High-accuracy structure-factor measurements in germanium

Abstract

Structure factors ${\mathit{F}}_{\mathit{h}}$ of five reflections in the range 0.15 \ensuremath{\le}sin\ensuremath{\theta}/\ensuremath{\lambda}\ensuremath{\le}1.07 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$ were measured in germanium. An accuracy of \ensuremath{\le}20 millielectron per atom was achieved for all values except one. This represents 1 order of magnitude improvement over previous measurements for the three highest-order ${\mathit{F}}_{\mathit{h}}$. Measurements were done using the W K${\mathrm{\ensuremath{\alpha}}}_{1}$ line (E=59.3 keV) and a monolithic thin-crystal Laue-case diffractometer, the rocking curves of which were computer fitted to yield ${\mathit{F}}_{\mathit{h}}$. Good agreement is obtained with previous measurements, where available. The bonding contribution to ${\mathit{F}}_{111}$ is found to be larger than predicted by ab initio calculations. No evidence is found for an anharmonic contribution to the atomic potential, within the accuracy of the measurements. This is in keeping with x-ray results for silicon, but in contrast with neutron and x-ray ``forbidden'' reflection measurements. The Debye parameter B=(0.5661\ifmmode\pm\else\textpm\fi{}0.0026) A${\mathrm{\r{}}}^{2}$ derived from our data is in excellent agreement with older results.