International Scholarly Research Notices

International Scholarly Research Notices / 2012 / Article

Research Article | Open Access

Volume 2012 |Article ID 368634 | https://doi.org/10.5402/2012/368634

Khadije Imani, Gholamhossein Jafari, Mohammad Reza Abolhasani, "Electronic Structure Calculation of Adsorbate Gas Molecules on an Armchair Graphene Nanoribbon", International Scholarly Research Notices, vol. 2012, Article ID 368634, 5 pages, 2012. https://doi.org/10.5402/2012/368634

Electronic Structure Calculation of Adsorbate Gas Molecules on an Armchair Graphene Nanoribbon

Academic Editor: V. Cataudella
Received30 Aug 2012
Accepted05 Oct 2012
Published05 Nov 2012

Abstract

By using the first-principle methods, we have investigated the adsorption of the CO, CO2, NO, and NH3 molecules on an armchair graphene nanoribbon (AGNR). The optimal adsorption positions and orientations of these molecules on AGNR are determined. The adsorption energies, the charge transfer, and the density of states (DOS) are obtained. The NO, CO, and CO2 adsorbed molecules act as an acceptor, and the NH3 adsorbed molecule acts as a donor. The NO and CO molecules contributed with localized states in the center of the original band gap. But the system exhibits -type or -type semiconductor after NH3 or CO2 adsorption.

1. Introduction

Recently the study of the sensing property of carbon nanostructures, such as carbon nanotubes (CNTs), graphene, and graphene nanoribbons (GNRs), has attached a lot of research activity [13]. Studies show that the graphene and CNTs and GNRs are good gas sensors. Experimental data have shown that the transport properties of nanotube changes upon exposure to gas molecules such as the O2, NO2, and NH3 molecules [2, 48]. Experimental and theoretical studies of gas molecule adsorption on the graphene surface have been reported already [916] showing that H2O, NO, CO, NO2, and NH3 molecules are physically adsorbed on the graphene. The NH3, NO, and CO molecules act as donors while H2O and NO2 act as acceptors. The conductance of graphene at the Fermi level decreases with adsorbing NO2 molecules while it increases with adsorbing NO molecules [17]. Due to having flat structure and thus larger accessible surface area, GNRs and graphene may act better than any other carbon-based materials as gas sensors. GNRs’ electronic states largely depend on the edge structure (armchair or zigzag). Calculations based on tight bonding approximation predict that zigzag graphene nanoribbons (ZGNRs) are always metallic while armchair graphene nanoribbons (AGNRs) can be either metallic or semiconducting, depending on their width [18]. However DFT calculations show that AGNRs are semiconducting with a finite band gap and the value of the gap depends on their width [1921]. Theoretical and ab initio studies of GNRs sensing properties have been reported already, showing that absorption of CO2 or O2 molecules changes the AGNR to -type semiconductor, while NH3 adsorption changes it to a -type semiconductor [2224].

In this work we performed the first-principle calculations for the adsorption of CO, CO2, NO, and NH3 molecules on armchair graphene nanoribbon consisting of 6 dimer lines across the ribbon width (6-AGNR), as shown in Figure 1(a). After geometrical optimization, we obtained the positions and orientations of the adsorbed molecules. We then calculate the adsorption energies , the density of states (DOS), and the charge transfers between nanoribbon and adsorbate molecules due to bindings between the molecules and carbon in the nanoribbon. By probing the density of states (DOS) of the systems, one can find out the direction of charge transfer (from the molecules to the nanoribbon or vice versa), and from this, one can determine whether the doped molecule acts as a donor or as an acceptor.

In the previous work [22], the exact orientation and position of the adsorbate molecules on the 6-AGNR surface was not calculated. However, we have used the atomic coordinates obtained from simultaneous relaxation in the positions of the adsorbate molecules, 6-AGNR sheet, and their atomic positions.

The organization of this paper is as follows. In Section 2 the computational details are discussed. In Section 3 we investigate the electronic structure of the 6-AGNR with adsorbate molecules, using density functional theory with the local density approximation.

2. Computational Details

Our calculations are based on the use of DFT and the ab initio pseudo-potential plane-wave method using the PWSCF code of the Quantum ESPRESSO [25]. We performed the calculation with LDA and LSDA ultrasoft Vanderbilt pseudopotentials [26]. The Kohn-Sham orbitals are expanded in a plane-wave basis set. The energy cutoff for the wave function and the charge are, respectively, 45 Ry and 300 Ry. The 6-AGNR was simulated by a relatively orthorhombic supercell of 36 carbon atoms, with lattice parameters  Å,  Å in the planes and  Å. The sampling of the Brillouin zone was done using a grid and tested to give convergent results for the total energy. For calculating the density of states (DOS), we used a grid.

The periodic boundary conditions and a supercell approximation were used. The supercell had 36 carbon atoms for a 6-AGNR in a hexagonal lattice. The structural optimizations were performed using a conjugated gradient procedure. Different configurations of gas molecules’ adsorption to the 6-AGNR were considered. For each molecule we chosen the position and the orientation in which the hole system has minimum energy. For this position and orientation, the structure are full relaxed until all the force components were smaller than , in order to obtain the exact position and orientation for the molecule.

The amount of charge transfer from 6-AGNR to the molecules can be estimated by projecting the charge density onto the atomic orbitals. We calculated the charge transfer as the difference between the Löwdin charges for pristine 6-AGNR and 6-AGNR with the adsorbate molecules. From this result, one can determine whether the adsorbate molecule acts as an acceptor or as a donor. It is important to note that the size of the charge transfer slightly depends on the method chosen for calculations. The adsorption energy () is defined as the difference between the energy of the fully relaxed 6-AGNR and the adsorbed molecule on it and the sum energy of the pristine 6-AGNR and the energy of the isolate molecule :

3. Molecular Adsorption on 6-AGNR

In this section, after full relaxation, the optimized geometry was obtained, then the charge transfer and the adsorption energy were determined.

As Figure 2 shows, the pristine 6-AGNR is a semiconductor with 1.1 eV band gap. Gas adsorption changes the DOS of 6-AGNR, so it could change 6-AGNR properties.

The CO molecules are adsorbed to the 6-AGNR in the 6-AGNR plane, via its carbon atom as shown in Figure 1(b). The bond length obtained for C–C is 1.35 Å and the angle C–C–O is while the bond length of the adsorbed CO is 1.17 Å. The calculated adsorption energy of CO molecules on the 6-AGNR is −2.34 eV. As Figure 2 shows, the lowest unoccupied molecular orbital (LUMO), which appeared as a peak, is located at the center of original band gap slightly above the Fermi level of the pristine 6-AGNR so a charge transfer from the 6-AGNR, to the CO molecule is expected. There is a total charge transfer of 0.02 e from the 6-AGNR to CO molecules; therefore it can be deduced that the CO molecule acts as an acceptor.

The results of CO2 molecule adsorbed on the ribbon show that in the CO2 molecule, the C atom is closer to the ribbon surface than the O atoms (Figure 1(c)) and the C–C bond length is 1.50 Å. The bond length and the angle of the adsorbed CO2 molecule are 1.25 Å and , respectively. The angle of the C–O bond with the ribbon plan . The calculated adsorption energy of the CO2 molecule on the 6-AGNR is −5.23 eV. As can be seen in Figure 3, the LUMO is above Fermi level; it is the orbital that can have an overlap with the 6-AGNR orbitals and thus can cause charge transfer from the ribbon to the molecule. There is a total charge transfer of 0.09 e from the 6-AGNR to the CO2 molecule. Therefore it can be deduced that the CO2 molecule acts as an acceptor. After adsorbing the CO2 molecule, the Fermi level shifts toward the valance band (Figure 3), so the system exhibits -type semiconducting behavior.

The results of calculations show that the NO molecule sits in the ribbon plane. NO molecules attached to the ribbon via the N atom, with their N–C bond length 1.43 Å and the O–N–C angle (Figure 1(d)). The calculated adsorption energy of the NO molecule on the 6-AGNR is −1.15 eV. As Figure 4 shows, the highest occupied molecular orbital (HOMO), which has appeared as a peak near the Fermi level of pristine 6-AGNR, is half filled and is associated with both and orbitals. Due to these two facts, it can also be ascribed as the lowest unoccupied molecular orbital (LUMO). It causes charge transfer in both directions due to the mixing of the HOMO or the LUMO of NO with the 6-AGNR orbitals below or above the Fermi level. There is a total charge transfer of 0.15 e from the 6-AGNR to the NO molecule. Therefore it can be deduced that the NO molecule acts as an acceptor.

NH3 molecules attach to the ribbon via the N atom (Figure 1(e)). The N atom sits 0.9 Å away from the edge of the ribbon, the length of N–C bond is 1.48 Å, and the H–N–H angle is . The angle that the N–C bond makes with the ribbon plane is . The calculated adsorption energy of the NH3 molecule on the 6-AGNR is −3.103 eV. There is a total charge transfer of 0.16 e from the NH3 molecule to the 6-AGNR, so the NH3 molecule acts as a donor. As Figure 5 shows the band gap decreases after adsorbing the NH3 molecule and the Fermi level shifts toward the conduction band, so the system exhibits -type semiconducting behavior.

4. Conclusions

In this work the adsorption of CO, NO, and NH3 molecules on 6-AGNR was investigated. We optimized the position of the adsorbate molecules on 6-AGNR. After full relaxation, the adsorption energy and the charge transfer properties between the molecules and the 6-AGNR are determined. We showed that the NO, CO2, and CO molecules act as an acceptor and that the NH3 molecule acts as a donor which has also been verified in experiment [9]. The NO and CO adsorbed molecules contributed with localized states in the center of original band gap. AGNR semiconductor became -type semiconductor after NH3 molecule adsorption. The adsorption of NH3 molecule converts the electronic structure of 6-AGNR as a degenerate semiconductor. These results are consistent with those obtained by Huang et al. [22] and Saffarzadeh [24].

References

  1. J. Kong, N. R. Franklin, C. Zhou et al., “Nanotube molecular wires as chemical sensors,” Science, vol. 287, no. 5453, pp. 622–625, 2000. View at: Publisher Site | Google Scholar
  2. P. G. Collins, K. Bradley, M. Ishigami, and A. Zettl, “Extreme oxygen sensitivity of electronic properties of carbon nanotubes,” Science, vol. 287, no. 5459, pp. 1801–1804, 2000. View at: Google Scholar
  3. P. Qi, O. Vermesh, M. Grecu et al., “Toward large arrays of multiplex functionalized carbon nanotube sensors for highly sensitive and selective molecular detection,” Nano Letters, vol. 3, no. 3, pp. 347–351, 2003. View at: Publisher Site | Google Scholar
  4. S. Chopra, K. McGuire, N. Gothard, A. M. Rao, and A. Pham, “Selective gas detection using a carbon nanotube sensor,” Applied Physics Letters, vol. 83, no. 11, pp. 2280–2282, 2003. View at: Publisher Site | Google Scholar
  5. L. Valentini, I. Armentano, J. M. Kenny, C. Cantalini, L. Lozzi, and S. Santucci, “Sensors for sub-ppm NO2 gas detection based on carbon nanotube thin films,” Applied Physics Letters, vol. 82, no. 6, pp. 961–963, 2003. View at: Publisher Site | Google Scholar
  6. T. Ueda, M. M. H. Bhuiyana, H. Norimatsua, S. Katsukia, T. Ikegamia, and F. Mitsugi, “Development of carbon nanotube-based gas sensors for NOx gas detection working at low temperature,” Physica E, vol. 40, no. 7, pp. 2272–2277, 2008. View at: Publisher Site | Google Scholar
  7. P. Qi, O. Vermesh, M. Grecu et al., “Toward large arrays of multiplex functionalized carbon nanotube sensors for highly sensitive and selective molecular detection,” Nano Letters, vol. 3, no. 3, pp. 347–351, 2003. View at: Publisher Site | Google Scholar
  8. D. Zhang, Z. Liu, C. Li et al., “Detection of NO2 down to ppb levels using individual and multiple In2O3 nanowire devices,” Nano Letters, vol. 4, no. 10, pp. 1919–1924, 2004. View at: Publisher Site | Google Scholar
  9. F. Schedin, A. K. Geim, S. V. Morozov et al., “Detection of individual gas molecules adsorbed on graphene,” Nature Materials, vol. 6, no. 9, pp. 652–655, 2007. View at: Publisher Site | Google Scholar
  10. J. P. Novak, E. S. Snow, E. J. Houser, D. Park, J. L. Stepnowski, and R. A. McGill, “Nerve agent detection using networks of single-walled carbon nanotubes,” Applied Physics Letters, vol. 83, no. 19, pp. 4026–4028, 2003. View at: Publisher Site | Google Scholar
  11. T. O. Wehling, K. S. Novoselov, S. V. Morozov et al., “Molecular doping of graphene,” Nano Letters, vol. 8, no. 1, pp. 173–177, 2008. View at: Publisher Site | Google Scholar
  12. J. Dai, P. Giannozzi, and J. Yuan, “Adsorption of pairs of NOx molecules on single-walled carbon nanotubes and formation of NO + NO3 from NO2,” Surface Science, vol. 603, no. 21, pp. 3234–3238, 2009. View at: Publisher Site | Google Scholar
  13. J. D. Fowler, M. J. Allen, V. C. Tung, Y. Yang, R. B. Kaner, and B. H. Weiller, “Practical chemical sensors from chemically derived graphene,” ACS Nano, vol. 3, no. 2, pp. 301–306, 2009. View at: Publisher Site | Google Scholar
  14. O. Leenaerts, B. Partoens, and F. M. Peeters, “Adsorption of H2O, NH3, CO, NO2, and NO on graphene: a first-principles study,” Physical Review B, vol. 77, no. 12, Article ID 125416, 6 pages, 2008. View at: Publisher Site | Google Scholar
  15. R. M. Ribeiro, N. M. R. Peres, J. Continho, and P. R. Briddon, “Inducing energy gaps in monolayer and bilayer graphene: local density approximation calculations,” Physical Review B, vol. 78, no. 7, Article ID 075442, 7 pages, 1990. View at: Publisher Site | Google Scholar
  16. Y. H. Zhang, Y. B. Chen, K. G. Zhou et al., “Improving gas sensing properties of graphene by introducing dopants and defects: a first-principles study,” Nanotechnology, vol. 20, no. 18, Article ID 185504, 2009. View at: Publisher Site | Google Scholar
  17. K. Imani, M. R. Abolhassani, and A. A. Sabouri-Dodaran, “Electronic transport calculation of adsorbate NO2 and NO molecules on graphene using maximally localized wannier functions,” The European Physical Journal B, vol. 74, no. 1, pp. 135–138, 2010. View at: Publisher Site | Google Scholar
  18. K. Nakada, M. Fujita, G. Dresselhaus, and M. S. Dresselhaus, “Edge state in graphene ribbons: nanometer size effect and edge shape dependence,” Physical Review B, vol. 54, no. 24, pp. 17954–17961, 1996. View at: Publisher Site | Google Scholar
  19. V. Barone, O. Hod, and G. E. Scuseria, “Electronic structure and stability of semiconducting graphene nanoribbons,” Nano Letters, vol. 6, no. 12, pp. 2748–2754, 2006. View at: Publisher Site | Google Scholar
  20. M. Y. Han, B. Özyilmaz, Y. Zhang, and P. Kim, “Energy band-gap engineering of graphene nanoribbons,” Physical Review Letters, vol. 98, no. 20, Article ID 206805, 4 pages, 2007. View at: Publisher Site | Google Scholar
  21. L. Tapasztó, G. Dobrik, P. Lambin, and L. P. Biró, “Tailoring the atomic structure of graphene nanoribbons by scanning tunnelling microscope lithography,” Nature Nanotechnology, vol. 3, no. 7, pp. 397–401, 2008. View at: Publisher Site | Google Scholar
  22. B. Huang, Z. Li, Z. Liu et al., “Adsorption of gas molecules on graphene nanoribbons and its implication for nanoscale molecule sensor,” Journal of Physical Chemistry C, vol. 112, no. 35, pp. 13442–13446, 2008. View at: Publisher Site | Google Scholar
  23. H. E. Romero, P. Joshi, A. K. Gupta et al., “Adsorption of ammonia on graphene,” Nanotechnology, vol. 20, no. 24, Article ID 245501, 2009. View at: Publisher Site | Google Scholar
  24. A. Saffarzadeh, “Modeling of gas adsorption on graphene nanoribbons,” Journal of Applied Physics, vol. 107, no. 11, Article ID 114309, 7 pages, 2010. View at: Publisher Site | Google Scholar
  25. P. Giannozzi, S. Baroni, N. Bonini et al., “Quantum espresso: a modular and open-source software project for quantum simulations of materials,” Journal of Physics, vol. 21, no. 39, Article ID 395502, 2009. View at: Publisher Site | Google Scholar
  26. D. Vanderbilt, “Soft self-consistent pseudopotentials in a generalized eigenvalue formalism,” Physical Review B, vol. 41, no. 11, pp. 7892–7895, 1990, The Pseudopotential generation. View at: Publisher Site | Google Scholar

Copyright © 2012 Khadije Imani et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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