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The presence of a nonrandom fractional number of atomic planes in each layer of a superlattice produces unusual diffraction patterns in which the peaks cannot be indexed in the usual fashion as due to a single series. The x-ray line broadenings are distinctly different from earlier measurements and calculations in which the interfacial roughness is due to random variations of the scattering function. Therefore, interfacial roughness encountered at a single interface may just be a consequence of controlled, but not random, roughness and that under proper growth conditions superlattices with atomically sharp interfaces may be produced. These results are in good agreement with experimental measurements.

We report on measurements of the dimensional crossover effect in superconducting Pb/Ge and Pb/C multilayers. The critical field data indicate the presence of a proximity effect at the interface between the Pb and the Ge or C. Using the model of Tachiki and Takahashi, we calculate the finite density of states near the Fermi-level in the Ge and C layers.

We have performed extensive structural and electronic transport measurements of Pb/Cu multilayered structures. The high-angle x-ray diffraction spectrum indicates the presence of continuous interfacial disorder. In the low-angle x-ray spectrum, pronounced minima occur at positions given by q = 2π/Λ, where Λ is the bilayer thickness. This is in sharp contrast to the results for Pb/Ge (crystalline/amorphous) multilayers, where minima are observed at positions q = 2π / tPb with tPb the Pb thickness. These low-angle x-ray spectra can be explained by taking into account lateral coherence and continuously distributed thickness fluctuations. The effect of this interfacial disorder on the electronic properties is investigated by measuring the low-temperature resistivity and the superconducting transition temperature of the multilayers. The calculated values for the elastic mean free path in the individual layers confirm the presence of strong interfacial scattering. The thickness dependence of the critical temperature is explained by taking into account an interfacial barrier with penetration probability σ ≃ 0.5.

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