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Investigates the synthesis of high-temperature superconducting oxides using solution chemistry. Comparison of the physical properties of the superconducting oxides to ceramics; Superconducting properties of ceramics.

Focuses on coherent multilayers of interheavy rare-earth metals that were synthesized by sputtering. Preparation of the multilayers; Instrument used to measure the magnetization.

Describes Raman scattering as a contactless room-temperature test of the quality of YBa[sub2]Cu[sub3]O[sub7-x] thin films. Sensitivity of Raman spectra to both the stoichiometry and the transition from semiconducting to the superconducting state as a function of oxygen annealing; Resistivity measurements for two coevaporated films after oxygen annealing; Details of two types of processing failures involving the lack of sufficient oxygen and incorrect stoichiometry.

The design and realization of a cryogenic rig for point-contact spectroscopy measurements in the needle-anvil configuration is presented. Thanks to the use of two piezoelectric nano-positioners, the tip can move along the vertical (z) and horizontal (x) direction and thus the rig is suitable to probe different regions of a sample in situ. Moreover, it can also form double point-contacts on different facets of a single crystal for achieving, e.g., an interferometer configuration for phase-sensitive measurements. For the later purpose, the sample holder can also host a Helmholtz coil for applying a small transverse magnetic field to the junction. A semi-rigid coaxial cable can be easily added for studying the behavior of Josephson junctions under microwave irradiation. The rig can be detached from the probe and thus used with different cryostats. The performance of this new probe has been tested in a Quantum Design PPMS system by conducting point-contact Andreev reflection measurements on Nb thin films over large areas as a function of temperature and magnetic field. [ABSTRACT FROM AUTHOR]

For a successful point-contact spectroscopy (PCS) measurement, metallic tips of proper shape and smoothness are essential to ensure the ballistic nature of a point-contact junction. Until recently, the fabrication of Au tips suitable for use in point-contact spectroscopy has remained more of an art involving a trial and error method rather than an automated scientific process. To address these issues, we have developed a technique with which one can prepare high quality Au tips reproducibly and systematically. It involves an electronic control of the driving voltages used for an electrochemical etching of a gold wire in a HCl-glycerol mixture or a HCl solution. We find that a stopping current, below which the circuit is set to shut off, is a single very important parameter to produce an Au tip of desired shape. We present detailed descriptions for a two-step etching process for Au tips and also test results from PCS measurements using them. [ABSTRACT FROM AUTHOR]

A technique for point-contact spectroscopy, based on an electromechanical mechanism for the contact formation, has been developed. It is designed to be used in both 4He and 3He cryostats. The performance has been demonstrated by conductance measurements on various kinds of superconductors, including the conventional superconductor Nb, the two-band superconductor MgB2, and the heavy-fermion superconductor CeCoIn5. Characteristic conductance spectra obtained prove that this technique is useful for the investigation of the superconducting order parameter. Advantages of this technique such as its simplicity and versatility are described. [ABSTRACT FROM AUTHOR]

We report on the design and implementation of an instrument for spectroscopic studies of materials at sub-terahertz (THz) frequencies at temperatures down to 340 mK. We achieved consistent operation under these rather extreme conditions by coupling a modified Martin–Puplett interferometer to a single cryogenic unit housing two independently controlled He-3 platforms: one as a sample stage and the other for bolometric detectors. Both the optical scheme of the interferometer and detector layout are tailored for the use of the two-channel data acquisition mode which is especially advantageous for measurement of absolute values of reflectance as well as for high-resolution spectroscopy. We document the reliable performance of the sub-THz apparatus with several experiments exploring electrodynamics of both conventional and high-T[sub c] superconductors. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Surface chemical modification is used to eliminate the problem of high surface recombination velocity and control surface band bending on InAs(100). Alkanethiols, RSH; R=CH3(CH2)n , both neat and in ethanolic solutions, are used to passivate this surface against oxidation, as characterized by Raman scattering and x-ray photoelectron spectroscopy of the adsorbate-covered and bare surfaces. The magnitude of the interfacial band bending is obtained by analysis of Raman scattering from the unscreened longitudinal optical phonon, which arises from the near-surface charge accumulation region. Removing the native oxide with a Br2:CH3OH chemomechanical etch reduces the surface band bending, but atmospheric oxidation increases band bending to its original level over several hours. In contrast, alkanethiol passivation of InAs(100) prevents band bending for periods of up to several weeks. [ABSTRACT FROM AUTHOR]

Studies the influence of target-substrate angle on the elemental concentration of thin films. Indications of the thermalization processes in sputtering; Common materials characterization techniques of scanning electron microscopy, x-ray diffraction, transport measurements and conventional Rutherford backscattering spectrometry.

We have investigated the effect of the post-deposition processing ambient on the preparation of YBa2Cu3O7-x thin films from a BaF2 source. The role of H2O vapor during the high-temperature anneal is understood through a thermodynamic analysis of the fluorine removal reaction. The role of a HF getter (e.g., SiO2) is understood through the same type of analysis. We have demonstrated that a zero resistance transition temperature at 77 K can be obtained for an annealing temperature as low as 690 °C for films deposited on SrTiO3 substrates by increasing the PH2O and decreasing PHF during the high-temperature soak cycle. [ABSTRACT FROM AUTHOR]

To determine intrinsic properties of the newly discovered Bi-Ca-Sr-Cu-O high Tc superconductors, single crystals are necessary. Compositions in this system have been heat treated to survey the melting temperatures and phase field in which superconductivity is detected. The nucleation and growth of the 85 K phase from the melted composition Bi4Ca3Sr3Cu4O16+x is observed to be a kinetically slow process which can be precluded by a sufficiently rapid quench, but post-anneals produce the 85 and 110 K phases in the quenched material. The melted composition (23% Bi2O3-46% CaO,SrO-31% CuO), after subsequent slow cooling, results in large discrete crystals of the 85 K superconducting phase and a residual flux. [ABSTRACT FROM AUTHOR]

A near room-temperature plasma oxidation process is shown to restore superconductivity and metalliclike behavior in oxygen deficient La2-x Srx CuO4-y and YBa2Cu3O7-x compounds. In the YBa2Cu3O7-x compound the conversion from an oxygen deficient n-type tetragonal to the p-type orthorhombic phase with a concomitant factor of 5×105 increase in room-temperature conductivity is also accomplished. This process is of technological importance because oxygen can be restored in these materials at temperatures compatible with device processing. Of scientific interest, the process allows us to carefully control the oxidation state and thereby systematically study the 90 and 55 K superconducting transitions in YBa2Cu3O7-x. [ABSTRACT FROM AUTHOR]

Strained layer superlattice structures with ultrathin, alternating InAs and GaAs layers have been grown on buffer layers lattice matched to InP. Low angle x-ray scattering and transmission electron microscopy studies were used to characterize the layers. [ABSTRACT FROM AUTHOR]