OBSERVATION OF PHASE CHANGE OF X-RAY POLARIZABILITY BY THE ROCKING CURVES IN THE BRAGG CASE. R. Negishi, T. Fukamachi, S. M. Zhou, Z. C. Xu, M. Yoshizawa, I. Matsumoto^l), T. Sakamaki²⁾, T. Kawamura³⁾, T. Nakajima^4), Saitama Institute of Technology, Okabe, Saitama 369-02,Japan, University of Library and Information Science, Tsukuba, Ibaraki 305, Japan, ²⁾JEOL LTD, Akishima, Tokyo 196, Japan, ³⁾Yamanashi University,Kofu, Yamanashi 400, Japan, ⁴⁾Photon Factory, KKK, Oho, Tsukuba, Ibaraki, 305, Japan

Rocking curves of the transmitted beam for GaAs 600 diffraction in the symmetric Bragg case were measured just below the K-absorption edge of Ga by using X-rays from synchrotron radiation. When X-ray energy is 9eV below Ga K-absorption edge, the rocking curve shows the asymmetry: the intensity in the lower angle region of the exact Bragg angle is larger than that in the higher angle region. The reversed asymmetry is observed in the rocking curve at 3eV below Ga K-edge, i.e. intensity in the higher angle region is larger than that in the lower angle region. The critical energy of this reversal is about 6eV below Ga K-edge.

Based on a dynamical theory of X-ray diffraction with absorption effect taken into account¹⁾, the diffracted and the transmitted intensities were calculated. By comparing the measured rocking curves with the calculated ones, it is elucidated that the asymmetry of the transmitted rocking curves described above depends on the value of the phase difference d, which is the difference of phase factors of the Fourier transforms of the real and the imaginary components of the X-ray polarizability. The phase difference d is a function of crystal structure as well as anomalous scattering factor. Similar asymmetric rocking curves in the Laue case have been reported by Fukamachi et al.²⁾. It is pointed out that this change of the asymmetry is potentially useful in the phase determination of the structure factors.

1) T. Fukamachi & T. Kawamura, Acta Cryst.(1993), A49,384.

2) T. Fukamachi, R. Negishi, S. M. Zhou, M. Yoshizawa, T. Sakamaki, T.Kawamura, T. Nakajima, Acta Cryst.(1996), in press.