X -ray scattering and covalent bonding in germanium

The effects of covalent bonding on Bragg X -ray scattering in germanium are predicted in terms of the results which have emerged from detailed studies of such effects evident in accurate X -ray data for silicon and diamond. Alternative possibilities consistent with trends found in these lighter systems are considered, and it is shown that one of the possibilities is in accord with a recent observation that | f (222)| = 0⋅14 ± 0⋅01. The predictions of nonspherical scattering in the orthodox data for this system are compared with the X -ray measurements of DeMarco & Weiss to illustrate how the requirements of high accuracy in experimental results rise steeply with increase in atomic number. It is shown that, on the present evidence from the 222 reflexion, the effects of covalent bonding in germanium will produce a peak of approximately 0⋅18 e/Å 3 at the midpoint of each bond. The need for more precise measurements in the future is pointed out.