Alan D. Berry

Formation of high Tc superconducting films by organometallic chemical vapor deposition

The first growth of superconducting YBaCuO films by organometallic chemical vapor deposition is described. Metal β‐diketonates were decomposed thermally on MgO substrates in an oxygen‐rich atmosphere to produce amorphous brown films. Subsequent annealing in oxygen yielded dull gray films whose thickness corresponded to deposition rates of approximately 8 nm min−1. These films showed semiconductor‐like behavior at higher temperatures, followed by a broad resistive transition from 80 to 36 K with the resistance becoming zero at ∼20 K. Analysis of x‐ray data indicated the presence of the orthorhombic superconducting phase and various other metal oxides. Profilometer measurements yielded film thicknesses up to 950 nm, and scanning electron microscopy revealed faceted grains from 0.5 to 1.0 μm in size.

Electronic connection to the interior of a mesoporous insulator with nanowires of crystalline RuO2

Highly porous materials such as mesoporous oxides are of technological interest for catalytic, sensing and remediation applications: the mesopores (of size 2–50 nm) permit ingress by molecules and guests that are physically excluded from microporous materials. Connecting the interior of porous materials with a nanoscale or ‘molecular’ wire would allow the direct electronic control (and monitoring) of chemical reactions and the creation of nanostructures for high-density electronic materials. The challenge is to create an electronic pathway (that is, a wire) within a mesoporous platform without greatly occluding its free volume and reactive surface area. Here we report the synthesis of an electronically conductive mesoporous composite—by the cryogenic decomposition of RuO 4—on the nanoscale network of a partially densified silica aerogel. The composite consists of a three-dimensional web of interconnected (∼4-nm in diameter) crystallites of RuO2, supported conformally on the nanoscopic silica network. The resulting monolithic (RuO2∥SiO 2) composite retains the free volume of the aerogel and exhibits pure electronic conductivity. In addition to acting as a wired mesoporous platform, the RuO2-wired silica aerogel behaves as a porous catalytic electrode for the oxidation of chloride to molecular chlorine.

Nonlinear optical properties of quantum-confined GaAs nanocrystals in Vycor glass

Quantum‐confined nanocrystallites of GaAs are fabricated in porous Vycor glass and the bound electronic nonlinear refractive index, the two‐photon absorption coefficient, and the refraction from carriers generated by two‐photon absorption are simultaneously determined using the Z‐scan method and compared to those of bulk GaAs. The measured nonlinear refractive index is an order of magnitude larger than that of bulk GaAs at 1060 nm.

OMCVD of thin films from metal diketonates and triphenylbismuth

Films containing the metals copper, yttrium, calcium, strontium, barium, and bismuth were grown by organometallic chemical vapor deposition (OMCVD). Depositions were carried out at atmospheric pressure in an oxygen-rich environment using metal beta-diketonates and triphenylbismuth. The films were characterized by Auger electron spectroscopy, Nomarski and scanning electron microscopy, and x-ray diffraction. The results show that films containing yttrium consisted of Y 2 O 3 with a small amount of carbidic carbon, those with copper and bismuth were mixtures of oxides with no detectable carbon, and those with calcium, strontium, and barium contained carbonates. Use of a partially fluorinated barium beta-diketonate gave films of BaF 2 with small amounts of BaCO 3 .

Growth of superconducting thin films of bismuth-strontium-calcium-copper oxide by organometallic chemical vapor deposition

Abstract The first growth of superconducting Bi-Sr-Ca-Cu-O films by organometallic chemical vapor deposition is described. Triphenyl bismuth and beta-diketonates of strontium, calcium, and copper were decomposed thermally at 500°C on MgO substrates in an oxygen-rich atmosphere to produce fine grained or amorphous, dark brown to black films. Subsequent annealing in oxygen yielded gray-black films with thicknesses of 0.95 to 1.25 μm. X-ray analysis indicated the presence of a tetragonal superconducting phase along with other metal oxides. The sheet resistance versus temperature for the sample with the highest T c had a resistive transition with a midpoint at 78.8 K, a width of 7.7 K, and R = 0 at 73.2 K.

Fabrication of GaAs and InAs wires in nanochannel glass

A newly developed porous glass, nanochannel glass, was used to fabricate uniform, high‐density GaAs and InAs micro‐ and nanowires with high aspect ratios. The fabrication process utilized reactions between organogallium and organoindium compounds with arsine to produce polycrystalline GaAs and InAs with crystallite sizes of approximately 50–130 A when annealed at 400–500 °C. At the higher annealing temperatures, the InAs wires exhibited an increase in surface porosity and grain size, whereas the GaAs wires maintained a uniform, smooth texture.

Organometallic chemical vapor deposition and characterization of indium phosphide nanocrystals in Vycor porous glass

Indium phosphide has been deposited in 40 and 150 A Vycor porous glass by the reaction of trimethylindium with excess PH3. X‐ray diffraction (XRD) of the red, transparent samples confirms the presence of crystalline indium phosphide. The amount of III‐V material deposited within the glass matrix (loading) and annealing conditions influence the crystallinity and particle size of the nanocrystallites. The absorption spectra of vacuum‐annealed samples is blue shifted with respect to bulk InP, with maxima ranging from 500 to 700 nm for both the 40 and 150 A samples and is consistent with size quantization. The nonlinear optical properties of these nanocrystallite composites have been evaluated by Z‐scan measurements and are characterized by a defocusing refractive nonlinearity influenced by a substantial nonlinear loss presumed to be caused by two‐photon absorption.

Ultrafast studies of gold, nickel, and palladium nanorods

Steady state and ultrafast transient absorption studies have been carried out for gold, nickel, and palladium high aspect ratio nanorods. For each metal, nanorods were fabricated by electrochemical deposition into approximately 6 microm thick polycarbonate templates. Two nominal pore diameters(10 and 30 nm, resulting in nanorod diameters of about 40 and 60 nm, respectively) were used, yielding nanorods with high aspect ratios (>25). Static spectra of nanorods of all three metals reveal both a longitudinal surface plasmon resonance (SPR(L)) band in the mid-infrared as well as a transverse band in the visible for the gold and larger diameter nickel and palladium nanorods. The appearance of SPR(L) bands in the infrared for high aspect ratio metal nanorods and the trends in their maxima for the different aspect ratios and metals are consistent with calculations based on the Gans theory. For the gold and nickel samples, time resolved studies were performed with a subpicosecond resolution using 400 nm excitation and a wide range of probe wavelengths from the visible to the mid-IR as well as for infrared excitation (near 2000 cm(-1)) probed at 800 nm. The dynamics observed for nanorods of both metals and both diameters include transients due to electron-phonon coupling and impulsively excited coherent acoustic breathing mode oscillations, which are similar to those previously reported for spherical and smaller rod-shaped gold nanoparticles. The dynamics we observe are the same within the experimental uncertainty for 400 nm and infrared (5 microm) excitation probed at 800 nm. The transient absorption using 400 nm excitation and 800 nm probe pulses of the palladium nanorods also reveal coherent acoustic oscillations. The results demonstrate that the dynamics for high aspect ratio metal nanorods are similar to those for smaller nanoparticles.

Primary and secondary trimethylsilylmethylstibines. Synthesis, characterization and chemical vapor deposition properties

The primary and secondary trimethylsilylmethylstibines (trimethylsilylmethyl = Me3SiCH2-) (Me3SiCH2)SbH2 and (Me3SiCH2)2SbH have been synthesized by the reduction of a corresponding dihalo- and monohaloantimony compound, respectively. Trimethylsilylmethylstibine was prepared by the reduction of (Me3SiCH2)SbBr2 with lithium aluminum hydride (LAH) in tetraglyme. The primary stibine is highly air-sensitive and exhibits a vapor pressure of 2.0 Torr at O°C. Bis-(trimethyl-silylmethyl)stibine was synthesized by the LAH reduction of either (Me3SiCH2)2SbBr or (Me3SiCH2)2SbI in diethyl ether. The secondary stibine is less sensitive to air than (Me3SiCH2)SbH2 but nonetheless decomposes quickly when exposed to air. The detailed synthesis, spectroscopic characterizations and physical properties of both stibines, as well as the preliminary chemical vapor deposition experiments of (Me3SiCH2)SbH2, are discussed.

Sodium fluoride thin films by chemical vapor deposition

Abstract Thin films of sodium fluoride have been deposited for the first time by chemical vapor deposition of the fluorinated metal organic precursors sodium hexafluoroisopropoxide, sodium perfluoro- t -butoxide, sodium hexafluoroacetylacetonate and sodium heptafluoro-octadionate. The best quality films were obtained using sodium hexafluoroisopropoxide in vacuo at a substrate temperature of 250–300°C.