(6kd) Hierarchically Engineered Structures Using Self- and Directed- Assembly for Unique Electronic, Optical and Mechanical Properties

The properties of materials are largely determined by their formed structures. The understanding of the structure and property relationship in multilength scales is crucial in developing the next generation functional materials. The manipulation of the nanomaterial assembly could directly control their conductivity, color, and strength. My previous research experience is focused on the assembly of polymer and colloidal nanoparticles. External electric and acoustic fields are demonstrated to guide conductive polymers to grow into aligned structures or fibers with high aspect ratio. The charge transport is thus enhanced. By carefully engineering the solvent-solvent and solvent-solute interactions, a ternary system can be designed to not only achieve desired structures, but also obtain stimuli-responsive materials with on-demand tunability of properties.

Research Interests:

Structure-property relationship has always been an important research topic to understand, advance, and discover materials. The development of a broad range of fields is closely relying on well-engineered structures, including electronics, optics, catalysis, energy storage, and biomaterials. Scattering-based techniques offer a versatile platform for structural characterizations. In particular, scattering-based techniques provide quantitative analysis of samples averaged over the total volume. Moreover, they also allow time-resolved characterization and capture in-situ structural changes under varied external stimuli, such as electric field, acoustic field, and temperature gradient. In conjugation with cutting-edge imaging techniques, such as electron microscopy and confocal microscopy, a complete view of the multi-length scales structures can be unveiled and quantified. For example, besides the size and shape of crystallized polymer can be described with X-ray and neutron scattering experiments, the amount of polymer that forms crystallites can be determined. More importantly, the formation kinetics and intermediate structures can also be quantitatively compared under different external fields. This is especially important to unravel the mechanism of different physical phenomena at each stage. My research interests are to utilize the powerful scattering-based structure characterization toolbox to understand and control the structures of the assembly process in order to achieve unique functions.

Successful Proposals:

Experimental proposals that have been granted beamtimes from synchrotron- and neutron-based national labs, including 8 proposals to NIST Center for Neutron Research (NCNR), 2 proposals to Argonne National Laboratory, 2 proposals to Brookhaven National Laboratory, and 1 proposal to Oak Ridge National Laboratory (ORNL).

Postdoctoral Project:

“Porous materials under extreme conditions”

Under supervision of Yun Liu,

1. NIST Center for Neutron Research
2. Department of Chemical & Biomolecular Engineering, University of Delaware

PhD Dissertation:

“Structure Engineering of Self- and Directed-Assembled Conjugated Polymers”

Under supervision of Lilo D. Pozzo, Chemical Engineering, University of Washington

Committee members: Christine K. Luscombe, Stuart Adler, and Lih Lin

Research Experience:

My research experience is mainly focused on interdisciplinary fields involving materials and engineering. My formal training was in colloidal science with an emphasis of structural characterization using scattering techniques. In order to achieve different functions, the assembly of materials are controlled to realize specific structures. I have learned the fundamental physics behind the assembly of polymers and nanomaterials, which can be used to achieve unique functions with hierarchically engineered structures. I acquired the knowledge and invaluable experience by conducting experiments by closely working with instrument scientists in national labs. At the same time, the purpose of engineering structures is to obtain unique functions. The projects that I worked on always involved collaborations and closely related fundamental science to applications. Examples include photovoltaics, transistors, sensors, optoelectronics, batteries and biomimetic materials.

Teaching Interests:

I also had extensive teaching experience related to colloidal science and chemical engineering. I spent two semesters teaching colloids and interfacial science laboratory and two semesters teaching unit operation laboratory. Aside from those, I also mentored graduate and undergraduate students in my research group. While working as postdoctoral researcher at National Institute of Standards and Technology, I also participated in mentoring an undergraduate researcher in a collaborative research project.

Future Direction:

As a faculty, I would like to continue applying X-ray/Neutron scattering techniques as a tool to guide the designing of the material assembly in multi-length scales with unique functions. Specifically, I would like to continue pursuing the direction of achieving functional and stimuli-responsive materials with well-controlled structures. I would combine the knowledge I acquired during my Ph.D and postdoctoral research: polymer physics and liquid critical phenomena. The research will be an interdisciplinary field with a focus of answering fundamental mechanistic questions in soft materials and colloidal science. It will also seize the applications in different fields, such as optics, energy storage and thermoelectrics, which would foster extensive collaborations with groups in different fields. On the one hand, I would like to explore fundamental physics that could be responsible to assemble polymers and nanomaterials. On the other hand, I will utilize the knowledge I obtained to enhance and realize new properties.

In addition, the working experience in different national labs will be maintained and passed on to my group. The research in my group will be utilizing the world class scattering instruments and working closely with instrumental scientist in national labs to address questions in a blend of disciplines.

Selected Publications:

Yuyin Xi, Caitlyn M. Wolf, Lilo D. Pozzo, “Self-assembly of Donor-acceptor Conjugated Polymers Induced by Miscible Poor Solvents”, Soft Matter, 15, 1799, (2019).

Yuyin Xi, David S. Li, Greg M Newbloom, Wesley K Tatum, Matthew O’Donnell, Christine K. Luscombe, Lilo D Pozzo, “Sonocrystallization of Conjugated Polymers with Ultrasound Fields” Soft Matter, 14, 4963, (2018).

Yuyin Xi, David S. Li, Yi-Ting Lee, and Lilo D. Pozzo, “In-Situ Ultrasound sample environment for small angle scattering studies” 2018 NCNR Highlight (2018).

Yuyin Xi, Lilo D. Pozzo, “Electric Field Directed Formation of Aligned Conjugated Polymer Fibers” Soft Matter, 13, 21, 3894, (2017).

Yuyin Xi, Yueh-Ling Hsieh, Ya-Hsi Hwang, Shun Li, Fan Ren, Stephen J Pearton, Erin Patrick, Mark E Law, Gwangseok Yang, Hong-Yeol Kim, Jihyun Kim, Albert G Baca, Andrew A Allerman, Carlos A Sanchez “Effect of 5 MeV proton radiation on DC performance and reliability of circular-shaped AlGaN/GaN high electron mobility transistors” Journal of Vacuum Science & Technology B 32, 012201(2014).

Yuyin Xi, Lu Liu, Fan Ren, Stephen J Pearton, Jihyun Kim, Amir Dabiran, Peter P Chow, “Methane detection using Pt-gated AlGaN/GaN high electron mobility transistor based Schottky diodes” Journal of Vacuum Science & Technology B 31, 032203(2013).

Yuyin Xi, Lu Liu, Ya-Hsi Hwang, Oluwadamilola Phillips, Fan Ren, Stephen J Pearton, Jihyun Kim, Chien-Hsing Hsu, Chien-Fong Lo, Jerry Wayne Johnson, “Study of hydrogen detection response time at room temperature with Pt-gated diodes fabricated on AlGaN/GaN hetero-structure” Journal of Vacuum Science & Technology B 31, 032202(2013).

Jiangsheng Yu, Yuyin Xi, Chu-Chen Chueh, Jing-Qi Xu, Hongliang Zhong, Francis Lin, Sae Byeok Jo, Lilo D Pozzo, Weihua Tang, Alex K-Y Jen, “Boosting Performance of Inverted Organic Solar Cells by Using a Planar Coronene based Electron-transporting Layer” Nano Energy, 39, 454, (2017).