Extended Nucleation and Superfocusing in Colloidal Semiconductor Nanocrystal Synthesis
P. Tim Prins, Federico Montanarella, Kim Corinna Dümbgen, Yolanda Justo, Johanna C. van der Bok, Stijn O. M. Hinterding, Jaco J. Geuchies, Jorick Maes, Kim De Nolf, Sander Deelen, H.E.H. Meijer, Thomas Zinn, Andrei V. Petukhov, Freddy T. Rabouw, Celso de Mello Donegá, Daniël Vanmaekelbergh, Zeger Hens
Abstract
Hot-injection synthesis is renowned for producing semiconductor nanocolloids with superb size dispersions. Burst nucleation and diffusion-controlled size focusing during growth have been invoked to rationalize this characteristic yet experimental evidence supporting the pertinence of these concepts is scant. By monitoring a CdSe synthesis in-situ with X-ray scattering, we find that nucleation is an extended event that coincides with growth during 15–20% of the reaction time. Moreover, we show that size focusing outpaces predictions of diffusion-limited growth. This observation indicates that nanocrystal growth is dictated by the surface reactivity, which drops sharply for larger nanocrystals. Kinetic reaction simulations confirm that this so-called superfocusing can lengthen the nucleation period and promote size focusing. The finding that narrow size dispersions can emerge from the counteracting effects of extended nucleation and reaction-limited size focusing ushers in an evidence-based perspective that turns hot injection into a rational scheme to produce monodisperse semiconductor nanocolloids.