ISAS - Institute for Analytical Sciences Dortmund and Berlin.
Optical spectroscopy is widely applied to study a manifold of fundamental excitations with high spectral or high temporal resolution. Analysis of nanoscale structures and surfaces, however, remains a challenge, due to the very large wavelength and penetration depth of light as compared to atomic distances in matter. Nevertheless linear optics like Raman and ellipsometry is suitable to study surface excitations in UHV environment. Surface selectivity can be achieved by utilizing symmetry arguments, polarization dependence or surface resonance enhancement. As an tutorial example I will discuss the study of surface electronic band structure and surface phonons of Sb monolayer terminated III-V(110) surfaces by Raman, RAS and ellipsometry. Ongoing research is focusing on the study of surface supported atomic nanowires like In on Si(111). In these systems surface structure formation and the related electronic properties is a controversial issue since it may involve electron-phonon end electron-electron coupling. I demonstrate that surface phonons, electronic surface transitions and electronic surface conductivity can indeed be studied by our optical spectroscopy techniques. Particularly I will discuss recent results on the phase transition of the (4x1) to (8x2) In/Si(111) surface. The metal-insulator transition as well as the structural modification is reflected in surface optical spectra. By comparison with ab-initio computational results (performed in the groups of F. Bechstedt and W.G. Schmidt) a direct link to the various surface structures under discussion is established.