Abu Sayeed

An electrically conductive buffer architecture can enable defect-tolerant RE-Ba-Cu-O (REBCO) superconductor tapes by providing a current shunt path to the substrate. We are developing suitable electrically conductive buffers based on Titanium Nitride (TiN) grown on an ion beam-assisted deposition (IBAD) template on Hastelloy C276 substrate. The aim is to prevent the oxidation of TiN during metal-organic chemical vapor deposition (MOCVD) of REBCO. The buffer architecture was modified to render TiN more oxidation-resistant while maintaining good electrical conductivity. A strong biaxial texture was achieved and a low electrical resistivity of 43 µΩcm was measured with this modified buffer architecture. An oxide layer based on the SrTiO₃ (STO) cap layer was epitaxially grown using RF magnetron sputtering followed by REBCO film growth by MOCVD. By avoiding oxidation of the modified buffer architecture based on TiN, we achieved a strong epitaxy of REBCO with a sharp texture, without non-00L orientations. Scanning Hall Probe Microscopy (SHPM) data showed uniformly high critical current density throughout the entire REBCO tape.

Rare Earth Barium Copper Oxide (REBCO) superconducting thin films on dielectric substrates are being developed for microwave and radio frequency applications such as transmission lines for quantum computing. Our group previously demonstrated the growth of REBCO thin films on short, flexible, yttria-stabilized-zirconia (YSZ) substrates. In this study, we report high-quality REBCO films on 12-cm-long flexible YSZ substrates. We planarized the surface of 40-µm-thick flexible YSZ substrate by vertical dip coating in n-propanol solution to achieve average surface roughness R _a3 (LMO) cap layer. The out-of-plane and in-plane texture values of the LMO films were 3.9° and 6.9° respectively. REBCO films of a thickness of 350 nm were grown on these 12-cm-long flexible YSZ substrates by metal organic chemical vapor deposition (MOCVD) and a critical current density (J _c) of 1.06 MA/cm² was achieved at 77 K, 0 T. We are also developing an electrically conductive buffer architecture for defect-tolerant REBCO tapes, to shunt current from the REBCO film to substrate. This buffer architecture is based on conductive titanium nitride buffer on Hastelloy C276 substrate, with an oxide cap layer deposited by magnetron sputtering. REBCO films, about 350 nm thick, have been grown by MOCVD on this buffer architecture with a J _c greater than 1 MA/cm² at 77 K, self-field. Texture, microstructure, composition and critical current density of REBCO tapes on electrically conductive buffers will be presented.

This work presents the fabrication of Zn_1−xS:Sn_xthin films using the chemical bath deposition method and investigates the effects of Sn doping and annealing temperature on the structural, optical and electrical properties of ZnS thin films. The XRD patterns show that the relative intensities of the major diffraction peaks increase with Sn dopant incorporation and annealing temperature. Because high-temperature annealing forms several nucleation centers throughout the lattice and dopant incorporation enhances point defects leading to crystallite boundary mobility enhancement, crystallinity is also improved. UV–vis-NIR spectrophotometric studies revealed that the films have good transmittance that is larger than 75% in both visible and near-infrared regions and their optical bandgap ranges from 3.34 eV to 3.90 eV. Both the Sn content and annealing temperature cause the transmittance and the optical bandgap to rise. The absorption edge shifts towards the longer wavelength for higher Sn contents and annealing temperatures. Also, the decreased Urbach energy with increased Sn content or annealing temperature can be attributed to the reduced structural disorders and dislocations of ZnS crystals that are indicated by improved crystallinity. Electrical characterization by the two-point probe method exhibits that at higher annealing temperature grain boundary scattering limits the number of mobile carriers by increasing interatomic binding. On the other hand, due to increased carrier concentration and decreased dislocations resulting from the Sn content or annealing, localized carriers dominate in the bulk crystal state and require higher activation energy to replace an interstitial atom and excite the bulk states.