J. H. Marshall

Single-Crystal Epitaxial Thin Films of the Isotropic Metallic Oxides Sr1–xCaxRuO3 (0 ≤ x ≤ 1)

Single-crystal epitaxial thin films of the isotropic metallic oxides Sr1–xCaxRuO3 (0 ≤ x ≤ 1) were grown on miscut SrTiO3(100) substrates in situ by 90� off-axis sputtering. These thin films exhibit low isotropic resistivities, excellent chemical and thermal stability, good surface smoothness, and high crystalline quality. Furthermore, the lattice parameters and magnetic properties can be varied by simply changing the strontium/calcium ratio. These epitaxial thin films, and their multilayer structures with other oxide materials, can be used for the fabrication of superconducting, ferroelectric, magneto-optic, and electro-optic devices.

Superconductivity near 70 K in a new family of layered copper oxides

A new family of high-temperature superconductors is described, with the general formula Pb2Sr2ACu3O8+δ. Although they have the planes of CuO5 square pyramids characteristic of the other copper-oxide superconductors, the new compounds belong to a distinct structural series, with wide scope for elemental substitution. Their unusual electronic configuration also gives new insight into the role of charge distribution among the structural building blocks in controlling superconductivity.

Fabrication and properties of epitaxial ferroelectric heterostructures with (SrRuO3) isotropic metallic oxide electrodes

Epitaxial ferroelectric SrRuO3/Pb(Zr0.52Ti0.48)O3/SrRuO3 heterostructures have been fabricated employing isotropic metallic oxide electrodes on (100) SrTiO3 and (100) Si with an yttria stabilized zirconia buffer layer. The structures have been grown in situ by 90° off‐axis sputtering, which allows the growth of uniform stoichiometric films over large areas with excellent step coverage. X‐ray diffraction, Rutherford backscattering spectroscopy, and cross‐sectional transmission electron microscopy reveal high crystalline quality and coherent interfaces. They exhibit superior fatigue characteristics over those made with metal electrodes, showing little degradation over 1010 cycles, with a large remnant polarization.

Zinc-indium-oxide: A high conductivity transparent conducting oxide

We report the fabrication and characterization of zinc‐indium‐oxide films with similar electrical conductivity and better transparency in both the visible and infrared compared with indium–tin–oxide, a widely used transparent conductor in many technological applications. Dramatically superior transmission properties in the 1–1.5 μm range in particular make zinc–indium–oxide attractive for use in infrared devices, where transparent electrodes are required. Resisitivities as low as 400 μΩ cm result from doping with small quantities of Sn; Al, Ga, and Ge are also effective dopants. Deposition on glass and quartz substrates as amorphous films by pulsed laser deposition and dc reactive sputtering is described.

Studies of oxygen-deficient Ba2YCu3O7−δ and superconductivity Bi(Pb)SrCaCuO

Abstract Ambient temperature measurements of the crystallographic cell parameters for oxygen deficient Ba 2 YCu 3 O 7−δ prepared by gettered annealing indicate the presence of microscopic differences in the oxygen configuration at fixed δ dependent on annealing temperature. The loss of superconductivity with increasing oxygen deficiency is shown to be due to a step-like increase in length of the plane copper-apical oxygen bond, and not to the orthorhombic to tetragonal transition. The crystal structure of the 84K superconductor Bi 2 Sr 2 CaCu 2 O 8+δ is described, as is the stabilization of 110K superconductivity via partial Pb/Bi substitution with long time annealing.

Transparent conducting thin films of GaInO3

GaInO3 is recently identified transparent conducting material which is structurally and chemically distinct from indium tin oxide [R. J. Cava, J. M. Phillips, J. Kwo, G. A. Thomas, R. B. van Dover, S. A. Carter, J. J. Krajewski, W. F. Peck, Jr., J. H. Marshall, and D. H. Rapkine, Appl. Phys. Lett. 64, 2071 (1994)]. We have used both dc reactive sputtering in the on‐ and off‐axis geometries and pulsed laser deposition to grow films of this material. Layers of pure GaInO3 as well as those partially substituted with Ge for Ga or Sn for In have been studied. Both growth techniques are capable of producing films with conductivity ∼400 (Ω cm)−1 and transmission as high as 90% throughout the visible spectrum for ∼1‐μm‐thick films. The growth techniques differ in the morphology of the films produced as well as in the degree of dopant incorporation that can be achieved. A post‐growth anneal in H2 can help produce an optimized oxygen content and a reduction of resistivity. Hall measurements indicate a carrier conce...

Spin Exchange in Nitroxide Biradicals

The dependence of the electron spin‐exchange energy upon temperature and solvent has been studied for the carbonate, oxalate, and succinate diesters of tetramethyl‐piperidinol‐oxyl. An analysis is given of exchange effects on ESR line positions, intensities, and widths. For the carbonate diester the exchange energy is constant at low temperatures. As the temperature is raised this energy gradually decreases, passes through a minimum, and then increases exponentially. Interpretation suggests that at low temperatures exchange occurs through an indirect process involving the core of sigma electrons, whereas at high temperatures a direct exchange process is more important.

GaInO3: A new transparent conducting oxide

GaInO3, a layered material with the β Ga2O3 crystal structure, can be doped with electrons through the introduction of oxygen deficiency, Sn doping for In, or Ge doping for Ga. At atomic doping levels of 10% or less, resistivities as low as 3 mΩ cm are obtained. In contrast to polycrystalline indium tin oxide (ITO), which is distinctly green, conductive gallium indium oxide is light grey with no visible coloration. Thin films of doped GaInO3 display good transparency over the whole optical window, superior to that of ITO in the green‐blue region.

Paramagnetic Relaxation in Liquid‐Crystal Solvents

The influence of a liquid‐crystal solvent on paramagnetic relaxation processes involving Zeeman and hyperfine anisotropies is examined. Secular and pseudosecular relaxation mechanisms are reduced by molecular ordering. Secular contributions are most effectively quenched, and, for high degrees of order in viscous media, pseudosecular processes are most important.ESR studies were made of solutions of vanadyl complexes with six β‐diketones in p‐azoxyanisole. The linewidths in the spectra depend upon the 51V nuclear spin quantum number M, and vary as A+BM+CM2. As the degree of molecular ordering increases, one predicts and observes that first C and then B change in sign.It was also found that almost perfect ordering of a solute in an imperfectly ordered liquid crystal can be achieved, provided the solute molecule is sufficiently large and rigidly planar. Implications of ESR observations concerning the structure of liquid‐crystal phases are discussed.

Optimization of annealing parameters for the growth of epitaxial Ba2YCu3O7-x films on LaAlO3 (100)

The superconducting and structural properties of Ba2YCu3O7−x (BYCO) films on LaAlO3(100) substrates can be improved by carefully optimizing the post‐deposition annealing parameters. Films are grown by co‐deposition of BaF2, Y, and Cu in the correct stoichiometric ratio to within 1% of 2:1:3. Annealing parameters in an ex situ furnace, including the ambient, annealing temperature, oxidation temperature, and duration of anneals are systematically studied. Films are characterized for epitaxial quality (χmin), morphology, critical temperature (Tc), sharpness of the superconducting transition (ΔT), and critical current density (Jc). For example, beyond simply dissociating BaF2, the use of wet O2 appears to prevent the agglomeration of oxides during the initial heating process, and then act to thermodynamically stabilize the basic BYCO film structure at high temperatures after being formed. Comparisons are made with the best single‐crystal BYCO structural and electrical data available. The optimized films have ...