John A. Belot

Selective-area atomic layer epitaxy growth of ZnO features on soft lithography-patterned substrates

Templated ZnO thin-film growth from the vapor phase is achieved on docosyltrichloro- silane-patterned Si substrates using atomic layer epitaxy (ALE) combined with soft lithography. Patterned hydrophobic self-assembled monolayers (SAMs) are first transferred to single-crystal Si surfaces by hot microcontact printing. Using diethylzinc and water as ALE precursors, crystalline ZnO layers are then grown selectively on the SAM-free surface regions where native hydroxy groups nucleate growth from the vapor phase. High-resolution ZnO patterns with 1.0–40 μm feature sizes are readily achieved, demonstrating that soft lithography combined with ALE is a simple and promising methodology for selective area in situ vapor phase fabrication of patterned oxide thin films.

Buffers for high temperature superconductor coatings. Low temperature growth of CeO2 films by metal–organic chemical vapor deposition and their implementation as buffers

Abstract Smooth, epitaxial cerium dioxide thin films have been grown in-situ in the 450–650°C temperature range on (001) yttria-stabilized zirconia (YSZ) substrates by metal–organic chemical vapor deposition (MOCVD) using a new fluorine-free liquid Ce precursor. As assessed by X-ray diffraction, transmission electron microscopy (TEM), and high-resolution electron microscopy (HREM), the epitaxial films exhibit a columnar microstructure with atomically abrupt film-substrate interfaces and with only minor bending of the crystal plane parallel to the substrate surface near the interface and at the column boundaries. With fixed precursor temperature and gas flow rate, the CeO 2 growth rate decreases from ∼10 A/min at 450°C to ∼6.5 A/min at 540°C. The root-mean-square roughness of the films also decreases from 15.5 A at 450°C to 4.3 A at 540°C. High-quality, epitaxial YBa 2 C 3 O 7− x films have been successfully deposited on these MOCVD-derived CeO 2 films grown at temperatures as low as 540°C. They exhibit T c =86.5 K and J c =1.08×10 6 A/cm 2 at 77.4 K.

Film microstructure-deposition condition relationships in the growth of epitaxial NiO films by metalorganic chemical vapor deposition on oxide and metal substrates

High-quality epitaxial or highly textured NiO thin films can be grown at temperatures of 400–750°C by low-pressure metalorganic chemical vapor deposition (MOCVD) on MgO, SrTiO 3 , C-cut sapphire, as well as on single crystal and highly textured Ni (200) metal substrates using Ni(dpm) 2 (dpm – dipivaloylmethanate) as the volatile precursor and O 2 or H 2 O as the oxidizer/protonolyzer. X-ray diffraction (XRD), scanning electron microscopy/energy dispersive detection (SEM/EDX), and atomic force microscopy (AFM) confirm that the O 2 -derived NiO films are smooth and that the quality of the epitaxy can be improved by decreasing the growth temperature and/or the precursor flow rate. However, low growth temperatures (400–500 °C) lead to rougher surfaces and carbon contamination. The H 2 O-derived NiO films, which can be obtained only at relatively high temperatures (650–750 °C), exhibit slightly broader ω scan full width half-maximum (FWHM) values and rougher surfaces but no carbon contamination. Using H 2 O as the oxidizer/protonolyzer, smooth and highly textured NiO (111) films can be grown on easily oxidized single crystal and highly textured Ni (200) metal substrates, which is impossible when O 2 is the oxidizer. The textural quality of these films depends on both the quality of the metal substrates and the gaseous precursor flow rate.

MOCVD precursor design issues. Recent advances in the chemistry and vapor pressure characteristics of Ba(hexafluoroacetylacetonate)2·polyether complexes

Abstract This contribution presents synthetic, structural and volatility results for a series of new Ba(hfa) 2 polyether (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.

Efficient route to TlBa2Ca2Cu3O9+x thin films by metal-organic chemical vapor deposition using TlF as a thallination source

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 885u2009°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=103u2009K and Jc=4.4×104u2009A/cm2 (77 K, 0 T). Magnetic hysteresis measurements yield Jc=1.9×105u2009A/cm2 (30 K, 0.01 T) and show considerable flux pinning at low temperatures with Jc=1.4×105u2009A/cm2 (5 K, 4.5 T).

Metal-organic chemical vapor deposition routes to films of transparent conducting oxides

This contribution reports the in situ growth of transparent, conducting Ga x In 2-x O 3 and Zn k In 2 O k+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 × 10 20 cm −3 , mobility = 68 cm 2 /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 × 10 20 cm −3 , mobility = 18.6 cm 2 /Vs) for K = 0.66 were measured. The optical transparency window is significantly broader than that of ITO.

Novel Metal-Organic Chemical Vapor Deposition / T1F Annealing Route to Thin Films of Tl1Ba2Ca2Cu3O9+x

Thin films of TI1Ba2Ca2Cu3O9+x have been grown on single crystal (110) LaAlO3 by a metal-organic chemical vapor deposition process 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. A subsequent phase-selective annealing procedure accomplishes thallination using TIF in a bulk oxide pellet. The resulting films are nearly phase-pure and highly oriented and contain negligible fluoride by windowless energy-dispersive x-ray measurements. The films exhibit transport measured Tc = 103 K and Jc > 104 A/cm2 (77 K. 0 T) and at low temperatures retain Jc > 105 A/cm2 (5 K, 4.5 T) as measured by magnetic hysteresis.

MOCVD routes to thin films for superconducting applications. Precursor synthesis and film processing issues

Low pressure metal-organic chemical vapor deposition has been used to grow dielectric thin films of the tetragonal perovskites LaSrGaO 4 and PrSrGaO 4 on (110) LaAlO 3 using the volatile metal sources Pr(dpm) 3 , La(hfa) 3 •tri, Ga(dpm) 3 , and Sr(hfa) 2 •tet (dpm = dipivaloylmethanate, hfa = hexafluoroacetylacetonate, tet = tetraglyme, and tri = triglyme). The PrSrGaO 4 , a new ternary oxide, was found to have a body-centered tetragonal lattice with a = b = 3.80 and c = 12.59 A. Epitaxial c -axis oriented growth of these materials has been revealed by both x-ray and electron diffraction, with an average surface roughness, measured by AFM, of 1.2 nm for LaSrGaO 4 and 3.0 nm for PrSrGaO 4 . In addition to this, the ability of these materials to function as lattice-matched buffer layers for the growth of the high temperature superconductor YBa 2 Cu 3 O 7− , has been explored. The superconductive properties of the YBCO layer do not indicate any degradation attributable to the buffer layers, with the onset of superconductivity displaying a sharp metal-superconductor transition at T c = 87.3 K and 84.5 K for the LaSrGaO 4 and PrSrGaO 4 systems, respectively.

Volatile, Fluorine-Free β-Ketoiminate Precursors for MOCVD Growth of Lanthanide Oxide Thin Films

Lanthanide oxide thin films are of increasing scientific and technological interest to the materials science community. A new class of fluorine-free, volatile, low-melting lanthanide precursors for the metal-organic chemical vapor deposition (MOCVD) of these films has been developed. Initial results from a full synthetic study of these lanthanide-organic complexes are detailed.

The effect of the reactant gas on YBa2Cu3Ox film formation

Abstract The reactant gas used as the deposition ambient has a large effect on the composition and properties of cuprate superconductor films. In this study YBa2Cu3Ox thin films are deposited by pulsed organometallic beam epitaxy (POMBE). The barium precursor used contains fluorine and it is therefore possible to incorporate unwanted fluorine into the deposited film. For our deposition process both the fluorine content and oxygen content of the film are highly dependent on the reactant gas used as the deposition ambient. Many of the reaction conditions that remove fluorine also deplete the film of oxygen. In this study a set of reaction conditions that produce YBa2Cu3Ox films which are both fluorine-free and fully oxygenated are presented.