CONTRAST OF HOLZ LINES IN ENERGY-FILTERED CONVERGENT-BEAM ELECTRON-DIFFRACTION PATTERNS FROM SILICON

Higher-order Laue-zone (HOLZ) lines were investigated in convergent-be am electron diffraction patterns from silicon near the low-indexed zon e axes [100], [110] and [111]. The visibility of these lines depends o n the effective structure potentials of the reflections from the first Laue zone depending on their Debye-Waller factor. The contrast of the HOLZ lines is strongly reduced by inelastically scattered electrons. They can be excluded by an imaging Omega filter for energy losses abov e 2 eV. The diffraction patterns were compared with many-beam calculat ions. Without absorption, an excellent agreement could be achieved for the [111] and [100] zone axes, while the simulation of the [110] zone -axis pattern needed a calculation with absorption. The reason for thi s observation is explained in the Bloch-wave picture. Calculations wit h absorption, however, lead to artefacts in the intensity distribution of the [100] HOLZ pattern. In order to obtain agreement with the expe riment, the Debye-Waller factor had to be modified in different ways f or the different zone axes. This corresponds to a strong anisotropy of the Debye-Waller factor. To confirm this observation, the temperature dependence of the itensity distributions of the HOLZ patterns was inv estigated between 50 and 680 K. At room temperature, the parameter D i n the Debye-Waller factor exp(-Ds(2)) was determined as 0.13, 0.26 and 0.55 Angstrom(2) for the zone axes [100], [111] and [110], respective ly. The reliability of the conclusions is discussed.