PENDELLÖSUNG EXPERIMENT OF SILICON AT LOW TEMPERATURES. T. Eto, H. Naruoka, S. Nagao, Z. Lu, Y. Soejima, A. Okazaki,

Department of Phisics, Kyushu University, Fukuoka 812-81,Japan

In connection with anomalous behavior at low temperature of the silicon lattice spacing in particular that of (444), the structure factors of 111, 220 and 004 have been examined as a function of temperature. It is found that the structure factor shows no anomaly in a temperature range 17-300 K, while the Debye-Waller factor shows anisotropic temperature dependence. Measurements were made by means of Xray diffraction according to the Pendellösung fringes method applied to specimens in a form of a thin plate. Descriptions are given of the experimental technique to keep the specimen at low temperatures free from strains that are mainly due to the difference of thermal expansion between the specimen and its holder. The characterization of the long-range strain field is given on the basis of the method in the literature. It is also found that strains introduced at low temperatures can be relieved at the lowest temperature; this phenomenon of a kind of aging is consistent with the observation in the previous experiment on the lattice spacing by means of high-angle double-crystal X-ray diffractometry and the Bond method. The procedure of the analysis of the fringe pattern is also examined, and the precision of the results is discussed. Finally, values of the structure factor at room temperature are compared with those in the literature, and a discussion is given of the accuracy of them.