(4ou) Advanced Terahertz Spectroscopies for Chemical and Biological Engineering

Advanced analytical methods have identified phenomena that were previously unobserved, leading to numerous new applications. This has been particularly evident with the development of various photon energy sources. For example, the introduction of infrared spectroscopy revealed previously unseen molecular spectra, ultimately popularizing techniques like Fourier-transform infrared spectroscopy (FTIR). Similarly, the advancement of chiroptical spectroscopies has facilitated breakthroughs in understanding the chirality of liquid crystals, biomolecules, and synthetic drugs.

The research I aim to pursue involves the development of new spectroscopic techniques based on ultrafast lasers. I aspire to lead materials discovery and advanced technology through this new capability. Having been engaged in terahertz spectroscopy since my PhD studies and continuing this research in my postdoctoral work at LLNL, I recognize terahertz radiation as a gap in the electromagnetic spectrum. With advancements in ultrafast laser technology, we can now generate and detect terahertz photons. However, there is still much to understand about their interactions, including molecular vibrations, electron oscillations in semiconductors, and spin-lattice coupling. This research holds significance not only in biochemistry but also in electronics and photonics.

The meV photon energy of terahertz radiation enables the measurement of fundamental motions across all states of matter. A notable development in this field is terahertz circular dichroism (TCD) spectroscopy, which I pioneered in 2019. This technique identified chiral phonon modes in natural materials such as the elytra of June Beetles and the petals of dandelions, leading to a publication in Nature Materials. Further exploration in this field includes investigating reflections, scattering, and developing new spectroscopic techniques such as pump-probe TCD measurements and 2D TCD spectroscopies. I am particularly interested in near-field TCD measurement, which could revolutionize our understanding by measuring molecular motions at the nanometer scale.

Chiral phonon modes, though previously perceived in the near- to mid-infrared range, were first recognized in the THz frequency range through my development of TCD spectroscopy, published in Nature Photonics in 2022. My research initially focused on analyzing 20 amino acids and proteins due to their fundamental role in molecular structure. TCD spectroscopy shows promise in distinguishing between L- and D-enantiomers, which typical THz spectroscopy cannot achieve. Through systematic studies, insights into the sharpness of peaks related to crystal space groups and the temperature dependence of chiral phonons have emerged.

My work on TCD spectroscopy has broader implications, including potential applications in biomedical imaging and the study of biological and chemical processes. Future research directions include exploring non-invasive and label-free applications of TCD, such as monitoring insulin fibrillization, and developing THz bioinformatics to impact collective vibration-mediated biochemical processes and the multiscale chirality of self-assembled biological nanostructures.

I aim to establish research groups that operate within multidisciplinary fields, capitalizing on my diverse background. With hands-on experience in the fabrication of electronic thin films, nanostructures, biomaterials, chirality, optical metamaterials, THz spectroscopies, and ultrafast laser technologies, I believe I can set myself apart from other candidates. Optical scientists often lack practical experience in fabricating films and nanostructures, which may limit their ability to suggest effective materials. Conversely, materials/chemical engineers may encounter difficulties in obtaining clear signals, particularly in environments with extremely low signal-to-noise levels. As a material chemist working in a laser lab, I recognize the potential at the intersection of optics and materials and aim to bridge these areas within our lab. My intention is to pioneer innovative technologies, develop new spectroscopic techniques, and make groundbreaking discoveries based on these advancements.

Teaching Interests

I wholeheartedly agree with the adage, 'a picture is worth a thousand words'. Drawing from my extensive experimental background spanning biomaterials, nanostructures, electronics, and optics, I am eager to design courses enriched with tangible examples and recent research findings. I firmly believe that linking knowledge to direct observation fosters heightened interest and deeper comprehension of phenomena among students. Incorporating a variety of science and engineering YouTube videos, which often present practical examples and scientific mechanisms, is a strategy I intend to actively employ, too. These days, these videos not only could draw many interests from students, but this could be the method that can even lead to scientific publications when elucidating underlying mechanisms.

Drawing from my teaching experience at institutions such as Yonsei University, South Korea, and the University of Michigan, I aim to emulate the impactful methods of seasoned educators like Professor Wynasky, who have a record of teaching the same course for more than 25 years. Learning from him, I acquired invaluable skills in test preparation, grading, and the art of engaging students with real-world examples, such as composite materials used in Boeing airplanes, medical ceramics for joints, and various rubbers. Witnessing the engrossed expressions of over 250 students during lectures underscored the effectiveness of hands-on demonstrations. I also have my own experience using eutectic GaIn (EGaIn) to illustrate phase diagrams. I elucidated concepts by showcasing how specific material compositions enable unique properties, such as the creation of liquid metal for flexible electrodes. Students were able to more deeply understand why we should learn phase diagram, and how to be utilized for making alloys by thermodynamic design.

My expertise extends to courses encompassing solid-state physics, chemistry, thermodynamics, materials science, electronics, and optics. Moreover, I aspire to develop advanced courses tailored for graduate students as needed. A long-standing ambition of mine is to author a comprehensive textbook, synthesizing my well-organized course materials into a valuable resource for academic institutions worldwide. One of my favorite textbooks is “Phase Transformations in Metals and Alloys” by David Porter and “Electronic Properties of Engineering Materials” by James Livingston. I admire how they weave horizontally with other disciplines and vertically within the properties, incorporating examples and problems that I often ponder. These texts serve as my role models.