THREE-BEAM DIFFRACTION ANOMALOUS FINE STRUCTURE OF
GALLIUM ASENIDE
Shih-Lin Chang,a Yen-Ru Lee,a Yu. P. Stetsko,b Sen-Yuan Cheng,a Guin-Gi Lin,a
Shih-Chang Wonga and Wen-Shien Suna
a
Department of Physics, National Tsing Hua University; bNational Synchrotron Radiation Research
Center, Hsinchu, Taiwan, 300, R.O.C.
The coherent interaction in three-beam diffraction provides information about
crystallographic phase [1] and resonance phase shift due to electronic transition [2]. This
phase information may be useful in understanding the atomic and electronic structures of the
constituent atoms of a crystal. Following this idea a three-beam diffraction anomalous fine
structure (DAFS) technique is developed, where three-beam diffraction intensity as a function
of x-ray photon energy in the vicinity of an absorption edge is measured.
A [111] cut GaAs single crystal is used as a sample crystal. The diffracted intensity of
the three-beam (222/113) case, as well as fluorescence yield are measured for the photon
energies covering the GaK and AsK edges. The phase information is used to link the real and
imaginary parts of the atomic scattering factors considered. Analysis based on the dynamical
diffraction theory and XAFS gives fine structures of DAFS spectra. The details about the
experimental aspects and the analysis procedures of this technique will be presented and
discussed.