The critical-voltage effect in convergent-beam high-voltage electron diffraction

On the accurate measurement of structure-factor amplitudes and phases by electron diffraction

“…These depend sensitively on temperature, since the IKL gap and the critical voltage both depend on the real part of the structure factor in centric crystals. Thus, temperature may be used as an adjustable parameter to fine-tune patterns near the critical voltage (Sellar, Imeson & Humphreys, 1980). In recent work, both critical voltages and K_ikuchi-line splittings for Si, Ge, Al, Cu and Fe have all been measured as a function of temperature (Matsumura, Tomokiyo & Oki, 1989).…”

“…This is the basis of the intersecting Kikuchi-line (IKL) method described in § 3.4, which might therefore be said to provide 'critical voltage at any voltage ' (Taft0 & Gj0nnes, 1985). It is also the basis of the 'CBED critical voltage' method of Sellar et al (1980). In this work, the temperature of the sample (and hence the Debye-Waller factor) was used for fine-tuning the critical-voltage condition.…”

Lithium depletion in precipitate free zones (PFZ's) in AlLi base alloys

“…a ~critical temperature" technique, originally adopted by Sellar et ale [22]. This approach leads to improved accuracy.…”

A comment on the calculation of rocking curves near the critical voltage in electron diffraction

“…At the degeneracies @" becomes infinite (describing the collapse" of X2 and X3) and the second term in (5) becomes a limit 0 x oo. Expression We therefore believe that the anomalous peaks predicted by Sellar et al (1980) are mathematical artefacts. The form of the main contribution to IEg near the critical voltage does not differ from 'the usual shape-transform type', as follows from (5) and fromthe fact that both cos 2qb and sin 2@ are proportional to o --~.…”

“…Thus, when Shoemaker, Schomaker, Donohue & Corey (1950) estab- Sellar, Imeson & Humphreys (1980) have published numerically calculated rocking curves of the 2g diffracted intensity (I2g) when an electron beam is incident on a crystal foil oriented so that only systematic reflections ng are important (g: reciprocal-lattice vector), the accelerating voltage being very close to the 'second-order critical voltage'. They reported, among other things, the occurrence of two sharp intensity peaks at orientations very close to the second-order Bragg orientation and positioned symmetrically with respect to the latter.…”