Oriented-Attachment- and Defect-Dependent PbTe Quantum Dots Growth: Shape Transformations Supported by Experimental Insights and DFT Calculations.

High-resolution transmission electron microscopy results reveal that oriented-attachment- and defect-dependent mechanisms rule the size and shape evolution of the monodispersed PbTe quantum dots (QDs). The former is characterized by the growth of quasi-cubic PbTe QDs, which depends on both the geometric constraints imposed by the {200} facets and the defect-free lattice, while the latter one is a defect-dependent mechanism which gives way to the formation of decahedral PbTe QDs (∼6 nm). Experimentally, formaldehyde is an important parameter for the mechanochemical synthesis of monodispersed PbTe QDs, which has not been studied until now. In a theoretical context, Fukui functions reveal that Pb surface atoms are the most reactive sites toward nucleophilic attacks, and the Lowdin charge analysis shows that formaldehyde molecules tend to donate their electron pairs to Pb atoms. Besides, formaldehyde-molecule-on-PbTe adsorption energies (-4.46 to -21.16 kcal mol-1) agree with ligand-surface polar electrostatic interactions. Based on dispersion-corrected density functional theory calculations, PbTe QDs exhibited decahedral and faceted shapes. According to modified Wulff constructions, the decahedral shape is a result of (111) facets (Δγ = -2.79 meV Å-2), whereas the faceted and rounded shapes are due to the interaction of (100), (110), and (111) facets.