Theoretical studies of geometry asymmetry in tellurium nanostructures: intrinsic dipole, charge separation, and semiconductor-metal transition

Bulk tellurium (Te) presents a threefold screw axis with highly anisotropic chain structure, where every Te atom forms strong covalent bonds in the chain and much weaker bonds in the adjacent chains. The bonds in the adjacent chains are critical to the total energies of Te nanostructures since the nearest neighbors are always saturated. Confirmed by our model simulation and first-principles calculations, the nanobelts would be stabilized at the temperature of 600 K due to the entropy effect, though the hexagonal nanowires have the smallest surface-to-volume ratio. Attributed to the geometry asymmetry of the highly anisotropic chain, we showed that the difference of weaker bonds' distribution induces an intrinsic dipole, and thus a charge separation at the two ends of Te nanobelts. Interestingly, it further leads to a semiconductor-metal transition which is also verified by our first-principles calculations. Our finding provides a new mechanism of charge separation and semiconductor-metal transition, due to the unique asymmetry of geometry in Te nanostructures.