CAREER: Experimental Investigation of Plasticity at Nano-scale via in-situ Mechanical Deformation

California Institute Of Technology, Pasadena CA

Investigators

Abstract

TECHNICAL: The device functionality directly depends on structural integrity and mechanical stability, driving the necessity to understand and to predict mechanical properties of materials at reduced dimensions. Yield and fracture strengths have been found to deviate from classical mechanics laws and therefore can no longer be inferred from the bulk response or from the literature. Unfortunately, the few existing experimental techniques for assessing mechanical properties at that scale are insufficient, not easily accessible, and are generally limited to thin films. In order to design reliable devices, a fundamental understanding of nano-scale mechanical response is desperately needed; with the remaining questions of whether materials really are stronger when the instrumental artifacts are removed and if so, then why and how. This project investigates fundamental plasticity mechanisms and defect evolution (specifically, dislocations) operating in nano-scale crystals subjected to a specified mechanical deformation. Experimentally determined stress-strain relationships will be enhanced by in-situ SEM observations, and microstructural characterization, which will help develop a comprehensive physical defect model consistent with the microscopic flow stress response. The project presents, for the first time a unified plan combining unique nano-scale sample preparation techniques with novel in-situ mechanical testing capability and post-deformation TEM microscopy. This project will take advantage of the PI's expertise in using Focused Ion Beam (FIB) as a unique tool for both nano-scale sample fabrication and subsequent manipulation and TEM cross-section preparation. Merging the boundaries across scientific disciplines will be essential in this project because to adequately address plasticity at the nano-scale, materials science, microscopy, and mechanics communities must combine their efforts. The research will cross length scales as it strives to identify and characterize dislocation processes occurring during deformation of crystalline materials whose dimensions are constrained to nanometer sizes. NON-TECHNICAL: With many nano-scale devices profoundly impacting our daily lives, this project lends itself as a perfect opportunity to make a broader impact. The outreach effort will focus on secondary science education by forming a collaborative with high school science teachers from two local school districts, serving large numbers of disadvantaged, low socio-economic, students. To bridge the gap between current progress in materials science and secondary science content, the PI will establish the "Local Educators Network" (LEN) program, which will help transform the current pedagogy practices in high schools. This effort will build upon the successful relationships already fostered between Caltech, Cal State University Los Angeles (CSULA), and the Los Angeles Unified (LAUSD) and Pasadena Unified (PUSD) School. The emphasis of LEN program will be to present updates on the latest progress in materials science to high school teacher participants and to help them develop educational modules to be subsequently taught to the students in their classrooms. In addition, the PI will develop a new course in materials science curriculum focusing on mechanical properties of materials at the nanoscale, which will incorporate the learning gained from this research. Caltech graduate and undergraduate students enrolled in this class will be required to prepare literature-based scientific reports on current progress in materials science with emphasis on mechanical properties and to present them to the high school teachers in the LEN program.