Monodisperse CdSe Quantum Dots Encased in Six (100) Facets via Ligand-Controlled Nucleation and Growth

Abstract

Zinc-blende CdSe quantum dots (QDs) encased in six equal (100) facets are synthesized in a noncoordinating solvent. Their monodispersed size, unique facet structure, and single crystallinity render the narrowest ensemble photoluminescence for CdSe QDs (full width at half-maximum being 52 meV). The nucleation stage can selectively form small-size CdSe QDs (≤3 nm) as seeds suited for the growth of cube-shaped QDs by reducing the concentration of cadmium carboxylates (Cd­(RCOO)2) as the sole source of ligands. While resulting in poorly controlled nucleation, chloride-ion ligands introduced in the form of soluble CdCl x (RCOO)1–x (x = 0.1∼0.2) would thermodynamically stabilize the cadmium-terminated (100) facets yet kinetically accelerate the deposition of selenium ions onto the (100) facets. Results suggest that it is fully feasible to synthesize QDs simultaneously with monodisperse size and surface structure through ligand-controlled nucleation and growth.

Efficient quasi-stationary charge transfer from quantum dots to acceptors physically-adsorbed in the ligand monolayer

“…It should be noted that, for the QDs after 3 cycles of dissolution/precipitation, the ligand density is significantly larger than that of the densely-packed ligand monolayer on a CdSe/CdS core/shell QD with thin CdS shells (or a CdSe QD). For CdSe QDs, the highest possible density of alkanoate ligands occurs on the polar (100) facets, which is theoretically and experimentally confirmed to be ~ 5.4 ligands/nm 2 [83,93]. For the QDs with multiple types of facets, this number would be significantly smaller [83,93].…”

“…For CdSe QDs, the highest possible density of alkanoate ligands occurs on the polar (100) facets, which is theoretically and experimentally confirmed to be ~ 5.4 ligands/nm 2 [83,93]. For the QDs with multiple types of facets, this number would be significantly smaller [83,93].…”

The role of organic ligand shell structures in colloidal nanocrystal synthesis

“…The nature of the ligands dictates the inorganic nanocrystal surface structure 11,19,21,22 , and has been designed to promote surfaces that minimize electronic trap states in quantum dots 15,17,23,24 . A variety of head groups are used to terminate colloidal nanocrystal surfaces, such as carboxylates, amines, phosphonates, thiols and halides, and often a mixture of capping groups is used [15][16][17]20,[25][26][27][28][29][30][31][32] . The amount, type and impurities of the ligands used in nanocrystal synthesis have implications for the nanocrystal size, shape, crystal structure and stability, as well as for their optical and electronic properties 33,34 .Head groups play a critical role in the control of colloidal nanocrystal growth, and different nanocrystal shapes can be formed by manipulating head group binding.…”

“…carboxylate and thiol capping ligands in lead sulfide nanocrystal syntheses results in {100} facet-terminated cubes and {111} facetterminated octahedrons, or shapes in between 35 . This is attributed to the variable surface energy of different nanocrystal facets, which can be manipulated by using different capping ligands 18,22,26,30,36 . As a result, shape control is mostly the result of mixed ligand syntheses.…”

Calibrate Ligand-ligand Interaction on Nanocrystals via the Dynamic Volume of Chain Segments

“…Many studies are focused on the head groups of the organic ligands as their coordination affects the formation of surface facets [16][17][18] , determines the binding strength of ligands 10,19,20 , and controls the abundance of surface defect sites [21][22][23][24] . Differently, the non-coordinating tails utilize weak interactions and entropic effects to offer tremendous power in controlling the colloidal stability and assembly 13 .…”