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

Abstract

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.

A Comparative DFT Study on Process Control Agents in the Mechanochemical Synthesis of PbTe

“…The highest occupied molecular orbital (HOMO) of formaldehyde exhibits σ bonding contributions in the case of C–H bonds, being larger in the H atom, as well as a p orbital in the oxygen atom, see Figure 2 . The above can be related to the preferential interaction between the H and O atoms of formaldehyde and lead telluride surfaces, which is congruent with data reported in the literature for this and other systems [ 1 , 16 ]. On the other hand, the lowest unoccupied molecular orbital (LUMO) of this molecule exhibits an antibonding π* orbital in the case of C–O bonds.…”

“…Calculations were carried out within dispersion-corrected DFT at the PBE-D2/USP level through Quantum Espresso 6.1 package, as reported in the literature [ 1 ]. Dispersion-corrected DFT computations were performed to simulate the PbTe bulk structures and surfaces.…”

“…The high-energy milling (HEM) process induces high-energy impacts on the loaded powders in the vial by collisions between milling media and precursors, causing severe plastic deformation, repeated fracturing and mechanical kneading of particles [ 1 , 2 , 3 ], which have effects on the final structure, morphology and properties of the as-milled products [ 1 , 4 ]. For instance, it has been documented that in ductile–ductile systems, the mechanical kneading of particles is dominant during milling over fracturing [ 3 , 5 ].…”

“…Even more, organic PCAs have been found to break down with the constituent elements during the HEM process, reacting with the raw powders [ 11 ]. Therefore, the usage of PCAs during milling has emerged as an efficient strategy not only to control the size and shape in NPs, but also to unravel structure–property relationships [ 1 ]. For that reason, approaches are offered to begin developing respective selection criteria and determine the correlations between different PCAs and milling outcomes, as has been reported in the literature [ 9 ].…”

“…To some extent, both physisorption and chemisorption processes seem to be clear in the stabilization of NPs during milling through organic molecules [ 12 , 13 ]. Because PCAs are the essential factor in maintaining stability and controlling facets in as-milled NPs, their effect on the as-milled NPs was analyzed by using experimental techniques [ 13 , 14 ], neural network models [ 15 ] and density functional theory (DFT) computations [ 1 ].…”