Rong-ping Wang

Second-harmonic generation in BaTiO3 films doped with cerium

Second-harmonic generation of 1.064 μm incident light was measured on BaTiO3 thin films, both a-axis and c-axis oriented, undoped and doped with cerium, prepared by pulsed laser deposition. The dependence of second-harmonic generation (SHG) coefficients of these films on the incidence angle and the polarization direction of the fundamental beam were investigated. The effective SHG coefficients was enhanced greatly when the films were doped with cerium.

A new direct process to prepare YBa2Cu3O7−δ films on biaxially textured Ag{110}〈211〉

YBa2Cu3O7-delta (YBCO) films were successfully prepared on biaxially textured Ag(110)(211) substrates by using pulsed laser deposition. X-ray diffraction results showed that the degree of preferential orientation of Ag(110)(211) substrates varied with increasing annealing temperature. With a thin template layer deposited at low temperature, YBCO film with c-axis orientation and in-plane biaxial alignment could be obtained at high deposition temperature. Scanning electron microscopy observation revealed that YBCO grains enlarged, but Ag grains on the surface of the YBCO films became smaller with increasing deposition temperature. At optimal deposition: conditions, Ag atoms diffuse into the YBCO grain boundaries, and then fill in the weak-link regions in the YBCO film, resulting in the easier conduction. J(c) value of 5 x 10(5) A/cm(2) was obtained at 77 K and zero magnetic field for the best YBCO film in our work

Fabrication and characteristics of CeO2 films on Si(1 0 0) substrates by pulsed laser deposition

A detailed investigation about the dependence of film orientation on deposition temperature and ambient oxygen pressure has been carried out for CeO2 films on Si(1 0 0) substrates using pulsed laser deposition. It has been found that the CeO2 film orientation varies with increasing oxygen pressure at 750 degrees C deposition temperature. In addition, the recovery of preferential orientation of CeO2 films grown at 20 Pa ambient oxygen pressure with increasing deposition temperature has also been found for the first time. X-ray photoelectron spectroscopy (XPS) measurements confirm that stoichiometric CeO2 films can be grown at lower oxygen pressure(similar to 5 x 10(-3) Pa). HRTEM result also indicates that the CeO2 films grown at low oxygen pressure are of high crystallinity

Third-order optical nonlinear properties of amorphous Si/SiO2 superlattices fabricated by magnetron sputtering

Abstract The nonlinear optical response of amorphous Si/SiO2 superlattices fabricated by magnetron sputtering are studied using the Z-scan technique. The real and imaginary parts of the third-order optical nonlinearity χ(3) have been measured at 532 nm and found to be 6.392×10−7 esu and −9.814×10−7 esu, respectively. The results indicate an enhancement over crystalline silicon and porous silicon, which may be attractive for potential application in electro-optic devices.

Structural characteristics of CeO2 films grown on biaxially textured nickel (001)

Preferential (001) orientation CeO2 films have been successfully grown on biaxially textured Ni substrates using ion beam assisted pulsed laser deposition. The x-ray diffraction (XRD) patterns for the CeO2 films and target have been measured. The in-plane lattice constants have been derived from the data of XRD. It was found that the in-plane lattice constants of the films increase with increasing deposition temperature. A reasonable explanation based on the difference of the linear thermal expansion coefficient between the CeO2 film and Ni substrate was proposed. Moreover, Raman spectra of the films and target have been recorded. It was shown that the oxygen deficiency in the CeO2 samples has a great effect on the full width at half maximum of the Raman lines. According to the relation between the Gruneisen shift and the lattice contraction, we have obtained the theoretical Raman shifts which are in good agreement with the experimental results.

Self-oxidized NiO on cube-textured Ni for YBCO coated superconductor

Abstract In this paper, we report a self-oxidation approach to obtain NiO on the surface of Ni substrates. Under optimal oxidizing conditions, high-textured NiO layers on the surface of Ni substrates were obtained. Detailed pole figure (PF) measurements show an improvement in the full width at half maximum of NiO layers compared with that of Ni substrate. Orientation distribution function calculated from two PFs shows that the best cubic texture of NiO can be formed at 680°C in 5 Pa oxygen. A grain size less than 1 μm is evident from scanning electron microscopy observation. Some possible ways were proposed to improve surface quality. The self-oxidation approach provides a potential to prepare high-Jc YBCO films on a large scale.

Stress reduction by ion bombardment in CeO2 films

We have investigated the influence of deposition parameters on film stress in CeO2 films grown on biaxially textured nickel (001) substrates using pulsed-laser deposition. The film stress is thought to consist of thermal stress and intrinsic stress. The thermal stress has been calculated at different deposition temperatures. The results reveal that the thermal stress is compressive with MPa order of magnitude and increases with increasing deposition temperature. The intrinsic stress has also been measured by standard X-ray diffraction technique. it has been found that the intrinsic stress is tensile with GPa order of magnitude, and decreases with increasing deposition temperature regardless of whether the films are deposited with ion bombardment or not. Moreover, this is the first time a quantitative confirmation of stress reduction with ion bombardment has been provided. Some possible origins of the influence of deposition parameters on film stress are discussed

High quality YBCO superconductive thin films fabricated by laser molecular beam epitaxy

High quality YBa2.Cu3O6 +x(YBCO) superconductive thin films have been fabricated on the SrTiO3(100) substrate using laser molecular beam epitaxy (laser-MBE). The active oxygen source was used, which made the necessary ambient oxygen pressure be 2–3 orders lower than that in pulsed laser deposition (PLD). Tc0 is 85–87 K, and Jc, 1.0 × 106 A/cm2. Atomic force microscopy (AFM) measurements show that no obvious particulates can be observed and the root mean square roughness is 7.8 nm. High stability DC superconducting quantum interference devices (DC-SQUID) was fabricated using this YBCO thin film.

Fabrication and character of reproducible high quality steps and step-edge junctions on STO substrates

Abstract We report a reproducible procedure to fabricate high quality steps and step-edge junctions on SrTiO3(STO) substrate. The dynamic process of Ion Milling(IM) was simulated in theory, there exists a maximum slope angle for the steps prepared from ion milling. For 500eV Ar+ bombarding STO system, the angle is about 73°. High quality steps can be acquired with new technique procedure. Voltage modulation is about 10μV for a typical DC-SQUIDs fabricated on this type of substrate.

Tunneling studies of Nb/Al superconducting proximity-effect bilayers

Abstract Nb / Al AlO x Ti tunneling junctions with fixed Nb and Ti thicknesses of 200 nm and Al thickness ranging from 10 to 70 nm were fabricated. Preliminary results on the measurements of I – V characteristics at T = 1.3 K are reported, and are compared with a proximity-effect model recently proposed by Golubov et al. .