.A., Shannon, M.D. and Buxton, B.F. (1983) Scanning Electron Microscopy 1983 31. (O. Johari, ed.). SEM Inc. AMF O'Hare, Illinois, 1051.Google Scholar
Ecob, R. G. Shaw, M.P., Porter, A.J. and Ralph, B. (1981) Phil. Mag. A44, 1117 CrossRefGoogle Scholar
Gjonnes, J. and Moodie, A.F. (1965) Acta Crystallogr., 19, 65 CrossRefGoogle Scholar
Goodman, P. (1975) Ibid. A3t, 804.Google Scholar
Goodman, P. and Johnson, A.W. S. (1977) Ibid. A33. 997.Google Scholar
Grey, I.E. and Gatehouse, B.M. (1979) Am. Mineral., 64, 1255.Google Scholar
Grimes, N.W. (1972) Phil. Mag., 26, 1217.CrossRefGoogle Scholar
Heuer, A.H. and Mitchell, T.E. (1975) J. Phys. Chem., 8, L541.Google Scholar
Hwang, L., Heuer, A.H. and Mitchell, T.E. (1973) Phil. Mag., 28, 241.CrossRefGoogle Scholar
Kelly, P.M., Jostens, A., Blake, R.G. and Napier, J.G. (1975) Phys. Star. Sol. A31, 771 CrossRefGoogle Scholar
Kossel, W. and M611enstedt, G. (1939) Ann. Phys., 36, 113.Google Scholar
Loretto, M.H. (1984) Electron Beam Analysis of Materials. Chapman and Hall, London.CrossRefGoogle Scholar
Neder, R.B. W. (1985) M.S. Thesis, Arizona State University.Google Scholar
Ozima, M. and Akimoto, S.-I. (1983) Am. Mineral., 68, 1119.Google Scholar
Porter, A.J., Shaw, M.P., Ecob, R.C. and Ralph, B. (1981) Phil. Mag. A44, 1135 CrossRefGoogle Scholar
Shaw, M.P., Ecob, R.C., Porter, A.J. and Ralph, B. (1981) In Quantitative Microanalysis with High Spatial Resolution, The Metals Society, London, 229.Google Scholar
Smith, P.P. K. (1978) Phil. Mag. B38, 99 CrossRefGoogle Scholar
Smith, P.P. K. (1980) Geol. Mag., 117, 385.CrossRefGoogle Scholar
Steeds, J.W. (1979) In Introduction to Analytical Electron Microscopy (J. J. Hren, J.I. G.ldstein and D. C. Joy, eds.) Plenum Press, New York, 387.CrossRefGoogle Scholar
Steeds, J.W. -(1981) In Quantitative Microanalysis with High Spatial Resolution, The Metals Society, London, 210.Google Scholar
Steeds, J.W. -(1984) In Quantitative Electron Microscopy (J. N. Chapman and A. J. Craven, eds.) Scottish Univ. Summer School in Physics.Google Scholar
Steeds, J.W. and Evans, N.S. (1980) Proc. Electron Microscopy Society of America. 38th Ann. Meeting. Claitor's Publishing, 188.Google Scholar
Steeds, J.W. and Vincent, R. (1983) J. Appl. Crystalloor., 16, 317.Google Scholar
Steeds, J.W. -Rackham, G.M. and Shannon, M.D. (1978) Inst. Phys. Conf. Ser., 41, 135.Google Scholar
Steeds, J.W. and the Bristol Group (1984) Convergent Beam Electron Diffraction of Alloy Phases (Mansfield, J. ed.). Hilger, Bristol.Google Scholar
Tanaka, M., Seikii, H, and Nagasawa, J. (1983) Acta Crystallogr. A39, 825.Google Scholar
Vincent, R. and Pretty, S.F. (1986) Phil. Mag, A53, 843.Google Scholar
Williams, D. B. (1984) Practical Analytical Electron Microscopy in Materials Science. Philips Electronic Instruments. Inc., New Jersey, 153 pp.Google Scholar