DYNAMICAL DIFFRACTION EFFECT ON HOLZ-PATTERN GEOMETRY IN SI-GE ALLOYSAND DETERMINATION OF LOCAL LATTICE-PARAMETER

Higher-order Laue zone (HOLZ) patterns are observed in convergent-beam electron diffraction (CBED) patterns of Si-Ge alloys and the dynamica l effect on HOLZ lines is discussed in relation to the kinematical app roximation to simulate the HOLZ lines. Double lines often appear from one HOLZ reflection due to the excitation of the first and second bran ches of the zeroth-layer dispersion surface. The magnitude of the syst ematic line shift from the line positions predicted by the kinematical simulation changes sensitively with specimen thickness and alloy comp osition depending on which branch is dominantly excited. The kinematic al simulation is applicable to accurate determination of lattice param eters with a proper correction Delta E: a difference between the effec tive electron energy and the actual microscope operating voltage. Usef ulness of the kinematical simulation is demonstrated in the investigat ion of the segregation in a Si-Ge alloy.