Electronic Structure Of Boron Research Articles

Designing an Efficient Singlet Fission Material with B-N Substitution in Pyrene: A Model Exact Study.

The electronic structure of boron (B)-nitrogen (N)-substituted pyrene molecules is the center of attraction in designing an efficient intermolecular singlet fission (x-SF) material. Thermodynamic energy criteria required for x-SF are obtained by captodative substitution with B and N in pristine pyrene to increase the lowest singlet-triplet energy gap. We computed low-lying excited states of BN-embedded pyrene molecules by exactly solving the Pariser-Parr-Pople (PPP) model Hamiltonian and compared these results with the TDDFT and EOM-CCSD values. Exact diagonalization of the PPP model Hamiltonian suggests that pristine pyrene, which is endothermic for x-SF, becomes isoergic with certain (BN)2 substitution. The low-lying excited state energies calculated using the model Hamiltonian match very well with experimental values over EOM-CCSD and TDDFT. Moreover, the low value of the spin-orbit coupling constant calculated for BN-substituted pyrene strengthens its applicability as an SF material.

Electronic structure of boron and aluminum δ-doped layers in silicon

Recent work on atomic-precision dopant incorporation technologies has led to the creation of both boron and aluminum δ-doped layers in silicon with densities above the solid solubility limit. We use density functional theory to predict the band structure and effective mass values of such δ layers, first modeling them as ordered supercells. Structural relaxation is found to have a significant impact on the impurity band energies and effective masses of the boron layers, but not the aluminum layers. However, disorder in the δ layers is found to lead to a significant flattening of the bands in both cases. We calculate the local density of states and doping potential for these δ-doped layers, demonstrating that their influence is highly localized with spatial extents at most 4 nm. We conclude that acceptor δ-doped layers exhibit different electronic structure features dependent on both the dopant atom and spatial ordering. This suggests prospects for controlling the electronic properties of these layers if the local details of the incorporation chemistry can be fine-tuned.

Electronic structure of boron and nitrogen doped isomeric graphene nanoflakes

Electronic properties of nitrogen and boron doped isomeric graphene nanoflakes have been explored using dispersion corrected B3LYP functional and CASSCF methods. The most thermodynamically stable isomers of nitrogen and boron doped systems contain phenalene and azulene motifs substituted in positions 7 and 9, respectively. Nitrogen doping promotes nanoflake planarity, increases singlet-triplet gap and a band gap, while boron doping promotes dome shaped nanoflake geometry, polyradicalic ground state, reduces singlet-triplet gap. Isomeric nanoflakes are less sensitive to doping compared to graphene nanoflakes. Nitrogen is a weak n type dopant for isomeric nanoflakes, while boron cannot be considered as a p type dopant. This effect is explained by non-uniform electron density distribution in pristine isomeric nanoflakes as compared to graphene nanoflakes.

Characterization of Growth Interface for Cubic Boron Nitride Synthesized by the Static High Temperature-High Pressure Catalytic Method

In this work, cubic boron nitride (cBN) was synthesized in Li3N-hBN system at high temperature-high pressure (HPHT). By characterizing experimental samples, it is found that phase structures in the growth interface are comprised of hBN, cBN micro-particles and Li3BN2, large cBN single crystal grows by annexing cBN micro-particles around the growth interface, and the electronic structures of boron and nitrogen atoms are changed from sp2 to sp3 gradually in the growth interface. The results show that cBN is more likely to be transformed directly from hBN with Li3BN2 as a catalyst phase under the course of cBN formation at HPHT.

Geometric and electronic structures of boron(III)-cored dyes tailored by incorporation of heteroatoms into ligands.

Complexation of a boron atom with a series of bidentate heterocyclic ligands successfully gives rise to corresponding BF2-chelated heteroarenes, which could be considered as novel boron(III)-cored dyes. These dye molecules exhibit planar structures and expanded π-conjugated backbones due to the locked conformation with a boron center. The geometric and electronic structures of these BF2 complexes can be tailored by embedding heteroatoms in the unique modes to form positional isomer and isoelectronic structures. The structure-property relationship is further elucidated by studying the photophysical properties, electrochemical behavior and quantum-chemical calculations.

Photoelectron spectra and electronic structure of boron acetylacetonates with organic substituents

Based on experimental data and theoretical results obtained by photoelectron spectroscopy and density functional theory, the electronic structure of the valence levels of boron diethyl acetylacetonate (C2H5)2BAA, boron diphenyl acetylacetonate (C6H5)2BAA, and 1,2-phenylene dioxyboron acetylacetonate C6H4O2BAA is examined. For the compounds studied, in contrast to F2BAA, a significant mixing of the π3 MO of the chelate ring with the orbitals localized on the boron atom, as well as on the (C2H5)2, and (C6H5)2 fragments, is revealed. The C6H4O2BAA complex is demonstrated to have MOs mainly localized on the oxygen atoms of the C6H4O2 fragment. It is shown that the calculated results closely reproduce the experimental sequences of energy levels and the energy intervals between the ionized states of the complex.

Designing band gap of graphene by B and N dopant atoms

Ab-initio calculations have been performed to study the geometry and electronic structure of boron (B) and nitrogen (N) doped graphene sheet. The effect of doping has been investigated by varying the concentrations of dopants from 2 % (one atom of the dopant in 50 host atoms) to 12 % (six dopant atoms in 50 atoms host atoms) and also by considering different doping sites for the same concentration of substitutional doping. All the calculations have been performed by using VASP (Vienna Ab-initio Simulation Package) based on density functional theory. By B and N doping p-type and n-type doping is induced respectively in the graphene sheet. While the planar structure of the graphene sheet remains unaffected on doping, the electronic properties change from semimetal to semiconductor with increasing number of dopants. It has been observed that isomers formed differ significantly in the stability, bond length and band gap introduced. The band gap is maximum when dopants are placed at same sublattice points of graphene due to combined effect of symmetry breaking of sub lattices and the band gap is closed when dopants are placed at adjacent positions (alternate sublattice positions). These interesting results provide the possibility of tuning the band gap of graphene as required and its application in electronic devices such as replacements to Pt based catalysts in Polymer Electrolytic Fuel Cell (PEFC).

First-Principles Study of Lithium Absorption in Boron- or Silicon-Doped Single-Walled Carbon Nanotubes

The lithium absorption energies and electronic structures of boron- or silicon-doped single-walled carbon nanotubes (SWCNT) were investigated using first-principles calculations based on the density-functional theory. As B and Si doping carbon nanotubes, the lithium atom adsorption energies decrease. The effects of B and Si doping are different on the lithium atomic adsorption. B-doping forms an electron-deficient structure in SWCNT. While the Si-doping forms a highly reactive center. The calculations suggest that boron- and silicon-doping in SWCNT will improve Li absorption performance.

Contrast in the Electronic and Magnetic Properties of Doped Carbon and Boron Nitride Nanotubes: A First-Principles Study

We determine atomic and electronic structures of boron- and/or nitrogen-doped carbon nanotubes (CNTs) and carbon-doped boron nitride nanotubes (BN-NTs) of armchair and zigzag types using first-principles pseudopotential-based density functional theory calculations. For comparison, we also determine the atomic and electronic structures of two-dimensional honeycomb lattices of carbon (graphene) and boron nitride. Although carbon doping at either the B or N site in BN-NTs results in anti-ferromagnetically ordered semiconducting state, B or N doping in CNTs gives a simple shift in the Fermi energy and a nonmagnetic state.

X-ray photoemission spectroscopy of nonmetallic materials: Electronic structures of boron and BxOy

Although an increasing volume of x-ray photoemission spectroscopic (XPS) data has been accumulated on boron and boron-rich compounds because of their unusual properties, including a unique three-center, two-electron bonding configuration, their common nonmetallic nature has been overlooked. Typically, the measured energy-state data are not clarified by surface Fermi level positions of these nonmetallic samples, which compromises the scientific contents of the data. In the present study, we revisited the XPS studies of sputter-cleaned β-rhombohedral boron (βr-B), the oxidized surface of βr-B, B6O pellet, and polished B2O3, to illustrate the impact and resolution of this scientific issue. These samples were chosen because βr-B is the most thermodynamically stable polytype of pure boron, B2O3 is its fully oxidized form, and B6O is the best known superhard family member of boron-rich compounds. From our XPS measurements, including those from a sputter-cleaned gold as a metal reference, we deduced that our βr-B had a surface Fermi level located at 0.7±0.1 eV from its valence-band maximum (VBM) (referred as EFL) and a binding energy for its B 1s core level at 187.2 eV from VBM (Eb,VBM). The latter attribute, unlike typical XPS binding energy data that are referenced to a sample-dependent Fermi level (Eb,FL), is immune from any uncertainties and variations arising from sample doping and surface charging. For bulk B2O3, we found an Eb,VBM for its B 1s core level at 190.5 eV and an Eb,FL at 193.6 eV. For our βr-B subjected to a surface oxidation treatment, an overlayer structure of ∼1.2 nm B2O3/∼2 nm B2O/B was found. By comparing the data from this sample and those from βr-B and bulk B2O3, we infer that the oxide overlayer carried some negative fixed charge and this induced on the semiconducting βr-B sample an upward surface band bending of ∼0.6 eV. As for our B6O sample, we found an EFL of ∼1.7 eV and two different chemical states having Eb,VBM of 185.4 and 187.2 eV, with the former belonging to boron with no oxygen neighbor and the latter to boron with an oxygen neighbor. The methodology in this work is universally applicable to all nonmetallic samples.

A first-principles study of lithium absorption in boron- or nitrogen-doped single-walled carbon nanotubes

The lithium absorption energies and electronic structures of boron- or nitrogen-doped single-walled carbon nanotubes (SWCNT) were investigated using first-principles calculations. B-doping decreases lithium absorption energy dramatically both at inner and outer sites. B-doping forms an electron-deficient structure in SWCNT, which can stabilize the Li absorption on the tube walls; however, N-doping forms an electron-rich structure, and will hinder the Li absorption in SWCNT. The calculations suggest that B-doping in SWCNT will improve its Li absorption performance.

Electronic structure of defects and impurities in III-V nitrides: Vacancies in cubic boron nitride.

The electronic structures of boron and nitrogen vacancies in cubic boron nitride (BN) are investigated using the full-potential linearized augmented-plane-wave, full-potential linear-muffin-tin-orbital, and linear-muffin-tin-orbital--tight-binding approaches. All the methods give quantitatively consistent results on ideal cubic BN that are also compared with previous calculations. Using a 64-atom supercell, we have examined the electronic states of boron and nitrogen vacancies. Lattice relaxation around the vacancies is not considered. Both boron and nitrogen defect states appear to form well-defined narrow bands in the forbidden gap of c-BN. The ones for boron vacancy are located near the top of the valence band and are partially occupied. They represent ``acceptor levels of boron vacancy.'' For the nitrogen defect, the ``vacancy levels'' overlap with the states at the conduction-band edge. The characteristics of vacancy states, their localization degrees and influence on the electronic density of states, and charge distribution in c-BN crystals are discussed. These results suggest that both boron and nitrogen vacancies can be ``p-type'' and ``n-type'' doping agents, respectively, when the composition of c-BN deviates from ideal stoichiometry. \textcopyright{} 1996 The American Physical Society.

Electronic Structure of Boron and Boron-Rich Borides

ABSTRACTI have calculated the electronic structure of cubic B12 and B12 P2 using the linear augmented plane wave method. These calculations are selfconsistent and include calculation of the total energy. Within the strict muffin tin approximation (spheres centered only on atomic positionsconstant potential otherwise) these systems are unbound with respect to the atomic constituents. Using interstitial spheres, up to 77% of the unit cell can easily be filled to yield much more reasonable total energies. Although the improvement in the total energy is significant upon including the interstitial spheres, the band structure and densities of states are not significantly changed. Similarly, the real atomic charge distributions (B, P) are little changed, while the interstitial distribution does change to reflect the additional freedom provided by the interstitial spheres. Results including the rhombohedral and icosohedral distortions in both systems are discussed. Gaps are found to open up in the alpha rhombohedral boron and in the B12 P2 systems as are observed experimentally.

Electronic structure of boron

Using a recently developed tight-binding theory with universal matrix elements, the electronic structure of α-rhombohedral boron and B 4C are calculated. The universal matrix elements, which correspond to matrix elements between Wannier functions in the zincblende structure, were found to be inappropriate for the unusual icosahedral unit found in α-rhombohedral boron and B 4C. However, a simple, approximate prescription relating universal matrix elements to matrix elements between nonorthogonal atomic orbitals is derived. The nonorthogonality does not separate into an additive, two-body repulsion as it does in the zincblende structure, and so must be included explicitly in the diagonalization of the Hamiltonian. This prescription is found to well characterize the internal energy levels, the equilibrium spacing and force constant of an icosahedron of boron. The cohesion and equilibrium spacings calculated for an icosahedron and the remaining bonding units in α-rhombohedral boron and B 4C agree well with experimental values: the cohesion is overestimated by the same ratio as for carbonrow semiconductors. Normal mode frequencies calculated for B 12H = 12, B 12D = 12 and B 12Cl = 12 are in good agreement with measured frequencies.