360 research outputs found
Novel Precursors for Boron Nanotubes: The Competition of Two-Center and Three-Center Bonding in Boron Sheets
We present a new class of boron sheets, composed of triangular and hexagonal
motifs, that are more stable than structures considered to date and thus are
likely to be the precursors of boron nanotubes. We describe a simple and clear
picture of electronic bonding in boron sheets and highlight the importance of
three-center bonding and its competition with two-center bonding, which can
also explain the stability of recently discovered boron fullerenes. Our
findings call for reconsideration of the literature on boron sheets, nanotubes,
and clusters.Comment: 4 pages, 4 figures, 1 tabl
Beyond Eliashberg superconductivity in MgB2: anharmonicity, two-phonon scattering, and multiple gaps
Density-functional calculations of the phonon spectrum and electron-phonon
coupling in MgB are presented. The phonons, which involve in-plane
B displacements, couple strongly to the electronic bands. The
isotropic electron-phonon coupling constant is calculated to be about 0.8.
Allowing for different order parameters in different bands, the superconducting
in the clean limit is calculated to be significantly larger. The
phonons are strongly anharmonic, and the non-linear contribution to
the coupling between the modes and the p bands is significant.Comment: 4 pages, 3 figure
DFT Study of Planar Boron Sheets: A New Template for Hydrogen Storage
We study the hydrogen storage properties of planar boron sheets and compare
them to those of graphene. The binding of molecular hydrogen to the boron sheet
(0.05 eV) is stronger than that to graphene. We find that dispersion of alkali
metal (AM = Li, Na, and K) atoms onto the boron sheet markedly increases
hydrogen binding energies and storage capacities. The unique structure of the
boron sheet presents a template for creating a stable lattice of strongly
bonded metal atoms with a large nearest neighbor distance. In contrast, AM
atoms dispersed on graphene tend to cluster to form a bulk metal. In particular
the boron-Li system is found to be a good candidate for hydrogen storage
purposes. In the fully loaded case this compound can contain up to 10.7 wt. %
molecular hydrogen with an average binding energy of 0.15 eV/H2.Comment: 19 pages, 7 figures, and 3 table
Primary alkylphosphine–borane polymers: Synthesis, low glass transition temperature, and a predictive capability thereof
With a multitude of potential applications, poly(phosphine–borane)s are an interesting class of polymer comprising main-group elements within the inorganic polymer backbone. A new family of primary alkylphosphine–borane polymers was synthesized by a solvent-free rhodium-catalyzed dehydrocoupling reaction and characterized by conventional chemicophysical techniques. The thermal stability of the polymers is strongly affected by the size and shape of the alkyl side chain with longer substituents imparting greater stability. The polymers show substantial stability toward UV illumination and immersion in water; however, they undergo a loss of alkylphosphine units during thermal degradation. The polymers exhibit glass transition temperatures (Tg) as low as −70 °C. A group interaction model (GIM) framework was developed to allow the semiquantitative prediction of Tg values, and the properties of the materials in this study were used to validate the model
Increase of SERS Signal Upon Heating or Exposure to a High-Intensity Laser Field: Benzenethiol on an AgFON Substrate
The surface-enhanced Raman scattering (SERS) signal from an AgFON plasmonic
substrate, recoated with benzenethiol, was observed to increase by about 100%
upon heating for 3.5 min at 100C and 1.5 min at 125C. The signal intensity was
found to increase further by about 80% upon a 10 sec exposure to a
high-intensity (3.2 kW/cm^2) 785-nm cw laser, corresponding to 40 mW in a
40+/-5-um diameter spot. The observed increase in the SERS signal may be
understood by considering the presence of benzenethiol molecules in an
intermediate or 'precursor' state in addition to conventionally ordered
molecules forming a self-assembled monolayer. The increase in the SERS signal
arises from the conversion of the molecules in the precursor state to the
chemisorbed state due to thermal and photo-thermal effects.Comment: 9 pages, 4 figures; J. Phys. Chem. C, accepte
Structures and Aggregation of the Methylamine−Borane Molecules, MenH3−nN·BH3 (n = 1−3), Studied by X-ray Diffraction, Gas-Phase Electron Diffraction, and Quantum Chemical Calculations
The structures of the molecules methylamine-borane, MeH(2)N.BH(3), and dimethylamine-borane, Me(2)HN.BH(3), have been investigated by gas-phase electron diffraction (GED) and quantum chemical calculations. The crystal structures have also been determined for methylamine-, dimethylamine-, and trimethylamine-borane, Me(n)H(3-n)N.BH(3) (n = 1-3); these are noteworthy for what they reveal about the intermolecular interactions and, particularly, the N-H...H-B dihydrogen bonding in the cases where n = 1 or 2. Hence, structures are now known for all the members of the ammonia- and amine-borane series Me(n)H(3-n)N.BH(3) (n = 0-3) in both the gas and solid phases. The structural variations and energetics of formation of the gaseous adducts are discussed in relation to the basicity of the Me(n)H(3-n)N fragment. The relative importance of secondary interactions in the solid adducts with n = 0-3 has been assessed by the semi-classical density sums (SCDS-PIXEL) approach
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