| AVS 62nd International Symposium & Exhibition | |
| 2D Materials Focus Topic | Wednesday Sessions |
| Session 2D+MN+NS+SP+SS+TF-WeM |
| Session: | Mechanical and Thermal Properties of 2D Materials |
| Presenter: | Yuuki Uchida, The University of Electro-Communications (UEC-Tokyo) and JST CREST, Japan |
| Authors: | Y. Uchida, The University of Electro-Communications (UEC-Tokyo) and JST CREST, Japan A. Akaishi, The University of Electro-Communications (UEC-Tokyo) and JST CREST, Japan J. Nakamura, The University of Electro-Communications (UEC-Tokyo) and JST CREST, Japan |
| Correspondent: | Click to Email |
Impurity doping is an efficient way to modify electronic properties of graphene. Several groups have reported the stability of dopants in graphene, especially near edges of graphene: Impurity atoms prefer to locate at the zigzag edge of graphene rather than the armchair one[1]. It has also been reported that the electronic properties are strongly dependent upon the location of dopants, which is derrived from the non-equivalence of the two sublattice[2]. It is well-known that the edge-localized state emerges at the zigzag edge[3], which is specific for the so-called bipartite lattice. However, it has not been clarified yet how the edge-state affects the dopant stability depending on the sublattice. In this study, we investigate the role of the sublattice-dependent edge-state on the stabilization of impurities. We evaluate the dependence of the structural stability on the distance of impurity atoms from the zigzag edge using first-principles calculations within the density-functional theory. We have employed two types of graphene nanoribbons (GNRs) with the armchair- (AGNR) or the zigzag- (ZGNR) edge.
For AGNR, the formation energy of dopants does not change neither systematically nor monotonically as a function of the distance from the edge. On the other hand, for ZGNR, the formation energy is lower than that for AGNR and decreases with decreasing distance from the edge. In addition, two types of tendencies are confirmed for odd- and even-numbered sites from the zigzag edge, corresponding to the different sublattices of the bipartite lattice.
Such peculiar behavior as for of the formation energy can be explained as follows : The doped N atom donates its electron to the unoccupied-edge-state just above the Fermi level, resulting in the lowering of the one-electron energy of this state. The smaller the distance of N atoms from the zigzag edge is, the larger the electrostatic attraction between electrons of edge-localized states and positively-charged ion-shell at the N site becomes. Further, N atoms are much more stabilized at the odd-numbered site, because the edge-state has finite amplitude only at the odd-numbered sites.
[1]S. F. Huang et al., Phys. Rev. B. 80, 235410 (2009)
[2]J. Jiang et al., J. Chem. Phys. 136, 014702 (2012)
[3]M. Fujita et al., J. Phys. Soc. 65, 1920 (1996)