- Email: [email protected]
Theoretical study of Ag doping-induced vacancies defects in armchair graphene
Physica B: Condensed Matter 538 (2018) 150–153
Contents lists available at ScienceDirect
Physica B: Condensed Matter journal homepage: www.elsevier.com/locate/physb
Theoretical study of Ag doping-induced vacancies defects in armchair graphene L. Benchallal b, S. Haffad a, L. Lamiri a, F. Boubenider b, H. Zitoune c, B. Kahouadji a, M. Samah a, * a b c
Universite A/Mira, Bejaia, Algeria Universite Houari Boumediene, Labotatoire Physique des Matreriaux, Alger, Algeria Universite Mohand Oulhadj, Bouira, Algeria
A R T I C L E I N F O
A B S T R A C T
Keywords: DFT Silver AGNR Magnetic
We have performed a density functional theory (DFT) study of the absorption of silver atoms (Ag,Ag2 and Ag3) in graphene using SIESTA code, in the generalized gradient approximation (GGA). The absorption energy, geometry, magnetic moments and charge transfer of Ag clusters-graphene system are calculated. The minimum energy configuration demonstrates that all structures remain planar and silver atoms fit into this plane. The charge transfer between the silver clusters and carbon atoms constituting the graphene surface is an indicative of a strong bond. The structure doped with a single silver atom has a magnetic moment and the two other are nonmagnetic.
1. Introduction Sheet of graphitic carbon, especially single-layered ones, have attracted enormous attention in the past decade. Recently, researchers have isolated and characterized flat sheets of graphene [1–4] showing that these structures have unique and outstanding mechanical and electrical properties. The chemical doping of graphene and graphene nanoribbons (GNRs) has a major influence on their properties [5]. Several theoretical studies were done for understanding the interaction between metal doping and carbon atoms of the GNRs is mainly based on energy calculations and molecular dynamics [6–10]. In experimental side, Individual heavy atoms have already been observed in early transmission electron microscopy (TEM) studies [11–13]. Chemical doping depends both on the nature of the dopant and on its location on/in the graphene structure [14]. Among these effects, we can include edge modifications, substitution and adsorption [14]. It has found that for single impurity substitution doping is energetically more stable [15,16]. Searching for potential applications of these kind of structures, several efforts and studies have been devoted to design more efficient catalysts and sensors for gases produced by our everyday life (such as CO, No, CO2, NO2 …). Poor stabilities and high cost of the noble metal used as typical catalysts for CO oxidation are their main characteristics [17–20]. Recent researches demonstrate that two-dimensional (2D) such as graphene and hexagonal BN monolayer (h-BN), are found to be
prominent catalyst supports to stabilize single metal atoms. Graphene supporting individual and isolated atoms [21–25] present great activity and selectivity to the CO oxidation reaction. Mao et al. [26] have demonstrated that gold atom on h-BN with boron vacancy exhibits great thermally stability even during the CO oxidation process. Huang et al. [27] have studied the stability of single Ru atom embedded on h-BN and obtained that it is extraordinarily stable. The great stability of the h-BN supporting single Pd atom is revealed, and the single Pd and Co atom prefers to stay at the boron vacancy is obtained by Lu et al. [28,29]. G. Xu et al. have investigated the mechanism of various reactions of CO catalysis on defected graphene doped Pd atom [30]. Elsewhere, the mechanisms of CO oxidation to CO2 by silver doped hexagonal boron-nitride was investigated by Ref. [31]. In this work, we study the structural, electronic and magnetic properties of silver atoms absorbed in armchair GNRs (AGNRs) by employing density functional theory (DFT) based first-principles calculations. The future work will be devoted to study the usage of these structures as catalyst and/or sensor of several gases molecules. 2. Computational details Ab initio calculations in this study were done using the SIESTA program package [32]. Calculations of atomic geometry and electronic structure were performed within first-principles DFT under the generalized gradient approximation (GGA) of Perdew, Burke, and Ernzerhof
* Corresponding author. E-mail address: [email protected] (M. Samah). https://doi.org/10.1016/j.physb.2018.03.001 Received 9 January 2018; Received in revised form 28 February 2018; Accepted 1 March 2018 Available online 20 March 2018 0921-4526/© 2018 Elsevier B.V. All rights reserved.
L. Benchallal et al.
Physica B: Condensed Matter 538 (2018) 150–153
3. Results and discussion
(PBE) [33] including spin polarization. For the primitive unit cell of graphene, the two C atoms are placed on two-dimensional honeycomb lattice with a hexagonal structure. The lattice constant is chosen to be 2.46 Å, which is same as the experimental value. To analyze the Ag absorption, supercells of 120 atoms of carbon and hydrogen are used as the ideal model. We take x and y directions parallel and the z direction normal to the graphene plane. To avoid coupling between graphene layers, the vacuum separation between layers along the z-axis is set to 25 Å. The Brillouin zone is sampled with a 1 16 1 centered k-point grid. The kinetic energy cutoff of 400Ry for the plane wave expansion is found to be sufficient. All forces were optimized until the values were less than 0.04 eV/Å.
Relaxed structures are depicted on Fig. 1. We can easily see that absorbed silver atoms still in the plane of graphene nanoribbons. The absorption energy (Eab) was calculated as Eab ¼ Esystem Egr nEAg where n is the number of silver atoms, Esystem is the total energy of the silver- graphene nanoribbons system, EAg is the total energy of an isolated atom, and Egr is the total energy of the defected GNR. Vacancies-defectedGNR doped with silver atoms exhibit great absorption energy. These values demonstrate the stability of this kind of structures. From our results, one silver atom absorption is less stable than the dimmer which is less stable then the trimmer absorption. These values are more important comparatively with result obtained with adsorption in graphene [34,35]. Agþ1V-GNR is constructed by substituting one carbon atom by one silver atom. Ag-C interatomic distances are between 1.45 and 2.35 Å. The Ag atom remains in the plane of the GNR. The second structure (Ag2þ2VGNR) is constructed by substituting two carbon atoms by two silver (Ag) ones. After relaxation, Ag atoms always remain in the plane of defected GNR. The Ag-Ag distance equals 2.18 Å. This bond length is smaller than that found by Kaur et al. for silver dimmer adsorbed on graphene (parallel orientation 2.67 Å, perpendicular 2.59 Å) [34]. The third structure is constructed in this case, by replacing four carbon atoms by three silver atoms. After relaxation, the three silver atoms form an isosceles triangle (see Table 1). The Ag-C interatomic distances extend between 1.48 and 2.30 Å. Table 1 shows the distribution of the spin moment among the metal atom and the nearest carbon neighbors for all our structures. The magnetic moment of Agþ1V-GNR exhibits a magnetic moment of 1.05μB. Ag atom holds the major part of this moment (0.62μB) and the two nearest carbon atoms contribute to the rest of magnetic moment. This fact can be explained by the charge transfer between these elements. We can see that the contribution from the metal atom is almost important, contrary to results reported in Ref. [36]. The spin moment is localized in the complex formed by the metal atom and its nearest neighbors. The contribution from the rest of the graphene layer to magnetic moment can be considered as zero. This reflects the dominant contribution from the relatively localized carbon sp lobes in the description of the defect states near EF for these impurities. We can picture the main role of noble-metal substitutionals in graphene as stabilizing the structure of the carbon monovacancy, which severely reconstruct and change its charge state [36]. Ag2þ2V-GNR and Ag3þ4V-GNR are non magnetic. Neither the carbon atoms nor the silver atoms carry any moment. In Fig. 2, we present the electronic band structures for absorbed silver atoms. Agþ1V-GNR are like semiconductor with a little band gap (approximately around 0.04 eV). The two other structures have like metal behavior. However, a critical analysis of the metal absorbed graphene depicts that the graphene bands are strongly perturbed and resembles a metal like character. A shift of Fermi level is observed with respect to the conical points at K- point consistent with previous studies [37–39]. The shift symbolizes basically the transfer of electron (charge) between metal and graphene. The flat bands close to the Fermi level results into the sharp peak at Fermi level in density of states (DOS). The system undergoes a small structural distortion that removes the
Table 1 Ag-Ag distances (DAg-Ag), Ag-Ag distances (dAg-C), magnetic moment of the structure (Mtotal), MAg and MC magnetic moments of Ag atoms and C atoms.
Fig. 1. Relaxed configurations of AGNRs doped with: – A- one atom of Ag, -BAg2 cluster and -C- Ag3 cluster. 151
Structure
DAg-Ag (Å)
dAg-C (Å)
MAg (μB)
MC (μB)
Mtotal (μB)
Agþ1V-GNR Ag2þ2V-GNR Ag3þ4V-GNR
– 2.18 2.19-2.19-2.98
1.45-2.35 1.48-2.30 1.48-2.30
0.62 0 0
0.2 0 0
1.05 0 0
L. Benchallal et al.
Physica B: Condensed Matter 538 (2018) 150–153
Fig. 2. Bands structure of AGNRs doped with: – A- one atom of Ag, -B- Ag2 cluster and -C- Ag3 cluster.
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L. Benchallal et al.
Physica B: Condensed Matter 538 (2018) 150–153
magnetic behavior are mainly dictated by the number of valence electrons [40] (see Fig. 3). 4. Conclusion DFT study of AGNRs doped with silver atoms demonstrates that these structures are more stable and exhibits different electronic behaviors following the number of dopants. The graphene nanoribbon is still planar even after doping. One silver atom doped GNR are magnetic and others are nonmagnetic. References [1] K.S. Novoselov, D. Jiang, F. Schedin, T.J. Booth, V.V. Khotkevich, S.V. Morozov, A.K. Geim, Proc. Natl. Acad. Sci. 102 (2005) 10451. [2] Y. Zhang, Y.W. Tan, H.L. Stormer, P. Kim, Nature 438 (2005) 201. [3] Carbon Nanotubes, in: Springer Topics in Applied Physics, vol. 111, Springer, Berlin, Germany, 2007. [4] A.K. Geim, K.S. Novoselov, Nat. Mater. 6 (2007) 183. [5] H. Terrones, Terrones R. Lv, M.S. Dresselhaus, Rep. Prog. Phys. 75 (6) (2012), 062501. [6] A. Moisala, A.G. Nasibulin, E.I. Kauppinen, J. Phys. Condens. Matter 15 (2003) 3011. [7] Y.H. Lee, S.G. Kim, D. Tomanek, Phys. Rev. Lett. 78 (1997) 2393. [8] A. Maiti, C.J. Brabec, J. Bernholc, Phys. Rev. B 55 (1997) 6097. [9] A. Maiti, A. Ricca, Chem. Phys. Lett. 395 (2004) 7. [10] K. Kong, Y. Choi, B.H. Ryu, J.O. Lee, H. Chang, Mater. Sci. Eng. C 26 (2006) 1207. [11] S. Iijima, Optik 48 (1977) 193. [12] N. Tanaka, H. Kimata, T. Kizuka, J. Electron. Microsc. 45 (1996) 113. [13] J.H.C. Spence, Experimental High-resolution Electron Microscopy, Oxford University Press, Oxford, 1988. [14] J. Lan, X.H. Zheng, L.L. Song, R.N. Wang, Z. Zhang, Solid State Commun. 152 (2012) 1635. [15] G. Yu, X. Lü, L. Jiang, W. Gao, Y. Zheng, J. Phys. D Appl. Phys. 46 (37) (2013), 375303. [16] F. Banhart, J. Kotakoski, A.V. Krasheninnikov, Nano 5 (1) (2011) 26. [17] Z.-P. Liu, P. Hu, A. Alavi, J. Am. Chem. Soc. 124 (2002) 14770. [18] K. Bleakley, P. Hu, J. Am. Chem. Soc. 121 (1999) 7644. [19] A. Eichler, Surf. Sci. 498 (2002) 314. [20] X.-Q. Gong, Z.-P. Liu, R. Raval, P. Hu, J. Am. Chem. Soc. 126 (2004) 8. [21] Y. Li, Z. Zhou, G. Yu, W. Chen, Z. Chen, J. Phys. Chem. C 114 (2010) 6250. [22] Y.-H. Lu, M. Zhou, C. Zhang, Y.-P. Feng, J. Phys. Chem. C 113 (2009) 20156. [23] X. Liu, Y. Sui, T. Duan, C. Meng, Y. Han, Phys. Chem. Chem. Phys. 16 (2014) 23584. [24] 23584. 16 Y. Tang, Z. Yang, X. Dai, Phys. Chem. Chem. Phys. 14 (2012) 16566. [25] E.H. Song, Z. Wen, Q. Jiang, J. Phys. Chem. C 115 (2011) 3678. [26] K. Mao, L. Li, W. Zhang, Y. Pei, X.C. Zeng, X. Wu, J. Yang, Sci. Rep. 4 (2014) 5441. [27] C. Huang, X. Ye, C. Chen, S. Lin, D. Xie, Comput. Theor. Chem. 1011 (2013) 5. [28] Z. Lu, P. Lv, J. Xue, H. Wang, Y. Wang, Y. Huang, C. He, D. Ma, Z. Yang, RSC Adv. 5 (103) (2015) 84381. [29] Z. Lu, P. Lv, Y. Liang, D. Ma, Yi Zhang, W. Zhang, X. Yang, Z. Yang, Phys. Chem. Chem. Phys. 18 (31) (2016) 21865. [30] G. Xu, R. Wang, F. Yang, D. Ma, Z. Yang, Z. Lu, Carbon 118 (2017) 35. [31] Z. Lu, P. Lv, Z. Yang, S. Li, D. Ma, R. Wu, Phys. Chem. Chem. Phys. 19 (2017) 16795–16805. [32] J.M. Soler, E. Artacho, J.D. Gale, A. Garcıa, J. Junquera, P. Ordejon, D. SanchezPortal, J. Phys. Condens. Matter 14 (2002) 2745. [33] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865. [34] G. Kaur, S. Gupta, P. Rani, K. Dharamvir, AIP Conf. Proc. 1591 (2014) 339. [35] G.M. Wang, J.J. BelBruno, S.D. Kenny, R. Smith, Surf. Sci. 541 (2003) 91. [36] E.J.G. Santos, A. Ayuela, D. Sanchez-Portal, N. J. Phys. 12 (2010), 053012. [37] K.S. Subrahmanyam, A.K. Manna, S.K. Pati, C.N.R. Rao, Chem. Phys. Lett. 497 (2010) 70. [38] Y. Mao, J. Yuan, J. Zhong, J. Phys. Condens. Matter 20 (2008), 115209. [39] G. Giovaneeti, P.A. Khomyakov, G. Brocks, V.M. Karpan, J van der Brink, P.J. Kelly, Phys. Rev. Lett. 101 (2008), 026803. [40] A.H. Castro Neto, F. Guinea, N.M. Peres, K.S. Novoselov, A.K. Geim, Rev. Mod. Phys. 81 (2009) 109.
Fig. 3. Total density of states of AGNRs doped with: – A- one atom of Ag, -BAg2 cluster and -C- Ag3 cluster.
degeneracy of these levels and the unpaired electron becomes spin polarized. However, the similarities between the electronic structure of all three noble metals are evident, which indicates that bonding and
153
Contents lists available at ScienceDirect
Physica B: Condensed Matter journal homepage: www.elsevier.com/locate/physb
Theoretical study of Ag doping-induced vacancies defects in armchair graphene L. Benchallal b, S. Haffad a, L. Lamiri a, F. Boubenider b, H. Zitoune c, B. Kahouadji a, M. Samah a, * a b c
Universite A/Mira, Bejaia, Algeria Universite Houari Boumediene, Labotatoire Physique des Matreriaux, Alger, Algeria Universite Mohand Oulhadj, Bouira, Algeria
A R T I C L E I N F O
A B S T R A C T
Keywords: DFT Silver AGNR Magnetic
We have performed a density functional theory (DFT) study of the absorption of silver atoms (Ag,Ag2 and Ag3) in graphene using SIESTA code, in the generalized gradient approximation (GGA). The absorption energy, geometry, magnetic moments and charge transfer of Ag clusters-graphene system are calculated. The minimum energy configuration demonstrates that all structures remain planar and silver atoms fit into this plane. The charge transfer between the silver clusters and carbon atoms constituting the graphene surface is an indicative of a strong bond. The structure doped with a single silver atom has a magnetic moment and the two other are nonmagnetic.
1. Introduction Sheet of graphitic carbon, especially single-layered ones, have attracted enormous attention in the past decade. Recently, researchers have isolated and characterized flat sheets of graphene [1–4] showing that these structures have unique and outstanding mechanical and electrical properties. The chemical doping of graphene and graphene nanoribbons (GNRs) has a major influence on their properties [5]. Several theoretical studies were done for understanding the interaction between metal doping and carbon atoms of the GNRs is mainly based on energy calculations and molecular dynamics [6–10]. In experimental side, Individual heavy atoms have already been observed in early transmission electron microscopy (TEM) studies [11–13]. Chemical doping depends both on the nature of the dopant and on its location on/in the graphene structure [14]. Among these effects, we can include edge modifications, substitution and adsorption [14]. It has found that for single impurity substitution doping is energetically more stable [15,16]. Searching for potential applications of these kind of structures, several efforts and studies have been devoted to design more efficient catalysts and sensors for gases produced by our everyday life (such as CO, No, CO2, NO2 …). Poor stabilities and high cost of the noble metal used as typical catalysts for CO oxidation are their main characteristics [17–20]. Recent researches demonstrate that two-dimensional (2D) such as graphene and hexagonal BN monolayer (h-BN), are found to be
prominent catalyst supports to stabilize single metal atoms. Graphene supporting individual and isolated atoms [21–25] present great activity and selectivity to the CO oxidation reaction. Mao et al. [26] have demonstrated that gold atom on h-BN with boron vacancy exhibits great thermally stability even during the CO oxidation process. Huang et al. [27] have studied the stability of single Ru atom embedded on h-BN and obtained that it is extraordinarily stable. The great stability of the h-BN supporting single Pd atom is revealed, and the single Pd and Co atom prefers to stay at the boron vacancy is obtained by Lu et al. [28,29]. G. Xu et al. have investigated the mechanism of various reactions of CO catalysis on defected graphene doped Pd atom [30]. Elsewhere, the mechanisms of CO oxidation to CO2 by silver doped hexagonal boron-nitride was investigated by Ref. [31]. In this work, we study the structural, electronic and magnetic properties of silver atoms absorbed in armchair GNRs (AGNRs) by employing density functional theory (DFT) based first-principles calculations. The future work will be devoted to study the usage of these structures as catalyst and/or sensor of several gases molecules. 2. Computational details Ab initio calculations in this study were done using the SIESTA program package [32]. Calculations of atomic geometry and electronic structure were performed within first-principles DFT under the generalized gradient approximation (GGA) of Perdew, Burke, and Ernzerhof
* Corresponding author. E-mail address: [email protected] (M. Samah). https://doi.org/10.1016/j.physb.2018.03.001 Received 9 January 2018; Received in revised form 28 February 2018; Accepted 1 March 2018 Available online 20 March 2018 0921-4526/© 2018 Elsevier B.V. All rights reserved.
L. Benchallal et al.
Physica B: Condensed Matter 538 (2018) 150–153
3. Results and discussion
(PBE) [33] including spin polarization. For the primitive unit cell of graphene, the two C atoms are placed on two-dimensional honeycomb lattice with a hexagonal structure. The lattice constant is chosen to be 2.46 Å, which is same as the experimental value. To analyze the Ag absorption, supercells of 120 atoms of carbon and hydrogen are used as the ideal model. We take x and y directions parallel and the z direction normal to the graphene plane. To avoid coupling between graphene layers, the vacuum separation between layers along the z-axis is set to 25 Å. The Brillouin zone is sampled with a 1 16 1 centered k-point grid. The kinetic energy cutoff of 400Ry for the plane wave expansion is found to be sufficient. All forces were optimized until the values were less than 0.04 eV/Å.
Relaxed structures are depicted on Fig. 1. We can easily see that absorbed silver atoms still in the plane of graphene nanoribbons. The absorption energy (Eab) was calculated as Eab ¼ Esystem Egr nEAg where n is the number of silver atoms, Esystem is the total energy of the silver- graphene nanoribbons system, EAg is the total energy of an isolated atom, and Egr is the total energy of the defected GNR. Vacancies-defectedGNR doped with silver atoms exhibit great absorption energy. These values demonstrate the stability of this kind of structures. From our results, one silver atom absorption is less stable than the dimmer which is less stable then the trimmer absorption. These values are more important comparatively with result obtained with adsorption in graphene [34,35]. Agþ1V-GNR is constructed by substituting one carbon atom by one silver atom. Ag-C interatomic distances are between 1.45 and 2.35 Å. The Ag atom remains in the plane of the GNR. The second structure (Ag2þ2VGNR) is constructed by substituting two carbon atoms by two silver (Ag) ones. After relaxation, Ag atoms always remain in the plane of defected GNR. The Ag-Ag distance equals 2.18 Å. This bond length is smaller than that found by Kaur et al. for silver dimmer adsorbed on graphene (parallel orientation 2.67 Å, perpendicular 2.59 Å) [34]. The third structure is constructed in this case, by replacing four carbon atoms by three silver atoms. After relaxation, the three silver atoms form an isosceles triangle (see Table 1). The Ag-C interatomic distances extend between 1.48 and 2.30 Å. Table 1 shows the distribution of the spin moment among the metal atom and the nearest carbon neighbors for all our structures. The magnetic moment of Agþ1V-GNR exhibits a magnetic moment of 1.05μB. Ag atom holds the major part of this moment (0.62μB) and the two nearest carbon atoms contribute to the rest of magnetic moment. This fact can be explained by the charge transfer between these elements. We can see that the contribution from the metal atom is almost important, contrary to results reported in Ref. [36]. The spin moment is localized in the complex formed by the metal atom and its nearest neighbors. The contribution from the rest of the graphene layer to magnetic moment can be considered as zero. This reflects the dominant contribution from the relatively localized carbon sp lobes in the description of the defect states near EF for these impurities. We can picture the main role of noble-metal substitutionals in graphene as stabilizing the structure of the carbon monovacancy, which severely reconstruct and change its charge state [36]. Ag2þ2V-GNR and Ag3þ4V-GNR are non magnetic. Neither the carbon atoms nor the silver atoms carry any moment. In Fig. 2, we present the electronic band structures for absorbed silver atoms. Agþ1V-GNR are like semiconductor with a little band gap (approximately around 0.04 eV). The two other structures have like metal behavior. However, a critical analysis of the metal absorbed graphene depicts that the graphene bands are strongly perturbed and resembles a metal like character. A shift of Fermi level is observed with respect to the conical points at K- point consistent with previous studies [37–39]. The shift symbolizes basically the transfer of electron (charge) between metal and graphene. The flat bands close to the Fermi level results into the sharp peak at Fermi level in density of states (DOS). The system undergoes a small structural distortion that removes the
Table 1 Ag-Ag distances (DAg-Ag), Ag-Ag distances (dAg-C), magnetic moment of the structure (Mtotal), MAg and MC magnetic moments of Ag atoms and C atoms.
Fig. 1. Relaxed configurations of AGNRs doped with: – A- one atom of Ag, -BAg2 cluster and -C- Ag3 cluster. 151
Structure
DAg-Ag (Å)
dAg-C (Å)
MAg (μB)
MC (μB)
Mtotal (μB)
Agþ1V-GNR Ag2þ2V-GNR Ag3þ4V-GNR
– 2.18 2.19-2.19-2.98
1.45-2.35 1.48-2.30 1.48-2.30
0.62 0 0
0.2 0 0
1.05 0 0
L. Benchallal et al.
Physica B: Condensed Matter 538 (2018) 150–153
Fig. 2. Bands structure of AGNRs doped with: – A- one atom of Ag, -B- Ag2 cluster and -C- Ag3 cluster.
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Physica B: Condensed Matter 538 (2018) 150–153
magnetic behavior are mainly dictated by the number of valence electrons [40] (see Fig. 3). 4. Conclusion DFT study of AGNRs doped with silver atoms demonstrates that these structures are more stable and exhibits different electronic behaviors following the number of dopants. The graphene nanoribbon is still planar even after doping. One silver atom doped GNR are magnetic and others are nonmagnetic. References [1] K.S. Novoselov, D. Jiang, F. Schedin, T.J. Booth, V.V. Khotkevich, S.V. Morozov, A.K. Geim, Proc. Natl. Acad. Sci. 102 (2005) 10451. [2] Y. Zhang, Y.W. Tan, H.L. Stormer, P. Kim, Nature 438 (2005) 201. [3] Carbon Nanotubes, in: Springer Topics in Applied Physics, vol. 111, Springer, Berlin, Germany, 2007. [4] A.K. Geim, K.S. Novoselov, Nat. Mater. 6 (2007) 183. [5] H. Terrones, Terrones R. Lv, M.S. Dresselhaus, Rep. Prog. Phys. 75 (6) (2012), 062501. [6] A. Moisala, A.G. Nasibulin, E.I. Kauppinen, J. Phys. Condens. Matter 15 (2003) 3011. [7] Y.H. Lee, S.G. Kim, D. Tomanek, Phys. Rev. Lett. 78 (1997) 2393. [8] A. Maiti, C.J. Brabec, J. Bernholc, Phys. Rev. B 55 (1997) 6097. [9] A. Maiti, A. Ricca, Chem. Phys. Lett. 395 (2004) 7. [10] K. Kong, Y. Choi, B.H. Ryu, J.O. Lee, H. Chang, Mater. Sci. Eng. C 26 (2006) 1207. [11] S. Iijima, Optik 48 (1977) 193. [12] N. Tanaka, H. Kimata, T. Kizuka, J. Electron. Microsc. 45 (1996) 113. [13] J.H.C. Spence, Experimental High-resolution Electron Microscopy, Oxford University Press, Oxford, 1988. [14] J. Lan, X.H. Zheng, L.L. Song, R.N. Wang, Z. Zhang, Solid State Commun. 152 (2012) 1635. [15] G. Yu, X. Lü, L. Jiang, W. Gao, Y. Zheng, J. Phys. D Appl. Phys. 46 (37) (2013), 375303. [16] F. Banhart, J. Kotakoski, A.V. Krasheninnikov, Nano 5 (1) (2011) 26. [17] Z.-P. Liu, P. Hu, A. Alavi, J. Am. Chem. Soc. 124 (2002) 14770. [18] K. Bleakley, P. Hu, J. Am. Chem. Soc. 121 (1999) 7644. [19] A. Eichler, Surf. Sci. 498 (2002) 314. [20] X.-Q. Gong, Z.-P. Liu, R. Raval, P. Hu, J. Am. Chem. Soc. 126 (2004) 8. [21] Y. Li, Z. Zhou, G. Yu, W. Chen, Z. Chen, J. Phys. Chem. C 114 (2010) 6250. [22] Y.-H. Lu, M. Zhou, C. Zhang, Y.-P. Feng, J. Phys. Chem. C 113 (2009) 20156. [23] X. Liu, Y. Sui, T. Duan, C. Meng, Y. Han, Phys. Chem. Chem. Phys. 16 (2014) 23584. [24] 23584. 16 Y. Tang, Z. Yang, X. Dai, Phys. Chem. Chem. Phys. 14 (2012) 16566. [25] E.H. Song, Z. Wen, Q. Jiang, J. Phys. Chem. C 115 (2011) 3678. [26] K. Mao, L. Li, W. Zhang, Y. Pei, X.C. Zeng, X. Wu, J. Yang, Sci. Rep. 4 (2014) 5441. [27] C. Huang, X. Ye, C. Chen, S. Lin, D. Xie, Comput. Theor. Chem. 1011 (2013) 5. [28] Z. Lu, P. Lv, J. Xue, H. Wang, Y. Wang, Y. Huang, C. He, D. Ma, Z. Yang, RSC Adv. 5 (103) (2015) 84381. [29] Z. Lu, P. Lv, Y. Liang, D. Ma, Yi Zhang, W. Zhang, X. Yang, Z. Yang, Phys. Chem. Chem. Phys. 18 (31) (2016) 21865. [30] G. Xu, R. Wang, F. Yang, D. Ma, Z. Yang, Z. Lu, Carbon 118 (2017) 35. [31] Z. Lu, P. Lv, Z. Yang, S. Li, D. Ma, R. Wu, Phys. Chem. Chem. Phys. 19 (2017) 16795–16805. [32] J.M. Soler, E. Artacho, J.D. Gale, A. Garcıa, J. Junquera, P. Ordejon, D. SanchezPortal, J. Phys. Condens. Matter 14 (2002) 2745. [33] J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865. [34] G. Kaur, S. Gupta, P. Rani, K. Dharamvir, AIP Conf. Proc. 1591 (2014) 339. [35] G.M. Wang, J.J. BelBruno, S.D. Kenny, R. Smith, Surf. Sci. 541 (2003) 91. [36] E.J.G. Santos, A. Ayuela, D. Sanchez-Portal, N. J. Phys. 12 (2010), 053012. [37] K.S. Subrahmanyam, A.K. Manna, S.K. Pati, C.N.R. Rao, Chem. Phys. Lett. 497 (2010) 70. [38] Y. Mao, J. Yuan, J. Zhong, J. Phys. Condens. Matter 20 (2008), 115209. [39] G. Giovaneeti, P.A. Khomyakov, G. Brocks, V.M. Karpan, J van der Brink, P.J. Kelly, Phys. Rev. Lett. 101 (2008), 026803. [40] A.H. Castro Neto, F. Guinea, N.M. Peres, K.S. Novoselov, A.K. Geim, Rev. Mod. Phys. 81 (2009) 109.
Fig. 3. Total density of states of AGNRs doped with: – A- one atom of Ag, -BAg2 cluster and -C- Ag3 cluster.
degeneracy of these levels and the unpaired electron becomes spin polarized. However, the similarities between the electronic structure of all three noble metals are evident, which indicates that bonding and
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