Heteroepitaxial Metal Nanostructure Diffusion Through Collective Slip

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TECHNICAL: This transformative, high-risk, high-payoff project would investigate the collective migration dynamics of metal nanostructures via the glide of misfit dislocations through the interface. The project has experimental and theoretical aspects that build on the strengths of the two principal investigators. A feasibility study done with low-temperature scanning-tunneling microscopy (STM) showed the diffusion of two- and three-dimensional Cu nanostructures on Ag(111). PIs suggest that the mechanism involves the formation and glide of misfit dislocations through the interface. The experimental component would use low-temperature STM to capture island diffusion dynamics, to establish the size- and temperature-dependence of diffusivity, and to link structural changes within the island to collective motion of the entire structure. PIs would investigate diffusion for Cu/Ag(111), for two other fcc systems, Cu/Au(111) and Pd/Ag(111), and for two bcc systems, Fe/W(110) and Fe/Nb(110). These systems were chosen so that PIs could explore the parameter space of lattice mismatch, bond strength, and crystal structure. Atomistic simulations would directly connect to experiment by employing (1) atomistic calculations of island structure as a function of size, (2) temperature-accelerated dynamics simulations of nanostructure diffusion to study mechanisms, and (3) electronic-structure methods to accurately predict the energy barriers associated with those mechanisms. NON-TECHNICAL: Nanoparticle diffusion through dislocation glide has never been observed before. It has been modeled in theory and simulation but that work did not attempt to predict the dynamics of motion. Through experiment and simulations, PIs would be able to study a new phenomenon for surfaces and interfaces that should have important implications. Misfit dislocations are ubiquitous in strained heteroepitaxy, which is important for materials technologies that include heterogeneous catalysis and microelectronics. Education and training are key components of the program. Students would work with senior group members while they become familiar with the laboratory. They would participate fully in the preparation of manuscripts, both their own and those of other group members, and of proposals such as this one. They are expected to compete for student prizes and to present papers at conferences. They are also expected to contribute to the education of younger students. Undergraduate students are fully integrated, and their contributions are reflected by co-authorship of publications. PIs' laboratories are open for visits by prospective undergraduate and graduate students; freshmen involved in Engineering Open House and upperclassmen involved in senior design projects benefit from access to them.