Colloquium Prof. P. James Schuck, Columbia University

Speaker: Prof. P. James Schuck, Department of Mechanical Engineering, Columbia University

Title: From Band Gaps to Bound Excitons: Disentangling optical transitions and localized emitters in TMDSs even at nanoscale dimensions

Abstract: Our research focuses on understanding the nano- and meso-scale interactions between localized states in materials, and relating these properties with system and device functionality. By using plasmonics for nano-optical spectroscopic imaging, we cross the boundary from insufficient to sufficient resolution, mapping critical optoelectronic properties in the exciting transition metal dichalcogenide (TMDC) materials at their native length scales. In doing so, we uncover new optoelectronic regions and spatially-varying features in single-layer TMDCs (1L-TMDCs) that were hidden in prior optical studies. These findings have broad implications for the development of atomically thin transistors, quantum optical components, photodetectors and light-emitting devices based on high-quality 1L-TMDCs. Most recently, we are demonstrating that a model hybrid architecture, a nano-optical antenna and a 1L-WSe2 nanobubble, activates the optical activity of bound exciton states at room temperature and under ambient conditions. These results show that engineered bound-exciton functionality as, in this case, localized nanoscale light sources, can be enabled by an architectural motif that combines localized strain and a nano-optical antenna, laying out a possible path for realizing room-temperature single-photon sources in high-quality 2D semiconductors.

In the final part of the talk, I will describe our development of a novel type of luminescent nanocrystal, upconverting nanoparticles (UCNPs). Lanthanide-doped upconverting nanoparticles (UCNPs) overcome problems of photostability and continuous emission inherent in fluorescent molecules and quantum dots, but their brightness has been limited by a poor understanding of energy transfer within the nanocrystal and an unavoidable trade-off between brightness and size. I will discuss our novel design paradigms that have resulted in UCNPs that are many orders of magnitude brighter under single-particle imaging conditions than the brightest existing compositions, allowing us to visualize single UCNPs as small as fluorescent proteins. I will finish by with our initial attempts at applying these nano-probes to deep-tissue biological sensing and brain imaging.

Bio: Jim Schuck is an Associate Professor of Mechanical Engineering at Columbia University. He earned his B.A. in Physics at UC Berkeley and his Ph.D. in Applied Physics at Yale University. Jim then did his postdoctoral studies with Prof. W. E. Moerner at Stanford University, studying optical nanoantennas and single molecule spectroscopy. His group aims to characterize, understand and control nanoscale light-matter interactions, with a primary focus on sensing, engineering and exploiting novel optoelectronic phenomena emerging from nanostructures and interfaces. Current research interests include the investigation and applications of 2D materials and upconverting nanoparticles (UCNPs).