Bin Han

Metal‐organic chemical vapor deposition/open flow thallium annealing route to epitaxial Tl2Ba2Ca2Cu3O10 thin films

Phase‐pure epitaxial Tl2Ba2Ca2Cu3O10 thin films have been grown on single crystal (110) LaAlO3 substrates using an improved metal‐organic chemical vapor deposition process. First, Ba‐Ca‐Cu‐Ox precursor films are grown on LaAlO3 (110) substrates using Ba(hfa)2⋅tet, Ca(hfa)2⋅tet, and Cu(hfa)2 (hfa=hexafluoroacetylacetonate; tet=tetraglyme) as volatile metalorganic precursors. Thallium is then incorporated into the films during a post‐anneal in the presence of a Tl2O3, BaO, CaO, CuO powder mixture at 820 °C for 12 h in a flowing 10% O2/Ar atmosphere. The films have a transport‐measured Tc=115 K and Jc=1.5×105 A/cm2 (80 K), while magnetic hysteresis measurements yield Jc=6×105 A/cm2 (77 K). Preliminary surface resistance measurements give Rs=0.35 mΩ at 5 K, 10 GHz.

Metalorganic chemical vapor deposition route to epitaxial neodymium gallate thin films

Phase‐pure epitaxial thin films of the YBa2Cu3O7−δ lattice‐matched, low dielectric loss perovskite insulator NdGaO3 have been grown on (110) LaAlO3 substrates by a metalorganic chemical vapor deposition (MOCVD)/post‐annealing process. Amorphous Nd‐Ga‐O films are first prepared by MOCVD using the volatile metalorganic β‐diketonate precursors Nd(dpm)3 and Ga(dpm)3 (dpm=dipivaloylmethanate). Subsequent postannealing affords phase pure, highly oriented [(001) and/or (110) orientations perpendicular to the substrate surface] and epitaxial NdGaO3 films as assessed by x‐ray diffraction θ‐2θ, ω, and φ scans. Cross‐sectional high‐resolution electron microscopic images show that the epitaxial growth occurs with atomically abrupt film‐substrate interfaces and with coexisting NdGaO3 (001) and (110) orientation domains.

Suitability of metalorganic chemical vapor deposition-derived PrGaO3 films as buffer layers for YBa2Cu3O7-x pulsed laser deposition

Phase‐pure thin films of the YBa2Cu3O7−x (YBCO) lattice matched and low loss tangent perovskite insulator PrGaO3 have been grown in situ on single‐crystal (110) LaAlO3 substrates by metalorganic chemical vapor deposition (MOCVD). Films were grown at temperatures of 750–800 °C using β‐diketonate precursors M(dpm)3 (M=Pr,Ga; dpm =dipivaloylmethanate). YBCO films were then grown on the MOCVD‐derived PrGaO3 by pulsed laser deposition (PLD). Scanning electron microscopy reveals that the PrGaO3 films have smooth, featureless surfaces. As assessed by x‐ray diffraction, the PrGaO3 films grow epitaxially on LaAlO3 with a high degree of (001) and/or (110) plane orientation parallel to the substrate surface, and the subsequent YBCO films grow with a (00l) orientation. Rocking curve and φ‐scan analyses reveal that the PrGaO3 and YBCO films grow epitaxially. Cross‐sectional high resolution electron microscopy and transmission electron microscopic selected area diffraction confirm that the PrGaO3 and YBCO layers grow e...

Transmission electron microscopic characterization of metal-organic chemical vapor deposition-derived superconducting Tl2Ba2Ca1Cu2Oχ thin films on Au substrates: Evidence for Au-Cu alloy formation and texturing on a nonplanar metal substrate

Abstract The microstructure of superconducting Tl 2 Ba 2 Ca 1 Cu 2 O χ thin films grown on Au substrates by metal-organic chemical vapor deposition (MOCVD) has been investigated. Characterization techniques included X-ray diffraction, variable temperature magnetization, scanning and transmission electron microscopy (SEM and TEM, respectively) and energy dispersive X-ray spectroscopy (EDX) measurements. The films exhibit a magnetically derived T c ≈80 K and a high degree of texturing with the crystallite c -axis oriented perpendicular to the Au substrate surface as evidenced by enhanced (00 l ) X-ray diffraction reflections. SEM/ EDX and TEM/EDX provide evidence of Au-Cu alloy formation but no Au diffusion into the film. The superconducting grains exhibit good compositional uniformity and excellent alignment with the substrate, even though the Au substrates were not smooth and exhibited a moderate density of steps.

Materials for superconducting electronics: In situ growth of PrGaO3 thin films by metalorganic chemical vapor deposition

Phase‐pure thin films of the YBCO, BSCCO, TBCCO lattice‐matched and low dielectric‐loss perovskite insulator PrGaO3 have been grown in situ on single‐crystal (110) LaAlO3 , (001) SrTiO3 , and (001) MgO substrates by metalorganic chemical vapor deposition (MOCVD). Films were grown at temperatures between 750 and 800 °C using the volatile metalorganic β‐diketonate precursors M(dpm)3 (M=Pr, Ga, and dpm=dipivaloylmethanate). As assessed by x‐ray diffraction, the films grow epitaxially on LaAlO3 and SrTiO3 substrates with a high degree of (001) and/or (110) plane orientation parallel to the substrate surface. The films grown on MgO substrates are polycrystalline. Scanning electron microscopy reveals that the MOCVD‐derived PrGaO3 films have smooth, featureless surfaces on all three kinds of substrates.

In Situ MOCVD of Dielectric Materials for High-Tc Superconducting Devices

Devices which utilize high-Tc superconducting films require dielectric materials with low dielectric losses (tan δ), low dielectric constants, chemical inertness, and similar coefficients of thermal expansion to HTS materials. A major advance in the fabrication of such devices would be the deposition of high quality dielectric films by MOCVD (metal-organic chemical vapor deposition) which would enable the efficient, large-scale fabrication of multilayer superconductor-insulator structures. In this paper, we report the MOCVD deposition of epitaxial thin films of various pervoskite HTS lattice-matched dielectric materials: NdGaO3, PrGaO3, YA1O3, and Sr2AlTaO6. These pervoskite dielectric films were grown in situ on single crystal substrates in a horizontal reactor using volatile metal-organic b-diketonate complexes as precursors. Film morphology and microstructure are characterized by SEM and cross-sectional TEM. Energy dispersive x-ray analysis is used to verify the stoichiometry. The crystallinity and epitaxy of the dielectric films are characterized by x-ray diffraction.