Routes to High-Tc Superconducting Tl-Ba-Ca-Cu-O Films Using Organometallic Chemical Vapor Deposition
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ROUTES TO HIGH-Tc SUPERCONDUCTING T1-Ba-Ca-Cu-O FILMS USING ORGANOMETALLIC CHEMICAL VAPOR DEPOSITION DARRIN S. RICHESON(a), LAUREN M. TONGE(a), JING ZHAO(b), lIMING ZHANG(b), HENRY 0. MARCY(c), TOBIN J. MARKS(a~d), BRUCE W. WESSELS(b,d), and CARL R. KANNEWURF(c,d) (a)Department of Chemistry (b)Department of Materials Science and Engineering (c)Department of Electrical Engineering and Computer Science (d)Authors to whom correspondence should be addressed Science and Technology Center for Superconductivity and the Materials Research Center Northwestern University, Evanston IL 60208. ABSTRACT Films of the TI-Ba-Ca-Cu-O high-Tc superconductor can be prepared by several organometallic chemical vapor deposition routes. Two of these involve Ba-Ca-Cu-O films that are first prepared using the volatile metal-organic precursors Ba(heptafluorodimethyloctanedionate)2, Ca(dipivaloylmethanate)2, and Cu(acetylacetonate)2. Deposition is carried out at a pressure of 5 Torr with argon as the carrier gas and water vapor as the reactant gas. Thallium is next incorporated into these films either by organometallic chemical vapor deposition using TI(cyclopentadienide) as the source, or by vapor diffusion using bulk T1-Ba-Ca-Cu-O as the source. Thallium deposition is carried out at atmospheric pressure with an argon carrier and watersaturated oxygen reactant gas, followed by rapid thermal annealing. Both procedures yield films that consist primarily of the T1Ba2Ca2Cu3Ox phase, have preferential orientation of the Cu-O planes parallel to the substrate surface, and exhibit onset of superconductivity at -125 K with zero resistance by 100 K. INTRODUCTION With the advent of superconducting oxides exhibiting critical temperatures, Tc, in excess of 77 K, intense worldwide interest has been stimulated toward the application of superconductivity to vast new areas of both scientific and technological importance. One area of activity has been the development of processes that produce high-quality thin films of these materials since it is likely that high-Tc superconductors will first have technological impact in this form. To date, efforts have primarily centered on physical vapor deposition (PVD) techniques such as sputtering t -3, thermal 4 and electron beam evaporation, 5 ,6 and laser ablation. 7 With the development of appropriate molecular precursors, organometallic chemical vapor deposition (OMCVD) would offer an attractive alternative approach with potential advantages of simplified deposition apparatus, high deposition rates, ability to coat complex shapes, compositional control, and excellent film uniformity. Among the currently known high-Tc superconductors, the TI-Ba-Ca-Cu-O materials (TlmBa2Can-lCunOm+2n+2; m = 1,2; n = 1,2,3) exhibit the greatest multiplicity of phases, high environmental stability, ease of synthesis, and Tc values as high as 122 K. 8-12 Such valuable characteristics dictate the need for the synthesis of high-quality films of these materials. We report here the preparation of high-Tc TI-Ba-Ca-Cu-O films by two complement
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