Traditional characterization methods provide averaged structural information and are only applicable to periodic structures, which limit our understanding towards amorphous materials. This project develops Atomic Electron Tomography method and determined the first experimental 3D atomic structures of metallic glasses. Further analysis revealed novel medium-range structural order in single- and multi-element metallic glasses, which provides new insights in understanding the glass transition. The AET method will also provide new opportunities in understanding early-stage nucleation, quasicrystals, and various functional and biological materials.

Related works:

1. "Three-dimensional atomic packing in amorphous solids with liquid-like structure" Nature Materials, 95-102, 21 (2022)

2. "Determining the three-dimensional atomic structure of an amorphous solid" Nature, 60-64, 592, (2021)

3. "Capturing 3D atomic defects and phonon localization at the 2D heterostructure interface" Science Advances, 7(38), (2021)

4. "Correlating the three-dimensional atomic defects and electronic properties of two-dimensional transition metal dichalcogenides" Nature Materials, 1-7, (2020)

The understanding and manipulation of interactions among different order parameters are of significant importance for both fundamental science and modern devices. This project develops several ultrafast time-resolved experimental setups that are sensitive to materials' thermal, electrical and structural properties, with probing wavelength ranging from UV to mid-IR and repetition rate from 1kHz to 80MHz. We have successfully probed eletron-phonon relaxation, optical induced ferroelecric switching and optical control of topological order in polar domains, which demonstrated the possibility of exploring new phenomena of materials from the time dimension.

Related works:

1. "Light-Activated Gigahertz Ferroelectric Domain Dynamics" Physical Review Letters, 096101, 120, (2018)

2. "Continuously Tuning Epitaxial Strains by Thermal Mismatch" ACS Nano, 1306–1312, 12, (2018)

3. "Optical creation of a supercrystal with three-dimensional nanoscale periodicity" Nature Materials, 377-383, 18, (2019)

4. "Ultrafast quasiparticle dynamics in the correlated semimetal Ca3Ru2O7" Physical Review B, 155111, 99, (2019)

Characterizing and understanding the 3D atomic structures of epitaxial interfaces are of great importance in fabricating high-performance electronic and magnetic devices. This project aims at developing a synchrotron X-ray based phase-retrieval imaging method, namely Coherent Bragg Rods Analysis (COBRA), and realizing the in-situ characterization of the precise 3D atomic structure of functional interfaces. By using COBRA method, this project systematically investigates the 'Tilt Epitaxy' effect near the complex oxides interfaces, which provides a general rule in optimizing the performance of ferroelectric devices. In the meantime, the phase-retrieval technique utilized in COBRA is applicable to a broad range of electron, X-ray, and laser based imaging methods.

Related works:

1. "Three-dimensional atomic scale electron density reconstruction of octahedral tilt epitaxy in functional perovskites" Nature Communications, 5220, 9, (2018)

2. "Polar metals by geometric design" Nature, 68-72, 533, (2016)

3. "Designing Optimal Perovskite Structure for High Ionic Conduction" Advanced Materials, 1905178, 32, (2020)

4. "Making EuO multiferroic by epitaxial strain engineering" Communications Materials, 1-10, 1, (2020)