Atomically thin films, which can be viewed as ideal two-dimensional physical systems, usually exhibit many unusual properties absent in the bulk counterparts. Our works mainly focus on the growth of these low-dimensional materials by molecular beam epitaxy, and in situ characterization of their electronic and transport properties by our advanced scanning probe microscopy. In this talk, I will present our recent progress on several different ultra-thin films: (1) the oscillation of electronic-band-gap size induced by crystalline symmetry change in ultrathin PbTe Films , (2) the BCS-BEC crossover of FeSe monolayer near the charge neutrality point , (3) direct visualization of electric current induced dipoles of atomic impurities in bilayer graphene by scanning tunneling potentiometry .
 Kai Chang et al., Phys. Rev. Lett. 131, 016202 (2023).
 Haicheng Lin et al., Phys. Rev. B 107, 104517 (2023).
 Yauwu Liu et al., arXiv:2309.01182.