Prenucleation Cluster Effects on Colloidal CdSe Semiconductor Samples in Dispersion at Room Temperature

Area of Science:

• Materials Science
• Nanotechnology
• Colloid Chemistry

Background:

• The existence and role of prenucleation clusters (PNCs) in colloidal semiconductor quantum dot (QD) synthesis are not well understood.
• Previous studies have not definitively identified PNCs in QD samples.

Purpose of the Study:

• To investigate the potential presence of PNCs in colloidal semiconductor quantum dots (QDs).
• To elucidate the role of PNCs in the nucleation and growth (N/G) processes of QDs.

Main Methods:

• Utilized Cadmium Selenide (CdSe) QDs as a model system.
• Analyzed QD samples synthesized via heating-up and hot-injection methods.
• Dispersed samples in cyclohexane (CH) and toluene (Tol) at 25 °C, with and without butylamine (BTA).
• Observed optical absorption peaks to identify magic-size clusters (MSCs).

Main Results:

• Confirmed the presence of PNCs in CdSe QD samples from both synthesis methods.
• Demonstrated that in cyclohexane or toluene at 25 °C, PNCs transform into monomers and subsequently nucleate and grow QDs.
• Showed that in the presence of butylamine, PNCs transform into magic-size clusters (MSCs), specifically MSC-390 and MSC-415.
• Observed that QD growth occurs in a size-focusing regime when PNCs are present.

Conclusions:

• Provided the first compelling evidence for the existence of PNCs in colloidal semiconductor QDs.
• Established that nucleation and growth of II-VI QDs can proceed via a PNC-based pathway from individual metal and chalcogenide precursors.
• Identified PNC-monomer-QD and PNC-MSC transformations occurring in dispersion at 25 °C.