Structure-Dependent Optical Properties of Self-Organized Bi 2 Se 3 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 (EBE) with high production efficiency. The structural investigations by energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM), and X-ray diffraction (XRD) revealed the sample stoichiometries and the structural transition mechanism from nanocrystals to nanoflakes. The optical properties systematically probed and analyzed by spectroscopic ellipsometry (SE) 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.