Functionalization of BN honeycomb structure by adsorption and substitution of foreign atoms

C. Ataca and S. Ciraci

Phys. Rev. B 82, 165402 – Published 1 October 2010

Abstract

We carried out first-principles calculations within density-functional theory to investigate the structural, electronic, and magnetic properties of boron-nitride (BN) honeycomb structure functionalized by adatom adsorption, as well as by the substitution of foreign atoms for B and N atoms. For periodic high-density coverage, most of $3 d$ transition metal atoms and some of group 3A, 4A, and 6A elements are adsorbed with significant binding energy and modify the electronic structure of bare BN monolayer. While bare BN monolayer is nonmagnetic, wide band-gap semiconductor, at high coverage of specific adatoms it can achieve magnetic metallic, even half-metallic ground states. At low coverage, the bands associated with adsorbed atoms are flat and the band structure of parent BN is not affected significantly. Therefore, adatoms and substitution of foreign atoms at low coverage are taken to be the representative of impurity atoms yielding localized states in the band gap and resonance states in the band continua. Notably, the substitution of C for B and N yield donorlike and acceptorlike magnetic states in the band gap. Localized impurity states occurring in the gap give rise to interesting properties for electronic and optical application of the single-layer BN honeycomb structure.

Received 4 January 2010

DOI:https://doi.org/10.1103/PhysRevB.82.165402

Authors & Affiliations

C. Ataca and S. Ciraci^*

Department of Physics, Bilkent University, Ankara 06800, Turkey and UNAM-Institute of Materials Science and Nanotechnology, Bilkent University, Ankara 06800, Turkey

^*ciraci@fen.bilkent.edu.tr

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Vol. 82, Iss. 16 — 15 October 2010

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Images

Figure 1
(Color online) A $(4 \times 4)$ supercell of 2D BN honeycomb structure, which consists of four $(2 \times 2)$ supercells. Various possible adsorption sites of adatoms are indicated. The hollow site, H: the adatom (gray/orange ball) is placed on top of the center of a hexagon. TN site: the adatom is placed on top of nitrogen (dark gray/red). TB site: the adatom is placed on top of boron (light gray/green). The bridge site BR: the adatom is located on top of the boron-nitrogen bond.Reuse & Permissions
Figure 2
(Color online) (a) The energy band structure of bare 2D BN folded to the $(2 \times 2)$ supercell and corresponding TDOS. Zero of band energy is set at the Fermi energy, $E_{F}$ . (b)–(d) The energy band structure of single Ni, Pd, and Pt adsorbed to each $(2 \times 2)$ supercell of 2D BN $(Θ = 1 / 8)$ . Corresponding TDOS (continuous black/blue line) and PDOS projected to the adatom (shaded dark/red) are also indicated. The energy gap of semiconductors are shaded (light/yellow). The ground states are nonmagnetic.Reuse & Permissions
Figure 3
(Color online) TDOS (dark/blue line) and PDOS (shaded gray/red) for B, C, O, Sc, Ti, and V adatoms at high coverage, $Θ = 1 / 8$ . Up (down) arrow on the right (left) site of TDOS and PDOS indicates spin direction. Zero of the DOS energy is set to the Fermi energy, $E_{F}$ of the $adatom + 2 D$ BN system which is indicated with dashed-dotted gray/green line. All adatoms treated in $(4 \times 4)$ supercell to allow antiferromagnetic interaction or reconstruction, whereby single adatom is adsorbed to each $(2 \times 2)$ supercells of $(4 \times 4)$ supercell amounting $Θ = 1 / 8$ . Sc, Ti, and V have antiferromagnetic ground state; O has ferromagnetic state; and B and C are nonmagnetic. The state densities are given in arbitrary units but have the same scale for all adatoms.Reuse & Permissions
Figure 4
(Color online) Schematic of the relevant energy levels (or bands) of adatom (B, C, O, Ti, and Pt) adsorbed to $(4 \times 4)$ supercell of the single layer BN. The light/gray shaded region in the background is the valence and conduction band region of 2D BN. Zero of band energy is set at the Fermi level of the parent, bare 2D BN, $E_{F}$ . Spin-up and spin-down bands are shown by dark/blue and light/green lines, respectively. Solid bands indicates that the contribution of adatom to the band is more than 50% except O adatom. Energies of some of the relevant adatom (impurity) states relative to valence band edge of parent 2D BN are indicated. Below each energy diagram of adatoms, charge density isosurfaces of specific states are shown. The isosurface value is taken as $7 \times 10^{- 5} electrons / Å^{3}$ . (Note that all localized states of O have significant contributions from BN states and are shown by solid dark/blue lines.)Reuse & Permissions
Figure 5
(Color online) Variation in energy of a single C and Ti adatom as they are moving along special directions of a hexagon of 2D BN honeycomb structure. The possible migration path of adatom facing minimum energy barrier is shown by stars on the hexagon. Calculations are carried out in $(4 \times 4)$ supercell.Reuse & Permissions
Figure 6
(Color online) Schematic energy-level diagram of Al and C substituting B; and C and P substituting N in a $(4 \times 4)$ supercell of 2D BN. The light/gray shaded region in the background is the valence and conduction-band continuum of 2D BN. Zero of energy is set to the Fermi level of bare 2D BN. Spin-up bands are indicated with dark/blue lines whereas spin-down bands are light/green. Thick solid bands (levels) are states localized at the substituted atom and nearest atoms of 2D BN. Thin solid bands stand for the delocalized states. The energies of some of the localized states with respect to the valence band edge are shown in units of eV. Charge density isosurfaces of some of the relevant states are shown below the corresponding band diagram. The isosurface value is taken as $7 \times 10^{- 5} electrons / Å^{3}$ .Reuse & Permissions

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