CAREER:Atomic Structure and Growth of Helical Nanostructures Studied by Advanced Electron Microscopy

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Non-technical Summary: This NSF CAREER program encompasses a research and educational plan that uses imaging and visualization as tools to answer key scientific questions as well as engage in scientific outreach. The research component of the program uses electron microscopy to understand how complex nanostructures form. Many properties of nanoscale materials are determined by structural imperfections that appear during the growth process and go on to affect the material's final structure. For example, adding a metallic coating to straight silver-gold alloy nanowires can cause the wires to transition to a double helix morphology. Before nanostructures such as these can be widely used in technological applications, there is a need to understand how the helical structure originates. Using advanced electron microscopy, this program will combine extremely detailed and high resolution studies in three-dimensions with high-throughput imaging to obtain a complete picture as to how the helical nanowires grow and twist. This research will advance the fundamental understanding of the processes that determine how complicated nanostructures can be chemically synthesized for future technological applications. The educational component of this program aims to provide access to academic extra-curriculars for high school students in severely underserved areas. Students in many areas in Oakland and Richmond face poverty, hunger, violence and racial discrimination. Social and economic hurdles often prohibit these students' participation in traditional summer extracurricular activities, which can increase the academic achievement gap in this population. Working with local high school teachers, this program will develop and implement a flexible and adaptable summer research experience for these and other students affected by inequitable systems. This program will use imaging and visualization as tools to convey scientific knowledge and excite the students about careers in science. It also aims to develop mentorship networks to help students attain their goals in the college and job market. Technical Summary: The research portion of this program will use electron microscopy to determine the structural origin of chirality in core-shell nanowires. Nanoscale three-dimensional characterization will be used to study the morphology of the nanowires as they transition from straight to twisted structures during addition of the shell. By varying the shell thickness and atomic species, the role that lattice mismatch plays in the structural transformation from straight to helical in these wires will be determined. Atomic resolution electron tomography will be used to measure the position of defects and the strain distribution in these materials to determine how these structural features are related to the helical structure that these materials adopt. A high-throughput electron microscopy workflow using a machine learning approach will be developed to measure structural heterogeneity in many populations of the straight and twisted nanowires. The comprehensive understanding of the development of the helical morphology demonstrated by the core-shell nanowires under study will relate the presence of microstructural features (defect, strain, grain boundaries) to the overall morphology of the nanowires. This in turn will enable the rational design of functional materials based on this system, application in optoelectronic, nanomechanical, biomimetic or catalytic applications. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.