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Lecture

High resolution FIB nanotomography of nanoporous Au nanoparticles

Thursday (27.09.2018)
10:15 - 10:30 S1/01 - A04
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Individual nanoporous Au nanoparticles which were fabricated by solid state dewetting by annealing of Ag-Au-bilayers on Si/SiO2 substrates and subsequent dealloying in HNO3 are reconstructed from SEM images captured by FIB nano tomography. The investigated particles have diameters in the range of a few hundred nanometers and ligament diameters around 12 nm. For the resolution of single ligaments in radial direction, the slicing is performed with a step size of 2 nm. Two different materials, C and Cr, were used as first layer of the protective film on top of the sliced particles. The choice of that material contacting the particle has significant influence on the analyzability of captured images. Ligaments in the background could be separated from those in the image plane from in-lens secondary electron images. From the 3D reconstructed particles the Au volume fraction is calculated and compared with the volume ratio of the bilayers and the shrinkage observed during the dealloying process. The specific internal surface area computed from the 3D data is approximately 12 m²/g, which matches well results from TEM tomography and electrochemical measurements of the internal active surface area of nanoporous Au with similar geometries. Furthermore, ligament diameter distributions and network properties such as the number of branches and junctions are derived. One of the biggest challenges at the limits of resolution to be considered is the large influence of the image segmentation parameters on quantitative results computed from the three dimensional reconstruction. Another one is the deviation of the actually milled slice spacing from the nominal spacing. Therefore, results from measurements with and without additional surface structures for a subsequent determination of the actual step sizes are compared.

Speaker:
Hauke Honig
Technische Universität Ilmenau
Additional Authors:
  • Prof. Dr. Peter Schaaf
    Technische Universität Ilmenau
  • Dr. Dong Wang
    Technische Universität Ilmenau