Understanding the interaction between fullerene and graphene nanoribbons using density functional theory

Carbon based heterostructures are extremely important in the field of material science as the junction of two carbon nanomaterials strongly influences the properties of a material [1]. A hybrid of graphene-fullerene architecture is called graphene nanobud (GNB), where a C60 cage is covalently attached on the surface of a graphene sheet and can be widely used in the field of thermoelectric power generation [2], Li ion batteries [3] and photocurrent generation [4]. Different properties of GNBs are studied so far, which enable the novelty of this hybrid material in the class of carbon nanostructures. The vast study on GNBs suggests that how the properties of a nanobud change when graphene is replaced with its nano counterparts. In this research paper, the structural, electronic and magnetic properties of covalently attached C60 cage with armchair and zigzag graphene nanoribbons (as shown in fig. 1) have been investigated using density functional theory. In order to check the effect of doping of formed graphene nanobuds, the C60 cage is substitutionally doped with nitrogen (N) and boron (B) i.e. C60-nNn+GNR and C60-nBn+GNR with n = 1, 2, 3, 6 and 12.     Fig.1. Ground state structures of A) AGNR nanobud and B) ZGNR nanobud. AGNR nanobuds don't form stable structures, owing to their positive values of the interaction energy. However, pure and N/B doped ZGNR nanobud form stable structures with [2+2]hhT mode, hence presenting the possibility of their formation. Average diameter for N doped ZGNR nanobuds decreases as the C-N bond length is lower than the C-C bond length whereas average diameter for doped ZGNR increases due to the large C-B bond length. The considered complexes are magnetic in nature having a finite value of total magnetic moment (as shown in fig. 2). Increase in total magnetic moment is due to the induced localized magnetic moments near dopant sites, whereas decrease in the total magnetic moments is due to the reduction in magnetic moments at C sites near connecting bond atoms. The finite energy difference between HOMO-LUMO gaps for the spin-up and spin-down states is responsible for the magnetic nature of considered complexes. The significant variation in electronic density of states near the Fermi level leads to change in the metallic behaviour of ZGNR nanobuds. Mulliken charge analysis (Table 1) shows that in N doped nanobud, there is a transfer of charge from N to surrounding C atoms due to their electronegativity difference, whereas in the case of B doped nanobud, there is a gain in charge of B from surrounding C atoms. The unique electronic and magnetic properties of nanobuds can lead to the possible applications in the field of magnetic nano devices. Fig.2. Total Magnetic Moment for N and B doped ZGNR nanobuds. Tabel 1. Muliken charge analysis for N and B doped ZGNR nanobuds. Nanobud N+ (e) Nanobud B- (e) C59N-ZGNR 0.44 C59B-ZGNR 0.78 C58N2-ZGNR 0.40 C58B2-ZGNR 0.73 C57N3-ZGNR 0.47 C57B3-ZGNR 0.75 C54N6-ZGNR 0.41 C54B6-ZGNR 0.72 C48N12-ZGNR 0.41 C48B12-ZGNR 0.67