[en] X-ray photoelectron spectroscopy of the high-T/sub c/ superconductor YBa₂Cu₃O₇ is performed varying the temperature of the measurement (350, 230, and 180 K). The intensity of the O 1s peak corresponding to the Cu-O bond decreased with decreasing temperature. The intensity of the peak due to the electrons in the Cu 3d--O 2p antibonding orbitals with x²-y² symmetry measured at 180 K is much smaller than that measured at 350 K. The top of the valence-band spectrum shifted -0.5 eV at 180 K relative to that at 350 K. A decrease of the O atoms in the crystal at lower temperature is observed in this experiment

[en] 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

[en] Photoemission from a solid is evidently a many-body process since the motion of each electron cannot be independent of the motions of other electrons. In this article we review the reported many-body effects in X-ray photoemission such as extra-atomic relaxation energy, charge transfer satellite and energy loss structure which are informative in relation to the characteristics of solids. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

[en] The structure, bonding, and T/sub c/ 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 A 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 Bi₂Sr₂Ca₂Cu₃O/sub y/ 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

[en] 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 ≅18A, corresponding to c/2, was observed before and after the 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

[en] X-ray photoelectron spectroscopy was performed on high-T/sub c/ superconducting Bi-Sr-Ca-Cu-O single crystals with T/sub c/∼80 K. The core-level electron spectra of Sr, Ca and Bi show the possibility of exchanging their lattice sites in the crystal. On the other hand, the core-level electron spectrum of Cu indicates a unique lattice site in the crystal. These features are consistent with the structure model for the crystal with formula unit Bi₂(Sr,Ca)₃Cu₂O/sub y/. We can readily determine the distribution of Sr, Ca and Bi in the cation sites by x-ray photoelectron spectroscopy in contrast to x-ray diffraction and high-resolution transmission electron microscopy

[en] This paper reports on Bi₂Sr₂CaCu₂O_x thin films prepared on (100) MgO substrates by rf magnetron sputtering 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 form +2 to +1 by the irradiation while the valence of Bl ions was not changed. These imply that the UV light tradition selectively reduces Cu ions and the superconductivity strongly depends on the Cu valence

[en] We have implanted N⁺ ions at an accelerating voltage of 10 kV and a dose of 5x10¹⁷ ions cm^-2 in molecular beam deposited stoichiometric CuInSe₂ thin films at various substrate temperatures (380, 515, 600, and 720 K). The conduction type of the films changed from n to p type when the substrate temperature was below 515 K during implantation. The conduction type was n type when the film temperature during implantation was above 600 K. The resistivity measured at 300 K was 1.07x10⁴, 0.417, 0.653, 160, and 121 Ω cm for the films before implantation, implanted at 380, 515, 600, and 720 K, respectively. Both the conduction type and the resistivity of the films could be changed by N⁺ doping. Fabrication of homojunction diodes may be achieved in n-type CuInSe₂ films by using the low energy nitrogen ion implantation

[en] An x-ray photoemission experiment was performed on high-T/sub c/ superconducting Bi-Sr-Ca-Cu-O single crystals with T/sub c/∼80 K. It is found that Sr and Ca are interchangeable on the lattice sites of the crystal and they are electronically distinguishable. This is consistent with the structure model for the crystal with formula unit Bi₂(Sr,Ca)₃Cu₂O/sub y/. We demonstrate how the distribution of Sr and Ca in the cation sites is determined by x-ray photoemission, which cannot be done by x-ray diffraction

[en] Electronic structure of Nd_2-xCe_xCuO_4-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