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David Emin - One of the best experts on this subject based on the ideXlab platform.
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raman spectroscopy of Boron Carbides and related Boron containing materials
AIP Conf. Proc.; (United States), 2008Co-Authors: J A Shelnutt, David Emin, B Morosin, A Mullendore, G Slack, C. WoodAbstract:Raman spectra of crystalline Boron, Boron carbide, Boron arsenide (B12As2), and Boron phosphide (B12P2) are reported. The spectra are compared with other Boron‐containing materials containing the Boron icosahedron as a structural unit. The spectra exhibit similar features some of which correlate with the structure of the icosahedral units of the crystals. The highest Raman lines appear to be especially sensitive to the B‐B distance in the polar triangle of the icosahedron. Such Raman structural markers are potentially useful in efforts to tailor electronic properties of these high temperature semiconductors and thermoelectrics.Raman spectroscopy is also useful in characterizing methods of preparation of Boron‐based materials. For example, inclusions of carbonaceous material in the Boron Carbides can be detected by the presence of two broad Raman lines 1370 and 1580 cm−1. In the hot‐pressed samples that exhibited the lines the carbonaceous material is amorphous and much like carbon black or pyrolytic glass...
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dielectric function of Boron Carbides from kramers kronig analysis of reflectance spectra
AIP Conference Proceedings (American Institute of Physics); (United States), 2008Co-Authors: Herbert L Tardy, Terrence L. Aselage, David EminAbstract:Dielectric functions e(E) are presented for four BxC compositions (x=4.0, 5.5, 6.5, 9.0) made by reactive hot pressing. The spectra were obtained by Kramers‐Kronig analysis of reflectance spectra measured from 450 to 37,000 cm−1 (250 nm–22 μm). The behavior of Im(e) is manifestly nonmetallic with no plasma edge and Re(e)≂6. There is also evidence of an indirect absorption edge at about 13,000 cm−1.
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Elastic properties of Boron Carbides
AIP Conference Proceedings, 2008Co-Authors: J. H. Gieske, T. L. Aselage, David EminAbstract:Boron Carbides made by hot pressing exist as a single phase with compositions between 10 and 20 atomic percent carbon. The longitudinal and shear ultrasonic velocities were measured on fully dense Boron Carbides with compositions throughout the single‐phase region. Both longitudinal and shear velocities decreased rapidly when the carbon content was below 13 atomic percent. Young’s modulus, shear modulus, bulk modulus, compressibility, and Poisson’s ratio, were calculated from the ultrasonic velocities. The results show that Boron Carbides become substantially more compressible for carbon concentrations below 13%. This softening is consistent with B12 icosahedra replacing B11C icosahedra in this composition range.
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on the crystal structure of Boron Carbides
AIP Conference Proceedings (American Institute of Physics); (United States), 2008Co-Authors: B Morosin, T L Aselage, David EminAbstract:Several crystals of Boron carbide, grown from molten Cu, Pt, and Pd solutions using natural occurring as well as isotopically enriched Boron, give essentially identical values for the lattice parameters. These parameters are consistent with carbon‐saturated compositions near B4C.Detailed crystal structure refinement on some of these crystals yields positional and thermal parameters in good agreement with each other. More importantly, the thermal parameters of these studies are compared with those of crystals with lower carbon content (e.g., B13C2) as well as carbothermal prepared crystals. The thermal parameters of chain atoms for crystals with lower carbon content are both exceptionally large and much larger than those of crystals with composition near B4C. This result suggests that the crystals of lower carbon content contain a solid solution of C‐B‐C and C‐B‐B chains.
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infrared absorption in Boron Carbides dependence on isotopes and carbon concentration
AIP Conference Proceedings, 2008Co-Authors: Herman Stein, Terry Aselage, David EminAbstract:Infrared reflectance and transmittance measurements between 500 and 1800 cm−1 were obtained on Boron Carbides with between 10 and 20 atomic percent carbon. Measurements on both Boron and carbon isotopically enriched samples indicate that all prominent modes involve Boron motion, and that all but a mode near 950 cm−1 involve carbon motion. Since the spectrum remains qualitatively unaltered as a function of carbon concentration, its prominent features must have a common structural origin.
Peter A Dowben - One of the best experts on this subject based on the ideXlab platform.
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composition dependent charge transport in Boron Carbides alloyed with aromatics plasma enhanced chemical vapor deposition aniline orthocarborane films
Langmuir, 2018Co-Authors: Adeola Oyelade, Peter A Dowben, Bin Dong, Sean Knight, Andrew J Yost, Nicole Benker, Mathias Schubert, Jeffry A KelberAbstract:Boron carbide films, alloyed with aniline moieties, were deposited by plasma enhanced chemical vapor deposition (PECVD) from aniline and orthocarborane precursors and were found to exhibit composition-dependent drift carrier lifetimes as derived from I(V) and C(V)) measurements. For a film with an aniline/carborane ratio of 5:1, the effective drift carrier lifetimes are ∼80 μs at low bias voltage but quickly drop to a few microseconds with increasing bias. A film with a 10:1 aniline/carborane ratio, however, exhibited lifetimes of ∼6 μs, or less, at 1 kHz, and much smaller values at 10 kHz. These lifetimes are orders of magnitude longer than those in polyaniline films and comparable to those in PECVD carborane films without aromatic content. X-ray photoelectron spectroscopy (XPS), FTIR, and ellipsometry, combined with density functional theory (DFT)-based cluster calculations, indicate that aniline and orthocarborane moieties are largely intact within the films. Bonding occurs primarily between aniline C ...
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increased drift carrier lifetime in semiconducting Boron Carbides deposited by plasma enhanced chemical vapor deposition from carboranes and benzene
Journal of Vacuum Science and Technology, 2017Co-Authors: George Peterson, Elena Echeverria, Bin Dong, Joseph P Silva, Ethiyal R Wilson, Jeffry A Kelber, Michael Nastasi, Peter A DowbenAbstract:Plasma-enhanced chemical vapor (PECVD) codeposition of benzene and 1,2-dicarbadodecaborane, 1,2-B10C2H12 (orthocarborane) and benzene, 1,7 dicarbadodecaborane, and 1,7-B10C2H12 (metacarborane) results in semiconducting Boron carbide composite films with significantly longer drift carrier lifetimes than plasma-enhanced chemical vapor deposited semiconducting Boron carbide synthesized from orthocarborane or metacarborane alone. Capacitance versus voltage C ( V ) and current versus voltage I ( V ) measurements indicate the hole carrier lifetimes for PECVD benzene/orthocarborane based semiconducting Boron carbide composites increase to 2.5 ms from values of ≤35 μs for the PECVD semiconducting Boron carbide films fabricated without benzene. For PECVD benzene/metacarborane based semiconducting Boron carbide composites, there is an increase in the hole carrier lifetime to roughly 300 ns from values of 50 ns for those films fabricated without benzene.
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insights into the local electronic structure of semiconducting Boron Carbides in the vicinity of transition metal dopants
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2010Co-Authors: Guangfu Luo, Jing Liu, Waining Mei, Peter A DowbenAbstract:Based on the experimentally determined pairwise site locations of transition metal atoms in doped semiconducting Boron Carbides, model spin-polarized electronic structure calculations indicate that some transition metal doped semiconducting Boron Carbides may act as excellent spin filters when used as the dielectric barrier in a magnetic tunnel junction structure. The local spin configuration of all the 3d transition metals, Ti to Cu, doped Boron Carbides are compared using first-principle total energy calculations on cluster and infinite icosahedral chain models. In the case of Ti and Fe doping, there may be considerable enhancements in the magneto-resistance of the heterostructure. The models also confirm that the favorable sites 3d transition metal atoms occupied are within the icosahedral cage, in a pairwise fashion on adjacent icosahedra.
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the local structure of transition metal doped semiconducting Boron Carbides
Journal of Physics D, 2010Co-Authors: Jing Liu, Jennifer I Brand, Guangfu Luo, Waining Mei, Orhan Kizilkaya, Eric D Shepherd, Peter A DowbenAbstract:Transition metal doped Boron Carbides produced by plasma enhanced chemical vapour deposition of orthocarborane (closo-1,2-C2B10H12) and 3d metal metallocenes were investigated by performing K-edge extended x-ray absorption fine structure and x-ray absorption near edge structure measurements. The 3d transition metal atom occupies one of the icosahedral Boron or carbon atomic sites within the icosahedral cage. Good agreement was obtained between experiment and models for Mn, Fe and Co doping, based on the model structures of two adjoined vertex sharing carborane cages, each containing a transition metal. The local spin configurations of all the 3d transition metal doped Boron Carbides, Ti through Cu, are compared using cluster and/or icosahedral chain calculations, where the latter have periodic boundary conditions.
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3d transition metal doping of semiconducting Boron Carbides
Materials Letters, 2009Co-Authors: Peter A Dowben, Jing Liu, Orhan Kizilkaya, Benjamin W Montag, Kyle A Nelson, Ildar F Sabirianov, Jennifer I BrandAbstract:The introduction metallocenes, in particular ferrocene (Fe(η 5 -C 5 H 5 ) 2 ), cobaltocene (Co(η 5 -C 5 H 5 ) 2 ), and nickelocene (Ni(η 5 -C 5 H 5 ) 2 ), together with the carborane source molecule closo-1,2-dicarbadodecaborane, during plasma enhanced chemical vapor deposition, will result in the transition metal doping of semiconducting Boron Carbides. Here we report using ferrocene to introduce Fe dopants, and a semiconducting Boron-carbide homojunction has been fabricated. The diode characteristics are very similar to those fabricated with Co and Ni doping.
Guangfu Luo - One of the best experts on this subject based on the ideXlab platform.
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insights into the local electronic structure of semiconducting Boron Carbides in the vicinity of transition metal dopants
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2010Co-Authors: Guangfu Luo, Jing Liu, Waining Mei, Peter A DowbenAbstract:Based on the experimentally determined pairwise site locations of transition metal atoms in doped semiconducting Boron Carbides, model spin-polarized electronic structure calculations indicate that some transition metal doped semiconducting Boron Carbides may act as excellent spin filters when used as the dielectric barrier in a magnetic tunnel junction structure. The local spin configuration of all the 3d transition metals, Ti to Cu, doped Boron Carbides are compared using first-principle total energy calculations on cluster and infinite icosahedral chain models. In the case of Ti and Fe doping, there may be considerable enhancements in the magneto-resistance of the heterostructure. The models also confirm that the favorable sites 3d transition metal atoms occupied are within the icosahedral cage, in a pairwise fashion on adjacent icosahedra.
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the local structure of transition metal doped semiconducting Boron Carbides
Journal of Physics D, 2010Co-Authors: Jing Liu, Jennifer I Brand, Guangfu Luo, Waining Mei, Orhan Kizilkaya, Eric D Shepherd, Peter A DowbenAbstract:Transition metal doped Boron Carbides produced by plasma enhanced chemical vapour deposition of orthocarborane (closo-1,2-C2B10H12) and 3d metal metallocenes were investigated by performing K-edge extended x-ray absorption fine structure and x-ray absorption near edge structure measurements. The 3d transition metal atom occupies one of the icosahedral Boron or carbon atomic sites within the icosahedral cage. Good agreement was obtained between experiment and models for Mn, Fe and Co doping, based on the model structures of two adjoined vertex sharing carborane cages, each containing a transition metal. The local spin configurations of all the 3d transition metal doped Boron Carbides, Ti through Cu, are compared using cluster and/or icosahedral chain calculations, where the latter have periodic boundary conditions.
R O Pohl - One of the best experts on this subject based on the ideXlab platform.
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thermal properties of Boron and Boron Carbides
AIP Conf. Proc.; (United States), 2008Co-Authors: P R H Turkes, E T Swartz, R O PohlAbstract:The specific heat of β‐B shows the features characteristic for pure dielectric crystals. At low temperatures, it varies as T3; from the prefactor the Debye temperature is determined to 1520 K. In Boron Carbides, however, low temperature anomalies have been observed. Most prominent in B4C, B15C2, and B9C is a mode at ≊70 cm−1 (f≊2.1×1012Hz) which contains ≊0.3% of the total number of vibrational modes in these solids. Its origin is unknown. The thermal conductivity of crystalline β‐B and Boron‐rich compounds like B12As2 is that typical for crystalline solids. That of crystalline YB66, however resembles greatly that of all glasses. Polycrystalline B4C has a conductivity larger than that of β‐B above 300 K, although its temperature dependence between 1 and 1000 K is that typical for highly disordered crystals. As the carbon contents decrease (B13C2, B9C), the conductivity decreases further and becomes comparable to that of YB66. The cause for the phonon scattering in YB66 and in the Boron Carbides is not known.
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lattice vibrations of Boron Carbides
IEEE Journal of Solid-state Circuits, 1997Co-Authors: P A Medwick, R O PohlAbstract:The internal friction at low temperatures has been measured on polycrystalline samples of {beta}-B, B{sub 4}C, B{sub 13}C{sub 2}, and B{sub 9}C. As the carbon deficiency increases in the Boron Carbides, the internal friction approaches that of amorphous solids. For comparison, the internal friction of amorphous B{sub 9}C, produced as a thin film by e-beam evaporation on a Si double-paddle oscillator, has also been measured. It is very similar to that of the polycrystalline B{sub 9}C sample. The results are discussed in terms of glass-like lattice vibrations which have been noted before in highly disordered crystals, e.g., Ba{sub 1-y}La{sub x}F{sub 2x}. It is concluded that the low thermal conductivity of B{sub 9}C near room temperature which has been observed previously is indeed equal to its theoretical lower limit.
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thermal conductivity and specific heat of Boron Carbides
Journal of Alloys and Compounds, 1994Co-Authors: P A Medwick, Henry E Fischer, R O PohlAbstract:Abstract We present measurements of the thermal conductivity (30 T T polycrystalline Boron Carbides (B 1- x C x ) for carbon concentrations spanning the single-phase field (0.1 x as it evolves from crystalline behavior for carbon-rich specimens to a glass-like conductivity characteristic of amorphous solids. The specific heat of Boron Carbides is insensitive to the carbon concentration for T > 60 K.
Jennifer I Brand - One of the best experts on this subject based on the ideXlab platform.
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the local structure of transition metal doped semiconducting Boron Carbides
Journal of Physics D, 2010Co-Authors: Jing Liu, Jennifer I Brand, Guangfu Luo, Waining Mei, Orhan Kizilkaya, Eric D Shepherd, Peter A DowbenAbstract:Transition metal doped Boron Carbides produced by plasma enhanced chemical vapour deposition of orthocarborane (closo-1,2-C2B10H12) and 3d metal metallocenes were investigated by performing K-edge extended x-ray absorption fine structure and x-ray absorption near edge structure measurements. The 3d transition metal atom occupies one of the icosahedral Boron or carbon atomic sites within the icosahedral cage. Good agreement was obtained between experiment and models for Mn, Fe and Co doping, based on the model structures of two adjoined vertex sharing carborane cages, each containing a transition metal. The local spin configurations of all the 3d transition metal doped Boron Carbides, Ti through Cu, are compared using cluster and/or icosahedral chain calculations, where the latter have periodic boundary conditions.
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3d transition metal doping of semiconducting Boron Carbides
Materials Letters, 2009Co-Authors: Peter A Dowben, Jing Liu, Orhan Kizilkaya, Benjamin W Montag, Kyle A Nelson, Ildar F Sabirianov, Jennifer I BrandAbstract:The introduction metallocenes, in particular ferrocene (Fe(η 5 -C 5 H 5 ) 2 ), cobaltocene (Co(η 5 -C 5 H 5 ) 2 ), and nickelocene (Ni(η 5 -C 5 H 5 ) 2 ), together with the carborane source molecule closo-1,2-dicarbadodecaborane, during plasma enhanced chemical vapor deposition, will result in the transition metal doping of semiconducting Boron Carbides. Here we report using ferrocene to introduce Fe dopants, and a semiconducting Boron-carbide homojunction has been fabricated. The diode characteristics are very similar to those fabricated with Co and Ni doping.
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pairwise cobalt doping of Boron Carbides with cobaltocene
Journal of Applied Physics, 2007Co-Authors: Yu A Ignatov, Yaroslav Losovyj, L Carlson, D Lagraffe, Jennifer I Brand, Peter A DowbenAbstract:We have performed Co K-edge x-ray absorption fine structure and x-ray absorption near edge structure measurements of Co-doped plasma enhanced chemical vapor phase deposition (PECVD) grown “C2B10Hx” semiconducting Boron Carbides, using cobaltocene. Cobalt does not dope PECVD grown Boron Carbides as a random fragment of the cobaltocene source gas. The Co atoms are fivefold Boron coordinated (R=2.10±0.02A) and are chemically bonded to the icosahedral cages of B10CHx or B9C2Hy. Pairwise Co doping occurs, with the cobalt atoms favoring sites some 5.28±0.02A apart.
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Doping of Boron Carbides with cobalt, using cobaltocene
Applied Physics A, 2007Co-Authors: L Carlson, Yaroslav Losovyj, D Lagraffe, Peter A Dowben, Snjezana Balaz, A. Ignatov, Jaewu Choi, Jennifer I BrandAbstract:The decomposition of cobaltocene under low energy electron irradiation appears facile, and evidence suggests that the decomposition products lead to an increase in the carrier concentration in semiconducting Boron Carbides. Using cobaltocene to introduce dopants, we fabricated a semiconducting Boron carbide homojunction
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Surface photovoltage effects on the isomeric semiconductors of Boron-carbide
Applied Physics Letters, 2004Co-Authors: Anthony N. Caruso, Yaroslav Losovyj, Jennifer I Brand, Peter A Dowben, Snjezana Balaz, Bo Xu, A.s. Mcmullen-gunn, David N. McilroyAbstract:During exposure to synchrotron radiation, closo 1,7-dicarbadodecaborane (metacarborane) and closo 1,2-dicarbadodecaborane (orthocarborane) decompose, and are accompanied by increasingly evident photoemission surface photovoltage effects. We show that metacarborane and orthocarborane form self-doped n-type and p-type Boron-Carbides, respectively. Surface photovoltage effects dominate the photoemission final state, not the changes in electronic structure due to decomposition.