X-ray-standing-wavemodulated electron emission near absorption edges in centrosymmetric and noncentrosymmetric crystals

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 and f; (ii) lattice deviations, including amorphous and crystalline surface layers; (iii) a mean electron escape depth; and (iv) crystal polarity.