A Combinatorial Approach to Grain Boundary Studies: Bicrystal Arrays via Lithographically Modulated Seed Growth

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

NON-TECHNICAL DESCRIPTION: The performance of many materials in a wide range of engineering applications is influenced by the external surfaces (solid-vapor interfaces) that define their overall shape, solid-vapor interfaces within the material (internal voids), and by internal solid-solid interfaces (grain boundaries) that arise when the composition or the atomic structure/arrangement changes abruptly. In nanoscale materials, the spatial density of surfaces and interfaces is higher than in conventional materials, and therefore they play an even more critical role. Important characteristics of surfaces and grain boundaries are their energy and how these energies depend upon the specific arrangement of atoms at the respective interfaces. In conventional model experiments, one surface or grain boundary is generated and examined. The proposed work will seek to develop a new flexible and efficient experimental vehicle for generating large numbers of distinct grain boundaries of very specific geometry that intersect highly-controlled surfaces in a single sample of controlled chemistry. The samples are specifically designed to simplify and greatly accelerate measurements of surface and grain boundary properties in a wide range of materials. The development of a successful fabrication approach would promote rapid advances in the knowledge of surface and grain boundary properties that have fundamental value in designing materials with improved performance characteristics. This work will involve students at the graduate, undergraduate, and high-school levels, and thereby promote the development of trained scientists with advanced degrees, and encourage younger students to pursue further study and graduate-level training in this exciting and vital area. TECHNICAL DESCRIPTION: Surfaces (solid-vapor interfaces) and grain boundaries (solid-solid interfaces) in materials are essential microstructural components that profoundly impact properties and performance. In the nanostructured materials of current interest, the spatial density of these interfaces is extremely high, and their importance is amplified. Generating, optimizing and stabilizing such structures will require fundamental knowledge of the surface and interface properties. Measurements of grain boundary and surface energetics are essential, but difficult and tedious. In this work, a novel approach involving selectively and locally impeded single crystal seed growth into a sacrificial polycrystalline layer will be explored and exploited to generate arrays of bicrystal island grains of varying misorientation in a single sample. The samples will provide an ideal vehicle for systematic (combinatorial) studies of grain boundary and surface properties in ceramics. Measurements of the geometry of potentially hundreds of grain-boundary-grooves in a single sample, coupled with analysis of the relevant surface orientations provides a rapid method of obtaining the surface energy-orientation relationship, and comparisons will be made between such results and those derived from more tedious direct methods. If successful, such an approach would have applicability to the full range of material types, promote rapid gains in our knowledge of surface structure (crystallography)-energy relationships, and encourage additional extensions designed to similarly impact studies of grain boundary properties. In turn, this fundamental information can be used to design materials with improved performance.