Eigenschaften von Silber-Nanodrähten

  • Properties of silver-nanowires

Wagner, Dieter; Kreibig, Uwe (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2008)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2008

Abstract

This thesis treats the preparation and properties of silver-nanowires. It is divided into four parts:1) Preparation and determination of the atomic structure and shape of the wires.A chemical reduction method was applied to produce silver-nanowires in an aqueous electrolyte. The thickness of produced wires proved to be constant over the whole length. The thickness distribution in the ensemble varied around a maximum at about 27 nm, the lengths extended in the experiments up to more than 100 µm. There was no correlation between thickness and length. The thinnest wires were of about 5 nm thickness. The cristalline structure was analysed by Dr. A. Graff (Uni Halle) with HRTEM diffraction. The wires consist of 5 triangular single-crystalline filaments, connected by (111) twin-boundaries. So the cross-section of the wires is pentagonal. The surfaces are atomically smooth. A statistically varying curvature of the wires was observed, which points to strains created by an angle defect in the pentagonal structure.2) Observation of the nanowires by optical darkfield microscopy, and, for comparison, by SEM and TEM. Selection of single, isolated wires was successful by micro-manipulation. The wires were either deposited on quartz glass substrates or they were prepared as free wires which were fixed only at their end-tips.3) Measurement of emission spectra of the scattered light from single nanowires and parts of them in dark-field Zsigmondy-Siedentopf configuration. Experimental results were presented as depending on linear polarisation of the light incident on the wire. The spectrometer, based upon a darkfield microscope, was constructed to measure the optical emission of single wires. Two peaks appeared in the optical emission spectra. The first is at about 440 nm. It was assumed to be due to a localized plasmon-polariton excitation with the electric field normal to the wire axis. It could be reproduced by simulation calculations of Dr. M. Quinten, for normal polarisation of the incident light. Another, broad, peak was observed at 650nm when the incident light was polarised parallel to the wire axis, which was asigned to longitudinal, extending plasma waves.4) Application of the silver-nanowire as plasmonic conductor. In collaboration with the group of Prof. F. Aussenegg and Prof. J. Krenn at the University of Graz, the propagation of plasma waves excited locally at one end-tip, was identified and their propagation length determined by two different experiments. This proved the plasmon propagation in silver-nanowires to be well suited for information transport on the µm-scale.

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