Axial Channeling in Electron Diffraction

Abstract

Kossei patterns from Silicon and Niobium were obtained with a convergent electron beam. An intensity maximum in the direction of the zone axes [001] and [111] of Nb was interpreted as axial channeling. The intensity distribution in Kossel patterns was calculated by means of the Bloch wave picture of the dynamical theory of electron diffraction. Particularly zone axis patterns were calculated for different substance-energy combinations and they were compared with experimental observations. The intensity distribution in the calculated Kossel patterns was very sensitive to the model of absorption and it was found that a treatment of the absorption close to the model of Humphreys and Hirsch [Phil. Mag. 18, 115 (1968)] gave the best agreement with the experimental observations. Furthermore it is shown which Bloch waves are important for the intensity distribution in the Kossel patterns, how they are absorbed and how they change with energy.

Imaginary potential for electrons of CaF2from a Bloch-wave analysis

“…In an earlier paper (Ichimiya & Lehmpfuhl, 1978) a similar model was found to fit the experimental observations. The exponential term represents the square of the Debye-Waller factor.…”

“…The new analysis was carried out by comparing the experimental intensity distribution with calculated intensity distributions as described in previous papers (Lehmpfuhl & Reissland, 1968;Ichimiya & Lehmpfuhl, 1978) but with a non-Hermitian complex crystal potential (1) and by convolution with the Gaussian profile of the incident beam with an angular half-width of 2 x 10 -5 rad. The complex crystal potential was used in a 50-beam calculation leading to eigenvalues, eigenvectors and absorption coefficients for the different Bloch waves.…”

Convergent-beam RHEED calculations of a `forbidden reflection' from the Si (111) surface

“…This was taken to have a value of 0.7 eV as guided by transmission work (Voss, Lehmpfuhl & Smith, 1980;Ichimiya & Lehmpfuhl, 1978;Radi, 1970). Furthermore, because of cubic symmetry and in order to eliminate redundant beams, a non-conventional hexagonal unit cell was chosen (Smith & Lynch, 1988).…”

Diffuse scattering of fast electrons in barium titanate

“…There is some analogy with the ALCHEMI technique for site location of specific ionized species through the orientation dependence of X-ray emission or characteristic losses in energyloss spectra [see, for instance, Spence & Taftel (1982) and Taft~ & Krivanek (1982)]. Descriptions of Kikuchi-line or Kossel-line formation (Gj¢nnes & Taft¢, 1976;Ichimiya & Lehmpfuhl, 1978)have been based on anomalous absorption acting independently on each Bloch-wave component of g~, applicable to multiple scattering from thick crystals. In the single scattering theory for relatively thin crystals presented in this paper, dynamical effects are accounted for by the natural peaking and diminishing of [~bl 2 on localized scattering sites as a function of thickness and orientation.…”