ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
The angular and voltage dependence of the diffracted intensity for electrons in the energy range of 150–900 volts from a clean tungsten (110) surface has been measured with a single-crystal diffractometer. Selecting the angle of incidence and the electron wavelength to satisfy the Bragg condition the crystal is rotated about its normal, and a Renninger plot of diffracted intensity versus azimuthal angle is made. Strong intensity variations are observed when the plane of diffraction is parallel to those low index crystallographic planes which contain relatively dense atomic rows. Additional structure occurs for each intersection of an extended reciprocal lattice point with the Ewald sphere. For some orientations the intensity is reduced to half the value within one degree, which is the beam divergence. When simultaneous diffraction does not occur, the intensities of the Bragg maxima are close to the background. The integral order Bragg maxima observed in electron diffraction are thus shown to have their origin in multiple diffraction. The frequently observed fractional order Bragg maxima are predicted to have the same origin. Renninger plots for such maxima show this to be the case. In addition the appearance of the fractional order peaks should depend only on the geometry for multiple diffraction. Intensity versus voltage curves for the beam incident along the [hkl] direction are predicted to have maxima of order (h2 + k2 + l2)−1, which is verified. The implication of these observations in terms of previous two-beam models is discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739468000264
