Energy-dispersive electron-emission yields were measured for (111) Bragg reflections of x rays from Ge and GaAs crystals. The reflection angle was changed continuously over the Bragg reflection range, thus causing the internal x-ray-standing-wave pattern to move across the atomic planes. With the use of synchrotron radiation, these measurements were performed at photon energies below and above the Ga and As $K$ absorption edges. This introduces an energy-dependent position shift of the noncentrosymmetric diffraction planes relative to the atomic planes. It is shown how to determine, from such measurements, (i) the dispersion parameters $f^{\prime }$ and $f^{\prime \prime }$; (ii) lattice deviations, including amorphous and crystalline surface layers; (iii) a mean electron escape depth; and (iv) crystal polarity.

• Received 31 October 1983

DOI:https://doi.org/10.1103/PhysRevB.30.2453