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Multilayer Nb0.53Ti0.47/Ge superlattices with varying Nb0.53Ti0.47 and Ge layer thickness were sputter deposited on sapphire substrates at 200°C. The physical properties of these superlattices depend on the Nb0.53Ti0.47 layer thickness which is in turn related to the degree of disorder of the metal layer. The spectrum of samples can be subdivided roughly into three regions according to their different transport properties—a superconducting region, a weak localization region and a strong localization region. The sheet resistance, R□ of films in the weak localization region is in the range of 300ω The magnetoresistance is anisotropic for both the weakly and strongly localized films with the perpendicular magnetoresistance always larger than the parallel values. The weak localization to strong localization transition is consistent with the theoretically predicted mobility edge near R□≂ħ/0.12e2≅30kω.

Sandwich and superlattice structures composed of the high critical field superconducting alloy Nb0.53Ti0.47 (where the compositions refer to weight percent) and amorphous Ge were sputter‐deposited on sapphire substrates using a novel multi‐sputter‐gun system. The thicknesses of both the superconducting Nb0.53Ti0.47 and the insulating Ge layers were varied over a wide range in order to study the two‐dimensional (2D) and three‐dimensional (3D) superconducting properties of these structures. The observed suppression of the measured resistive superconducting transition temperature Tc with increasing sheet resistance is tentatively interpreted using the Maekawa–Fukuyama theory which incorporates contributions from localization and Coulomb interaction effects. The upper critical fields, with the field both normal Hc2⊥ and parallel Hc2∥ to the film, were measured up to 50 kG. Hc2∥ exhibited 2D behavior when the thickness of the superconducting layer was less than 200 A. The zero temperature values of Hc2∥(0) wer...

We describe a four‐gun sputtering system which has been used successfully to prepare composition‐modulated structures consisting of amorphous semiconductors and superconducting alloys or binary compounds. The substrates are mounted in ovens which can be individually heated to over 1000 °C. The ovens are mounted on a wheel which is driven by a computer‐controlled stepping motor. With appropriate programming of the movement of the stepping motor, the deposition sequence is determined.

We have studied the effect of annealing on the transport properties of an epitaxial bismuth film. By annealing close to the melting temperature, the helium temperature resistivity is found to decrease by a factor of 15. The results are potentially of importance in connection with quantum size effect (QSE) measurements and the combined Shubnikov-de Haas effect-QSE.

We have made a preliminary study of vertical electrical transport in Nb 0.53 Ti 0.47 Ge multilayers having the structure Nb/Ge/Nb0.53Ti0.47/Ge … Nb0.53Ti0.47/Ge/Nb. The initial and final Nb layers serve as equipotential electrodes, and measurements are analyzed only in the temperature range below which the thick Nb electrodes are superconducting. In-plane (parallel) transport studies were made on identical Nb 0.53 Ti 0.47 Ge multilayers (deposited at the same time on a different part of the substrate using an appropriate mask). The layered structure is confirmed by low angle X-ray diffraction and SEM microscopy. Depending on the transition temperature of the Nb 0.53 Ti 0.47 Ge multilayers, the temperature-dependent junction resistance shows several interesting features. The I–V characteristics and the first derivative dI/dV were measured, yielding a sum gap of nearly 20meV for a 16 layer structure having a Tc of 7K. Possible interpretations of these results are presented.

The growth and structural characteristics of three semiconductor-semimetal superlattices are presented. The superlattices were prepared by thermal evaporation in high vacuum. Although the constituents in each system have different crystal structures, only a small lattice mismatch (

Studies are reported of the upper critical fields of Nb0.53Ti0.47-Ge multilayers consisting of thick Ge layers and varying-thickness Nb0.53Ti0.47 layers. Both the angular dependence and the temperature dependence of the upper critical fields indicate a dimensional crossover at a Nb0.53Ti0.47 layer thickness near 200 A. All the 2D samples display a cusplike upper critical field angular dependence with a sharper cusp for thinner Nb0.53Ti0.47 layers. The parallel upper critical fields are tentatively fitted with an expression combining the 2D field dependence of Rickayzen, the paramagnetic limiting behavior of Maki, and the disorder-related Coulomb interaction effects of Maekawa and Fukuyama. The perpendicular fields are fitted with the Maekawa, Ebisawa, and Fukuyama theory; better agreement is obtained for thinner Nb0.53Ti0.47 sublayers when the paramagnetic limiting effect is included.

A new composition modulated structure composed of semiconducting SnTe and semimetallic Sb has been grown epitaxially on mica substrates with differing SnTe to Sb ratios. The samples were characterized by x‐ray diffraction using the transmission Laue patterns and θ‐2θ diffractometer scans with scattering vectors both normal and in the plane of the film. We observed that the modulation satellites were 180° out of phase for films with short modulation wavelengths, but were in phase for long wavelengths. This change in the phase of the modulation can be understood by assuming that Sb adopts a quasicubic structure at short modulation wavelength, due to the coherency strain, but relaxes back to a distorted rhombohedral structure, with the loss of coherency, at long wavelengths. A simple 1‐D model was used to estimate the modulation wavelength dependence of the sublattice displacement of Sb.

A versatile, compact, constant current‐voltage, bipolar power source for quasi‐static or derivative measurements of the characteristics of superconducting junctions has been developed. The circuitry is based on a negative feedback strategy that is effective in maintaining constant current‐voltage behavior at the junction itself and all lead resistances are included in the feedback loop. Constant currents and voltages can be delivered of up to ±0.5 A and ±0.75 V, respectively. Both fast and slow sweeps, as well as a single sweep mode, are available in variable ranges. The single sweep feature is used to avoid heating effects in low resistance junctions which are not in good thermal contact with a thermal reservoir (e.g., liquid 4 He).

Y‐Ba‐Cu‐O thin films have been deposited on MgO substrates by dc magnetron sputtering from a stoichiometric YBa2Cu3O7−δ target, after which they are subjected to a short heat treatment. Zero resistance is routinely achieved near 60 K, and one film shows zero resistance at 68.0 K.

We have studied the superconducting properties of V/Cr superlattices. Superlattices of V100Crx, V150Crx, and V200Crx, with x varying between 3 and 80 atomic planes have been prepared. The films have a strong (110) texture and were grown on sapphire substrates at 250°C in an ultra-high vacuum system. The zero field transition temperature of the V150Crx and V200Crx, but not the V100Crx films have been adequately modeled using Werthamer's theory for proximity effect coupled films. The films have a dimensional crossover in the parallel upper critical field when the thickness of the Cr layers is about 60 atomic planes.

The surface wave velocity in SnTe/Sb superlattices has been determined using Brillouin scattering. The velocity is independent of modulation wavelength over the range studied but is lower than would be expected if the layers of Sb and SnTe possessed their bulk properties. This is consistent with x‐ray data which can be interpreted as evidence of a cubic polymorph of Sb which is unstable in bulk form.

AℓN has been used as a barrier material in large josephson junctions. The chemical and structural compatibility of AℓN with NbN make it possible to fabricate NbN/AℓN/NbN junctions by sequential reactive sputtering in a common Ar and N2 atmosphere. In a junction with an area of about 1.0×1.0 mm2, having a transition temperature of 14.5K. the measured I–V and first derivative curves yield a sum gap value of about 3.0 meV.