Panels (a) and (b) demonstrate the ideal structural models of B₄C star-shaped FTNW and Ag pentagonal FTNW, respectively. The black arrow lines indicate the twinning axes (TA) of both of the nanowires. The twin planes of the FTNW structural models are shadowed in panels (a) and (b). (c) The atomic structure of B₄C rhombohedral unit cell. S1, S2, S3, and S4 indicate the four atomic sites in the unit cell. S1 and S2 are at the polar and equatorial sites of the icosahedral clusters, respectively. S3 and S4 are at the end and the center of the linear atomic chain. Ic represents the icosahedral cluster. The carbon content-dependent lattice parameter α varies in the range from 65.4° to 65.7°. To form five-fold twinned structure, the B₄C single crystalline segments share a common [001] twining axis as indicated by black arrow line and join together by (100) and (010) twin planes which are shadowed. (d) The atomic structure of Ag FCC unit cell indicated by red solid lines. The corresponding Ag rhombohedral primitive unit cell is indicated by black dashed lines. Its rhombohedral unit cell parameters are as a = 2.89 Å, α = 60°. (e) The reciprocal lattice of a B₄C single crystal. (f) The reciprocal lattice of an Ag FCC single crystal.