Surface optical spectroscopy of phonon and electron excitations in quasi one-dimensional metallic nanostructures

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In this project we explore the intertwinement of structural and electronic properties from optical spectroscopy of prototypical metallic nanowires on Si and Ge substrates. We will address vibrational, plasmonic, and electronic excitations in a broad spectral range from the far IR up to the UV combining absorption/transmission spectroscopy, ellipsometry and Raman scattering. In close collaboration with T1, we will promote the microscopic understanding of the optical response in terms of fundamental electronic and phononic excitations and relate that to atomic and electronic nanowire structures and to transport properties. Using in-situ optical spectroscopy we will follow the changes induced by controlled nanowire modification with adsorbates (doping, structure), temperature, and strain and will thus contribute to a comprehensive picture of low-dimensional metal systems. For quasi-1D metallic nanowires, there are competing electronic/structural phases, the stability of which can be effectively tuned by doping, structural perfection and strain. We intend to disentangle the effects from these parameters, focusing on two quasi-1D metallic systems, i.e. Indium nanowires on Si(111) for which the pure structure optimization is already well established in our group, and gold nanowires on vicinal Si(111) as well as higher index surfaces, i.e. Si(553), Si(557) and Si(775), which will be characterized in much detail by other projects during the next years.Apart from this, Reflection Anisotropy Spectroscopy (RAS) will be continuously used as a fast, non-destructive tool for precise control of the surface electronic structure in collaboration with the other experimental projects, in particular on nanowire systems such as Tb/Si(001), Dy/Si(001) and Au/Ge(001).