The many-beam moiré effect in electron micrographs of epitaxic Sn/SnTe layers

The many-beam dynamical theory of moiré fringes of Gevers [Phys. Status Solidi (1963). 3, 2289-2297] has been applied to the parallel moiré case and the results have been verified on epitaxically grown Sn/SnTe specimens showing the sensitivity of moiré patterns to the presence of systematic reflections. The Fourier analysis of the calculated intensity profiles showed that each additional diffracted beam gives rise to a new term in the Fourier series so that the profile can be sinusoidal only in the two-beam approximation. The same result has been obtained recently by Pardo, Pariset & Renard [Phys. Status Solidi A. (1981). 64, 283-295], who applied a slightly different theoretical approach to Sb/Bi specimens. It is shown that the corrections to scattering factors for temperature effects are not important since they do not affect the general character of the moiré profiles. Some experiments were performed showing the dependence of the moiré pattern on the number of beams that are transmitted through the objective aperture. The effect of the gradual thinning of one layer on the moiré pattern could be reproduced by computer simulation.