Event

Abstract: 

At the nanoscale, magnetic, optical, electronic, and thermal processes can differ drastically from their bulk counterparts. These deviations stem from reduced crystalline domains and quantum confinement, leading to physical and chemical properties intricately dependent on size, morphology, and ligand identity as opposed to purely compositional structure. This remarkable tunability, combined with their solution processability, positions colloidal nanocrystals as promising candidates for diverse applications, including photovoltaics, lighting technology, lasers, photocatalysis, spintronics, and quantum-based technologies, among others. It is crucial to gain a comprehensive understanding and control over the fundamental processes governing the formation and functionality of these materials.
In this talk I will share two stories about how carrier dynamics and mechanisms of nanocrystal formation were untangled through my graduate and postdoctoral work. In the first story, we delve into the realm of charge transfer in hybrid inorganic-organic donor-acceptor systems. We investigate charge transfer rates in a series of CdSe nanocrystals coupled with an electron acceptor (naphthalene diimide) using transient absorption techniques. Additionally, through time-resolved EPR experiments, we validate the coherent transfer of spin polarization and determine the energetic splitting between dark and bright states. We also explore the extension of charge separation lifetimes through subsequent hole transfer steps and localization at coinage metal defects.
The second story centers around ternary copper-based materials. We examine thermal dissipation and carrier dynamics in CuInSe2 nanocrystals while varying the ligand identity. Time-resolved X-ray diffraction measurements reveal that substituting the native oleylamine ligand with a small anion results in significantly increased cooling rates due to an order of magnitude higher interfacial thermal conductivity. The choice of ligand during synthesis also exerts a profound impact on carrier lifetimes and the performance of photovoltaic devices. Lastly, we will take an in-depth look at the formation of magnetic CuCr2Se4 nanocrystals.
 

Bio: 

Dr. Samantha Harvey earned her B.S. in chemistry from Indiana University. While there she discovered her love of nanomaterials while studying the formation and refractive index sensitivity of Au/Pd bimetallic octopods in Prof. Sara Skrabalak’s research group. She spent a summer doing an NSF REU program at UIUC in Prof. Cathy Murphy’s group towards understanding the synthesis of Au nanorods through a multivariate fractional factorial analysis design of experiments. After graduating from IU, she attended Northwestern University where she received a chemistry Ph.D. under the guidance of Profs. Richard Schaller and Michael Wasielewski. Her graduate work focused on ultrafast spectroscopy of semiconductor nanocrystals and covered a range of projects including heat dissipation, ligand modulated carrier dynamics, and magnetic field effects in spin-based systems. Currently she is a postdoctoral fellow at the University of Washington in Profs. Daniel Gamelin and Brandi Cossairt’s groups where she has developed a niche for examining the synthesis, doping, and magneto-optical properties of nanocrystalline spinels. She has also collaborated on multiple studies looking at charge transfer in quantum dot – molecular acceptor systems and is expanding into spin processes and data-driven optimization of oxide nanocrystals.