In this paper it is shown that diffuse-scattering experiments within the region of total external reAection can be explained quantitatively using the distorted-wave Born approximation for layer systems. Three Si/Ge samples with different degrees of complexity were investigated. The simultaneous analysis of the specular rejected intensity and the diffuse scattering leads to one consistent set of interface and layer parameters, which is able to fit both the shapes and the locations of all dynamic peaks in the off-specular scans and the characteristics of the rejected intensity. Therefore the distorted-wave Born approximation seems to give a correct and complete description of the diffuse scattering in the region of total external reflection.

The detailed interface structure of a CoSi 2 /Si/CoSi 2 /Si͑111͒ layer system grown by molecular-beam epitaxy is investigated in this paper. Measurements of the diffuse scattering in the region of total external reflection were performed and analyzed within the distorted-wave Born approximation. The analysis of the specularly reflected and the diffusely scattered intensity leads to a consistent set of interface and layer parameters, which are compared with results of Rutherford backscattering/channeling, transmission electron microscopy, and scanning tunneling microscopy. Although the diffuse intensity is dominated by a very rough surface layer, the roughness distribution of the buried interfaces of the epitaxial layers was determined rather exactly. It was found that the roughnesses of the interfaces of all epitaxial layers are of the order of monolayer steps. Very good agreement between the measurements and the calculations is achieved, if conformal roughness of the adjacent interfaces of each CoSi 2 layer is included. Furthermore, the interfaces of the sandwiched Si layer are partially correlated, which means that the step structure is partially transferred through all interfaces up to the surface of the upper CoSi 2 layer.

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The protonic conductivity of has been measured using the complex-admittance method in the frequency range 30 Hz-200 MHz and the temperature interval 290-500 K covering both the ferroelastic and the paraelastic phases. The dc conductivity shows quasi-two-dimensional behaviour and in the trigonal paraelastic phase its values in the (001) plane are typically super-protonic with low activation enthalpy . The temperature dependence of the monoclinic superstructure reflection 120 has been studied using elastic neutron diffraction. It was found that the observed anomalies of the macroscopic and microscopic quantities, such as the morphic birefringence and the high-frequency dielectric constant on the one hand and the diffusion proton dynamics as well as the integrated intensity of the reflection 120 on the other hand, show pronounced differences in their temperature evolution below the ferroelastic phase transition temperature. The neutron scattering results as well as the dielectric measurements indicate precursor effects above . The results are discussed on the basis of a phenomenological two-order-parameter model for the - ferroelastic phase transition. It is argued that properties which originate from the disorder of the oxygen and proton subsystem can be described by irreducible representations of the wave vector at the point and the L point of the Brillouin zone, while properties which originate from displacements of the heavy atoms (the displacement mode) are solely described by the wave vector at the L point of the Brillouin zone of the paraphase.