Jiming Zhang

Organometallic chemical vapor deposition routes to high Tc superconducting Tl-Ba-Ca-Cu-O films

Films of the Tl‐Ba‐Ca‐Cu‐O high Tc superconductor can be prepared by either of two organometallic chemical vapor deposition routes. Ba‐Ca‐Cu‐O films are first prepared on yttria‐stabilized zirconia using the volatile precursors Ba(heptafluorodimethyloctanedionate)2, Ca(dipivaloylmethanate)2, and Cu(acetylacetonate)2. Deposition is carried out at 5 Torr pressure with argon as the carrier gas and water vapor as the reactant gas. Thallium is next incorporated in these films either by vapor diffusion using bulk Tl‐Ba‐Ca‐Cu‐O as the source, or by organometallic chemical vapor deposition using Tl(cyclopentadienide) as the source. The latter deposition is carried out at atmospheric pressure with an argon carrier and water‐saturated oxygen reactant, followed by rapid thermal annealing. Both types of films consist primarily of the TlBa2Ca2Cu3Ox phase, have preferential orientation of the CuO planes parallel to the substrate surface, and exhibit onset of superconductivity at ∼120 K with zero resistance by 100 K.

Organometallic chemical vapor deposition of high Tc superconducting Bi‐Sr‐Ca‐Cu‐O films

Films of the high Tc Bi‐Sr‐Ca‐Cu‐O superconductor have been prepared by organometallic chemical vapor deposition using the volatile metalorganic precursors Cu(acetylacetonate)2 , Sr(dipivaloylmethanate)2 , and Ca(dipivaloylmethanate)2, and triphenylbismuth. Deposition is carried out at 2 Torr with argon as the carrier gas and oxygen and water vapor as reactants. Film growth rates of 2–3 μm/h are achieved. After annealing under oxygen, energy dispersive x‐ray analysis and x‐ray diffraction data reveal that such films on [100] single‐crystal MgO consist predominantly of the Bi2(Sr,Ca)3Cu2Ox, Tc=85 K, phase and have preferential orientation of the crystallite c axes perpendicular to the substrate surface. Four‐probe resistivity measurements reveal the onset of film superconductivity at ∼110 K and zero resistance by 75 K.

Organometallic chemical vapor deposition of high T/sub c/ superconducting Bi-Sr-Ca-Cu-O films

Films of the high Tc Bi‐Sr‐Ca‐Cu‐O superconductor have been prepared by organometallic chemical vapor deposition using the volatile metalorganic precursors Cu(acetylacetonate)2 , Sr(dipivaloylmethanate)2 , and Ca(dipivaloylmethanate)2, and triphenylbismuth. Deposition is carried out at 2 Torr with argon as the carrier gas and oxygen and water vapor as reactants. Film growth rates of 2–3 μm/h are achieved. After annealing under oxygen, energy dispersive x‐ray analysis and x‐ray diffraction data reveal that such films on [100] single‐crystal MgO consist predominantly of the Bi2(Sr,Ca)3Cu2Ox, Tc=85 K, phase and have preferential orientation of the crystallite c axes perpendicular to the substrate surface. Four‐probe resistivity measurements reveal the onset of film superconductivity at ∼110 K and zero resistance by 75 K.

Organometallic chemical vapor deposition of superconducting, high Tc Pb‐doped Bi‐Sr‐Ca‐Cu‐O thin films

Highly oriented films of the high Tc Bi‐Pb‐Sr‐Ca‐Cu‐O (BPSCCO)superconductor have been prepared by two organometallic chemical vapor deposition (OMCVD) approaches. In the first approach, Pb is introduced by alternate deposition of BSCCO and PbOx films using the volatile metalorganic precursors Cu(acetylacetonate)2, Sr(dipivaloylmethanate)2, Ca(dipivaloylmethanate)2, triphenyl bismuth, and tetraphenyl lead. In the second approach, Pb is incorporated into an OMCVD‐derived BSCCO film by vapor diffusion using PbO as the source. X‐ray diffractometry and scanning electron microscopy reveal that Pb doping significantly improves the crystalline orientation and the film morphology. Films deposited by both methods on [100] single‐crystal MgO consist predominantly of the Bi2(Sr,Ca)3Cu2Ox phase and have a high preferential orientation of the crystallite c axes perpendicular to the substrate surface. Four‐probe resistivity measurements indicate the onset of film superconductivity at ∼110 K and zero resistance by 80 K.

Preparation of high‐Tc superconducting Bi‐Sr‐Ca‐Cu‐O films by organometallic chemical vapor deposition using second‐generation fluorocarbon‐based precursors

High‐Tc superconducting Bi‐Sr‐Ca‐Cu‐O thin films with good electrical properties and smooth surface morphologies have been prepared by low‐pressure organometallic chemical vapor deposition using the new fluorocarbon‐based precursors Sr(hexafluoroacetylacetonate)2⋅tetraglyme and Ca(hexafluoroacetylacetonate)2⋅triglyme together with Cu(acetylacetonate)2 and triphenylbismuth [Bi(C6H5)3]. The fluorinated precursors are air‐stable and exhibit high, stable volatility even after prolonged heating. X‐ray diffraction measurements reveal that the films deposited at 650 °C contain some fluoride phases but no high‐Tc phases. However, post‐annealing in oxygen produces films composed predominantly of the Bi2Sr2CaCu2Ox phase with high preferential orientation of the crystallite c axes perpendicular to the substrate surface. Four‐probe resistivity measurements indicate the onset of film superconductivity at ∼100 K and zero resistivity achieved at 73 K.

Formation of oriented high Tc superconducting Bi‐Sr‐Ca‐Cu‐O thin films on silver substrates by organometallic chemical vapor deposition

Highly oriented thin films of the high Tc Bi‐Sr‐Ca‐Cu‐O superconductor have been deposited on silver substrates by low‐pressure organometallic chemical vapor deposition. The volatile metalorganic complexes Cu(acetylacetonate)2, Sr(dipivaloylmethanate)2, Ca(dipivaloylmethanate)2, and triphenyl bismuth are used as precursors with N2O as a reactant gas. X‐ray diffraction measurements reveal that the films deposited at 625 °C contain a mixture of the Bi2(Sr,Ca)2CuOx and Bi2(Sr,Ca)3Cu2Ox phases. The post‐annealed films are predominantly composed of the Bi2(Sr,Ca)3Cu2Ox phase with preferential orientation of the crystallite c axes perpendicular to the substrate surface. Magnetic susceptibility measurements indicate the superconducting onset temperature of the annealed films to be at 80 K. The zero‐field critical current density, estimated from magnetization measurements, is ∼3.9×105 A/cm2 at 5.5 K.

Liquid source metal–organic chemical-vapor deposition of high-quality YBa2Cu3O7−x films on polycrystalline silver substrates

High-temperature superconducting YBa2Cu3O7−x films were grown by liquid delivery metal–organic chemical-vapor deposition on silver-coated stainless-steel substrates. The films are highly c-axis oriented, have a Tc above 90 K, and exhibit a surface resistance of 110 μΩ at 77 K and 3 GHz.

A new route to high‐Tc superconducting Bi–Sr–Ca–Cu–O thin films: Improved deposition efficiency and film morphology using ammonia–argon mixtures as the carrier gas

Highly oriented films of the high‐Tc superconductor Bi2Sr2CaCu2Ox have been prepared by a low‐pressure organometallic chemical vapor deposition process using a mixture of ammonia and argon as the carrier gas together with Sr(dpm)2 (dpm‐dipivaloylmethanate), Ca(dpm)2, Cu(acac)2 (acac‐acetylacetonate), and triphenylbismuth as the organometallic precursors. By introducing ammonia into the carrier gas, a significant improvement in the volatility and thermal stability of both Sr(dpm)2 and Ca(dpm)2 is observed. Typical required source temperatures for Sr(dpm)2 and Ca(dpm)2 with the introduction of ammonia are about 40–50 °C lower than the source temperatures of the precursors without the introduction of ammonia. Enhancement of source volatility for Cu(acac)2 is also observed. After annealing at 865 °C in flowing oxygen, the films consist predominantly of the Bi2Sr2CaCu2Ox phase and exhibit high preferential orientation of the crystallite c axes perpendicular to the substrate surface. Four‐probe resistivity meas...

Preparation and properties of superconducting Bi–Sr–Ca–Cu–O thin films on polycristalline silver substrates by organometallic chemical vapor deposition

Abstract High- T c superconducting Bi–Sr–Ca–Cu–O thin films have been successfully prepared by low-pressure organometallic chemical vapor deposition using metallic silver as a substrate. N 2 O is employed as an efficient reactant gas in combination with the volatile metal-organic complexes Cu(acetylacetonate) 2 , Sr(dipivaloymethanate) 2 , Ca(dipivaloymethanate) 2 , and triphenyl bismuth (Bi(C 6 H 5 ) 3 ) as sources. X-ray diffraction measurements reveal that the as-deposited films deposited at 625–650°C contain a mixture of the Bi 2 (Sr,Ca) 2 CuO x and Bi 2 (Sr,Ca) 3 Cu 2 O x phases, and that the proportion of the high- T c phase increases with increasing deposition temperature. The post-annealed films are composed predominantly of the Bi 2 (Sr,Ca) 3 Cu 2 O x phase with high preferential orientation of the crystallite c axes perpendicular to the substrate surface. Deposition on polycrystalline Ag substrates significantly improves the texture and morphology of BSCCO films as compared with films deposited on MgO. Possible mechanisms for the improvement of BSCCO films when using Ag as a substrate are discussed.

High‐Tc Undoped and Pb‐Doped BI‐SR‐CA‐CU‐O thin Films Prepared by Organometallic Chemical Vapor Deposition

Films of the high‐T c undoped and Pb‐doped Bi‐Sr‐Ca‐Cu‐O (BSCCO) superconductors have been prepared by low pressure organometallic chemical vapor deposition (OMCVD) using the volatile metal‐organic precursors Cu(acetylacetonate) 2 , Sr(dipivaloylmethanate) 2 , Ca(dipivaloylmethanate) 2 , and triphenyl bismuth. Factors which influence texture and morphology of the OMCVD‐derived films have been investigated, including the effects of annealing, doping, and substrates.