Apparatus for studying the structure and evolution of atomically-ordered domain boundaries, kinks and vertexes

点击翻译按钮获取中文摘要

In many classes of electronic materials, such as polycrystalline Si or high-k dielectrics, properties such as solar cell efficiency or breakdown field depend on the size and spatial arrangement of crystalline grains and the distribution of interfaces (microstructure). Materials are frequently annealed to initiate micro-structural transformation via re-crystallization and grain growth. Although, there is a large literature on grain grown and grain coarsening, in lieu of detailed crystallographic information about interfaces and interface energies, theoretical models normally assume that interface energies are isotropic. To go beyond this, it is necessary to classify interfaces according to their microstructure and this could lead to a quantitative understanding of the relationship between processing, structure and material properties. Consequently, we are excited by the fact that we have discovered a two-dimensional analog of a three-dimensional electronic material that has a highly anisotropic distribution of interfaces (domain boundaries) that is amenable to detailed investigation at the atomic level. Specifically, we have developed a way of growing a Ge film on an atomically flat Si surface so that it contains crystalline domains separated by atomically ordered boundaries. Using this model system it is possible to study: the distribution of domains, the distribution of boundaries, the atomic structure of boundaries and the temporal evolution of boundaries, kinks and vertexes. To take full advantage of this system we require electronics that will allow us to perform tunneling and force microscopy simultaneously. This will allow us accurately determine the position of atoms in the boundary region and also discriminate between Si and Ge atoms in many cases. These studies will provide atomic-level information about the physical factors that determine the anisotropic distribution of boundaries and the growth of domains in well-characterized model system. This apparatus will also provide novel training opportunities for six highly qualified personnel/year.