X-ray standing wave technique as a tool in the study of the imperfect crystals

The application of the X-ray standing wave (XSW) technique in the case of imperfect crystals meets serious theoretical and interpretational problems. However, well-known advantages of the XSW technique make it especially interesting to the study of the ordering of impurities and of various processes leading to changes in this ordering in various types of imperfect crystals. We try to answer the question how imperfection of a crystal may influence the changes in fluorescence yield during the XSW measurement. Two types of imperfect crystals are studied: Si(111) implanted with high energetic Bi+ ions, and Zn1-xCoxSe single crystal with natural (111) face. The discussion of obtained results shows that general features of the X-ray standing wave field are conserved despite the considerable imperfections of the crystals. The results seem to support the applicability of the SXW technique to the study of imperfect materials, although some further theoretical effort would be required. 4 figs., 8 refs. (author)