Tight-binding modeling of the current in zigzag-edge graphene nano-ribbons indicates that 120-degrees turns of the ribbon have virtually no effect on the ballistic transmission within single-band conduction window. At the same time 60-degrees turns are highly reflective. Figures below illustrate these statements. A simple pictorial explanation of the underlying physics is provided in the following article: 120_vs_60_Conductance_03_CNT_Learning_Materials.pdf (728 KB, uploaded by Denis Areshkin 7 years 7 months ago)

Figure 1 Atomically-resolved current in 120-degrees Z-GNR turn for the given energy E. The transmission plot is presented in insert. The dashed dark-blue line is the transmission of a perfect straight Z-GNR of the same width. The dark-red curve is the transmission of the 120-degrees turn. The green vertical line marks energy E. These Results were obtained using pi-orbital tight binding in the second nearest neighbor approximation.

Figure 2 Atomically-resolved current in 120-degrees Z-GNR splitter for the given energy E.
Input (vertical) Z-GNR splits in two output Z-GNRs of the same widths oriented at 120-degrees angles with respect to the input current direction. Current splits symmetrically into outputs virtually without losses. The dashed green line in the insert is the transmission of a perfect straight Z-GNR. The green curve is the transmission into one of the output leads. The dark-blue curve is the net transmission into two leads. The vertical red line marks energy E. These results were obtained using pi-orbital tight binding in the second nearest neighbor approximation.

Figure 3 Transmission (dark-red curve) of a single 60-degrees turn (top) and two consecutive 60-degrees turns (bottom). The dashed blue line is the transmission of the straight Z-GNR of the same width as the input lead. These results were obtained in the pi-orbital tight binding in the second nearest neighbor approximation.