Kinetic Instability of Boron Heterofullerenes

Although boron heterofullerenes are produced abundantly in the gas phase, they cannot be isolated in macroscopic amounts. Those with two to six boron atoms were found to have minimum bond resonance energies (min BRE) of less than -0.100 |β|. All carbon-boron bonds have negative BREs, suggesting that boron atoms markedly destabilize nearby π bonds. on this theoretical basis, typical boron heterofullerenes are predicted to be kinetically very unstable and chemically very reactive. In contrast, the molecular anions with 60 π electrons of boron heterofullerenes are predicted to be kinetically much more stable. These anions do not have bonds wirh large negative BREs. Some of them may be isolable as salts or endohedral complexes. This study constitutes the first attempt to apply the BRE method to heteroconjugated systems.     

A study on the aromaticity and kinetic stability of fullerene C38 isomers and their molecular ions

The aromaticity of the fullerene C₃₈ isomers and their molecular ions is examined by the topological resonance energy (TRE) method. The aromaticity order obtained by the TRE method is compared with relative energies found in DFT calculation results reported in literature. It is found that all C₃₈ isomers exhibit antiaromaticity when in the neutral state. However, they are highly aromatic in the hexaanionic states. The minimum bond resonance energy (min BRE) method is utilized to estimate the kinetically stability of the C₃₈ isomers and their molecular ions. According to the min BRE method, C₃₈ isomers are only have kinetic stability in penta- and hexavalent molecular anionic states.     

Recent progress in boron nanomaterials

Abstract

Various types of zero, one, and two-dimensional boron nanomaterials such as nanoclusters, nanowires, nanotubes, nanobelts, nanoribbons, nanosheets, and monolayer crystalline sheets named borophene have been experimentally synthesized and identified in the last 20 years. Owing to their low dimensionality, boron nanomaterials have different bonding configurations from those of three-dimensional bulk boron crystals composed of icosahedra or icosahedral fragments. The resulting intriguing physical and chemical properties of boron nanomaterials are fascinating from the viewpoint of material science. Moreover, the wide variety of boron nanomaterials themselves could be the building blocks for combining with other existing nanomaterials, molecules, atoms, and/or ions to design and create materials with new functionalities and properties. Here, the progress of the boron nanomaterials is reviewed and perspectives and future directions are described.     

硼异质富勒烯制备过程中巴基管与巴基葱的异常生长行为

电弧法制备掺硼富勒烯过程中发现，与纯富勒烯相比，掺硼富勒烯烟灰的电导率提高一个数量级以上。电镜观察显示掺硼富勒烯烟灰中含有较多的巴基管和巴基葱，而阴极沉积物中则发现含有珠链状巴基葱。     

The Effect of Boron on the Structure and Conductivity of Thin Films Obtained by Laser Ablation of Diamond with Deposition at 700°C

Structural features of CB_x films obtained by pulsed laser ablation of targets made of pressed diamond powder with boron-powder additions at B/C atomic ratio of x = 0.33 have been studied. The films were deposited on heated substrates, so that diffusion processes involving C and B atoms on the surface and in the volume of films were possible. Selected conditions of film deposition ensured their effective doping with boron (0.4 ≤ x ≤ 0.6). The incorporation of B atoms was accompanied by the formation of B–C chemical bonds, whereas the formation of sp² graphite bonds and their ordering in clusters with laminar packing was suppressed. The films possessed very low resistivity (~1.4 mΩ cm) at room temperature and exhibited metallic type of conductance on decreasing the temperature to 77 K.     

Synthesis of an orthorhombic high pressure boron phase

Abstract

The densest boron phase (2.52 g cm^-3) was produced as a result of the synthesis under pressures above 9 GPa and temperatures up to ～1800 °C. The x-ray powder diffraction pattern and the Raman spectra of the new material do not correspond to those of any known boron phases. A new high-pressure high-temperature boron phase was defined to have an orthorhombic symmetry (Pnnm (No. 58)) and 28 atoms per unit cell.     

Properties of very thin La-B films deposited onto tantalum

The properties of very thin (up to about ten lanthanum monolayers) La-B films deposited onto a tantalum substrate were investigated by Auger electron spectroscopy, by measuring changes in the work function and by ion sputtering to remove successive layers of the film. The composition of the films was changed from almost pure lanthanum to stoichiometric LaB₆ and in some cases to almost pure boron.Decreases in the work function during film deposition depend on the boron content in the film and are greatest for the $\text{LaB}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}$ film. We propose a qualitative explanation for this dependence. Films with boron contents up to LaB₃ are inhomogeneous in the direction perpendicular to the surface, i.e. the boron content is greatest near the substrate surface. This indicates that boron atoms are bound more strongly to the substrate atoms than to the lanthanum atoms.The work functions and compositions of the surfaces of the films were investigated during annealing in the temperature range 20–800 °C.     

Large “Pillow” Fullerenes Hydrogenated at the Inter‐sheet “Seam”

Abstract

In a previous paper on large “pillow” fullerenes, various systems were described with 12 pentagons connecting 2 parallel hexagonal arrays of benzenoid rings (graphene fragments functioning as the faces of the “pillow”) on top of each other. Additional bonds between these identical arrays formed only from sp²‐hybridized carbon atoms gave rise to hexagons and 12 pentagons along the “seam” or “rim.” High steric strain was associated with curvature around the pentagons due to connections between the 2 pillow faces involving bonds between 2 sp²‐hybridized carbon atoms. The present paper examines similar “quasi‐graphitic” structures in which some carbon atoms of the rim between the two raphene faces have hydrogen atoms attached to them, i.e., have sp³‐hybridization, alleviating thereby some strain.     

超导体MgB_2成相过程及试验检验

粉末反应中MgB2成相过程可分三步完成:两种粉粒由于热运动接触碰撞,做反相微幅受迫振动,形成MgB2成相区;两个硼原子接近,价轨道发生sp2杂化,反应生成B2,镁原子的两个3s价电子自旋相反且成对填入B2的π轨道形成π键生成MgB2,此即MgB2初始晶核。初始晶核有不对称的电场分布和四个外露半满杂化电子轨道;初始晶核分别沿a和c三个轴六个方向接近反应,生长成单晶晶粒。晶粒表面的外露半满杂化电子轨道、镁离子和电子的局域电场可能将相邻晶粒中的晶格周期性接通,形成库伯对穿过晶粒界面的通道;不同晶面中的两种化学键可能导致两种费米分布、两种库伯对和双能隙。利用初始晶核顺磁性和晶粒表面局域电子,对成相过程可做进一步试验检验。     

Synthesis and crystal structure of cesium actinide(VI) tricarbonate complexes Cs4AnO<Subscript>2</Subscript>(CO<Subscript>3</Subscript>)<Subscript>3</Subscript>·6H<Subscript>2</Subscript>O,An(VI) = U,Np, Pu

Tricarbonate complexes of hexavalent U, Np, and Pu with outer-sphere cesium cations, Cs₄AnO₂·(CO₃)₃·6H₂O, were synthesized and studied by single crystal X-ray diffraction analysis. Crystals of Cs₄AnO₂·(CO₃)₃·6H₂O consist of [AnO₂(CO₃)₃]^4– complex anions and hydrated Cs⁺ cations. The coordination polyhedron (CP) of An(VI) atoms is a distorted hexagonal bipyramid with three CO ₃ ^2– anions arranged in the equatorial plane. Four independent Cs+ cations have the coordination surrounding in the form of 11-, 10-, and 9-vertex polyhedra formed by the O atoms of CO ₃ ^2– anions, AnO ₂ ²⁺ cations, and water molecules. Six crystallographically independent water molecules in the structure of Cs₄AnO₂(CO₃)₃·6H₂O form a three-dimensional system of hydrogen bonds in which the O atoms of carbonate ions and water molecules act as proton acceptors. The “yl” oxygen atoms of AnO ₂ ²⁺ cations are not involved in hydrogen bonding. The lengths of the An–O_carb bonds in the equator of the U, Np, and Pu hexagonal bipyramids are noticeably influenced by incorporation of the O atoms of the CO ₃ ^2– anions in the coordination polyhedra of Cs⁺ ions and by involvement of these atoms in hydrogen bonding.     

Stability,electronic and magnetic properties of the Octagraphene-like boron nitride Nanosheets: In silico studies

The characterization of the structural, electronic, and magnetic properties of octagraphene-like boron-nitride: BN (B₃₂N₃₂H₂₄, B₃₇N₂₇H₂₄, and B₂₇N₃₇H₂₄), nanosheets were performed by means of density functional theory all-electron calculations at the HSEh1PBE/GGA level. Orbital 6–311G(d,p) basis sets were used. Non-stoichiometric B₃₇N₂₇H₂₄ and B₂₇N₃₇H₂₄ compositions: rich in boron or nitrogen atoms, forming homonuclear B or N bonds, respectively, were chosen. The obtained results reveal that these BN nanosheets reach structural stability in the anionic form, where semiconductor behaviors are promoted. Indeed, the HOMO-LUMO gap values are: 5.09, 1.48 and 2.53 eV, for stoichiometric and non-stoichiometric models, respectively. Whereas the magnetic moments are coming from the boron atoms in all cases (1.0 bohrs magneton). The rich in boron and nitrogen nanosheets presents high-polarity; either in the gas phase or embedded in aqueous mediums like water. Also appears low chemical reactivity, signifying potential applicability as nanovehicles of pharmaceutical species. The nanosheets rich in boron atoms are promising candidates for the design of nanosensors, because they possess low-work functions, mainly arising from the homonuclear boron bond formation.     

Effect of boron on hot ductility oflow carbon low alloyed steel

Abstract

The influence of boron on the hot ductility of C-Mn-Al-Cr steel has been investigated. At <980°C M(CB)₃ precipitated out and about half of the boron content was in solution in austenite at >900°C. It was found that solute boron atoms segregate to austenite grain boundaries and occupy the vacancies induced by deformation. This prevents the formation and propagation of microcracks at boundaries and results in improved hot ductility and a reduced dynamic recrystallisation temperature.     

Characterization of boron-doped diamond-like carbon prepared by radio frequency sputtering

Instead of the sophisticated deposition processes and boron sources reported in literature, the study used the radio frequency magnetron sputtering method to prepare boron-doped diamond-like carbon (DLC) films with p-type conduction. The adopted sputtering targets were composed of boron pellets buried in a graphite disc. The undoped DLC films prepared exhibited n-type conduction, based on the Hall-effect measurement. For boron content ≥ 2.51 at.%, the films showed semiconductor behavior converted from n-type to p-type conduction after annealing at 450 °C. B-DLC films with a boron content of 5.91 at.% showed a maximum carrier concentration of 1.2 × 10¹⁹ cm⁻³, a mobility of 0.4 cm²/V s, and an electrical resistivity of 1.8 Ω cm. The results of XPS and Raman spectra indicated that the motion of boron atoms was thermally activated during post-annealing, helping promote the formation of C-B bonds in the films. Moreover, the doping of boron in DLC films decreased sp³ bonding and facilitated carbon atoms to form sp² bonding and graphitization.     

Structure and superconductivity of isotope-enriched boron-doped diamond

Abstract

Superconducting boron-doped diamond samples were synthesized with isotopes of ¹⁰B, ¹¹B, ¹³C and ¹²C. We claim the presence of a carbon isotope effect on the superconducting transition temperature, which supports the ‘diamond-carbon’-related nature of superconductivity and the importance of the electron–phonon interaction as the mechanism of superconductivity in diamond. Isotope substitution permits us to relate almost all bands in the Raman spectra of heavily boron-doped diamond to the vibrations of carbon atoms. The 500 cm^?1 Raman band shifts with either carbon or boron isotope substitution and may be associated with vibrations of paired or clustered boron. The absence of a superconducting transition (down to 1.6 K) in diamonds synthesized in the Co–C–B system at 1900 K correlates with the small boron concentration deduced from lattice parameters.     

Dodecaborane‐Based Dopants Designed to Shield Anion Electrostatics Lead to Increased Carrier Mobility in a Doped Conjugated Polymer

One of the most effective ways to tune the electronic properties of conjugated polymers is to dope them with small‐molecule oxidizing agents, creating holes on the polymer and molecular anions. Undesirably, strong electrostatic attraction from the anions of most dopants localizes the holes created on the polymer, reducing their mobility. Here, a new strategy utilizing a substituted boron cluster as a molecular dopant for conjugated polymers is employed. By designing the cluster to have a high redox potential and steric protection of the core‐localized electron density, highly delocalized polarons with mobilities equivalent to films doped with no anions present are obtained. AC Hall effect measurements show that P3HT films doped with these boron clusters have conductivities and polaron mobilities roughly an order of magnitude higher than films doped with F₄TCNQ, even though the boron‐cluster‐doped films have poor crystallinity. Moreover, the number of free carriers approximately matches the number of boron clusters, yielding a doping efficiency of ≈100%. These results suggest that shielding the polaron from the anion is a critically important aspect for producing high carrier mobility, and that the high polymer crystallinity required with dopants such as F₄TCNQ is primarily to keep the counterions far from the polymer backbone.     

New insight in boron chemistry: Application in two-photon absorption

Two groups of one-dimensional (1D) boron containing two-photon absorbing fluorophores have been prepared and characterized. One group includes boron atoms incorporated in the conjugated or pseudo conjugated central core and the other contain a boron cluster as an acceptor group at one end of the fluorophores. Two boron containing central cores (with two boron atoms) have been explored: the cyclodiborazane and the pyrazabole moieties. The chosen boron cluster, p-carborane, contains 10 boron atoms. All the prepared fluorophores present high two-photon absorption cross-sections. Some water-soluble as well as lipophylic dyes have been prepared and used in bio-imaging.     

Chemical states of carbon in amorphous boron carbide thin films deposited by radio frequency magnetron sputtering

Boron carbide thin films were deposited by radio frequency (RF) magnetron sputtering and characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and high resolution transmission electron microscopy. The results reveal that the structure of thin films deposited at substrate temperatures lower than 350 °C is amorphous. We found that there are four chemical states for carbon in amorphous boron carbide thin films deposited by RF magnetron sputtering. One is the segregated carbon in form of the graphitic inclusions in the thin film identified by Raman spectroscopy and Raman mapping using two strong peaks at ~ 1360 cm^− 1 and ~ 1590 cm^− 1, but the XPS results show that the graphitic inclusions do not connect to the substrate directly. On the surface the carbon forms C=O bonds characterized by the peak of C1s core level at 285.0 eV besides B-C bonds in the boron carbide with the peak of C1s being at 282.8 eV. The detailed analysis of B-C bonds in the boron carbide shows that there are two states for carbon atoms in B-C bonds: in the C-B-C models with C1s peak at 282.3 eV and in the icosahedra with C1s peak at 283.3 eV.     

C60-like boron carbide and carbon nitride fullerenes: Stability and electronic properties obtained by DFT methods

The structural stability, electronic and magnetic properties of novel boron carbide and carbon nitride fullerenes, of chemical compositions: C₃₆B₂₄ and C₂₄B₃₆ (CBF) and C₃₆N₂₄ and C₂₄N₃₆ (CNF), rich in carbon, boron and nitrogen atoms, were determined by means of density functional theory based-methods. Calculations were done using a exchange–correlation functional developed by Heyd-Scuseria-Ernzerhof, within the generalized gradient approximation (HSEh1PBE-GGA) in concert with 6–311G(d,p) basis sets. The DFT simulation results for the neutrals, cations and anions reveal structural stability for the four chosen compositions. Several spin multiplicities were determined for each system. Although distorted, the located low-lying states preserve the basic fullerene features. In the addressed compositions, the lowest energy structures occur for the anions, which behave as semi-metallic and magnetic nanomaterials. Indeed, they have HOMO-LUMO gaps of 0.55, 0.66, 0.34 and 2.17 eV and 3.0, 5.0, 1.0 and 3.0 magneton bohrs, respectively. These CB and CN hybrid fullerenes show high polarity and low-chemical reactivity. Additionally, they have low-work functions, which is crucial for the design of electronic devices.