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 Wong^a and Wen-Shien Sun^a

^aDepartment of Physics, National Tsing Hua University; ^bNational Synchrotron Radiation Research Center, Hsinchu, Taiwan, 300, R.O.C. (slchang@phys.nthu.edu.tw).

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 this technique will be presented and discussed.

References

1 Chang, S.-L., King, H. E., Huang, M.-T., and Gao, Y. (1991) Phys. Rev. Lett. 67, 3113-3116.

2 Stetsko, Yu. P., Lin, Huang, Y.-S., Chao, C.-H., and Chang, S.-L. (2001) Phys. Rev. Lett. 86, 2026-2029.