This experimental research project focuses a wide range of surface physics techniques to probe electron density waves at metal surfaces. A central topic is the surface transition from Friedel oscillations to Charge Density Waves. Friedel oscillations at the surface will be imaged with a variable temperature STM and compared to measurements of the energy bands (high-resolution ARPES) and to the response function at the Fermi energy determined with momentum-resolved electron scattering. The atomic structure of the surface as a function of temperature will be determined by combining surface x-ray scattering (simple analysis) with LEED (for surface sensitivity). The presence of a metal-to-nonmetal transition is observable in inelastic electron scattering. Surface phonon dispersion will be measured by high resolution inelastic electron scattering, and, in collaborations with Hulpke (Germany), using inelastic helium scattering. All work will be done in close collaboration with theorists around the world. Topics of specific interest are: a) the transition from Friedel oscillations to a CDW, b) wavelengths of Friedel oscillations for a non-free-electron band structure, c) role of many-body effects in Freidel oscillations and surface transitions, d) difference of surface screening due to long range Friedel oscillations, via the temperature dependence of the surface phonon dispersion, and e) the temperature dependent surface structure driven by the temperature dependent surface response function. This research program is interdisciplinary in nature and involves several pre- and post-graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. %%% This experimental research project is devoted to the distinct behavior of the atoms at the surface of a crystalline metal compared to atoms located in the bulk of the crystal. These differences are subtle and difficult to measure, but they have practical importance. Surface properties of metals are important for example in chemical catalysis, where the chemical reagents involved come into contact only with surface atoms. In modern laboratories advanced techniques are available which reveal specifically the properties of atoms at the surface. Several of the techniques are the Scanning Tunneling Microscope, Low Energy Electron Diffraction, Angle Resolved Photoemission Spectroscopy and high resolution inelastic electron scattering. All of these techniques are employed in this basic research project. This basic research will add to the understanding of atomic properties at surfaces, and could indirectly lead, e.g., to improved catalysts. This research program is interdisciplinary in nature and involves several pre- and post-graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. ***
