Thin solid films are the basic structure in most microelectronic and optoelectronic devices. During annealing of a polycrystalline film, grain-boundary grooves can deepen to form holes, which tend to grow to breakup the film. The investigators' preliminary theoretical work has shown that surface energy anisotropy can reduce the grooving rate significantly. However, if the exposed surface orientations do not contain a facet orientation, then the anisotropic groove is smooth and looks exactly the same as an isotropic groove; only the grooving rate is reduced. This proposal aims to investigate this intriguing relationship between surface energy anisotropy and grain-boundary grooving using three methods: continuum analysis, experiment, and atomistic simulations. The investigators' preliminary work assumes that the crystallographic orientations of the bicrystal are symmetric about the grain boundary. However, most bicrystals are unlikely to be symmetric. Thus, the self-similar continuum analysis will be extended to asymmetric bicrystals. The investigators will also consider grain boundaries migrating at constant speed and study the coupling between the grain-boundary groove and the grain-boundary profile. Because grooving is self similar, the grooving rate is very large at the beginning of groove development, and atomistic methods are ideally suited to capture the groove formation. The investigators will perform molecular dynamics on aluminum and silicon bicrystals. The long-time evolution of the thermal groove will be studied by kinetic Monte Carlo simulations. Both tilt and twist boundaries will be considered. Surface and grain boundary energy anisotropy and their effect on faceting and growth rate will be systematically investigated. In the experimental part, two materials will be used for which surface energy anisotropy is established and measured. Bicrystal samples with symmetric crystallographic orientations will be prepared from commercially available material. The evolving groove shape at the grain boundary will then be microscopically examined as a function of thermal annealing time-temperature cycle to compare its shape with theoretical predictions. Grain-boundary grooving is the most commonly used technique for measuring surface diffusion coefficients. However, the retardation effect of surface energy anisotropy has never been considered in the measurement technique. The proposed investigation will clarify the effects of surface energy anisotropy on grooving and improve the accuracy of the technique. Better understanding and control of grooving will allow smaller microelectronic and optoelectronic devices to be made. This translates into faster and smaller computer chips, which will sustain continuous advancement of information technology. This project has also broad impact on materials education. Presently, there is no Materials degree offering program in the whole State of Louisiana. However, local industries need students with materials training, and Louisiana State University (LSU) is building a materials program to meet that demand. This proposal is a collaborative effort between two departments at LSU and will enhance materials research activities on campus. It will support graduate and undergraduate students and expose them to materials research in both departments. It will also allow more materials courses to be offered at LSU.
