Probing structural-property relationships at the femtosecond-picometer scales
We push the spatial and temporal resolutions of transmission electron microscopy to understand functional materials at the atomic scale and ultrafast time scale. Taking advantages of recent advances in aberration-corrected scanning transmission electron microscopy, electron ptychography, and ultrafast electron microsocpy, we investigate the structure, electronic/optical properties, and dynamics processes of quantum and electronic/optoelectronic materials in parameter spaces previously unaccessible. Overall, we aim to utilize the incredible capability of electron microscopy to guide the design of new materials and devices.
Low-dimensional Quantum Materials
Low-dimensional materials, such as monolayers of graphene, hexagonal boron nitride, and transition metal dichalcogenides, exhibit unique electronic, optical, and mechanical properties that differ significantly from their bulk counterparts, leading to new designs of nanoelectronics and nanophononics. Controlling structures and interfaces at the single atom level is critical for such thin systems because the properties can be strongly modulated with defect and interfacial engineering. We are developing electron-microscopy methods to in data acquisition, image processing, and computation to investigate quantum phenomena associated from individual atomic defects.
van der Waals Ferroelectrics
We are interested in studying van der Waals ferroelectrics due to their atomically thin, layered structure and switchable spontaneous polarization. These materials exhibit robust ferroelectricity at reduced dimensions, enabling the development of nanoscale nonvolatile memory, low-power logic devices, and reconfigurable electronics. The compatibility with other van der Waals materials to form heterostructures allow us to gain precise control of interfacing coupling and provide a platform for designing advance functional devices in spintronics, optoelectronics, and neuromorphic computing.
Advanced Electron Microscopy Techniques
Scanning Transmission Electron Microscopy
Scanning transmission electron microscopy (STEM) allows us to extract important structural and chemical information beyond beautiful pictures. We use aberration-corrected STEM and 4D STEM combined with in-situ imaging capabilities to understand static and dynamic behavior of materials with single atom precision.
Electron Ptychography
Electron ptychography is a computation-aided electron microscopy technique that can overcome the spatial resolution limit set by the aberrations in the electromagnetic lenses. Not only do we achieve unprecedented spatial resolutions, we can reconstruct the 3D structures of materials at the single-layer limit. This new capability has enabled us to identify every atom in 2D moiré, understand domain wall structures, map properties atom by atom.
Ultrafast Electron Microscopy
Temporal resolution is critical for studying lattice and electronic dynamics spanning a wide range of space and time. With pulsed electrons, ultrafast electron microscopy (UEM) provides access to rarely explored spatiotemporal regimes. We aim to harness the incredible capability of UEM to develop comprehensive understanding of energy processes.
JOEL NEOARM (https://www.jeolusa.com)
Comparison of STEM and ptychography image of twisted bilayer WSe2
Left: STEM. Right: ptychography
