Structure-Dependent Optical Properties of Self-Organized Bi₂Se₃ Nanostructures: From Nanocrystals to Nanoflakes

Bismuth selenide (Bi₂Se₃), with a wide bulk band gap and single massless Dirac cone at the surface, is a promising three-dimensional topological insulator. Bi₂Se₃ possesses gapless surface states and an insulator-like bulk band gap as a new type of quantum matter. Different Bi₂Se₃ nanostructures were prepared using electron beam evaporation with high production efficiency. Structural investigations by energy-dispersive X-ray analysis, scanning electron microscopy, and X-ray diffraction revealed the sample stoichiometries and the structural transition mechanism from nanocrystals to nanoflakes. The optical properties systematically probed and analyzed by spectroscopic ellipsometry showed strong dependence on the nanostructures and were also predicted to have structure-modifiable technological prospects. The optical parameters, plasma frequencies, scattering rates of the free electrons, and optical band gaps were related to the topological properties of the Bi₂Se₃ nanostructures via light-matter interactions, offering new opportunities and approaches for studies on topological insulators and spintronics. The high-quality Bi₂Se₃ nanostructures provide advantages in exploring novel physics and exploiting prospective applications.