Fig. 1: Crystal structure and characterization of NbSe2.
a. Top and side views of NbSe2 crystal. Nb atoms (shown dark green) are sandwiched between two layers of Se (shown light green) atoms. Monolayer NbSe2 exhibits spatial inversion symmetry breaking because the Nb and Se sites are not equivalent. b. Optical image of a few-layer flake of NbSe2 cleaved on a SiO2/Si substrate with a spin-coated PMMA/MMA polymer on it. The number of layers is labeled. Scale bar: 5 μm. c. High-resolution TEM image taken from a NbSe2 flake suspended on a TEM grid, in which the Nb and Se atomic columns are marked by green and yellow dots. And the selected point defects located at Nb and Se sites are highlighted by green and yellow circles, respectively. Scale bar: 1 nm. d. SAED taken from the NbSe2 flake along [0001] zone axis. Scale bar: 2 nm−1.
