(4l) Symmetry Breaking in Optical Nanomaterials.

The past decade has seen massive advances in nanofabrication using a large variety of nanoparticles as “building blocks”. Solution-processed electronic and optical metamaterials emerged as a promising direction of their technological applications because this method can utilize the intrinsic property of nano colloids to (a) self-organize into the patterned structure and (b) impart new functionalities to the product. However, the technological impact of solution-processable nanomaterials has been so far limited because of the complexity of the colloidal system. For instant, surfactants and other organic materials being used to synthesize and/or disperse nano-colloids introduce an unexpected electromagnetic asymmetry¹ or/and barrier for inter-particle charge transport², which alters their performance in optoelectronics, sensors or catalysts. These deficient pieces of knowledge make it difficult to predict properties of NPs and thus hardly achieve the desired performance.

My research interests are largely direct towards understanding how we recognize and control the symmetry breaking factors in nanomaterials, especially when they are interacting with electromagnetic waves. How do we assign a correct symmetry of the nanoparticles (NP) in static condition? Can we define some symmetry breaking factors and their functionality under electromagnetic radiation to precisely predict particle physics or dynamics? How does the polarity of light affect to the symmetry of matter? These are fundamental questions that my lab will address, using interdisciplinary approaches at the intersection of chemical engineering, materials science, and electrical and computing engineering.

My research expertise lies in synthesis, advanced microscopy and electromagnetic simulation of nanoscale anisotropic structures. I mastered and combined advanced microscopies and in-depth high-quality modeling work to understand nanomaterials and develop a new systems, which are rarely found among the synthesis chemists. By using my broad experience in different disciplines, I bridged the research gaps in many projects and helped to improve my colleague’ research.

During my graduate and training years, I proposed/demonstrated

1) Electrostatic and optical symmetry breaking in gold NP by organic patches.^1,3

2) Chiral ligand-mediated self-assembly of mesoscale semiconductor helices.⁴

3) Synthesis of chiral plasmonic nanoparticles using circularly polarized light.⁵

4) Optomechanical force of chiral plasmonic NP assemblies which promoted enhanced differentiation of neural stem cells.⁶

5) Broadband Circular Polarizers via Coupling in 3D Plasmonic Meta-Atom Arrays⁷

6) Chirality induced nonlinear optical response from mesoscale semiconductor helices. (in preparation)

7) Enantioselective synthesis of polymers using chiral NP catalysis (in preparation)

Using these approaches and skills, I would like to obtain in-depth knowledge in light-matter interaction at nanoscale and produce a new class of optical nanomaterials which can be potentially used for optoelectronics and enantioselective catalysis.

Selected Publications:

(1) Kim, J.-Y.; Han, M.-G.; Lien, M.-B.; Magonov, S.; Zhu, Y.; George, H.; Norris, T. B.; Kotov, N. A. Dipole-like Electrostatic Asymmetry of Gold Nanorods. Sci. Adv. 2018, 4 (February), e1700682.

(2) Kim, J. Y.; Kotov, N. A. Charge Transport Dilemma of Solution-Processed Nanomaterials. Chemistry of Materials. 2014, pp 134–152.

(3) Lien, M. Bin; Kim, J. Y.; Han, M. G.; Chang, Y. C.; Chang, Y. C.; Ferguson, H. J.; Zhu, Y.; Herzing, A. A.; Schotland, J. C.; Kotov, N. A.; et al. Optical Asymmetry and Nonlinear Light Scattering from Colloidal Gold Nanorods. ACS Nano 2017, 11 (6), 5925–5932.

(4) Feng, W.; Kim, J.-Y.; Wang, X.; Calcaterra, H. A.; Qu, Z.; Meshi, L.; Kotov, N. A. Assembly of Mesoscale Helices with Near-Unity Enantiomeric Excess and Light-Matter Interactions for Chiral Semiconductors. Sci. Adv. 2017, 3 (3), e1601159.

(5) Kim, J.-Y. †; Yeom, J. †; Zhao, G.; Calcaterra, H.; Munn, J.; Zhang, P.; Kotov, N. Assembly of Gold Nanoparticles into Chiral Superstructures Driven by Circularly Polarized Light. J. Am. Chem. Soc. 2019, 141, 11739–11744.

(6) Qu, A. †; Sun, M. †; Kim, J. Y.; Xu, L.; Hao, C.; Ma, W.; Wu, X.; Liu, X.; Kuang, H.; Kotov, N. A.; et al. Stimulation of Neural Stem Cell Differentiation by Circularly Polarized Light Transduced by Chiral Nanoassemblies. Nat. Biomed. Eng. 2021, 5 (1), 103–113.

(7) Guo, J†.; Kim, J. Y. †; Yang, S.; Xu, J.; Choi, Y. C.; Stein, A.; Murray, C. B.; Kotov, N. A.; Kagan, C. R. Broadband Circular Polarizers via Coupling in 3D Plasmonic Meta-Atom Arrays. ACS Photonics 2021.

† These authors contributed equally

Teaching Interest

Teaching Philosophy

What is the best way to educate students so they can accurately analyze and optimally solve problems in science and engineering? I believe students can be best educated when instructors follow these three steps: 1) help students gain broad knowledge, 2) train students’ analysis and problem-solving skills, and 3) improve students’ logical and critical thinking. My beliefs have been established by several teaching experiences introduced in the following section.

Teaching and Mentoring Experiences

I will first introduce my teaching experiences regarding helping students to develop their critical thinking. As a teaching assistant (TA) for the undergraduate course “Principles of Engineering Materials” at University of Michigan (UM), I realized that providing several (counter) examples and showing different approaches that resulted in the same equations or solutions were very useful. In addition, the skills were effective in improving students’ mathematical intuition. Teaching experience for the graduate- level course “Electron Microscopy I” for assisting Prof. Hovden at UM convinced me that outlining state-of-the-art techniques and connecting them with the course materials are practical in expanding students’ knowledge. The TA experience at UM and many private tutoring experiences during undergraduate years for high-school-level mathematics, physics, and chemistry (for four years) have given me the confidence that students can train their analysis and problem-solving skills and logical thinking skills by being introduced to real-world problems or potential applications, tackling various application problems, and experiencing implementation projects. While a senior member and a postdoc of the Kotov Group, I mentored about four junior- graduate students and one undergraduate students. These were rewarding (and ongoing) experiences from which two journal (two ongoing) papers and about five conference presentations were produced.

Teaching Plans

Based on my academic background, in the long run I would like to design three new courses that can be offered to graduate students or senior undergraduate students:

• Introduction to Imaging, Modeling and Simulation would provide several imaging physics topics in imaging using electron and optical microscopy. Different from conventional imaging courses, which are mainly focused on imaging physics, this course would additionally provide stochastic process perspectives and their benefits in computational modeling and analysis through finite element analysis or/and finite-difference time-domain.
• Interfacial Phenomena in Colloids would provide more practical insights on physical, chemical, and biological phenomena of interactions between colloidal particles by presenting an in-depth discussion of electrostatic and polymer-induced colloid stabilization and assembly. In recent years, symmetry breaking from “patches” of colloidal particles has become a special focus in many areas due to their unexpected electrostatic, optical and reconfiguration properties. Therefore, I would introduce this topic by expanding the existing course – colloids and interfaces.
• Engineering Nanotechnology would cover fundamental concepts of energy and electron transport in materials confined or geometrically shaped at the nanoscale, including discussion about specific applications to contemporary engineering challenges in energy, biology, medicine, electronics, and material design.

Due to the effectiveness of the “flipped classroom” on both teaching and learning, I will consider applying this instructional approach to graduate-level courses, with some additional methods including case-based problem-solving exercises, small-group discussion, peer instruction exercises, and recorded lectures. In particular, small-group discussion and peer instruction exercises would further promote student engagement.