High energy electron diffraction at Si(001) surfaces

Elastic scattering of 10 keV electrons at Si(001) surfaces at grazing incidence was investigated. The intensity of the specularly reflected elastically scattered electrons as a function of the angle of incidence I_el(γ) was measured for different azimuthal angles and was compared with calculations using the dynamical diffraction theory. It turned out that the contribution of the elastically scattered electrons to the total intensity of the reflections strongly decreases with decreasing angle of incidence. Exciting the reflection (008) the elastic contribution is around 30%, decreasing to about 12% in the case of the reflection (004). In the calculations multiple beam effects, absorption, a smooth variation of the potential at the surface and a reduction of the topmost interlayer spacing were taken into account. There is satisfactory agreement between the structures of experimental and calculated intensity curves, I_el(γ) indicating a slight compression of the surface lattice to be probable. Quantitative agreement, however, for absolute intensities was not obtained.