Preparation and characteristics of superconducting cuprate thin films: Nd(2-x)Ce(x)CuO4 and substituted Bi-system

Characteristics of the electron-doped-type Nd(2-x)Ce(x)CuO4 systems and substituted Bi2(Sr,Ln)3Cu2Oy system were systematically studied using the high quality thin-film samples. The Nd(2-x)Ce(x)CuO4 thin films with various Ce concentrations, x, were prepared by RF magnetron sputtering on SrTiO3 heated at around 500 C. After subsequent annealing at 1100 C in air, the films showed the c-axis orientation normal to the substrates. By means of the reducing treatment (annealing in a vacuum), superconductivity was induced for the films with 0.14 is less than or equal to x is less than or equal to 0.18. The superconductivity and transport properties of the films were strongly affected by the reducing treatment. The x = 0.15 film exhibited a sharp superconducting transition with zero resistivity at 22 K, in consistent with the diamagnetic properties. The resistivity of the films was fairly low with metallic characteristics, and the sight of the Hall coefficient was negative in the normal state. On the other hand, the normal-state optical measurements showed that the undoped Nd2CuO4 is a semiconductor with a charge transfer gap of 1.3 eV, and that, when Ce ions were doped, a plasma reflection due to the free-carriers came to be seen with the plasma frequency of 1.07 eV for 0.14 is less than or equal to x is less than or equal to 0.18. Moreover, x ray photoemission study revealed that the Cu valence of the film decreased for 2(+) for x = 0 to 1(+) for x = 0.15. These physical properties are in contrast with those of hole-doped-type cuprate superconductors. Bi2(Sr,Ln)3Cu2Oy thin films were also prepared on MgO substrates heated at 600 to 700 C by similar methods. It was found that the growth conditions for Bi-systems with two CuO2 planes were different for each composition and species of lanthanoid in the films. Moreover, preparation of Bi-system with three CuO2 planes was very difficult when lanthanoid atoms were doped in the system. Their electric transport properties and x ray photoemission spectroscopy were investigated. Carrier concentration and Cu valence were discussed with regard to the superconductivity

Preparation and characteristics of superconducting cuprate thin films: Nd(2-x)Ce(x)CuO4 and substrated Bi-system

Characteristics of the electron-doped-type Nd(sub 2-x)Ce(sub x)CuO4 system and substituted Bi-system were studied using the high quality thin film samples grown by rf magnetron sputtering and/or subsequent heat treatment. The Nd(sub 2-x)Ce(sub x)CuO4 samples with excellent superconducting properties were obtained in thin films and their optical and X-ray photoelectron spectroscopy (XPS) studies were performed with regard to the Ce content and reducing treatment. Substituted BiSr-Ln-Cu-O thin films were prepared and growth conditions for Bi-system with 2-2-1-2 and 2-2-2-2 phases were found. Moreover, a new 2-2-1-2 phase in the simple Bi-Sr-Cu-O system was fabricated by thin film processing and 80 K superconductivity was obtained

Synthesis and Crystal Structure of a Copper(II) Benzoate Complex Bearing a Bis-2,2′-Tetrahydrofuryl Peroxide Moiety

Complex [Cu2(ben)4·2THF−(η1–O2)]∞ (2) (ben=C6H5CO2− benzoate; THF=tetrahydrofuran) was isolated when a solution of Cu2(ben)4·2THF (1) in THF upon natural sunlight irradiation yields crystals suitable for single-crystal X-ray diffraction analysis. 2, crystallized in the C2/c monoclinic space group, Z=8, V=3394.2 (4) Å3, and the unit cell parameters a=9.7935(7) Å, b=19.0055 (13) Å, c=18.2997 (13) Å, α=90°, β=94.7996 (11)º and γ=90°. This is the first example of a polymeric copper(II) carboxylate compound stabilizing a peroxo group via its apical ligand (THF molecule). Additionally, 2 was also characterized by elemental analysis, Fourier-transformed infrared spectroscopy (FTIR) and Raman spectroscopyUniversidad de Costa Rica/[804-B7-279]/UCR/Costa RicaUniversidad de Costa Rica/[804-B0-650]/UCR/Costa RicaUCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de QuímicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Electroquímica y Energía Química (CELEQ

Superconductivity and Cu Valence of Bi-Sr-Ca-Cu-O Thin-films

Bi-Sr-Ca-Cu-O superconducting films were prepared by rf magnetron sputtering using a target with modulated composition and successive annealing in oxygen. The resistivity and Cu valence of the films varied before and after annealing. The zero-resistance temperature of the films was 10 K before the annealing, and rose up to 96 K (midpoint 105 K) after annealing. Essentially no change in the characteristic layer spacing (d value) of ≅ 18 Å, corresponding to c2, was observed before and after annealing as seen by x-ray diffraction. The Cu valence of the films was investigated by x-ray photoemission before and after annealing. The photoemission core-level spectra and LMM Auger emission spectra revealed that the Cu valence after annealing became larger than that obtained before annealing. The superconductivity obviously is correlated with the Cu valence of the films

Effect of Annealing in Oxygen on The Structure Formation of Bi-Sr-Ca-Cu-O Thin-films

The structure, bonding, and Tc of Bi-Sr-Ca-Cu-O superconducting films, prepared by rf magnetron sputtering, changed systematically upon varying the annealing conditions in oxygen. The spacing between the double Bi-O layers decreased from 22 to 18 Å and the degree of c-axis orientation became higher with the annealing. No change in the Bi core-level electron spectra with the annealing was observed. The Cu core-level electron spectra indicated an increase of the Cu valence with the annealing. The core-level electron spectra of Sr and Ca showed the possibilities of random distribution of the Ca and Sr atoms between the double Bi-O layers prior to annealing and exchanging their lattice sites in the Bi2Sr2Ca2Cu3Oy crystal structure after annealing. The zero-resistance temperature of the films was 10 K before annealing, and rose up to 96 K (midpoint 105 K) after annealing. The annealing favors both oxidation of Cu and ordering of Sr and Ca atoms within the unit cell of the 2:2:2:3 crystal structure

UV-Light Irradiation Effects on Oxide Superconducting Thin Films

Bi2Sr2CaCu2O(x) thin films prepared on (100) MgO substrates by rf magnetron sputtering were irradiated with ultra-violet (UV) light in He gas of about 500 Pa using a low pressure mercury lamp. The zero-resistance temperature and the critical current density were gradually decreased with irradiation time. X-ray photoemission spectra showed that the mean Cu valence of the film was decreased approximately from +2 to +1 by the irradiation while the valence of Bi ions was not changed. These imply that the UV light irradiation selectively reduces Cu ions and the superconductivity strongly depends on the Cu valence

X‐ray photoelectron spectroscopy of Nd2−xCexCuO4−y (x=0 and 0.15) thin films

Electronic structure of Nd2−xCexCuO4−y (x=0 and 0.15) thin films was examined by x-ray photoelectron spectroscopy. The films were prepared by rf magnetron sputtering and successive annealing under reducing condition (reduction). The reduced films showed semiconducting and superconducting behaviors depending on the value x. The Cu, O, and Nd core-level spectra revealed that the doped electrons were predominantly in CuO2 plane of the Nd2CuO4 crystal. The Cu core-level spectra from x=0.15 films before and after the reduction suggested that the reduction added electrons to Cu4s-O2p extended conduction band, and strengthened Cu O bond covalency to screen the core hole state by mobile itinerant electrons. Journal of Applied Physics is copyrighted by The American Institute of Physics