Nearly Free Electron Superatom States of Carbon and Boron Nitride Nanotubes

Abstract

By first-principles theory we study the nearly free electron (NFE) states of carbon and boron nitride nanotubes. In addition to the well-known π bands, we found a series of one-dimensional (1D) NFE bands with on-axis spatial distributions, which resemble atomic orbitals projected onto a plane. These bands are 1D counterparts of the recently discovered superatom orbitals of 0D fullerenes. In addition to the previously reported lowest energy NFE state with the angular quantum number l = 0 corresponding to s atomic orbital character, we find higher energy NFE bands with l > 0 corresponding to the p, d, etc., orbitals. We show that these atom-like states of nanotubes originate from the many-body screening, which is responsible for the image potential of the parent two-dimensional (2D) graphene or BN sheets. With a model potential that combines the short-range exchange-correlation and the long-range Coulomb interactions, we reproduce the energies and radial wave function profiles of the NFE states from the density functional theory calculations. When the nanotube radius exceeds the radial extent on NFE states, the NFE state energies converge to those of image potential states of the parent 2D molecular sheets. To explore possible applications in molecular electronics that take advantage of the NFE properties of nanotube building blocks, we investigate the modification of NFE states by transverse electric fields, alkali metal encapsulation, and lateral and concentric nanotube dimerization.

Exceptional Optoelectronic Properties of Hydrogenated Bilayer Silicene

“…Because the NFE states are not localized on the lattice site of a material, in principle, it will be less affected by structural defects and, therefore, could realize stable charge transport. It has been reported that NFE states can exist in isolated crystalline carbon sheets and nanotubes [63][64][65][66], and this is the first report that NFE states can also exist in silicon materials. The Si 12 H 4 is a quasidirect semiconductor.…”

Charge-Controlled Switchable CO2 Capture on Boron Nitride Nanomaterials

“…[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] They have excellent mechanical properties, high thermal conductivity, and high resistance to oxidation. [10][11][12][13][14][15] These properties make them very promising in a variety of potential applications such as optoelectronic nanodevices, spintronics, light emission, photocatalysts, thermal rectifiers, functional composites, etc.…”

Non-nuclear electron transport channels in hollow molecules

“…3 we show the molecular and electronic structure of the (8,8) JGNT, where we designate the structure according to the convention for carbon nanotubes (CNTs) [43]. Wrapping a molecular sheet into a nanotube creates an attractive axial potential, which is well documented for carbon and BN nanotubes [24]. For the (8,8) JGNT with internal H atoms, a band gap of ß2 V separates the VB, which is localized on the C atom cage, from the CB, which is a superatom state forming a NNM within the hollow nanotube core.…”

“…Molecular materials with strong intermolecular electronic interactions, such as those mediated by the superatom states, would be of great interest in the field of molecular electronics if such bands could mediate charge transport. In fact, BN nanotubes are predicted to have a conduction band (CB) with non-nuclear NFE character corresponding to the 1D analog of the s-symmetry superatom state of fullerenes [16,24], though their band gap of ß5 eV is inconvenient for applications [25]. In the case of unsaturated hollow molecules derived from graphene, non-nuclear transport is obviated by the femtosecond-time-scale electronic relaxation of the superatom states into the lower-lying π -symmetry lowest unoccupied molecular orbitals [21].…”

“…Building on the propensity of the superatom orbitals of hollow molecules [17,18,24], the related IP states of graphene [14], and the WE states [13,27] to form NFE bands, we combine their advantages to engineer the unoccupied electronic structure of chemically modified graphene sheets, namely, graphane and its derivatives. By optimizing the NFE properties [28,29], we propose synthetically feasible graphane-derived nanostructured materials forming stable and protected environments, with band gaps that are accessible to practical applications for 1D and 2D non-nuclear charge transport within single molecular constructs and having moderate electron-phonon interaction.…”