Correlating the atomistic nature of grain boundary phase transformations to their macroscopic kinetic properties

In this project, we study the atomistic structure and phase transformations of tilt grain boundaries in Cu by using aberration-corrected scanning transmission electron microscope to build a relation to the transport properties of the grain boundaries via macroscopic tracer diffusion experiments. In the meantime, we address the impact of the grain boundary bicrystallography and solute segregation on both the grain boundary structure and diffusion properties.

For example, the rapid development of microelectronics requires robust integrated circuits, however, their performance is often compromised due to atomic-diffusion-driven phenomena. One major contribution that impacts properties is related to grain boundaries, which provide fast diffusion pathways and hence impact the microstructure evolution. Up to date, great efforts have been undertaken to study the impact of grain boundary crystallography on macroscopic material properties, but an intimate link to their atomic nature is missing. For instance, it has been demonstrated that grain boundary diffusion depends on the macroscopic misorientation of the bulk crystals, which was interpreted in terms of the evolution of different grain boundary structures.

We first characterize the atomic structure of grain boundaries and determine local strain fields using scanning / transmission electron microscopy (S/TEM). We then employ in situ heating in the STEM to study the structural evolution and possible grain boundary phase transformations at temperatures relevant for bulk diffusion measurements. Furthermore, we investigate the influence of solute atoms such as Ag and Co on the grain boundary structure and design in situ TEM-diffusion couple experiments to observe atomic scale grain boundary diffusion processes. We aim to bridge the atomic-scale characterization of the grain boundary structure and phase transformations with the macroscopic diffusion measurements to establish an atomistic understanding of the transport properties of interfaces.