Structural and electronic properties of bare and capped Cd nSe n/Cd nTe n Nanoparticles (n = 6, 9)

Abstract

Relationships between structures and properties (energy gaps, vertical ionization potentials (IP v), vertical electron affinities (EA v), and ligand binding energies) in small capped CdSe/CdTe nanoparticles (NPs) are poorly understood. We have performed the first systematic density functional theory (DFT) (B3LYP/Lanl2dz) study of the structural (geometries and ligand binding energies) and electronic (HOMO/LUMO energy gaps, IPs v, and EAs v) properties of Cd nSe n/Cd nTe n NPs (n = 6, 9), both bare and capped with NH 3, SCH 3, and OPH 3 ligands. NH 3 and OPH 3 ligands cause HOMO/LUMO energy destabilization in capped NPs, more pronounced for the LUMOs than for the HOMOs. Orbital destabilization drastically reduces both the IP v and EA v of the NPs compared with the bare species. For SCH 3-capped Cd 6X 6 NPs, formation of expanded structures was found to be preferable to crystal-like structures. SCH 3 groups cause destabilization of the HOMOs of the capped NPs and stabilization of their LUMOs, which indicates a reduction of the IP v of the capped NPs compared with the bare species. For the Cd 9X 9 NPs, similar trends in stabilization/destabilization of frontier orbitals were observed in comparison with the capped Cd 6X 6 species. Also, pinning of the HOMO energies was observed for the NH 3- and SCH 3-capped NPs as a function of a NP size. © 2012 American Chemical Society.