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

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Physik: DPG Tagungen - Sitzung O 28 http://www.dpg-tagungen.de/archive/2004/o_28.html Nanostructures as a result of the thermal instability of metal thin films on insulators •Torsten Kolb, Dominik Enders, Annemarie Pucci und Gerhard Fahsold Kirchhoff-Institut für Physik, Universität Heidelberg, Im Neuenheimer Feld 227, D-69120 Heidelberg We investigate the possibility of structuring metal thin films on a nanoscale by exploiting their thermal instability. Various metal thin films (Cu, Au, Fe) were deposited on different substrates (MgO, SiO 2 ) and subsequent annealing processes were applied for fractioning these films. For in-situ and online analysis of this fractioning we use infrared spectroscopy, which we perform during annealing in UHV. Measuring IR transmission enables investigation of both dynamics and energetics (critical temperatures) of the processes caused by the thermal instability of metal thin films. Their morphological properties were characterized ex-situ by atomic force microscopy (AFM). The dependence of the resulting morphology on annealing temperature and crystalline structure will be demonstrated. O 28.44 Poster Mi 16:00 Bereich C Metal-on-insulator nanostructures via surface color centers •Svend Vagt, Tammo Block, Volkmar Zielasek und Herbert Pfnür Institut für Festkörperphysik, Universität Hannover, Appelstr. 2, 30167 Hannover We present first experimental results obtained in a pursuit of a new type of electron beam nanolithography in UHV that is based on the generation of surface color center patterns on epitaxial insulator films and the selective nucleation of metal islands. Experiments were performed in a combined system of an SEM (1-25 keV, resol. 4 nm) and a confocal variable temperature STM (80-900 K). Epitaxial NaCl layers on Ge(100) (up to 6 ML thick) were irradiated by the electron beam of the SEM under varying doses. EELS and scanning Auger microscopy showed the generation of color centers and Na clusters and colloids associated with electron-induced desorption of Cl in the irradiated areas. The NaCl films turned out to be extremely sensitive to a 3 keV electron beam and due to high surface mobility of Na metal clusters formed easily. After high e-beam exposure STM at 2 monolayer thick NaCl layers revealed the formation of beam-induced line-shaped gaps in the film down to the substrate. Depending on the electron dose, a width down to 35 nm was observed, probably limited by secondary electrons. Deposition of Ag on the surface leads to metal aggregation in the center of the gaps, presently being investigated by STM and SEM. The underlying physical mechanisms as well as the potential use of this type of nanostructuring technique and possible refinements will be discussed. O 28.45 Poster Mi 16:00 Bereich C Pb on Si(557) - Steps towards a one-dimensional conductivity •Ziad Kallassy, Martin Henzler, Heinz-Lorenz Günter und Herbert Pfnür Institut für Festkörperphysik,Applestrasse 2,30167 Hannover The conductivity of ultrathin Pb films evaporated onto a highly stepped Si(557) surface was investigated by modified macroscopic 4-point measurements in UHV. After annealing 4 to 10 ML of Pb, evaporated at a sample temperature of 80K, to temperatures of 990K we obtained a strongly anisotropic conductivity at temperatures below 100K, with up to a factor of 20 higher conductance in the direction parallel to the step edges compared with the direction normal to them. While conductivity in this direction was found to be thermally activated and close to the conductivity of 1 ML of Pb on Si(111), it strongly decreases with increasing temperature in directions parallel to steps. The measurements will be correlated with LEED and STM results. O 28.46 Poster Mi 16:00 Bereich C Dependency of the scattering of light by small planar particles on the direction of incidence and polarization •Manuel Gonçalves und Othmar Marti Department of Experimental Physics, University of Ulm, D-89069 Ulm, Germany 16 of 32 07.06.2009 22:14
Physik: DPG Tagungen - Sitzung O 28 http://www.dpg-tagungen.de/archive/2004/o_28.html The scattering of light by small particles has been intensively researched in the last decades. The well known dependencies of the scattering of light on the size, shape, material and environment of the particles reveals the complexity of the problem. Several publications have shown numerical simulations and experimental results demonstrating resonances and local field-enhancements on sub-wavelength particles. Particles of size comparable to the wavelength and of sub-wavelength size, of planar geometry i.e. where the thickness is much smaller than their linear dimensions, are of great interest in photonics. We have investigated planar particles of different shapes by confocal and SNOM microscopy. These particles show interesting dependencies on the direction of the incidence of light, on polarization and on the dielectric constant of the material. We have observed important differences in the scattering patterns for each material, and each relative orientation of the particles with the direction of incidence of the light. O 28.47 Poster Mi 16:00 Bereich C Self-imaging observed on colloid crystals and Fischer projection patterns •Manuel Gonçalves und Othmar Marti Department of Experimental Physics, University of Ulm, D-89069 Ulm, Germany The self-imaging phenomenon in optical systems is known since the Talbot effect was discovered in the 19th century. The Talbot effect is generated by the interference of the incoming light from a diffraction array of apertures of size a that takes place near the array (Fresnel zone). In general, a >> λ. Apertures separated by a distance d, when illuminated by a coherent and plane wave of wavelength λ produce self-images at distances d T = ν 2 d 2 / λ, for ν = 1, 2, ... [1],[2]. We have observed that arrays of colloidal crystals of polystyrene spheres with diameter of few µm produce self-images, at distances of several tenths of µm. The theoretical Talbot length is compared with the measured distances for self-images, for different illumination modes of coherent light. A discussion of the multiple scattering and diffraction of light by a regular array of colloidal particles is introduced and analyzed. [1] K. Patorski, in Prog. Opt. XXVII, Elsevier, 1989. [2] A. Lohmann and J. A. Thomas, Appl. Opt., 29 29, 4337-4340. O 28.48 Poster Mi 16:00 Bereich C Plasma CVD-grown carbon nanotubes studied by field emission •Daniell Malsch 1 , Martin Sveningsson 2 , Eleanor Campbell 2 und Juergen A. Schaefer 1 1 Institut für Physik und Zentrum für Mikro- und Nanotechnologien, TU Ilmenau, P.O. Box 100565, 98684 Ilmenau, Germany 2 Department of Experimental Physics, Gothenburg University and Chalmers University of Technology, 41296 Gothenburg, Sweden Films of carbon nanotubes show an excellent field emission behaviour that allows a wide range of application in field emitting devices. The influence of the different emission parameters has to be investigated in order to improve their performance. We study the field emission of vertically aligned PCVD-grown multiwall carbon nanotubes. A systematic influence of the tube length on the emission current, the light emission, and the surface temperature of the film is found. We also examine blackbody radiation from resistive heating during field emission. This leads, in agreement with light emission behaviour and long-time stability measurements, to a stepwise degradation of the carbon nanotube films. 17 of 32 07.06.2009 22:14
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