Pulsed laser deposition of REBCO

Pulsed laser deposition is used as a standard technique to prepare superconducting YBCO layers on single crystals as well as on different buffer architectures. The YBCO deposition is typically carried out in a high vacuum chamber using a KrF excimer laser and a background pressure of about 0.3 mbar oxygen. After deposition, the samples are cooled in 0.4 bar O₂. The standard thickness of the YBCO layer is about 300 nm for all samples. Beside the standard on-axis geometry, also off-axis PLD is used to prepare smooth films on single crystalline substrates.

The preferred orientations and the texture of the prepared samples are investigated using X-ray diffraction.The resulting pole figure of the YBCO film shows a clear cube texture with similar out-of-plane and an in-plane FWHM values as the underlying buffer (Fig.1). Additionally, optical microscopy, scanning electron microscopy and atomic force microscopy is used to investigate the surface topography and to measure the local roughness. The surface structure of the YBCO layer, as determined by SEM, shows a homogeneous structure with typical pinholes (Fig. 2). The quality of the deposited YBCO layers is routinaly determined with inductive measurements of the critical temperature T_c and the critical current density J_c. The local distribution of the inductive J_c values over the sample size is  measured using the Cryoscan^TM by THEVA. Furthermore, the critical temperature and the critical current density are measured resistively in various magnetic fields up to 9 T with a Quantum Design PPMS system by a standard four-probe method on a bridge of 500 mm (for RABiTs tapes) or 50 µm (for single crystals) width, patterned by photolithography. The magnetic field is directed parallel to c-axis and normal to current direction. An electric field criterion of E_c = 1 µV/cm is used for the determination of the critical current density. A typical example is shown in Fig. 3.

Fig. 1	Fig. 2	Fig. 3

Fig. 1: YBCO pole figures of grown on a SrTiO₃ / BaZrO₃ / NiO / Ni-Ag architecture

Fig. 2: SEM-images of a typical YBCO layer grown on a NiO/Ni-Ag substrate using a SrTiO₃/BaZrO₃ buffer layer architecture

Fig. 3: Magnetic field dependence of the critical current density for YBCO films grown on different substrates using a SrTiO₃/BaZrO₃ buffer layer architecture

recent publications

Hühne, R., Selbmann, D., Eickemeyer, J., Hänisch, J., Holzapfel, B.: „Preparation of buffer layer architectures for YBa₂Cu₃O_7-x coated conductors based on surface oxidized Ni tapes”, Supercond. Sci. Technol. 19 (2006) 169-174 abstract

Fernandez, L.,  Holzapfel,B., Schindler, F., de Boer, B.,  Attenberger, A., Hänisch, J., Schultz, L.: „Influence of the grain boundary network on the critical current of YBa₂Cu₃O₇ films grown on biaxially textured metallic substrates”, Physical Review B 67 (2003) 52503/1-4

Fernandez, L., Holzapfel, B.,  Schindler, F.,  de Boer, B., Schultz, L.: „Grain boundary network transport properties of YBa₂Cu₃O₇ film on biaxially textured metal substrates”, Physica C 372-376 (2002) 656-658