Topic: Overcoming Old and New Challenges with Semiconductor Nanocrystals
Speaker: Professor Remi Beaulac - Michigan State University
Host: Professor James McCusker
Date: Thursday, August 2, 2018
Time: 4:10 PM
Colloidal semiconductor nanocrystals (NCs) combine the behavior typically associated with isolatable molecular species with the electronic, optical, and chemical properties that characterize extended solid-state semiconductor materials. Electronic excitations of NCs are typically very sensitive on their overall size and shape, an effect designated under the term “quantum confinement” and which has led to the other commonly-used appellation of “quantum dots”. NCs are particularly well-suited for a host of applications – optical sensing and imaging, light-emission, photovoltaics, or photo-redox transformations – that rely on the extraction of work, of one form or another, from electronically-excited NCs, but are also unique in their ability to reversibly and substantially store electrical charge, making them ideal for applications such as high-storage capacitors, tunable plasmonics or in the design of photoredox catalysts.
This seminar will emphasize recent work by our group to unravel some of the complexity associated with the behavior of NCs. In a first part, we will describe work aimed at better understanding one of the most well-studied NC materials, namely CdSe. The excited-state of CdSe is characterized by very complex, multi-exponential, dynamics generally associated with detrimental photophysical processes such as non-radiative losses and photoluminescence intermittency (“blinking”) which have so far eluded detailed descriptions. Here, we will show that specific structural features of the CdSe NC surfaces can be associated with their peculiar photochemical behavior, and we will demonstrate how the inherent disorder (inhomogeneity) of NCs ensemble can be captured and modeled. In a second part, we will discuss the properties of one of the least studied materials in the family of semiconductor NCs, indium nitride, and will show how this new member differs rather radically from other materials studied up to now, in particular in its ability to spontaneously accumulate delocalized charges and its resilience in exhibiting strong size-dependent behavior.