Broad boron sheets and boron nanotubes: An ab initio study of structural, electronic, and mechanical properties

摘要

Based on a numerical ab initio study, we discuss a structure model for abroad boron sheet, which is the analog of a single graphite sheet, and theprecursor of boron nanotubes. The sheet has linear chains of sp hybridizedsigma bonds lying only along its armchair direction, a high stiffness, andanisotropic bonds properties. The puckering of the sheet is explained as amechanism to stabilize the sp sigma bonds. The anisotropic bond properties ofthe boron sheet lead to a two-dimensional reference lattice structure, which isrectangular rather than triangular. As a consequence the chiral angles ofrelated boron nanotubes range from 0 to 90 degrees. Given the electronicproperties of the boron sheets, we demonstrate that all of the related boronnanotubes are metallic, irrespective of their radius and chiral angle, and wealso postulate the existence of helical currents in ideal chiral nanotubes.Furthermore, we show that the strain energy of boron nanotubes will depend ontheir radii, as well as on their chiral angles. This is a rather uniqueproperty among nanotubular systems, and it could be the basis of a differenttype of structure control within nanotechnology.