Fig. 2. ARPES spectra of Bi₂Se₃/Si(111) samples with different thicknesses.

a–f are the ARPES spectra of the Bi₂Se₃ sample of 7, 6, 5, 4, 3, and 2 QL, respectively. The black dots are the peak positions fitted by MDCs and EDCs, while the red dot lines are the fitting results of black dots with massive or massless Dirac dispersion. $E_{\mathrm{B}}$ is the binding energy and $k_{\mid \mid }$ is the in-plane wave vector.