Abstract: Light-matter interactions are closely related to everyday life and are the fundamental basis for optical communications and light microscopy and spectroscopy. In the first part of my talk, I will present my study of small lasers for on-chip optical communications. Plasmon lasers represent a type of small laser that supports ultrasmall mode confinement and ultrafast dynamics with device feature sizes below the diffraction limit. However, plasmon-based lasers show emission with limited far-field directionality. In addition, most plasmon-based lasers rely on solid gain materials (e.g., inorganic semiconducting nanowire or organic dye in a solid matrix) that preclude the possibility of dynamic tuning. I will show that arrays of gold nanoparticles surrounded by liquid dye molecules exhibit directional lasing emission that can be modulated by the dielectric environment. By integrating gold nanoparticle arrays within microfluidic channels and flowing in liquid gain materials with different refractive indices, dynamic tuning of the lasing wavelength has been achieved.

In the second part of the talk, I will present more recent research using in situ light microscopy and spectroscopy approaches to study electrochemical devices. Lithium-sulfur (Li-S) batteries are attractive candidates for energy storage with high energy density. Sulfur, the charge product in Li-S batteries, was believed to be solid, but we discovered that sulfur can stay in a supercooled state as liquid sulfur. To reveal the implications of this finding, I use a typical 2-D material, molybdenum disulfide (MoS₂), as a platform to show distinct growth behavior of sulfur on the basal plane (liquid) and edges (solid). By correlating the sulfur states (liquid or solid) with the electrochemical performances, we demonstrate that liquid sulfur has much faster kinetics compared with solid sulfur. Using a similar in situ optical set-up, I will also show ion intercalation of 2-D materials through electrochemical approach as a promising low-temperature modification strategy to manipulate material properties for nanoelectronics devices. I will conclude by presenting future prospects for exploiting light-matter interactions in nanostructured materials and systems for applications in both optical communications and energy-related applications.

Bio: Ankun Yang is a postdoctoral research fellow in the Department of Materials Science and Engineering (MSE) at Stanford University. Ankun received his Bachelor’s and Master’s degrees in MSE at Tsinghua University, China. Ankun then went on to pursue his Ph.D. in MSE at Northwestern University. His research interests broadly lie in light-matter interactions in various low-dimensional material systems including plasmonic materials, 2-D materials, and energy-related materials for optoelectronics and electrochemical devices.