Theoretical and Experimental Techniques for the Determination of X-ray Anomalous Dispersion Corrections

Abstract

Aust. J. Phys., 1985,38, 371-404 Theoretical and experimental techniques for the determination of the X-ray anomalous dispersion corrections f'(w, LI) and fl/(w, LI) are discussed. The results of experiments on metallic, ionic and covalently bonded materials typified by copper and nickel, lithium fluoride, and silicon respectively are compared with the theoretical predictions. Attention is drawn to deficiencies in both the experimental and the theoretical approaches.

Recent Advances in the Calculation and Measurement of the X-ray Dispersion Corrections

“…Another technique uses measurements of /"(CJJ, 0). The deficiencies of this approach have been discussed by Creagh (1980Creagh ( , 1984Creagh ( , 1986. However, serious attempts to determine f'(CJJ, 0) through measurements of f"(CJJ, 0) have been made by Gerward et al (1979), Dreier et al (1984), Creagh (1980), Bonse and Henning (1985), Bonse and Hartmann-Lotsch (1984), Kawamure and Fukamachi (1978) and Fukamachi et aL (1978).…”

“…It is not my intention here to describe these techniques since I have reviewed the subject recently (Creagh 1986). Suffice to say that direct measurements of f'(CJJ, 0) using X-ray interferometers have been made by, inter alia, Cusatis and Hart (1975), Siddons and Hart (1983), Begum et al (1986), Bpnse and Materlik (1975), Bonse and Hartmann-Lotsch (1984), Bonse and Henning (1985) and Creagh (1984).…”

“…The error in estimating the scattering amplitude at infinite frequency made by using the dipole approximation was thought to have been taken into account by use of the Stibius-Jensen correction. This, however, is not the case, and many authors (Kissel and Pratt 1985;Ornote and Kato 1987;Creagh 1980Creagh , 1984Creagh , 1986) have shown that a major source of the discrepancies between the modern theories lies in the inaccuracy in determining the scattering amplitude at infinite frequency 1'( 00, ~). Table 1.…”

“…A variety of explanations have been given for the discrepancies between theoretical and experimental values for f'(CIl, 0). They range from theories concerning the band pass of the measuring equipment (Creagh 1986) to theories based on the fact that the XANES structure overlaps the edge. No completely satisfactory explanation exists at present.…”

“…The development of both theoretical and experimental techniques for the determination of the dispersion corrections has been outlined by Gavrila (1981) and Creagh (1986). The use of the dispersion corrections to enhance the measurement of a wide range of physical systems has been described recently by Creagh (1987 b).…”