Absolute measurement of structure factors of Si by using X-ray Pendellösung and interferometry fringes

The absolute values of crystal structure factors |F_g| of silicon were determined accurately for five low-order lattice planes, with probable errors of less than 0.05%. The principle of the measurement is to take the ratio of |F_g| and |F₀|, which are geometrically proportional to the spacings of the Pendellösung and interferometry fringes respectively. Thus, this method is not only based on a principle appropriate for a truly absolute measurement, but the difficulty in determining the proportional factors is essentially eliminated, and the experimental errors can be reduced to about 0.1%. Some geometrical corrections, however, are required to attain an accuracy better than this. These corrections as well as the theoretical ones are discussed and the necessity of taking into account the effect of the nuclear Thomson scattering is pointed out. The consistency of the results was checked with respect to the following points; (i) |F_g| = |F_-g|, (ii) |F_g| values being independent of whether the interference fringes in the direct beam or those in the Bragg-reflected beam are used, and (iii) the agreement of |F_g| for different specimens. The atomic scattering factors |F_g| standardized at 20°C are as follows; 111: 10.66₀, 220: 8.46₀, 333: 5.83₉, 440: 5.40₄, and 444: 4.16₈. A comparison is made with the values of other authors.