Precursor Self‐Assembly Identified as a General Pathway for Colloidal Semiconductor Magic‐Size Clusters

Abstract

Little is known about the formation pathway of colloidal semiconductor magic‐size clusters (MSCs). Here, the synthesis of the first single‐ensemble ZnSe MSCs, which exhibit a sharp optical absorption singlet peaking at 299 nm, is reported; their formation is independent of Zn and Se precursors used. It is proposed that the formation of MSCs starts with precursor self‐assembly followed by Zn and Se covalent bond formation to result in immediate precursors (IPs) which can transform into the MSCs. It is demonstrated that the IPs in cyclohexane appear transparent in optical absorption, and become visible as MSCs exhibiting one sharp optical absorption peak when a primary amine is added at room temperature. It is shown that when the preparation of the IP is controlled to be within the induction period, which occurs prior to nucleation and growth of conventional quantum dots (QDs), the resulting MSCs can be produced without the complication of the simultaneous coproduction of conventional QDs. The present study reveals the existence of precursor self‐assembly which leads to the formation of colloidal semiconductor MSCs and provides insights into a multistep nucleation process in cluster science.

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.…”

“…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] .…”

One-Step Approach to Single-Ensemble CdS Magic-Size Clusters with Enhanced Production Yields

“…5,6 The two pathways are connected by an intrinsic MSC to PC to QD pathway, which is consistent with the experimental observation that the growth of QDs is accompanied by the decrease of MSCs. [7][8][9][10][11][12] Semiconductor ME MSCs have generally been acknowledged to be side products in the production of colloidal semiconductor ME QDs. [10][11][12] For samples sequentially extracted from hot-injection or non-hot-injection reaction batches, MSCs display sharp optical absorption peaking usually at particular wavelengths, while QDs exhibit relatively broad optical absorption that continuously redshifts as their size increases.…”