First-principles study on surface and interface properties of colloidal semiconductor nanocrystals

Abstract

This dissertation aims to study the surface and interface properties of colloidal semiconductor nanocrystals based on the atomistic approach and first-principles calculations. For the colloidal nanocrystals with complex interfaces, atomic interfacial models are constructed based on the understandings of surface properties such as surface defects, doping, ligand bindings, etc. By analyzing the electronic structures and thermodynamic properties of the atomic models, the physicochemical properties of the nanocrystals such as energy levels, equilibrium shapes, and structural stabilities, have been controlled. The formation of the tetrahedrally-shaped InP quantum dots is demonstrated using the halide-amine co-passivation method. We further generalize the surface-ligand interactions in other covalent systems, and thus successfully describe the equilibrium shapes of the II-VI and III-V colloidal quantum dots. In III-V/II-VI core-shell quantum dots, we also construct the alloyed interfacial structures with the Coulombic lattice disorders via ion-doping. Furthermore, the origin of the enhanced structural stability of $CsPbBr_{3}$ nanocrystals due to the additional metal halides is revealed through the surface ligand transition. Lastly, we propose the piezoelectric quantum dot solids that can control the surface properties by the applied external pressure.