Nucleation and quantum confinement of nano-platelet Bi-2-Bi2Se3

The nucleation, nano-platelet growth, and optical properties under quantum confinement are investigated in the topological semimetal superlattice Bi-2-Bi2Se3 as a function of thickness and Ar + ion pressure in sputtered growths. Quantum confinement and evolution of the band structure with a series of reduced dimensionality and surface terminations are studied by density functional theory corroborating the observed optical properties. An initial Volmer-Weber growth mode of nano-platelets is observed until a pressure-dependent critical thickness, where a transition to Frank-van der Merwe growth occurs. Nucleation statistics characterized using atomic force microscopy find the nearest-neighbor ordering of nano-platelets. Optical properties using ultraviolet to visible light spectroscopy measurements in transmission mode reveal a marked increase in optical bandgap below a nano-platelet critical volume reaching a maximum of 2.21 eV. Raman vibrational spectroscopy is performed, revealing softening of vibrational modes as the nano-platelet volume decreases.