Surface traps in quantum dots

My main project during my PhD was identifying the source of trap states in CdSe quantum dots. CdSe quantum dots have many applications, including displays, bioimaging, sensing. These applications hinge on the excitation into, and emission from, a "bulk" excited state in the quantum dot, where the excited hole or electron is delocalized over the entire structure. However, in practice, quantum dots often are plagued by highly localized trap states on the surface, that deter emission from the bulk state and thus thwart many common applications. Using density functional theory, time-dependent density functional theory, and ab initio molecular dynamics, I was able to reveal that a few specific surface structures were responsible for nearly all of the trap states in the systems we studied. 

This work was highly data-driven. This project required transforming terabytes of excited state data into simple descriptors that could be used to identify both which states were trap states, as well as what structural features were responsible for those traps. This work provided atomistic mechanisms for experimental results, facillitating design of new quantum dots that are either trap-free, for display applications, or engineered to have certain traps, for catalysis and qubit applications.

This work was done in close collaboration with Tamar Goldzak (on the theory side), and Katie Schulenberger (on the experimental side).

For more information on this work, please see my publications:

1. McIsaac, A.R.; Goldzak, T.; Van Voorhis, T. It's a Trap!: The Effect of Self-Healing of Surface Defects on the Excited States of CdSe Nanocrystals. J. Phys. Chem. Lett., 2023, 14 (5), 1174-1181. link

2. Shulenberger, K.E.; Coppieters ‘t Wallant, S.C.; Klein, M.D.; McIsaac, A.R.; Goldzak, T.; Berkinsky, D.B.; Utzat, H.; Barotov, U.; Van Voorhis, T.; Bawendi, M.G. Resolving the Triexciton Recombination Pathway in CdSe/CdS Nanocrystals through State-Specific Correlation Measurements. Nano Lett., 2021, 21 (18), 7457-7464. link

3. Goldzak, T.*; McIsaac, A.R.*; Van Voorhis, T. Colloidal CdSe Nanocrystals are Inherently Defective. Nat. Commun., 2021, 12, 890. link