Identifying the Driving Forces for Alloying in Ultra-Thin Films Karsten Pohl, Department of Physics, University of New Hampshire, Durham, NH LEEM-IV: Our new technique of analyzing data from low-energy electron microscopy (LEEM) exceeds x-ray and electron diffraction in spatial composition profiling. Designing and controlling the formation of high-performance surface alloys for unique catalytic and electronic application is an important problem of materials research. Understanding the detailed driving forces of alloy formation in ultra-thin film relies on the ability to measure the heterogeneous compositional profiles in 3 dimensions within the surface region with a resolution of a few nanometers. We have shown that LEEM-IV has revealed this fundamental insight for the first time by measuring the concentration of palladium (Pd) atoms in the first 3 layers of a copper (001) single crystal in a region of 1 mm with a resolution of 8 nm; see graphic. We are now applying this new technique to develop methods to grow graphene layers epitaxially on silicon carbide wafers. First results indicate that silicon depletion of the surface region at high temperatures is a viable process. March 2009