Epitaxial Tl 2 Ba 2 CaCu 2 O 8 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 Tl 2 O 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) LaAlO 3 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 Tl 2 Ba 2 CaCu 2 O 8 at temperatures of 720–890 °C in flowing atmospheres ranging from 0–100% O 2 . The resulting Tl 2 Ba 2 CaCu 2 O 8 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 T c = 105 K, transport-measured J c = 1.2 × 10 5 A/cm 2 at 77 K, and surface resistances as low as 0.4 mΩ (40 K, 10 GHz).

The 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. J c 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.

MgO films and YBa2Cu3O7−δ/MgO multilayer films were developed with the pulsed organometallic beam epitaxy (POMBE) growth technique, and grain boundary junctions were fabricated from the films to demonstrate the utility of the multilayers. High-quality MgO films were grown on LaAlO3 substrates by POMBE using a Mg(dpm)2 precursor. MgO crystallinity, as assessed by x-ray diffraction rocking curves, improved with the use of CuOx or YBa2Cu3O7−δ buffer layers. YBa2Cu3O7−δ films grown on the MgO layer by POMBE exhibited a Tc0 of 83 K and a Jc (12 K) exceeding 106 A/cm2 for applied magnetic fields up to 3 × 104 G. Grain boundary junctions were formed by growing YBa2Cu3O7−δ on MgO films that had been pretreated with a simple sputtering technique. This sputtering induces a controlled, 45°grain boundary in subsequently deposited YBa2Cu3O7−δ films. The resulting boundary showed weak-link current-voltage behavior and an IcRn product of 52 μV at 10 K, demonstrating that sputter-induced grain boundary junctions are compatible with multilayer technology.

The synthesis, characterization, and incorporation in volatile metal-organic chemical vapor deposition (MOCVD) precursors of a new class of linked beta-ketoiminate-polyether-beta-ketoiminate ligands is presented. These ligands are designed to encapsulate alkaline-earth cations having low charges and large ionic radii. Barium complexes having the general formula Ba[(RCOCHC(R')N)2(R")] (R = tert-butyl or CF3; R' = tert-butyl, methyl, or CF3; R" = -(CH2CH2O)4CH2CH2- or -(CH2CH2O)5CH2CH2)-) were prepared and characterized by 1H and 13C NMR spectroscopy, elemental analysis, and mass spectrometry. Single-crystal X-ray diffraction analysis of 2,2,5,25,28,28-hexamethyl-9,12,15,18,21-pentaoxa-4,25-diene-6,24- diimino-3,27-pentacosadionatobarium(II) reveals a monomeric, nine-coordinate, tricapped trigonal prismatic coordination geometry. Single-crystal X-ray structural analysis of 1,1,1,24,24,24-hexafluoro-4,21-ditrifluoromethyl-8,11,14,17- tetraoxa-3,21-diene-5,20-diimino-2,23-tetracosadionatobarium(II).2DMSO reveals a monomeric, ten-coordinate, distorted tetracapped trigonal prismatic coordination geometry. Volatility data are presented for these barium complexes, demonstrating viability as MOCVD precursors. In addition, it is demonstrated that thin epitaxial films of BaTiO3 can be grown on (001) MgO by low-pressure MOCVD techniques using one of these barium complexes and Ti(dipivaloylmethanate)2(isopropoxide)2 as precursors.

Magnetoresistance describes a phenomenon in which the electrical resistance of the material depends strongly on an externally applied magnetic field. Colossal magnetoresistance (CMR) was observed in a new class of oxides, (La,A)MnO 3 (A = Ca, Sr, or Ba), and the Magnetoresistance ratio of ΔR/R(H)> -100,000% has been reported in epitaxially grown La 0 .67Ca 0.33 MnO 3 films. The new types of intrinsic magnetoresistive oxides offer exciting possibilities for improved magnetic sensors, magnetoresistive read heads, and magnetoresistive random access memory (MRAM). The CMR magnetic oxides have a perovskite-type crystal structure with ferromagnetic ordering in the a-b planes and antiferromagnetic ordering along the c-axis (Figure 1). The ferromagnetically ordered Mn-O layers of the a-b planes are isolated by a non-magnetic La(A)-O monolayer. This spin-coupling structure is intrinsic. La 1-x AxMn03 compounds having the extreme values x = 0, 1 are neither ferromagnetic nor good electrical conductors; they are semiconductors. Only compounds with intermediate values of x are ferromagnetic,

Epitaxial cuprate oxycarbonate Sr2CuO2(CO3) thin films have been prepared by metal–organic chemical vapor deposition. The effects of deposition conditions on phase stability have been determined. X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, inductively coupled plasma atomic emission spectroscopy, and Fourier transform infrared spectroscopy were used to characterize the oxycarbonate thin films. The resistivity of the undoped Sr2CuO2(CO3) thin films decreases from ∼0.2 Ω cm to ∼0.01 Ω cm upon post annealing in oxygen, but semiconducting behavior is observed. Doping has been achieved through partial substitution of BO33− for CO32−. Superconductivity with a Tc (onset) of 34 K and a Tc (zero) of 20 K has been obtained.

The synthesis and characterization of a series of polyethers and volatile, low-melting polyether complexes of bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedio)barium having the general formula Ba(hfa)(2) . RO(CH2CH2O)(n)R' where R = R' = CH3, n = 3; R = CH3, R' = C2H5, n = 3; R = R' = H, n = 5, 6; R = R' = CH3, n = 4; R = CH3, R' = C2H5, n = 5; R = CH3, R' = n-C4H9, n = 5, 6; R = CH3, R = C5H11O, n = 3; R = CH3, R' = n-C6H13, n = 4, 5; R = C2H5, R' = n-C4H9, n = 5; R = n-C4H9, RI = n-C4H9, n = 4, 6; R = n-C4H9, R' = n-C6H13, n = 5 are reported. The complexes are conveniently synthesized by reaction of n-propylammonium(+)-hfa(-) in DMF with an aqueous solution of Ba(NO3)(2) and the polyether or, alternatively, by reaction of the polyether with Ba(hfa)(2) in toluene. These new complexes were characterized by elemental analysis, FT-IR, H-1, C-13, and F-19 NMR, MS, X-ray diffraction (Ba(hfa)(2) . CH3O(CH2CH2O)(3)CH3 . H2O, Ba(hfa)(2) . CH3O(CH2CH2O)(5)C2H5), and thermogravimetric analysis. The melting points of the complexes are strongly dependent on the architecture of the polyether chain and dimensions of the terminal polyether substituent, with the lowest melting points corresponding to the longest polyethers having the largest terminal groups. The volatility of the Ba(hfa)(2) . polyether compounds is dependent on molecular weight and molecular structure; however, there is little direct correlation between melting point depression and enhanced volatility. The applicability of these complexes in metal-organic chemical vapor deposition is demonstrated by the successful growth of phase-pure BaTiO3 thin films using Ba(hfa)(2) . CH3O(CH2CH2O)(5)C2H5 as the Ba source. Phase composition and epitaxy in these films is analyzed by energy-dispersive X-ray spectroscopy and X-ray diffraction Theta-2 Theta, omega, and phi scans.

Cuprate oxycarbonate Sr2CuO2(CO3) thin films have been obtained from the “parent” infinite-layer compound thin films by thermal annealing at 700°C in air. The precursor infinite-layer compound thin films were grown by metal-organic chemical vapor deposition. The effect of oxygen annealing on electronic properties of these films and the attempt of converting the Ca substituted Sr0.9Ca0.1CuO2 thin film by annealing in ordinary air are reported. The as-converted Sr2CuO2(CO3) films are p-type semiconductors with a hole density of 1019 cm−3 and a room temperature resistivity of 0.1 Ω cm. Annealing in 1.0 atm oxygen at temperatures of 550–700°C decreases the room temperature resistivity to 0.02–0.03 Ω cm and increases the hole concentration to 1020–1021 cm−3. Metal-like behavior is observed in the transport properties, and a superconducting transition onset is observed at 30 K, with zero-resistivity obtained at 9 K.

This contribution presents synthetic, structural and volatility results for a series of new Ba(hfa)2polyether (hfa=1,1,1,5,5,5-hexafluoropentane-2,4-dionate) MOCVD precursors. The major emphasis of this study is on the synthesis and characterization of new Ba(hexafluoroacetylacetonate)2·polyether complexes as on well as elucidating relationships between volatility, melting point and molecular architecture using a variety of techniques, including reduced pressure thermogravimetric analysis (TGA). The results provide insights into tuning Ba precursor volatility characteristics based on straightforward modifications of the polyether structure.

Thin films of beta barium borate (β-BaB2O4) have been deposited by metalorganic chemical vapor deposition on fused silica, sapphire, platinum, and silicon substrates. Deposition conditions were optimized to reproducibly grow films with the c axis normal to the substrate. Second harmonic generation measurements have been made on selected films. The films grown on fused silica exhibit a maximum χeff(2) of 0.78 pm/V, and on single-crystal sapphire, 1.6 pm/V.

High-purity alkaline earth ß-diketonate compounds such as [M(thd)2]x (M = Mg, Ca, Sr, Ba) have been utilized for liquid delivery MOCVD.[1] The “parent” compounds are oligomeric species with bridging ß-diketonate ligands and display both limited volatility and thermal instability. To enhance the precursor transport and film growth rates, Lewis base ligands are used to produce mononuclear precursors.[2] Lewis base coordinated metal (ß-diketonates) also exhibit increased solubilities in organic solvents. In this study, two classes of Group II ß-diketonates were compared; thermal stability and transport were evaluated by simultaneous thermal analyses, using both thermogravimetric (TGA) and differential scanning calorimetry (DSC). Liquid delivery and vaporization were evaluated in an “experimental” liquid delivery system and preliminary film growth, including electrical film properties were measured. The identity of the Lewis base and Group II precursor molecular structure as relates to liquid delivery vaporization and CVD film growth of BaxSr1–xTiO3 are described.

Phase-pure epitaxial (Sr1-xCax)CuO2 thin films having the infinite-layer crystal structure were grown on SrTiO3 (100) substrates by low pressure metal-organic chemical vapor deposition using fluorinated metal-organic precursors. The substrate temperature and reactant gas (O-2, H2O) partial pressure are crucial for stabilizing the tetragonal infinite-layer structure. Films with compositions over the range x=0-0.3 can be stabilized. In-plane epitaxy was confirmed by x-ray diffraction phi scan. The films were semiconducting but exhibit resistivity anomalies. The orthorhombic phases of Sr2CuO3 and SrCuO2 were stabilized at 700 degrees C and 750 degrees C, respectively. (C) 1996 American Institute of Physics.

The evolution of HTS device technologies will benefit from the development of MOCVD (Metal-organic Chemical Vapor Deposition) routes to high quality HTS films 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 quantify the role of gas phase diffusion in film growth. To form high quality Tl 2 Ba 2 Ca n-1 Cu n O 4+2n (n = 2,3) films, BaCaCuO(F) films are first deposited by MOCVD using the liquid precursors Ba(hfa) 2 .mep, Ca(hfa) 2 .tet, and solid Cu(dpm) 2 (hfa = hexafluoroacetylacetonate, dpm = dipivaloylmethanate. mep = methylethylpentaglyme, tet = tetraglyme). The film growth process is shown to be mass transport-limited, and an interesting ligand exchange process is identified. The superconducting TBCCO phase is formed following an ex-situ anneal in the presence of Tl 2 O at temperatures from 820-900°C. Transport properties of TBCCO-2223 films include a T C as high as 115K. J C of 2x10 5 A/cm 2 (77K), and Rs of 0.35mΩ (5K, 10 GHz). The MOCVD growth of low loss, lattice-matched dielectric NdGaO 3 , PrGaO 3 , Sr 2 AlTaO 6 , and SrPrGaO 4 films is also discussed. High quality YBa 2 Cu 3 O 7-x films have been grown upon MOCVD-derived PrGaO 3 substrates.

Epitaxial SrTiO3 thin films were prepared using low pressure metalorganic chemical vapor deposition. The volatile metalorganic precursors employed were Sr(hexafluoroacetyl acetonate)2⋅tetraglyme and titanium tetraisopropoxide. Single-phase, epitaxial films were deposited on (100)LaAlO3 at a temperature of 810 °C. In-plane epitaxy was verified using x-ray phi scan analysis. The SrTiO3 films exhibit a significant tetragonal distortion with c/a=1.010(±1.6×10−4) at room temperature. No evidence of fluorine contamination is noted by x-ray diffraction or by Auger electron spectroscopy measurements.

Highly textured strontium barium niobate thin films were deposited in situ by low pressure metalorganic chemical vapor deposition. [001]-oriented strontium barium niobate films on single crystal (100) magnesium oxide substrates were obtained at a growth temperature of 800 °C. Second-harmonic generation of 1.064 μm incident light was measured on the thin films. The nonlinear optical susceptibility of the films was as high as 8.7 times that of quartz (∼3.0 pm/V), which is comparable to the bulk value.

Ferroelectric oxide thin films show considerable potential as electro-optic and nonlinear optical materials. Of particular interest are the niobates such as strontium barium niobate and potassium niobate. The growth of these epitaxial oxide films by metal-organic chemical vapor deposition (MOCVD) has been investigated. This technique has yielded epitaxial thin films with excellent nonlinear optical properties. Issues concerning the epitaxy of these thin films and its relationship to their optical and nonlinear optical properties are discussed.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNew Precursors for Barium Metal-Organic Chemical Vapor Deposition. In situ Growth of Epitaxial Barium Titanate Films Using a Liquid Barium PrecursorDeborah A. Neumayer, Daniel B. Studebaker, Bruce J. Hinds, Charlotte L. Stern, and Tobin J. MarksCite this: Chem. Mater. 1994, 6, 7, 878–880Publication Date (Print):July 1, 1994Publication History Published online1 May 2002Published inissue 1 July 1994https://pubs.acs.org/doi/10.1021/cm00043a002https://doi.org/10.1021/cm00043a002research-articleACS PublicationsRequest reuse permissionsArticle Views168Altmetric-Citations44LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts