Redetermination of Absolute Structure Factors for Silicon at Room and Liquid Nitrogen Temperatures

Many new determinations of silicon structure factors have been made in the last few years providing confidence in dynamical diffraction methods and challenging the basis of available theories. The first analysis of experiments done in the early 1970s (Aldred and Hart 1973) has been repeatedly compared with theories and more recent experiments. A number of minor problems have come to light, for example, the crucial need to detect strain gradients and small changes in the accepted values of some parameters. Fortunately, the raw data was published by Aldred and we have reanalysed these experiments, making corrections for strain gradients. These new results still comprise the only low temperature high precision data on silicon, which is an important feature since it is becoming increasingly clear that anharmonic effects are insufficiently well measured in silicon compared with other features of the electron density.