Fig. 1: Representative twisted monolayer/bilayer phosphorene heterostructures.

a A side-view illustration of device’s configuration, where 1L and 2L label monolayer and bilayer, respectively. b, HAADF-STEM image of a ~5.7° twisted monolayer/bilayer phosphorene heterostructure. It shows rectangular shape moiré superlattices, as indicated by two orthogonal superlattices vectors labeled a₁ and a₂. Scale bar, 2 nm. c A top-view illustration of the twisted monolayer/bilayer phosphorene heterostructure with a large angle of 19°. The top monolayer (red) is rotated by 19° respected to the bilayer phosphorene (light cyan for the middle layer and blue for the bottom layer). The gray dashed rectangle indicates the supercell that contains four special stacking configurations, namely A, B, C, and D configurations. d The optical microscopy image of device D1. The red, blue, and white dashed lines indicate the monolayer, bilayer, and the twisted monolayer/bilayer phosphorene region, respectively. Scale bar, 5 µm. e Polarization-dependent PL emissions of the isolated monolayer and bilayer phosphorene, respectively. It shows a 19° twist angle between the top monolayer and bottom bilayer phosphorene. f PL spectra of the monolayer phosphorene (black), bilayer phosphorene (blue), and the 19° twisted phosphorene heterostructure (red). An emerging moiré optical transition at 0.83 eV is observed in the heterostructure, which is distinctly different from the monolayer resonance at 1.73 eV and the bilayer resonance at 1.10 eV. It shows that moiré superlattice strongly modulates optical transition in phosphorene heterostructure even for twist angles as large as 19°.