Physik: DPG Tagungen - Sitzung O 28 - Nano-science.de

More documents

Recommendations

Info

Physik: DPG Tagungen - Sitzung O 28 http://www.dpg-tagungen.de/archive/2004/o_28.html Struktur durch den Kontakt mit verschiedenen Substraten. O 28.65 Poster Mi 16:00 Bereich C Einfluss der Brechzahl des dielektrischen Substrats auf die optischen Eigenschaften einzelner Goldnanopartikel •Katharina Schätzler, Benjamin Schmidt, Christian Dahmen und Gero von Plessen I. Physikalisches Institut (IA), RWTH Aachen In Berechnungen auf dem Gebiet der optischen Eigenschaften von Metallnanopartikeln wird die inhomogene dielektrische Umgebung des Partikels oft durch einfache Mittelwertbildung über die Umgebungsbrechzahlen berücksichtigt. In unserer Arbeit wird der Einfluss der Brechzahl des dielektrischen Substrats auf die optischen Eigenschaften sphärischer Goldnanopartikel mit Hilfe der Dunkelfeld-Mikroskopie sowie -Spektroskopie untersucht. Diese Methode macht es möglich, einzelne Nanopartikel zu spektroskopieren und so inhomogene Verbreiterungseffekte zu vermeiden. O 28.66 Poster Mi 16:00 Bereich C Optische Eigenschaften kleiner Aggregate aus Goldnanopartikeln •Benjamin Schmidt, Katharina Schätzler, Christian Dahmen und Gero von Plessen I.Physikalisches Institut A, RWTH Aachen Liegen Edelmetall-Nanopartikel nah genug beieinander, um elektromagnetisch miteinander zu koppeln, bilden sich ausgedehnte Plasmonen-Moden aus. Hier untersuchen wir mit Dunkelfeldmikroskopie kleine Aggregate aus gekoppelten, kugelförmigen Goldnanopartikeln, insbesondere Partikelpaare. Um eine Korrelation der Aggregat-Topographie und der optischen Eigenschaften herzustellen und um inhomogene Verbreiterungseffekte zu vermeiden, wird polarisationsselektive Spektroskopie an einzelnen Aggregaten durchgeführt. Die nötigen topographischen Informationen werden aus elektronenmikroskopischen Aufnahmen gewonnen. Die experimentellen Ergebnisse werden mit Resultaten aus der Verallgemeinerten Mie-Theorie verglichen, und es wird der Versuch unternommen, die Beiträge bestimmter Moden zu den Spektren zu identifizieren. O 28.67 Poster Mi 16:00 Bereich C Homogeneous linewidth of gold nanoshells •S. Brogl, G. Raschke, A. Susha, A. L. Rogach, T. A. Klar und J. Feldmann Photonics and Optoelectronics Group, Physics Department and CeNS, University of Munich, Amalienstr. 54, D-80799 Munich, Germany Nanoshells composed of a few nanometer thin gold layer coated on Au 2 S nanoparticles show a pronounced resonance in their scattering spectra for visible light. Similar to solid noble metal nanoparticles the origin of the resonance is a collective oscillation of the conduction band electrons, which is known as the nanoparticle plasmon (NPP). The NPP resonance position of a gold nanoshell can be tuned over a large spectral range by varying the relative size of the nanoparticle core and the thickness of the gold shell. Experiments carried out on ensembles of nanoshells show a broad absorption linewidth (FWHM) of about 600 meV. This is by far exceeding what is expected by Mie-theory calculations which yield a NPP resonance line width of less than 100 meV. We investigate this discrepancy by measuring the homogeneous scattering spectrum of a single gold nanoshell using dark field microscopy. The results show a homogeneous linewidth narrowed by 50% compared to ensemble measurements. This indicates that inhomogeneities e.g. distribution of shell thicknesses and/or core diameters are one important parameter for line broadening. O 28.68 Poster Mi 16:00 Bereich C 24 of 32 07.06.2009 22:14
Physik: DPG Tagungen - Sitzung O 28 http://www.dpg-tagungen.de/archive/2004/o_28.html STM/STS on large silver clusters at germanium (001) •Karl-Ludwig Jonas, Armin Kleibert, Fanny Geisler, Ralf-Peter Methling, Joachim Bansmann, Viola von Oeynhausen und Karl Heinz Meiwes-Broer Fachbereich Physik, Universität Rostock, Universitätsplatz 3, D-18051 Rostock Cluster deposition is used to create metal-nanodots with a high aspect ratio. We present scanning tunneling spectroscopy (STS) measurements on isolated silver clusters at germanium (001). The clusters are generated using an arc cluster ion source (ACIS), mass selected and deposited under soft landing conditions (E kin /atom < 0.5eV). Before performing STM experiments the cluster structure has been investigated using TEM, electron diffraction and EDX. Particle diameters between 5 and 14 nm have been used for the present studies. Scanning tunnelling microscopy images of large clusters always contain considerable tip folding at the steep cluster edges. Beside the accurately measured cluster height the imaging of particles of this height is therefore restricted to cluster facets at the top. Using STM and STS on deposited silver clusters structural and electronic properties are observed. In contrast to silver islands grown on germanium (001) the orientation of the crystal lattice is not fixed if cluster melting is neglected. However, some of the clusters show hexagonal facets at the top. STS is sensitive to occupied and unoccupied states near the Fermi level and reveals the existence of distinct states in the tunneling conductivity of the substrate as well as on the clusters. Thus, the richly structured density of states of the germanium (001) surface has been discovered and serves as STM/STS condition test. O 28.69 Poster Mi 16:00 Bereich C Application of the variable phase theory to the systems with quasistationary states. •Oleg Kidun 1 , Jamal Berakdar 1 und Natasha Fominykh 2 1 Max-Planck Institut fuer Mikrostrukturphysik, Halle, Germany 2 Institute of Physics, St. Petersburg State University, St. Petersburg, Russia We develop a method of investigation of the quasistationary (QS) states of different physical systems based on the variable phase approach [1-3]. We consider the modification of the physical properties of the QS states (energy position and resonance width) under the spatial transformation of the potential field as well as its asymptotical behavior. The role of the possible nonlocality of the potential in the observability of the QS states is also estimated. The realization of our approach in the studies of molecules and nanostructures is discussed. [1] F. Calogero, Variable Phase Approach in Potential Scattering, AP, NY (1967) [2] V. Babikov, Method of the Phase Functions in Quantum Mechanics, Nauka, Moscow (1969) [3] O. Kidun, N. Fominykh, J. Berakdar, J. Phys. A 35, 9413 (2001) O 28.70 Poster Mi 16:00 Bereich C Electron dynamics of buried interface states in Ar/Cu(100) probed by time-resolved two-photon photoemission •M. Rohleder, W. Berthold, K. Duncker, J. Güdde und U. Höfer Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universtät, D-35032 Marburg We demonstrate for the system Ar/Cu(100) how in favourable cases the dynamics of electronic states located at the interface between a metal and an insulator can be investigated by means of time-resolved two-photon photoemission (2PPE). The interface states of Ar/Cu are located above the vacuum level in the band gaps of both the Cu(100) surface and the Ar films which were as thick as 70 monolayers (ML). With increasing layer thickness the states evolve from quantum-well-like resonances into well-defined bound states which arise from the screened image-potential of the metal. Electrons excited into these states decay on timescales between 100 fs and 250 fs by electron-hole pair excitation in the metal and - for thin Ar layers ( < 20-30 ML) - also by electron transfer through the insulating Ar layers into the vacuum. In comparison to the image-potential states of the clean surface, the interface states are modified by the potential inside the dielectric layers. Screening reduces 25 of 32 07.06.2009 22:14
Page 1 and 2: Physik: DPG Tagungen - Sitzung O 28
Page 23: Physik: DPG Tagungen - Sitzung O 28

Physik: DPG Tagungen - Sitzung O 28 - Nano-science.de

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?