Etude en microscopie electronique·de 1'influence des reflexions accidentelles sur les tensions critiques

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Abstract
Study by electron microscopy of the influence of accidental reflections on critical voltages In this article it is shown that strongly excited non-systematic reflections have very apparent effects on the profile contrasts of extinction contours in the vicinity of a critical voltage. Our results have been obtained with wedge shaped single crystals of magnesium oxide. The effects of strong non-systematic reflections show important changes in the intensity profiles of equal thickness fringes given by the second order Bragg reflection: in our study we have considered the 400 reflection. The comparison between these experimental results and those of the calculations carried out in N waves dynamical theory using the atomic scattering factors of electrons indicated on different, tables has enabled us to deduce some Fourier coefficients V 8 of the inner potential. In the case of MgO we have found V 200 = 6·93 volts, I400≃3·1 volts, V 024 ≃ 2·6 volts and V224≃2·3 volts at room temperature T= 300°K.