(7dj) Multiscale Design of Heterogeneous Nanomaterials for Energy Applications: Solution Synthesis, Structures, and Properties

Research experience. Developing superior materials for energy production, conversion, and storage is crucial for meeting the global energy demand. Bottom-up design of heterogeneous nanomaterials offers abundant opportunities for tuning the electronic, optical, thermal and catalytic properties of these novel materials to address the various challenges we face in energy applications. My research centers around solution phase synthesis of complex nanomaterials, bottom-up fabrication of functional nanocomposites, and understanding the structure-property relationship from atomic scale to macro scale.

My graduate research at Purdue University focused on the solution phase synthesized metal chalcogenide nanomaterials for thermoelectric applications. I developed or optimized the synthesis of copper zinc tin sulfide (CZTS) nanocrystals, bismuth telluride, lead telluride, and silver telluride nanowires and/or heterostructures. Upon purification, ligand removal and consolidation of the solution-synthesized nanomaterials, we developed functional thermoelectric composites with nano-sized grains and designable nanoscale heterostructures, which were demonstrated to exhibit superior thermoelectric properties.

My postdoc work at University of Pennsylvania emphasized the charge transport behavior in semiconducting nanocrystal (NC) solids, in which the charge transport properties are determined not only by the nature of individual NCs but also by the interface and organization of the NCs. I showed that doping semiconductor NC solids with metal nanoparticles, in analogy to atomic doping, modifies the macroscopic carrier density and the charge transport dynamics of the NC solids. The doped NC solids represent a novel family of artificial materials which can be designed in nanometer scales and are of great interest for many emerging nanocrystal-based technologies including electronics, optoelectronics, and thermoelectrics.

Recently, I moved to Lawrence Berkeley National Laboratory, where I extended my research area into nanocrystal growth kinetics and high-throughput synthesis of core-shell CdS-CdS_xSe_1-x nanocrystals based on kinetic designed reactions. By using a mixture of S and Se precursors and by controlling the relative decomposition rates of the two precursors, we could theoretically create desired heterostructures from the one-pot synthesis, which greatly simplifies the production of heterogeneous nanocrystals compared with the existing layer-by-layer method. To validate the hypothesis, we perform the high-throughput robotic synthesis to explore the large parameter space of the reaction.

Future directions. I am fascinated by the ability to design novel materials from nanoscale through scalable, wet-chemical, bottom-up approach. As many physical events, such as electrical and thermal transport and light absorption and emission, have characteristic lengths in the nanometer range, the ability to design materials on nanoscale will enable more effective manipulation of electrons, heat, and light. This requires the capability to create nanostructures with atomic precision and to integrate these nanostructures into working devices. I envision this as a multi-scale problem which needs to be tackled from the following three scales/aspects: (1) on the atomic scale, understand the kinetics of the synthesis, especially for complex materials or structures, to enable the atomic-precision control of the nanomaterials; (2) on the mesoscale, understand the interfacial properties which dominate the assembly of the nanomaterials and therefore affect the device integration; (3) on the device scale, understand the collective properties of the assembled nanomaterials and their surroundings. Finally, energy applications will be built upon the multi-scale design of nanomaterials, including but not limited by waste heat recovery, solid state lighting and display, etc.

Teaching Interests:

I have developed my interest in teaching the fundamental courses in chemical engineering, including thermodynamics, kinetics, reaction engineering, and mass and energy balances since my service as a teaching assistant at Purdue University. I enjoy leading the students to deepen their understanding on the concepts in these courses and to develop their problem-solving skills utilizing their new knowledge. As a future instructor, my goal is not only to deliver the knowledge, but also to connect the knowledge to practical problems and to inspire the students to think critically using the knowledge.

In addition to the core courses, I am also interested in developing and teaching elective courses to the senior undergraduate students and the graduate students based on my own research. During my postdoc training, I have obtained valuable experience in designing and teaching such courses as a guest lecturer both at University of Pennsylvania and University of Virginia. The course will focus on the synthesis, properties, and applications of nanomaterials, and my goal is to introduce both the fundamentals and the cutting-edge research progress of nanomaterials to the interested students.