Back to the Future: Mechanistic Insights into Semiconductor Nanocrystal Syntheses
Kelly Sowers a, Leah Frenette a, Amanda Preske a, Todd Krauss a, Brett Swartz a
a University of Rochester, 120 Trustee Road, Rochester, New York, 14534, United States
Invited Speaker, Todd Krauss, presentation 002
Publication date: 27th June 2014

For over 30 years semiconductor nanocrystals (NCs) have been the subject of much interest for fundamental and applied studies. The synthesis of NCs has developed and matured over this time such that production of monodisperse, photostable NCs with close to an exact size and shape are readily achievable.  However, an understanding of the chemical reaction mechanism behind the synthesis of NCs has lagged the ability to synthesize high quality nanoparticles. In this presentation, NC synthetic mechanisms that have been proposed for metal-chalcogenide (ME) semiconductor NCs, particularly CdE and PbE, will be discussed. Specifically, for PbE NCs synthesized under relatively low temperatures (< 200 ºC) it was found that secondary phosphine chalcogenides are the primary reactive species that determines the formation of NC nuclei. Tertiary phosphine chalcogenides are completely unreactive at these temperatures. Small quantities of secondary phosphine impurities in the conventional tertiary phosphine based synthesis thus play an important role in determining the number of NCs formed and the rates of the reaction. For NCs synthesized under much higher temperatures (generally > 250 ºC), such as CdE NCs, several other mechanistic pathways start to dominate the reactivity. In particular, strong evidence exists for the formation of highly reactive metal-alkyl species in situ, which fundamentally bears a striking resemblance to some of the original CdSe NC syntheses developed over 20 years ago.  Also to be discussed will be how an understanding of fundamental reaction mechanism can lead to improved NCs with controllable surface chemistry and with tailored optical properties.

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