Germanene nanomeshes: Cooperative effects of degenerate perturbation and uniaxial strain on tuning bandgap

Based on the detailed first-principles calculations, we have carefully investigated the defect induced band splitting and its combination with Dirac cone move in bandgap opening. The uniaxial strain can split the pi-like bands into pi(a) and pi(z) bands with energy interval E-strain to shift the Dirac cone. Also, the inversion symmetry preserved antidot can split pi(a) (pi(z)) into pi(a1) and pi(a2) (pi(z1) and pi(z2)) bands with energy interval E-defect to open bandgap in the nanomesh with Gamma as four-fold degenerate Dirac point according to the band-folding analysis. Though the E-defect would keep almost unaffected, the E-strain would be increased by enhancing the uniaxial strain to continuously tune the gap width. Then the bandgap can be reversibly switched on/off. Our studies of the inversion symmetry preserved nanomesh show distinct difference in bandgap opening mechanism as compared to the one by breaking the sublattice equivalence in the (GaAs)(6) nanoflake patterned nanomesh. Here, the pi-band gap remains almost unchanged against strain enhancing.