Ordering atSi(111)a−Siand Si(111)/SiO2Interfaces

X-ray diffraction has been used to measure the intensity profile of the two-dimensional rods of scattering from a single interface buried inside a bulk material. In both $\frac{\mathrm{Si}(111)}{a\ensuremath{-}\mathrm{Si}}$ and Si(111)/Si${\mathrm{O}}_{2}$ examples there are features in the perpendicular-momentum-transfer dependence which are not expected from an ideal sharp interface. The diffraction profiles are explained by models with partially ordered layers extending into the amorphous region. In the $\frac{\mathrm{Si}(111)}{a\ensuremath{-}\mathrm{Si}}$ case there is clear evidence of stacking faults which are attributed to residual 7\ifmmode\times\else\texttimes\fi{}7 reconstruction.