Growth and electronic structure of boron-doped graphene

J. Gebhardt, R. J. Koch, W. Zhao, O. Höfert, K. Gotterbarm, S. Mammadov, C. Papp, A. Görling, H.-P. Steinrück, and Th. Seyller

Phys. Rev. B 87, 155437 – Published 29 April 2013

Abstract

The doping of graphene to tune its electronic properties is essential for its further use in carbon-based electronics. Adapting strategies from classical silicon-based semiconductor technology, we use the incorporation of heteroatoms in the 2D graphene network as a straightforward way to achieve this goal. Here, we report on the synthesis of boron-doped graphene on Ni(111) in a chemical vapor deposition process of triethylborane on the one hand and by segregation of boron from the bulk of the substrate crystal on the other hand. The chemical environment of boron was determined by x-ray photoelectron spectroscopy, and angle-resolved photoelectron spectroscopy was used to analyze the impact on the band structure. Doping with boron leads to a shift of the graphene bands to lower binding energies. The shift depends on the doping concentration and for a doping level of 0.3 ML a shift of up to 1.2 eV is observed. The experimental results are in agreement with density-functional calculations. Furthermore, our calculations suggest that doping with boron leads to graphene preferentially adsorbed in the top-fcc geometry, since the boron atoms in the graphene lattice are then adsorbed at substrate fcc-hollow sites. The smaller distance of boron atoms incorporated into graphene compared to graphene carbon atoms leads to a bending of the doped graphene sheet in the vicinity of the boron atoms. By comparing calculations of doped and undoped graphene on Ni(111), as well as the respective freestanding cases, we are able to distinguish between the effects that doping and adsorption have on the band structure of graphene. Both doping and bonding to the surface result in opposing shifts on the graphene bands.

Received 2 December 2012

DOI:https://doi.org/10.1103/PhysRevB.87.155437

Authors & Affiliations

J. Gebhardt^1,*, R. J. Koch^2,*, W. Zhao³, O. Höfert³, K. Gotterbarm³, S. Mammadov², C. Papp^3,†, A. Görling¹, H.-P. Steinrück³, and Th. Seyller⁴

¹Lehrstuhl für Theoretische Chemie, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
²Lehrstuhl für Technische Physik, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
³Lehrstuhl für Physikalische Chemie II, Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
⁴Institut für Physik, TU Chemnitz, 09126 Chemnitz, Germany

^*These authors have contributed equally to this work.
^†christian.papp@chemie.uni-erlangen.de

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Issue

Vol. 87, Iss. 15 — 15 April 2013

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Images

Figure 1
High-resolution XP spectra of (a) the C $1 s$ and (b) the B $1 s$ region of boron-doped graphene with different doping levels. The inset in (a) shows the shift of the graphene C $1 s$ peak with the doping concentration.Reuse & Permissions
Figure 2
ARPES measurement along $M$ - $K$ - $Γ$ - $M$ of boron-doped graphene with boron concentrations of (a) 0.28 ML, (b) 0.09 ML, and (c) 0.045 ML.Reuse & Permissions
Figure 3
Shift of the binding energy $E_{B}$ with the boron content of the carbon $π$ band at the $Γ$ point of graphene on Ni(111) as measured in experiment (black) and predicted by theory (red).Reuse & Permissions
Figure 4
Band structures of freestanding, pristine graphene (a), freestanding graphene doped substitutionally by boron (b), pristine graphene adsorbed top-fcc on Ni(111) (c), and boron-doped graphene adsorbed top-fcc on Ni(111) (d) calculated in a reciprocal cell to a graphene (2 $\times$ 2) cell along paths displayed in Fig. 5. The special points marked green at the upper ordinate refer to the reciprocal (2 $\times$ 2) cell of the calculations, while the special points marked orange at the bottom ordinate refer to the reciprocal (1 $\times$ 1) cell and are relevant for comparison with the ARPES measurements in Fig. 2; see text for details. Red, orange, and yellow circles represent carbon 2 $s$ , 2 $p_{x}$ /2 $p_{y}$ , and 2 $p_{z}$ contributions to carbon $s$ , $σ$ , and $π$ bands, with their radius being correlated to the magnitude of the contribution to the bands. For pristine graphene calculated in vacuum (a) and on nickel (c) only those bands that are observed experimentally are colored, while backfolded bands are shown as black lines. For better visualization the nickel bands are represented by gray instead of black lines in (d).Reuse & Permissions
Figure 5
(a) shows a sketch of a reciprocal cell (black) to a (1 $\times$ 1) hexagonal graphene unit cell with orange labeled unit cell vectors and positions of high symmetry points $M$ , $K$ , $K^{'}$ , and $Γ$ and the respective Brillouin zone (light gray). In addition, a reciprocal cell (dark gray) to a (2 $\times$ 2) unit cell is shown with green labeled unit cell vectors. The positions of the high-symmetry points of the reciprocal (1 $\times$ 1) unit cell $M$ , $K$ , $K^{'}$ , and $Γ$ are drawn green at their backfolded positions in the reciprocal (2 $\times$ 2) unit cell. Translated (2 $\times$ 2) unit cells that are backfolded onto the central (2 $\times$ 2) unit cell are drawn as dashed, light gray lines. Due to backfolding, the calculation of a band structure first along $Γ$ - $z$ (light red path) and then along $z^{'}$ - $Γ$ (blue path) in the reciprocal (2 $\times$ 2) unit cell contains the same bands (bands from red and blue paths) that are obtained along $M$ - $K$ - $Γ$ experimentally and in a calculation of the reciprocal (1 $\times$ 1) cell. $z$ and $z^{'}$ label the two opposing corners of the reciprocal (2 $\times$ 2) unit cell along the chosen direction. In addition, bands along the light and dark red and blue paths are measured. The band structure of freestanding graphene calculated for the discussed path along $Γ$ - $z$ and $z^{'}$ - $Γ$ in the (2 $\times$ 2) unit cell is shown in (b). The bands originating from the red and blue paths in (a), i.e., those that are observed experimentally and that are obtained in a calculation of the (1 $\times$ 1) reciprocal cell along $M$ - $K$ - $Γ$ , are colored accordingly.Reuse & Permissions

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