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Project E3: Surface optical spectroscopy of phonon and electron excitations in quasione dimensional metallic nanostructures

Eugen Speiser, Norbert Esser, Annemarie Pucci

Our project will contribute to the understanding of the interplay between structure and electronic properties of metal-atom wires, based on fingerprints of the optical conductivity. We will study surface phonon modes and surface electronic excitations with linear optical spectroscopy. The atomic and electronic structure of the nanowires and, in particular, phase transitions and electronic correlation effects in such 1D-like systems will be addressed. The impact of defects (steps, adsorbates) on the electronic and structural properties will be systematically studied. The application of surface optical spectroscopy is the main expertise of the collaborating groups. We will combine complementary methods like Raman scattering, IR-UV Ellipsometry, IR-UV Reflection Anisotropy Spectroscopy, and IR transmission/reflection spectroscopy. They give access to a manifold of elementary excitations, covering a broad spectral range with uniquely high spectral resolution. IR and Raman spectroscopy are well established to study structural phase transitions and electron-correlation effects in bulk-like materials, for instance such with anisotropic structure and effectively reduced dimensionality. For tiny metal-atom wires on surfaces, the measurement of characteristic optical spectra and the extraction of specific physical quantities will be a big challenge and exactly that kind of studies will be the essential part of the research in this project. Our project will firstly focus on two model systems for quasi-1D-behavior: In/Si(111) which is known to undergo a Peierls transition and Au/Ge(001) which is expected to exhibit Luttinger liquid behavior. The preparation of single domain surfaces is important for the surface optical analysis, thus metal nanowires on vicinal Si and Ge will be investigated (e.g. In, Au/Si(hhk)). In collaboration with other groups, reflection anisotropy spectroscopy (RAS) will be established as a unique method to control preparation of nanowires in different experimental environments and, subsequently, silicide nanowires will be studied. In order to achieve a detailed understanding of structure and correlation effects from optical spectra, a close collaboration with both theory projects will be particularly essential. 

(Picture: The metal to insulator transition of In wires on Si(111) verified by IR transmission.)