Search

Single-crystal ZrN films, 830 nm thick, are grown on MgO(001) at 450 °C by magnetically unbalanced reactive magnetron sputtering. The combination of high-resolution x-ray diffraction reciprocal lattice maps, high-resolution cross-sectional transmission electron microscopy, and selected-area electron diffraction shows that ZrN grows epitaxially on MgO(001) with a cube-on-cube orientational relationship, (001)ZrN‖(001)MgO and [100]ZrN‖[100]MgO. The layers are essentially fully relaxed with a lattice parameter of 0.4575 nm, in good agreement with reported results for bulk ZrN crystals. X-ray reflectivity results reveal that the films are completely dense with smooth surfaces (roughness = 1.3 nm, consistent with atomic-force microscopy analyses). Based on temperature-dependent electronic transport measurements, epitaxial ZrN/MgO(001) layers have a room-temperature resistivity ρ300K of 12.0 μΩ-cm, a temperature coefficient of resistivity between 100 and 300 K of 5.6 × 10−8 Ω-cm K−1, a residual resistivity ρo below 30 K of 0.78 μΩ-cm (corresponding to a residual resistivity ratio ρ300Κ/ρ15K = 15), and the layers exhibit a superconducting transition temperature of 10.4 K. The relatively high residual resistivity ratio, combined with long in-plane and out-of-plane x-ray coherence lengths, ξ‖ = 18 nm and ξ⊥ = 161 nm, indicates high crystalline quality with low mosaicity. The reflectance of ZrN(001), as determined by variable-angle spectroscopic ellipsometry, decreases slowly from 95% at 1 eV to 90% at 2 eV with a reflectance edge at 3.04 eV. Interband transitions dominate the dielectric response above 2 eV. The ZrN(001) nanoindentation hardness and modulus are 22.7 ± 1.7 and 450 ± 25 GPa.

We have imaged vortices in superconducting thin films with a low‐temperature magnetic force microscope that utilizes microfabricated piezoresistive cantilevers with built‐in tips. The films of YBa2Cu3O7−x and Bi2Sr2Ca1Cu2O8+x, are made by laser ablation and molecular beam epitaxy, respectively. The vortices usually appear as round features in the noncontact image with a diameter of about 1 μm or slightly less. In some cases the position of the vortices is correlated to defects observed in the topographic image of the same area. The vortices move sometimes, especially after taking a topographic (contact mode) scan.

A technique for atomic layer‐by‐layer epitaxy of cuprate superconductors and other complex oxides has been developed at Varian. The samples are engineered by stacking molecular layers of different compounds to assemble multilayers and superlattices, by adding or omitting atomic monolayers to create novel compounds, and by doping within specified atomic monolayers. Apart from manufacturing trilayer Josephson junctions with IcRn≳5 mV, this technique enables one to address fundamental issues such as the dimensionality of HTSC state, existence of long‐range proximity effects, occurrence of resonant tunneling etc., as well as to synthesize novel metastable HTSC compounds.

We use reflection high‐energy electron diffraction (RHEED) oscillations to study the growth condition dependence of the growth of pseudomorphic InGaAs layers on GaAs, as well as van der Pauw/Hall measurements to evaluate the growth parameter dependence of the electrical properties of InGaAs/AlGaAs high electron mobility transistor structures. We present our conclusions regarding growth conditions for which smooth RHEED oscillations can be obtained, and the parameters for which optimal electrical properties can be reached.

We have grown thin, highly oriented, polycrystalline DyBa2Cu3O7−x films using molecular‐beam epitaxy (MBE) techniques that show the onset of superconductivity at temperatures above 90 K and complete transitions at temperatures as high as 87 K. These films have critical current densities as high as 5×105 A/cm2 at 4.2 K. Films were grown in a modified Varian 360 MBE machine using effusion sources containing the metal constituents, along with a gaseous oxygen source. The early stages of deposition were monitored with reflection high‐energy electron diffraction (RHEED). The best films were obtained on SrTiO3 substrates at substrate temperatures of 600–750 °C. At these temperatures, the initial stage of growth is dominated by epitaxy of copper islands. At lower temperatures, the growth is amorphous, while at higher temperatures, copper may not be incorporated into the film. Copper incorporation is also affected by oxygen flux. In all cases, the films are semiconducting or insulating as grown, and become superc...

We report the development of molecular‐beam epitaxy (MBE) techniques for the growth of high‐temperature, perovskite‐like superconductors. The use of a plasma source of active oxygen allows the in situ growth of such layers. Some of the films grown this way were superconducting as grown. Smooth films exhibiting streaked reflection high‐energy electron diffraction (RHEED) patterns, were obtained by using shuttering to kinetically control the growth process. We also report initial results of experiments in which kinetic control is used to layer metastable, nonequilibrium structures in the bismuthstrontium–calcium–copper–oxide system.