Tadao Miura

Electric properties of the YBa2Cu3O7−δ/Au interface

The electric properties of YBa/sub 2/Cu/sub 3/O/sub 7/..sqrt../sub delta/Au interfaces were investigated. An electric contact better than 10/sup 8/ ..cap omega../sup -1/cm/sup 2/ was obtained at 4.2 K for the interface. There existed, however, a normal layer between the superconducting bulk and the gold electrode, preventing the observation of the proximity effect and the quasiparticle tunneling for this materialThe electric properties of YBa2Cu3O7−δ/Au interfaces were investigated. An electric contact better than 108u2009Ω−1/cm2 was obtained at 4.2 K for the interface. There existed, however, a normal layer between the superconducting bulk and the gold electrode, preventing the observation of the proximity effect and the quasiparticle tunneling for this material.

A high-resolution electron microscopy study on epitaxial infinite- layer SrCuO2 thin films grown on a SrTiO3 (100) substrate

Abstract The authors investigated defect structures introduced into so-called infinite-layer SrCuO 2 thin films sputtered on a SrTiO 3 (100) substrate. By means of both cross-sectional and plan-view high-resolution electron microscopy (HREM), it has been revealed that the films were epitaxially grown with their c -axis normal to the substrate surface, and several types of defect structures have been estimated. They were essentially composed of double Sr-O planes that make {100} atomic walls. It is remarkable that such walls tended to arrange as loop-like configurations, and also could produce a different ordered structure, i.e., a Sr 2 CuO 3 -like structure in local regions. The authors propose defect structural models in the epitaxial infinite-layer SrCuO 2 thin films in detail.

Growth mechanism for (11n) orientations in Bi-Sr-Ca-Cu-O thin films

Abstract We have investigated the film growth mechanism for Bi-Sr-Ca-Cu-O (BSCCO). Effects of initial film growth stage and of substrate have been examined. Results show that (001) orientation is based on anisotropic growth kinetics for the crystal and that (11 n ) orientations are based on epitaxy between the perovskite layer in the crystal structure and a substrate, such as (110)SrTiO 3 and (110)LaAlO 3 . The epitaxy is based on a part of the crystal structure. Furthermore, (119) orientation is formed when the epitaxy is mainly influenced; (117) orientation is formed when the epitaxy and crystal structural stability have equal influence.

Defect structure study of YBa2Cu3O7−x epitaxial thin films on SrTiO3(100) and (110) substrates

Abstract The authors investigated the micro-defect structures in YBa 2 Cu 3 O 7− x (YBCO) superconducting thin films sputtered on SrTiO 3 (100) and SrTiO 3 (110) substrates without post-deposition annealing. HREM observations and RHEED studies were performed. Near the surface regions of YBCO films on SrTiO 3 (100) were oriented mainly with the a axis normal to the substrate, and the film showed many {103} domain boundaries with a zigzag trace. On the other hand, the YBCO films on SrTiO 3 (100 ) were oriented with the [110] axis normal to the substrate, and the films often showed out-of-phase boundaries along the c direction. These out-of-phase boundaries can be originated by the introduction of misfit dislocations with extra planes in the substrate crystal. The localization defect structures in YBCO thin films are proposed.

An electron microscopic study on the incipient crystal growth of Bi-Sr-Ca-Cu-O superconducting thin films on a MgO(001) substrate

Abstract Several types of growth modes of superconducting Biue5f8Srue5f8Caue5f8Cuue5f8O thin films on a MgO(001) single crystal substrate have been clarified by means of electron diffraction and moire imaging techniques. Both Bi 2 Sr 2 CaCu 2 O x (2212-phase) and Bi 2 Sr 2 Ca 2 Cu 3 O y (2223-phase) were investigated, and all of them had “ c -axis up” microstructures. It is remarkable that the films contain many grains rotated about the c -axis, and the authors have revealed that such rotations tend to appear with low-angle tilt boundaries near the growth modes of [100] substrate //[100] film and [100] substrate //[110] film . It is also an interesting phenomenon that the [230] substrate //110] film growth mode was frequently observed in the films presently examined, and this mode is considered to have a favorable lattice coincidence between the film and substrate. A possibility of the formation of special grain boundaries connected with the coincidence site lattice theory (CSL theory) is also discussed. The determination of the above-mentioned several types of growth mode can be achieved using transmission electron microscopy (TEM), and the authors note that the moire patterns are very useful in measuring the rotation angle between the film and substrate precisely for individual small-size domains.

Molecular beam epitaxial growth of superconducting Pb2Sr2Dy1−χCaχCu3O8+δ thin films Disordered surface layer during Pb deposition

Abstract Superconducting Pb 2 Sr 2 RE 1−χ Ca χ Cu 3 O 8-δ (RE=Dy, Eu) films have been grown by sequential deposition using the molecular beam epitaxy (MBE) technique. The growth mechanism of these films has been studied by in situ reflection high-energy electron diffraction (RHEED). Over the growth period, the intensity of the streak pattern decreases during Pb deposition and then recovers during the deposition of other elements. At an early stage of Pb deposition during initial growth, a RHEED pattern with no sign of surface diffraction rods appears, suggesting that a liquid-like layer of Pb oxide wets the growing surface. After the liquid-like layer was re-evaporated during an intermission, the surface lattice order of flatness of the perovskite structure seemed to be improved. The origin of RHEED intensity oscillations is discussed and a comparison with the case of Bi 2 Sr 2 CaCu 2 O 8+δ is made.

Hot-electron transport through Au/CaF2/Si(111) structure studied by ballistic electron emission spectroscopy

The influence of calcium fluoride (CaF2) [about two monolayers (ML)] in Au/CaF2/Si(111) heterostructure on hot-electron transport across the CaF2 intralayers has been studied using ballistic electron emission microscopy (BEEM) and Fourier transform infrared spectroscopy (FTIR). The BEEM current–voltage spectra show that the electron transport property is strongly affected by the CaF2 intralayers. The threshold voltage V0 for the onset of the BEEM current for an insulating CaF2 intralayer, which is about 3.6 V, is obtained only for the sample in which CaF2 was deposited at 700u2009°C. In contrast, the threshold voltage of the sample in which CaF2 was deposited at 550u2009°C is determined to be about 0.74 V. The FTIR spectra of these CaF2 layers show that Ca–Si–F bonds exist in the latter, but not in the former. The existence of Ca–Si–F bonds implies that the CaF2 heteroepitaxial growth at 550u2009°C is unsuccessful in obtaining a high-quality CaF2 layer and will induce many defects in the CaF2 layer and/or at the inte...

Initial growth mechanism of BiSrCaCuO thin films on SrTiO3(110) surfaces studied by in-situ reflection high energy electron diffraction observation

Abstract The initial growth mechanism of Bi 2 Sr 2 Ca n −1 Cu n O x (BSCCO) films was investigated on SrTiO 3 (110) surfaces by in-situ reflection high energy electron diffraction (RHEED) observation. The orientations in the BSCCO thin films were controlled by the flux of metal elements in the initial growth stage. A preceding deposition of Bi produced a RHEED pattern indicating the formation of a bismuth oxide layer which assisted the growth of a half-unit cell at the beginning of codeposition. A ( Bi : Sr : Ca : Cu =) 2:2:1:2 phase (117) orientation mixed with a c axis orientation was obtained. A preceding deposition of Sr, Ca and Cu produced a pattern indicating the formation of (Sr 1− x Ca x ) 2 CuO 3 and caused epitaxial growth just after the start of codeposition, based on the structural relationship between the substrate and the perovskite structure part of the films. A 2:2:1:2 phase (119) orientation was formed.

MBE growth of a Pb2Sr2RE1−xCaxCu3O8+δ superconductor: disordered surface layer during Pb deposition and the recovery of the surface lattice order

Abstract Superconducting Pb 2 Sr 2 RE 1−x Ca x Cu 3 O 8+δ ( RE = Dy , Eu ) films have been grown by sequential deposition using the molecular beam epitaxy (MBE) technique and the growth mechanism has been studied by in-situ reflection high-energy electron diffraction (RHEED). A RHEED pattern with no sign of surface diffraction rods appears during Pb-deposition in the initial growth stage, suggesting that a liquid-like layer of Pb oxide wets the growing surface. The observed regular oscillations in RHEED intensity may be due to the existence of a disordered surface layer during Pb-deposition and the subsequent recovery of surface lattice order during the deposition of othe elements.

A structural study on the crystal regularity of YBa2Cu3O7-x thin films composed of several types of oriented domains

Abstract The authors have investigated the of superconducting YBa 2 Cu 3 O 7- x (YBCO) thin films grown on SrTiO 3 (100) and (110) single crystal substrates without postdeposition annealing. These films consist of several peculiarly oriented domains. The microstructural difference of each oriented domain has been investigated by means of cross-sectional and plan-view high resolution transmission electron microscopy from the viewpoint of crystal regularity. The microscopic defect structure and its density in each domain were estimated.