Date: Tuesday, September 13, 2022
Time: 11:00 am
Location: Chemla Room (67-3111) and Zoom
Talk Title: Probing the ultrafast electron and phonon dynamics of 2D materials on the nanoscale
Controlled and predictable energy and phonon transport in 2D materials is critical for their practical applications in nanoscale electronics and thermoelectrics. However, at the 2D limit, abundant morphological variations such as strain, layer thickness, grain boundaries, edges, and interlayer rotation effects can modify the optoelectronic and thermoelectric properties. In order to establish a new paradigm of predictably controlled novel functionalities in 2D materials and 2D material heterostructures, it is imperative to determine the interplay of morphological effects and intrinsic optoelectronic and thermoelectric properties in homogeneous and heterogeneous systems. Using polarization-dependent photoemission electron microscopy (PEEM) we have imaged the spatially dependent optical selection rules of black phosphorus, distinguishing edge-specific modes, and the structural heterogeneity of monolayer perylene diimide (PDI) and monolayer MoS2 hetero-bilayers with spatial resolution as good as 25 nm. I’ll also show a preview of time resolved and spatially resolved PEEM experiments on PDI/MoS2, showing that material morphology modifies the charge carrier dynamics of these molecular hetero-bilayers on the nanoscale. Using ultrafast transmission electron microscopy, we’ve also been able to probe how the phonon dynamics in few-layer black phosphorus is modified by structural morphology. In the first direct observation of anisotropic phonon propagation on the nanoscale in black phosphorus, we measured the direction-dependent velocity of longitudinal acoustic phonons, verifying that that phonon propagation occurs faster along the zigzag direction compared to the armchair direction of black phosphorus and showing how phonon dynamics are modified by crystal morphology. Ultimately my group seeks to identify ways to modify the impact of structural heterogeneity in materials and rationally design energy efficient inorganic and organic/inorganic hybrid interfaces on the nanoscale using morphology and molecular interfaces.
 P. P. Joshi, R. Li, J. L. Spellberg, L. Liang, and S. B. King, Nano Lett. (2022) 10.1021/acs.nanolett.1c03849.
Prof. King’s research centers on using spectroscopy and microscopy to probe the electronic
structure and dynamics of materials and the role of interfaces and nanoscale structure in the
function of materials and condensed phase systems. She has her Bachelor of Science in
Chemistry from MIT and a Ph.D. from the University of California, Berkeley. After time as an
Alexander von Humboldt Postdoctoral Fellow at the Fritz Haber Institute of the Max Planck
Society in Berlin, Germany, Prof. King started her independent career at the University of
Chicago in 2018. Among her many awards, she has received a Beckman Foundation Young
Investigator Award, a DOE Early Career Award, and an Air Force Office of Scientific Research
Young Investigator Award.