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O: Oberflächenphysik

O 28: Methodisches (Exp. und Theorie)

O 28.4: Vortrag

Samstag, 5. März 2005, 15:45–16:00, TU EB407

Two-Photon Photoemission Microscopy of Self-organized Ag-Nanostructures on Si(001) — •L. I. Chelaru, O. Heinz, P. Zhou, M. Horn-von Hoegen, D. von der Linde, and and F. Meyer zu Heringdorf — Institut für Laser-und Plasmaphysik, Universität Duisburg-Essen (Campus Essen), 45117 Essen

During epitaxial growth of Silver on Si(001), compact islands and quasi-one-dimensional nanowires are formed. These self-organized nanostructures have been investigated by photoemission electron microscopy (PEEM) where the electrons are generated by femtosecond laser pulses through a two-photon photoemission process (2PPE). Shadow like features are observed around the nanostructures when the Ag islands and wires exceed a certain lateral dimension. The features are different for both directions of the polarization of the incoming light (s- and p-polarization, respectively). In p-polarization the shadows consist of several interference fringes. We interpret the shadows to represent the near field around the islands that is strongly emphasized in photoemission through the nature of the non-linear 2 photon photoemission process. The Ag-nanowire photoemission yield also shows a dependence on the polarization direction of the incoming light with respect to the orientation of the nanowire. Ag-nanowires oriented parallel to the polarization vector of the incoming light are not visible in the microscope images, in contrast to Ag-nanowires that are oriented normal to the vector of polarization. Also, the photoemission yield depends on the size of the islands. We explain these findings with a plasmon state in the silver nanostructures that is the intermediate state for 2 photon photoemission.