(3dz) 3D Ordered Inorganic Nanocrystalline Thin-Films: Growth Chemistry, Strain Field Analysis, and Energy Applications

Authors: 
Oh, M. H., Lawrence Berkeley National Laboratory
Alivisatos, A. P., University of California
Hyeon, T., Seoul National University
Research Interests

The global demand for novel materials and advanced technologies for energy science and engineering is growing as we confront the reduction of natural resources and a variety of environmental issues. Structural inorganic nanomaterials will be critical for meeting these challenges because of their high mechanical robustness in conjunction with remarkable interfacial functionalities. Nanocrystalline materials have a vast number of crystallites (i.e., grains) with sizes of a few nanometers. Their properties are collectively determined by the numerous interfaces between the nano-scale building blocks. It can be the most promising structural nanomaterials when the consisting grains are well-ordered with reduced interfacial heterogeneity.

Techniques to generate designed interfaces and associated defects in inorganic nanocrystalline materials promise a host of new potential applications. Nano-interfaces often contain topological or geometric defects, which play an essential role in the optoelectronic, magnetic, mechanical, and chemical properties of the materials. In the meantime, researchers have found ways of cataloging the contribution of different forms of interfacial defects to the properties of materials. Still, the non-uniformity in grain size, grain shape, and grain orientation makes these tasks difficult. It remains a challenge to fabricate nanocrystalline materials with structural order from the nano- to the macro-scale as well as identifiable local interfaces.

Two technological breakthroughs are required for the practical use of interfacial functionality of the ordered nanocrystalline materials: 1) a fundamental understanding of the nano-scale physical phenomena arise at the nano-interfaces, 2) the advancement of the manufacturing process for fast and reproducible assemblies and the pattern-ability of the nanocrystal (NC) building blocks, nano-grains. To date, neither academic nor industrial research on crystalline materials has been able to find a reliable way of controlling interfacial defects between the crystallites and has therefore focused on reducing their occurrence. Researchers also strive to develop nano-fabrication techniques that can fabricate nanostructures with the same exquisite structural control of e-beam and optical lithography, but with better interfacial defect placement/management, and the low cost and scalability of conventional chemical synthesis and thermal treatment methods.

Through my research, I have found a novel approach to inorganic nanomaterial synthesis, where we can grow complex nanocrystalline thin-films from multiple phases with complete control over the interfacial and surface structures. My synthesis route can produce fully ‘orientation’ ordered assemblies with extremely regular Three dimensional (3D) ordering and can be potentially scaled up for macro-scale synthesis. I have discovered that delicate control of orientation, faceting, and strain in the epitaxial growth of nano-grain is possible in the solution phase by using faceted nanocrystals as substrates and surface ligands as a free energy modulator, which enables the formation of the desired interfacial structures. The results from my research pave the way for regular and well-defined patterns of grain/phase/surface boundaries and also provide an excellent opportunity to explore unprecedented physical effects resulting from interfacial strain and topological defects. (Myoung Hwan Oh et. al. Nature 2020, 577, 359)

My current research focuses on investigating and engineering novel functionality of the boundaries of nanocrystalline materials. I will expand the library of highly ordered nanocrystalline materials through epitaxy-based hierarchical "supercrystal" growth and apply them to energy devices (e.g., catalysts and solid-state electrolytes) and nano-electronics (e.g., ferroelectrics). Throughout my future research career, I want to realize the next generation of functional nanomaterials by designing complex interfacial structures tuned at the atomic scale, using synthesis methods that are both low cost and scalable to arbitrary geometries. My research interests primarily have synergy with the research theme of functional nano-interfaces, and also significant overlap with the topics of combinatorial nanoscience, multimodal nano-scale imaging, as well as the recent global emphasis on materials research for energy and nano-electronics.

My research group will take an interdisciplinary and multiscale approach to the physical chemistry of (orientationally) ordered nanocrystalline thin-films by elucidating the chemistry of crystal growth from nano- to macro-scale and dynamics of deformation and related strain, phonon, and electronic states at the nanointerfaces using atomic-resolution transmission electron microscopy, vibrational and x-ray spectroscopy, and scanning electrochemical microscopy and by applying this knowledge to the design of energy conversion and nano-electronic devices.

I will leverage my unique combination of research skills, gained from my Ph.D. and postdoc training: 1) advanced inorganic chemistries including solution-phase synthesis and assembly of inorganic NCs using microemulsion, surface ligand modifications, heteroepitaxial growth and chemical etching on the NC substrate, design and introduction of grain boundary defects to the NCs, epitaxy based assembly of NC building blocks at the liquid interface, 2) materials characterizations, trained through works in the facilities in the Lawrence Berkeley National Laboratory (LBNL), including 3D strain analysis using high resolution scanning transmission electron microscopy (HRSTEM), electron energy loss spectroscopy (EELS), and image processing algorithms, in-situ XPS, XAS, XRD, and Raman, and electric conductivity and product measurements during heterogeneous catalysis.

I will carry out structure-property correlation studies using my strong academic background in inorganic chemistry, catalysis, physical chemistry, electrochemistry, structural mechanics, solid-state physics, and optoelectronics. This correlation study will also be supported by my experience in various nanoparticle applications, including X-ray computed tomography (CT) contrast agents, lithium-ion batteries, fuel cells, dye-sensitized solar cells, photo/electrochemical CO2 reduction reactions, alkane dehydrogenation thermocatalysis, and quantum dot photodetectors.

Teaching Interests

I am interested in pursuing an academic career primarily because of the opportunity to help students develop as scientists, engineers, and leaders who can meet the challenges of real-world technological problems. As a graduate student teaching assistant and mentor for undergraduate/graduate researches, I was challenged to teach a diverse audience, motivate students to take ownership of projects, and translate complex subjects into understandable lessons. I have learned that successful educators are capable of conveying the joy of discovery and intellectual development. My ultimate goal as an instructor is to impart problem-solving skills, creativity, and independence, and to give my students the knowledge and confidence to aspire to great heights in their professional careers. As an instructor, I will focus on the fundamentals of engineering, but will also provide scientific and historical background and examples of modern research or current events.

As a chief teaching assistant for organic-inorganic chemistry and teaching assistant for physical chemistry, I found that a lot of struggling students learn best by talking themes out loud or sketching chemical equations and diagrams repeatedly. They benefit from group-based collaborative work that appeals to social and verbal learners, but the chemistry courses they attended consisted mainly of blackboard lectures suitable for visual-aural learners. I will supplement my potential seminars with group activities and practical presentations to appeal to a varied student population and to open participants to learning styles that may not be at their natural tendency. Students can share their problem-solving processes and practice teamwork through this exercise. Another strategy to develop problem-solving skills and physical intuition that I would incorporate into my classes is project-based learning. The long-term planning and focus needed for a project to prepare students for real-world problems that usually have a broader scope than the classroom problem sets. Projects can be designed to be open-ended, allowing students to choose appropriate tools for a given problem and to discover unique pathways to the desired goal. Most research projects are well suited for laboratory courses, but I would also incorporate projects into lecture-based courses by using software such as Matlab and Python to simulate complex chemical systems or visualize mathematical solutions.

I served as a mentor for seven undergraduate research assistants at UC Berkeley, and as a mentor to four graduate researchers at Seoul National University. In both situations, I left it to my students to complete their projects, first by demonstrating the necessary experimental techniques, and then by talking to students to monitor progress and help overcome obstacles. I allowed my students enough latitude to make their own mistakes and learn from them.

Finally, I will keep an open mind about adjusting my teaching methods to respond to student feedback or better serve the changing student population. My favorite teachers were humble and flexible in their ideas, even when they had unrivaled mastery of their chosen subjects. I will maintain an open dialog with my students by being available through e-mail and in one-on-one or small group office hours outside of class, and carefully consider student questions during the course to create an inclusive rather than a defensive discussion environment. With these guiding principles, I believe I can successfully introduce students to the "learning how to learn" process, which, I believe, is at the heart of university education.

I am qualified to teach the following core and elective courses: Inorganic Chemistry, Physical Chemistry, Solid State Chemistry. I would be interested in developing a course on the topic of "Strain Analysis and Engineering in Heterostructured Nanocrystalline Materials"