Surface and interface study on MBE-grownNd1.85Ce0.15CuO4

Abstract

Nd 1.85 Ce 0.15 CuO 4 ͑NCCO͒ surfaces and metal ͑Au, Ag, and Pb͒/NCCO interfaces have been extensively investigated by x-ray and ultraviolet photoelectron spectroscopies using films grown by molecular beam epitaxy ͑MBE͒. The photoelectron spectra obtained in situ on the surfaces of MBE-grown NCCO films are free from any dirt peak and show a fine structure with a Fermi edge in the valence region. Experiments were performed on the prepared clean surfaces, focusing on the evolution of the surface or interface electronic structure with oxygen nonstoichiometry at the surface or interface regions. The results show ͑1͒ a systematic spectral change due to the oxygen content at the surface, and ͑2͒ a redox phenomena at the metal/NCCO interface. In oxygenated surfaces or insufficiently reduced surfaces, excess oxygens seem to occupy the interstitial ͑apical͒ oxygen sites, which compensates Ce doping, eventually leading to a nonmetallic surface. In excessively reduced surfaces, oxygen deficiencies seem to occur at regular oxygen sites, leading to a metallic but not a superconducting surface. The photoelectron spectroscopy data are discussed in comparison with complementary tunnel spectroscopy data. Both sets of data indicate that precise control of oxygen stoichiometry at NCCO surface is essential to obtain an intrinsic ͑i.e., superconducting͒ NCCO surface, which is indispensable in obtaining reliable data using surface sensitive experiments and in fabricating tunnel junctions and superlattices with desirable characteristics. ͓S0163-1829͑97͒01629-9͔

Core-hole screening response in two-dimensional cuprates: A high-resolution x-ray photoemission study

“…32 The O-1s spectrum of Nd 2 CuO 4 is depicted in Fig. 9 33 show a considerably larger FWHM of 3.39 eV ͑here 2.2 eV͒, results on polycrystalline samples are roughly in agreement with our results. 11,34,38 The intensity ratio between the satellite and main line for Nd 2 CuO 4 is also the smallest for all compounds studied here ͑see Table II͒.…”

Doping dependence of the gap anisotropy inLa2−xCexCuOPronin1, Pimenov2, Loidl3 et al. 2003Phys. Rev. BSelf Cite12140View full textAdd to dashboardCite

“…Similar studies are reported for Nd 2−x Ce x CuO 4 films in Ref. 23. The temperature dependence of dc resistivity of both films, as measured by the standard four probe method with evaporated Ag electrodes, is shown in Fig.…”

Origin of superconducting carriers in “non-doped” T′-(La,RE)2CuO4 (RE=Sm, Eu, Gd, Tb, Lu, and Y) prepared by molecular beam epitaxy

“…It should also be mentioned that although the partial oxygen pressure during "reduction" after the growth significantly affects the superconducting properties of the films, it affects the lattice constants very little, which we discuss elsewhere [11]. Figure 3 shows the variations of a 0 and c 0 in T'-La well known that, in T'-structure superconductors, the excess oxygen occupies apical sites and never leads to metallicity nor superconductivity [8,16,17]. With regard to the second possibility, the a 0 (x) curves of T'-La 2-x RE x CuO 4 as shown in Fig.…”