Marcus Kuhn

Large area pulsed laser deposition of YBCO thin films

A special PLD-setup for large area deposition of homogeneous YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films and buffer layers as large as 7 cm/spl times/20 cm is presented. A new concept for homogeneous large area substrate heating and the influence of the deposition rate on the film properties is discussed. YBCO is deposited on r-plane sapphire substrates (10 cm/spl times/10 cm) as well as on smaller (2 inch O, 1 cm/spl times/1 cm) SrTiO/sub 3/, MgO, LaAlO/sub 3/, and on yttria stabilized ZrO/sub 2/ substrates distributed over the deposition area. The homogeneity of the deposited YBCO films concerning structural and electrical properties is investigated by XRD, RBS/channeling, and spatially resolved inductive measurements of T/sub c/ and J/sub c/. The variation of J/sub c/ on a 2 inch MgO wafer is less than /spl plusmn/9%, the mean c-axis length is 11.681 /spl Aring/, the FWHMs of the [005] rocking curves are 0.40 and the channeling minimum yield /spl chi//sub min/ varies between 3.7% and 4.9% over the 2 inch wafer. The J/sub c/ values of YBCO on 7 cm x 20 cm in situ buffered sapphire substrates are (2.0/spl plusmn/0.4 MA/cm/sup 2/) at T=77 K and B=0 T.

Patterning of YBCO thin films by ion implantation and magneto-optical investigations

Abstract YBa 2 Cu 3 O 7− δ thin films deposited by pulsed laser deposition were patterned by ion implantation. The patterning technique is based on the local disordering of the crystal structure due to elastic collisions of the implanted O + -ions and thus on a strong breakdown of superconductivity in the irradiated areas. With this patterning method circular and meandering structures with a size of 1 mm were prepared for investigations regarding high current applications. O + -ions with an energy of 180 keV were used to avoid a contamination of the film. The achieved structures were investigated concerning a dependence on the dose by means of RBS, XRD, AFM and magneto-optical characterization. Using a fluence of 5×10 14 O + /cm 2 a fully planar and stable structure can be obtained. The patterning depth can be adjusted by varying the implantation energy. So this technique was also used successfully on YBCO thin films covered already with a 200 nm Au top layer.

Pulsed laser deposition of YBCO thin films on 7×20-cm2 substrates

Abstract A specially designed and patented setup has been built up for Pulsed Laser Deposition (PLD) of homogeneous YBa 2 Cu 3 O 7− x (YBCO)-films on substrates as large as 7×20 cm 2 . YBCO films have been deposited on small substrates (SrTiO 3 , LaAlO 3 and buffered polycrystalline YSZ). Their structural and superconducting properties have been measured. The mean values of the transition temperatures and the critical current densities at T =77 K and zero magnetic field on single crystal substrates are 90 K and 4.3 MA/cm 2 , respectively. The YBCO films on buffered polycrystalline YSZ substrates reach critical current densities up to 1.1 MA/cm 2 at T =77 K and B =0 T.

Large area magneto-optical investigations of YBCO thin films

A new apparatus for magneto-optical investigations of high temperature superconducting (HTS) films as large as 20×20 cm2 is presented. With this equipment flux penetration of an external magnetic field into YBCO thin films has been studied by scanning the samples through an inhomogeneous magnetic field (magneto-optical scanning technique, MOST). The normal penetration of magnetic flux into a superconductor will be changed drastically in the presence of defects. The apparatus was constructed to realize an effective quality control of large area HTS thin films used for device fabrication. With this technique, a visualization of flux pattern in superconducting films larger than 1×1 cm2 is presented for the first time. The results are compared to inductive jc measurements as well as to micrographs [optical microscope (OM), scanning electron microscopy (SEM)] and show that also in the large area characterization the magneto-optical method is very sensitive to microstructural defects impairing the critical curr...

Large area deposition of YBa2Cu3O7−x films by pulsed laser ablation

A special patented design is built up to produce homogeneous YBa2Cu3O7−x (YBCO) films by pulsed laser deposition (PLD) over areas as large as 7×20 cm2. The use of a line focus (8 cm) reduces the substrate movement to one dimension. The demands on plasma homogenization, substrate scanning and film temperature during the deposition process for large area PLD are discussed and their technical realization is presented. First results of 1×1 cm2 YBCO films at different positions on the substrate holder (11×28 cm2) show homogeneous deposition conditions. The transition temperatures of the deposited YBCO thin films on 1×1 cm2 SrTiO3 substrates are TC=89 K with critical currents of 4×106 A/cm2 at T=77 K. The structural properties of these films (χmin=4.5%) indicate also their high crystalline quality. The variation of film thickness perpendicular to the scanning direction is less than ±9% and along the scanning direction ±7%.

Defect visualization in large area YBCO thin films by magneto-optical scanning technique

Flux penetration in large area YBCO thin films has been studied by a magneto-optical scanning technique. With a new apparatus HTS films as large as 20 cm/spl times/20 cm can be investigated by scanning the films through an inhomogeneous magnetic field. The apparatus has been built to realize an effective homogeneity control of the electrical properties of large area HTS thin films used for device fabrication. Magnetic flux penetration into YBCO thin films of different sizes and with intrinsic defects as well as artificial ones have been studied at 50 K. Magneto-optical measurements are compared with optical microscopy (OM) and inductive j/sub c/-characterizations. A correlation between the kind of defect and its influence on the electrical properties has been studied with regard to device applications, YBCO films structured especially for high current applications were investigated magneto-optically. These results will be compared to optical photographs of the quenching process caused by currents I>I/sub c/.

Characterization of Plasma Immersion Deposited Multilayer Coatings by Ion Beam Techniques Combined with Energy Filtered Transmission Electron Microscopy

Multilayered and nanostructured coatings of amorphous carbon (DLC), silicon composite multilayers and nanocluster containing films today have great potential for applications as hard coatings, wear reduction layers and as diffusion barriers in biomaterials. Plasma immersion ion implantation and deposition (PIII&D) is a powerful technique to synthesize such films. The quantitative nanoscale analysis of the elemental distribution in such multielemental films and thin film stacks however is demanding. In this paper it is shown how the high spatial resolution capabilities of energy filtered trans-mission electron microscopy (EFTEM) chemical analysis can be combined with accurate and standard-less concentration determination of ion beam analysis (IBA) techniques like Rutherford Backscattering Spectroscopy (RBS) and Elastic Recoil Detection Analysis (ERDA) to achieve absolute and accurate multielement concentration profiles in complicated nanomaterials.

Magnetooptical investigations of large transport currents in Y-Ba-Cu-O-thin films

Inhomogeneities in large area YBCO-thin films can be studied in external magnetic fields with a specially designed magnetooptical apparatus. Moreover, an investigation of transport current induced magnetic fields in patterned HTS-thin films is possible as well. In the present work we studied the flux penetration of the current induced fields into YBCO-bridges of 8/spl times/0.7 cm/sup 2/ dimensions as a function of the applied currents at 77 K. For the first time transport currents up to I/sub tr//spl sim/60 A could be investigated magnetooptically in HTS-thin films. Flux penetration starts just above a threshold value of the applied current I/sub tr//I/sub c//spl ges/0.3. The influence of the bridge geometry and of inhomogeneities on flux penetration has been investigated. Flux and therefore current distributions change drastically with increasing bend-angle of the YBCO-path. A magnetic interaction between adjacent bridges with parallel and antiparallel current directions as well as a thermal interaction could be observed.