Epitaxial Tl2Ba2CaCu2O8 thin films with excellent electrical transport characteristics are grown in a two-step process involving metal-organic chemical vapor deposition (MOCVD) of a BaCaCuO(F) thin film followed by a postanneal in the presence of Tl2O vapor. Vapor pressure characteristics of the recently developed liquid metal-organic precursors Ba(hfa)2 • mep (hfa = hexafluoroacetylacetonate, mep = methylethylpentaglyme), Ca(hfa)2 • tet (tet = tetraglyme), and the solid precursor Cu(dpm)2 (dpm = dipivaloylmethanate) are characterized by low pressure thermogravimetric analysis. Under typical film growth conditions, transport is shown to be diffusion limited. The transport rate of Ba(hfa)2 • mep is demonstrated to be stable for over 85 h at typical MOCVD temperatures (120 °C). In contrast, the vapor pressure stability of the commonly used Ba precursor, Ba(dpm)2, deteriorates rapidly at typical growth temperatures, and the decrease in vapor pressure is approximately exponential with a half-life of ∼9.4 h. These precursors are employed in a low pressure (5 Torr) horizontal, hot-wall, film growth reactor for growth of BaCaCuO(F) thin films on (110) LaAlO3 substrates. From the dependence of film deposition rate on substrate temperature and precursor partial pressure, the kinetics of deposition are shown to be mass-transport limited over the temperature range 350–650 °C at a 20 nm/min deposition rate. A ligand exchange process which yields volatile Cu(hfa)2 and Cu(hfa) (dpm) is also observed under film growth conditions. The MOCVD-derived BaCaCuO(F) films are postannealed in the presence of bulk Tl2Ba2CaCu2O8 at temperatures of 720–890 °C in flowing atmospheres ranging from 0–100% O2. The resulting Tl2Ba2CaCu2O8 films are shown to be epitaxial by x-ray diffraction and transmission electron microscopic (TEM) analysis with the c-axis normal to the substrate surface, with in-plane alignment, and with abrupt film-substrate interfaces. The best films exhibit a Tc = 105 K, transport-measured Jc= 1.2 × 105 A/cm2 at 77 K, and surface resistances as low as 0.4 mΩ (40 K, 10 GHz).
cm 3 in comparison to 1.8 g/cm 3 obtained for SiBCN 3 synthesized by polymer pyrolysis. High hardness values up to 22 GPa are found, which might be further increased by reducing the residual hydrogen content by applying higher bias potentials or by reduced precursor flow.Metal-organic chemical vapor deposition (MOCVD) is already an indispensable thin film growth technique for advancing microelectronics technologies, and it is predicted to play an even larger role in the future. [1] The inherent advantages of MOCVD (low growth temperatures, high continuous throughput, growth at high reactant gas pressures,
This communication reports rapid, efficient syntheses of the zirconium-organic metal-organic chemical vapor deposition (MOCVD) precursors Zr(acac)4 and Zr(dpm)4 (acac = acetylacetonate; dpm = dipivaloylmethanate) as well as a new, highly volatile, air- and moisture-stable Zr precursor based on a tetradentate Schiff-base ligand, Zr(tfacen)2 (tfacen = bis-trifluoroacetylacetone-ethylenediiminate). The improved one-step synthetic routes employ tetrakis(dimethylamido)zirconium as a common intermediate and represent a major advance over previous methods employing ZrCl4 or diketonate metathesis. Furthermore, Zr(tfacen)2 is shown to be an effective metal-organic precursor for the MOCVD-mediated growth of (100) oriented yttria-stabilized zirconia thin films.
T h e evolution of HTS device technologies will benefit fsorn the development 01' MOCVD (Metal-organic Chemical Vapor Deposition) routes to high quality HTS I'ilms as well as to those of insulators with low dielectric loss and close HTS lattice matches. Reviewed here are research efforts at precursor design focusing on Ba sources. A novel low pressure TGA technique is used to compare volatilities of MOCVD precursors and to quantif'y the role of' gas phase diffusion in film growth. TO form high quality T12Ba2Can-1C~1104+2n (n = 2.3) films, BaCaCuO(F) films are first deposited by MOCVD using the liquid precursors Ba(hl'ai?*rncp. Ca(hfa)2*tet, and solid Cu(dpm)2 (hfa = hexafluoroacetylacetonatc, clp~n = dipivaloyl~netha~iatc. mep = methylethyIpentaglyme, tet = tetraglyme). The film growth process is shown to he Inash transport-limited, and an interesting ligand exchange process is identified. The supei.conductu~; TBCCO phase is formed following an ex-situ anneal in the presence of T120 ar tentperau~i-cs from 820-900°C. Transport properties of TBCCO-2223 films include a Tc as high as I15K. Jc of 2x105 A/cm2 (77K), and Rs of 0.35mQ (5K, 10 GHz). The MOCVD growth of low loss, lattice-matched dielectric NdGa03, PrGa03, SrzAlTaOg, and SrPrGa04 f'il~ns is also discussed. High quality YBa2Cu307-, films have been grown upon MOCVD-dm-ived PsGaO? suhsri.a~cs.
Thin TlBa2Ca2Cu3O9+x films were grown on single crystal (110) LaAlO3 from metal-organic chemical-vapor deposition-derived Ba–Ca–Cu–Ox precursor films employing Ba(hfa)2⋅mep, Ca(hfa)2⋅tet, and Cu(dpm)2 (hfa=hexafluoroacetylacetonate; dpm=dipivaloylmethanate; tet=tetraglyme; mep=methylethylpentaglyme) as the volatile metal sources. Thallination is then accomplished by annealing the precursor films in the presence of a bulk BaO+CaO+CuO+TlF source at 885 °C in flowing O2. The presence of TlF is essential for nucleating the Tl-1223 phase. The resulting Tl-1223 films are nearly phase-pure, highly oriented, epitaxial by x-ray diffraction, and contain negligible fluoride by windowless energy-dispersive x-ray measurements. The films exhibit a transport measured Tc=103 K and Jc=4.4×104 A/cm2 (77 K, 0 T). Magnetic hysteresis measurements yield Jc=1.9×105 A/cm2 (30 K, 0.01 T) and show considerable flux pinning at low temperatures with Jc=1.4×105 A/cm2 (5 K, 4.5 T).
This contribution reports the in situ growth of transparent, conducting GaxIn2-xO3 and ZnkIn2Ok+3 films by MOCVD (metal-organic chemical vapor deposition) techniques using In(dpm)3, Ga(dpm)3, and Zn(dpm)2 (dpm = dipivaloylmethanate) as volatile precursors. In the former series, film microstructure in the x = 0.4 – 1.0 range is predominantly cubic with 25° C electrical conductivities as high as 1300 S/cm (n-type; carrier density = 1.2 × 1020 cm−3, mobility = 68 cm2/Vs) and optical transparency in the visible region greater than that of ITO. In the latter series, films in the composition range K = 0.16 – 3.60 were studied; the microstructural systematics are rather complex. Electrical conductivities (25° C) as high as 1000 S/cm (n-type; carrier density = 3.7 × 1020 cm−3, mobility = 18.6 cm2/Vs) for K = 0.66 were measured. The optical transparency window is significantly broader than that of ITO.
Phase-selective growth of TlBa2Ca2Cu3O9−x films is greatly enhanced by annealing chemical vapor deposition derived BaCaCuO(F) precursor films in the presence of TlF. Nucleation of superconducting phases (≥840 °C under O2) progresses in the order 2212 → 2223 → 1212 → 1223. Annealing at 855 °C results in well-defined platelet grains, a significant number of which are a-axis oriented. Residual fluoride is not detectable at any stage of the annealing process. Thin films synthesized by TlF annealing differ markedly from films processed in the presence of Tl2O3 with Tc = 103 K and Jc > 105 A/cm2 (5 K, 4.5 T).
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