Nobue Tanaka

Improvement of YBa2Cu3Ox Single-Crystal Surface by Chemical Etching

The single-crystal YBa2Cu3Ox (YBCO) surface presents precipitates that aggregate to form a very thin damaged layer on the surface after mechanical polishing and thermal annealing. The damaged layer was removed by dipping it into a chemical etchant, HCl/methanol. After applying the etching process, YBCO(001) surfaces exhibited a well-defined step-and-terrace feature with unit-cell step height. No precipitates were observed from the etched substrates after annealing. Homoepitaxial films on etched substrates grew with unit-cell-high steps and step-edge facets, while those on as-polished substrates exhibited a grain structure with rough edges.

Evaluation of a new Ba precursor, Ba(DPM)2-2tetraen, for MOCVD of oxide superconductors

Abstract Metalorganic sources of Ba are very important in preparing perovskite thin films by metalorganic chemical vapor deposition (MOCVD). We evaluated a new Ba precursor, Ba(DPM) 2 -2tetraen. It has a much higher volatility than conventional Ba(DPM) 2 . The supply rate of Ba can be kept constant for 130 h, by optimizing the MOCVD conditions. Using this precursor, high-quality YBa 2 Cu 3 O x thin films were grown , with T c >80 K, good crystallinity (Rutherford backscattering spectroscopy, χ min =2.6%) and good surface morphology with no precipitates.

X-Ray Photoemission Spectroscopy Study for the Flat YBa2Cu3Oy Single-Crystal Surface Prepared by Chemical Etching and O2 Annealing

The effect of chemical etching with a HCl/methanol solution on a polished sample of single-crystal YBa2Cu3Oy (001) was investigated by emission-angle-dependent X-ray photoemission spectroscopy (XPS). By chemical etching, the extrinsic Ba state in the surface region was removed without the effect of halogen. The bulk state of Y was also restored in the surface by subsequent annealing in an oxygen atmosphere at 400°C.

Effects of Chemically Etched YBa 2 Cu 3 O x Surface on Homoepitaxial Growth

We prepared homoepitaxial films on chemically etched (001)YBa2Cu3Ox (YBCO) single-crystal substrates, examining the effect of etching applied to their surfaces. It was difficult to grow high-quality YBCO films on deeply etched YBCO substrates, because no epitaxial layer grew laterally on these substrates. By depositing one molecular layer of Cu oxide on the etched surface, the homoepitaxial films showed good crystallinity of χmin = 4.3% and surface morphology with {100} facets.

Substrate Etching for Homoepitaxial NdBa 2 Cu 3 O 7-δ Film Deposition

NdBa2Cu3O7-δ (001) substrate was etched with 0.003 wt% HCl-methanol for homoepitaxial film fabrication by metalorganic chemical vapor deposition (MOCVD). The etched substrate was examined to be thermodynamically stable on our deposition conditions. The homoepitaxial film prepared on the etched substrate showed various surface morphologies according to the substrate etching time. Etching back the homoepitaxial films revealed that defect on the substrate surface is a major cause to call the film growth mode.

Surface Treatments and Stability of YBa2Cu3Ox Single-Crystal Substrates for Homoepitaxial Growth

We observed degradation on mechanically-polished single-crystal YBa2Cu3Ox(001) substrates after an annealing by atomic force microscope. We have removed the degraded layer by using a chemical wet etchant; 0.01wt%HCl-methanol solution. As the substrates immersed in this solution during 10–60sec, the post-annealed surface morphology was improved. We have completed the surface stability diagram in temperatures vs oxygen pressures.