Transformation of ZnS Precursor Compounds to Magic-Size Clusters Exhibiting Optical Absorption Peaking at 269 nm

Abstract

We report our investigation on the transformation pathway from precursor compounds (PCs) to magic-size clusters (MSCs) for semiconductor ZnS. We show, for the first time, a synthetic approach to ZnS MSCs in a single-ensemble form exhibiting optical absorption peaking at 269 nm. We thus symbolize the MSCs as MSC-269. The synthesis was performed with zinc oleate (Zn(OA) 2 ) and elemental sulfur (S) as the respective Zn and S sources and 1-octadecene (ODE) as the reaction medium. Prior to the addition of S, oleylamine (OLA) is mixed with Zn(OA) 2 . ZnS MSC-269 evolved at a relatively high temperature from a reaction mixture or at room temperature during a dispersion incubation of a reaction product in a solvent. Both optical absorption and NMR studies support that the evolution of colloidal semiconductor MSCs contains three different stages. The present study narrows our knowledge gap on PC-to-MSC transformations that involve a loss of ligands from the PC.

Room-temperature formation of CdS magic-size clusters in aqueous solutions assisted by primary amines

“…Moreover, we show that purified CdS MSC-360 disappears gradually in deionized water, but reappears after a primary amine is added. This behavior indicates that a reversible PC ⇔ MSC transformation takes place, which is similar to that in the nonaqueous approaches [18][19][20][21][22][23][24][25][26][27][28] . The present findings introduce a room-temperature aqueous-phase approach to the production of single-ensemble CdS MSC-360 without the co-production of QDs, clarifying that the PC to MSC transformation is applicable for the aqueous-phase formation of semiconductor MSCs.…”

“…4). Although the conventional characterization tools have some shortcomings with regard to providing precise structural and compositional information of colloidal semiconductor small-size QDs and MSCs 20,[25][26][27][28] , Supplementary Fig. 4 suggests that the aqueous-phase CdS MSCs are spherical with a diameter smaller than 3 nm, and have a similar structure as that of organic-phase CdS MSC-361 42 , with the ligand to inorganic core weight ratio of 20 to 80 (Supplementary Note 1).…”

“…The multistep model, designated by nonclassical nucleation theory, accounts for the presence of intermediates in the pre-nucleation stage . Such intermediates have been illustrated in several materials systems including calcium-based inorganics [4][5][6][7][8] , organics [9][10][11] , polymers [12][13][14] , metals [15][16][17] , and semiconductor quantum dots (QDs) [18][19][20][21][22][23][24][25][26][27][28] .…”

“…For organic-phase approaches to semiconductor metal (M) chalcogenide (E) QDs, a two-pathway model has been proposed for the pre-nucleation stage [18][19][20][21][22][23][24][25][26][27][28] . One pathway involves the formation of monomers and fragments, which result in QDs as per the LaMer model of the CNT.…”

“…The approach to the evolution of the CdSe MSCs requires long reaction times (such as 7 days), and the Se source Na 2 SeSO 3 has to be freshly prepared due to its limited stability. The aqueous-phase synthesis of CdS MSCs has not been demonstrated, and whether the formation pathway of aqueous-phase MSCs is similar to that of nonaqueous phase ones is not known [18][19][20][21][22][23][24][25][26][27][28] .…”