sample positions are connected to another by a 180° rotation about the primary beam
(more exactly: the zone axis). Therefore, this kind of ambiguity is called “180°-ambiguity”.
Furthermore a new kind of ambiguous solutions is reported, the so-called ““coincidence
ambiguity”. It occurs only in highly symmetrical lattices like especially the cubic one. The
two orientations producing the same spot pattern are nof connected by any symmetry
relations. The reason is based in „coinciding” reflections like e. g. (355) and (173) which are
different but produce the same indices square sum h’+k* +1? which is 59 for both cases.
Possible ways are reported to solve both kinds of ambiguity. Furthermore a survey is given
concerning the presentday possibilities to improve the accuracy in determination of the
sample orientation from the spot or Kikuchi pattern analyses.
Strenggenommen um die Zonenachse [uvw] 1969. LRL-Report UCRL-19016, University of
senkrecht zu den reziproken Gitterpunkten, die California, Berkeley, USA
das Beugungsbild erzeugen?2, Für das vorliegen- 8 O. Johari, G. Thomas, The Stereographic Pro-
de Problem der Zweideutigkeit ist aber der Un- jection and its Applications, Vol. IIa in Tech-
terschied zwischen [uvw] und P ohne Belang. niques of Metals Research, Hrsg. R. F. Bunshah,
LP. L. Ryder, W. Pitsch in: Methodensammlung Intersc. Publ. (1969)
der Flektronenmikroskopie, Hrsg. G. Schimmel, 9 M. v. Heimendahl, phys. stat. sol. (a) 5 (1971)
W. Vogell, Wissenschaftl. Verlagsgesellschaft 137
mbH., Stuttgart (1970) 10 P. Z. Ryder, W. Pitsch, Phil. Mag. 18 (1968)
2 M. v. Heimendahl, Einführung in die Elektro- 807
nenmikroskopie, Vieweg-Verlag Braunschweig 11 M. v. Heimendahl, G. Wassermann, Z. Metall-
(1970) (Hrsg. E. Macherauch, V. Gerold, Bd. 1 kd. 53 (1962) 275
in Reihe Werkstoffkunde) 12 M. v. Heimendahl, Journ. Appl. Phys. 35
} P. B. Hirsch. A. Howie, R. B. Nicholson, D. W. (1964) 457
Pashley, M. J. Whelan, Electron Microscopy of 13 M.D. Drazin, H. M. Otte, phys. stat. sol. 3
Thin Crystals, Butterworths, London (1965) (1963) 824
4 G. Thomas, Transmission Electron Microscopy 144. G. Crocker, M. Bevis, phys. stat. Sol. 6
of Metals, Wiley Inc., New York, London (1964) 151
(1962) 15: PL. Ryder, W. Pitsch, Phil. Mag. 15
5 C. Laird, E. Eichen, W. R. Bitler, Journ. Appl. (1967) 437
Phys. 37 (1966) 2225 16 E. Eichen, C. Laird, W.R. Bitler, Reciprocal
6 M. v. Heimendahl, W. Bell, G. Thomas, Journ. Lattice Diffraction Patterns for f.c.c., b.c.c.,
Appl. Phys. 35 (1964) 3614 h.c.p., and Diamond Cubic Crystal Systems.
7 G. Thomas, Kikuchi Electron Diffraction and Sonderdruck des Scientific Laboratory, Ford
Applications, Nato Summer School, University Motor Comp., Dearborn, Mich. (USA) (1966)
of Antwerp, Belgium, July 28 — August 8,
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