Borophene
36° borophene, front and side view
Borophene is a proposed crystalline allotrope of boron. One unit consists of 36 atoms arranged in an 2-dimensional sheet with a hexagonal hole in the middle.[1][2] Another form made in 2015 is a buckled two dimensional sheet on silver.[3]
Theory
Computational studies suggested that extended borophene sheets with partially filled hexagonal holes are stable.[4][5] Global minimum searches for B−
36 lead to a quasiplanar structure with a central hexagonal hole. Borophene is predicted to be fully metallic.[1]
Borophene is analogous to graphene in that it is expected to form extended sheets. The latter is a semi-metal, implying that borophene may be a better conductor.[6] The boron-boron bond is also nearly as strong as graphene’s carbon-carbon bond.[1] At the atomic-cluster scale, pure boron forms simple planar molecules and cage-like fullerenes.[7]
Boron is adjacent to carbon in the periodic table and has similar valence orbitals. Unlike carbon, boron cannot form a honeycomb hexagonal framework (like graphene) because of its electron deficiency.[1]
History
In 2014 a research team at Brown University, led by Lai-Sheng Wang, showed that the structure of B
36 was not only possible but highly stable.[2][6][8] Photoelectron spectroscopy revealed a relatively simple spectrum, suggesting a symmetric cluster. Neutral B
36 is the smallest boron cluster to have sixfold symmetry and a perfect hexagonal vacancy, and it can be viewed as a potential basis for extended two-dimensional boron sheets.[1]
In 2015 a research team synthesized borophene on silver surfaces under ultrahigh-vacuum conditions. Atomic-scale characterization, supported by theoretical calculations, revealed structures reminiscent of fused boron clusters with multiple scales of anisotropic, out-of-plane buckling. Unlike bulk boron allotropes, borophene shows metallic characteristics that are consistent with predictions of a highly anisotropic, 2D metal.[7]
Borospherene
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40° borospherene
In July 2014 researchers announced the creation of a 40-atom buckyball-like spherical cage made of boron that the team dubbed borospherene (derived from the original "buckminster fullerene".) Where buckyball molecules feature 20 hexagons and 12 pentagons of carbon atoms producing a smooth spherical surface, borospherene consists of 48 triangles, four seven-sided rings and two six-sided rings. The resulting shape is also spherical, but with several atoms sticking out from the sides.[9][10]
See also
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Look up borophene in Wiktionary, the free dictionary. |
References
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