Carl R. Kannewurf

Highly conductive epitaxial CdO thin films prepared by pulsed laser deposition

Epitaxial growth of both pure and doped CdO thin films has been achieved on MgO (111) substrates using pulsed laser deposition. A maximum conductivity of 42 000 S/cm with mobility of 609 cm2/V s is achieved when the CdO epitaxial film is doped with 2.5% Sn. The pure CdO epitaxial film has a band gap of 2.4 eV. The band gap increases with doping and reaches a maximum of 2.87 eV when the doping level is 6.2%. Both grain boundary scattering and ionized impurity scattering are found to contribute to the mobility of CdO films.

Organometallic chemical vapor deposition of high Tc superconducting films using a volatile, fluorocarbon-based precursor

Uniform films of the high Tc superconductor YBa2Cu3O7−δ have been prepared by organometallic chemical vapor deposition using the volatile metalorganic precursors Cu(acetylacetonate)2, Y(dipivaloylmethanate)3, and Ba(heptafluorodimethyloctanedionate)2. With argon as a carrier gas and water vapor as a reactant, film growth rates of 10–30 nm/min are achieved. After annealing under oxygen, energy dispersive x‐ray analysis, profilometry, and x‐ray diffraction data reveal that such YBa2Cu3O7−δ films on [100] single‐crystal MgO have good compositional and dimensional uniformity as well as preferential orientation of crystallite c axes perpendicular to the substrate surface. Four‐probe resistivity measurements reveal the onset of superconductivity at ∼90 K and zero resistance by 66.2 K.

Indium-cadmium-oxide films having exceptional electrical conductivity and optical transparency: Clues for optimizing transparent conductors

Materials with high electrical conductivity and optical transparency are needed for future flat panel display, solar energy, and other opto-electronic technologies. InxCd1-xO films having a simple cubic microstructure have been grown on amorphous glass substrates by a straightforward chemical vapor deposition process. The x = 0.05 film conductivity of 17,000 S/cm, carrier mobility of 70 cm2/Vs, and visible region optical transparency window considerably exceed the corresponding parameters for commercial indium-tin oxide. Ab initio electronic structure calculations reveal small conduction electron effective masses, a dramatic shift of the CdO band gap with doping, and a conduction band hybridization gap caused by extensive Cd 5s + In 5s mixing.

Charge transport, optical transparency, microstructure, and processing relationships in transparent conductive indium–zinc oxide films grown by low-pressure metal-organic chemical vapor deposition

Indium–zinc oxide films (ZnxInyOx+1.5y), with x/y=0.08–12.0, are grown by low-pressure metal-organic chemical vapor deposition using the volatile metal–organic precursors In(TMHD)3 and Zn(TMHD)2 (TMHD=2,2,6,6–tetramethyl–3,5–heptanedionato). Films are smooth (rms roughness=40–50 A) with complex microstructures which vary with composition. The highest conductivity is found at x/y=0.33, with σ=1000 S/cm (n-type; carrier density=3.7×1020 cm3; mobility=18.6 cm2/V s; dσ/dT<0). The optical transmission window of such films is broader than Sn-doped In2O3, and the absolute transparency rivals or exceeds that of the most transparent conductive oxides. X-ray diffraction, high resolution transmission electron microscopy, microdiffraction, and high resolution energy dispersive X-ray analysis show that such films are composed of a layered ZnkIn2O3+k phase precipitated in a cubic In2O3:Zn matrix.

Phase‐selective route to high Tc superconducting Tl2Ba2Can−1CunO2n+4 films: Combined metalorganic chemical vapor deposition using an improved barium precursor and stoichiometry‐controlled thallium vapor diffusion

Films of the Tl2Ba2Can−1CunO2n+4 high Tc superconductors (n=2 or 3) can be prepared with a high degree of phase selectivity using a combination of metalorganic chemical vapor deposition (MOCVD) and vapor diffusion. Ba‐Ca‐Cu‐O films are first prepared by MOCVD using the volatile metalorganic precursors Ba(hexafluoroacetyl‐ acetonate)2(tetraglyme), Ca(dipivaloylmethanate)2, and Cu(acetylacetonate)2. The ‘‘second‐generation’’ barium precursor exhibits significantly improved thermal stability and volatility over previously used compounds. Thallium is then incorporated into these films by vapor diffusion using a Tl‐Ba‐Ca‐Cu oxide mixture of controlled composition as the source of volatile thallium oxides. Phase control is achieved by a combination of improved stoichiometry of the deposited film, a result of the new Ba source, and annealing with the appropriate oxide mixture. The resultant films consist predominantly of the Tl2Ba2Ca2Cu3Ox or Tl2Ba2CaCu2Ox phase, each having preferential orientation of the cryst...

Highly conductive metallophthalocyanine assemblies. Structure, charge transport, and anisotropy in the metal-free molecular metal H2(Pc)I

Abstract That a metal ion is not required for high electrical conductivity is unequivocally demonstrated by structural, charge transport, optical, and magnetic characterization of the simplest phthalocyanine “molecular metal” H 2 (Pc)I. The crystal structure consists of staggered H 2 (Pc) +0.33 units stacked at 3.251(3) A intervals and parallel chains of I − 3 counterions. At 300 K, σ ‖ = 700 Ω −1 cm −1 and σ ‖ σ⊥ > 500 . At 15 K, σ ∼ reaches a maximum of ca. 4000 Ω −1 cm −1 and falls only to ca. 3500 Ω −1‖ cm −1 at 1.5 K. Analysis of single crystal polarized specular reflectance data (ir to uv) yields ω p = 6360(30) cm −1 and a tight-binding bandwidth of 1.3(1) eV. The magnetic susceptibility is Pauli-like ( X S = 2.21(5) × 10 −4 emu mol −1 ) except for a small, sample dependent Curie component.

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.

Computer automated charge transport measurement system

A description is given of the electronic configuration of a versatile computer-controlled measurement system that can be used to obtain AC and DC conductivity, Hall effect, and magnetoresistance data over the temperature range of 1.5 to 350 K. The system can process one to eight samples simultaneously in the resistance range from 0 to 10/sup 12/ Omega . >

First-principles calculations for understanding high conductivity and optical transparency in InxCd1−xO films

Abstract We investigate In x Cd 1− x O materials, where x =0.0, 0.031, 0.063 and 0.125, to understand their high electrical conductivity and optical transparency windows, using the full-potential linearized augmented plane wave (FLAPW) method. In addition, we employ the screened exchange LDA (sX-LDA) method to evaluate accurate band structures including band gap that is underestimated by the LDA calculations. The results show a dramatic Burstein–Moss shift of the absorption edge by the In doping, reflecting the small effective mass of the Cd 5s conduction band. The calculated direct band gaps, 2.36 eV for x =0.0 and 3.17 eV for x =0.063, show excellent agreement with experiment. The effective mass of the conduction band of CdO is calculated to be 0.24 m e (in the ▵ direction), in good agreement with an experimental value of 0.27m e , explaining its high electrical conductivity. The hybridization between the Cd 5s and the In 5s states yields complex many-body effects in the conduction bands: a hybridization gap in the conduction bands and a band-gap narrowing which cancels the further Burstein–Moss shift for higher In doping.