Tuning the electronic structure of graphene nanoribbons through chemical edge modification: A theoretical study

We report combined first-principle and tight-binding (TB) calculations to simulate the effects of chemical edge modifications on structural and electronic properties. The C-C bond lengths and bond angles near the graphene nanoribbon (GNR) edge have considerable changes when edge carbon atoms are bounded to different atoms. By introducing a phenomenological hopping parameter $t_1$ for nearest-neighbor hopping to represent various chemical edge modifications, we investigated the electronic structural changes of nanoribbons with different widths based on the tight-binding scheme. Theoretical results show that addends can change the band structures of armchair GNRs and even result in observable metal-to-insulator transition.

Figure 1

Optimized structure of a (9,0) armchair GNR (all edge bonds are bound by hydrogen atoms). Here, the bond length is in $\AA$. Note that a zigzag $(n,0)$ GNR can be rolled to form an armchair [$(n,0)$ CNT, and an armchair $(n,n)$ GNR can be rolled as a zigzag $(n,n)$] CNT.

Figure 2

(Color online) Top two valence bands and bottom two conduction bands of zigzag GNRs in $t_1=t$ and $t_1=1.2t$ cases. Here $t=-2.66\mathrm{eV}$ is the hopping parameter of two-dimensional infinite graphene with the lattice constant $a_{c-c}=1.42\mathrm{\AA }$.

Figure 3

The energy gap of armchair GNRs depends on their widths: (a) when $t_1=t$ and (b) when $t_1=1.2t$.

Figure 4

(Color online) The effect of hopping parameter $t_1$ on energy gaps of armchair GNRs with different widths ($n=8$, 9, and 10).