Oral Presentation 24th Australian Conference on Microscopy and Microanalysis 2016

High resolution characterization of nanotopography on nonconductive biological surfaces: Comparative study of Helium Ion Microscopy (HIM) and Scanning Electron Microscopy (SEM) (#126)

Chaturanga D Bandara 1 2 , Sanjleena Singh 3 , Peter Hines 3 , Annelena Wolff 3 , Tuquabo Tesfamicheal 1 , Adekunle Oloyede 1
  1. Science and Engineering Faculty, Queensland University of Technology (QUT), Brisbane, QLD 4000, Australia
  2. The Institute of Health and Biomedical Innovation (IHBI), Queensland University of Technology (QUT), Kelvin Grove, QLD 4059, Australia
  3. Central Analytical Research Facility, Queensland University of Technology (QUT), Brisbane, QLD 4000, Australia

Characterization of bactericidal insect wing surfaces 1 2 with minimal processing is essential for the detailed study of bactericidal mechanism by surface topography. Accurate characterisation will lead to production of effective biomimetic surfaces. This requires fast, precise and high resolution data acquisition techniques without damaging the nanotopography of sample surface. Such a process is challenging in Scanning Electron Microscopy (SEM) as sample is non-conductive and electron beam can cause damage to the nanotopography of the wing surface. We investigated the nanotopography of bactericidal dragonfly wing using SEM and Helium Ion Microscopy (HIM) and the results obtained from the two techniques were compared.

SEMs of the dragonfly wing were captured using both variable pressure (VP) mode for uncoated samples and high vacuum mode for gold (10 nm) or chromium (1 nm) coated samples. In the VP mode nanotopology of the wing surface was resolved above 1 kV but the damage caused by the electron beam to the wing topology is evident. Coated thin metal layer reduced the charging effect, showed less beam damage, improved image quality and higher magnification could be achieved compared to VP mode, but different coatings were showing differences in the topography.

The problem of damaging the surface and charging artefacts was successfully resolved by HIM with charge neutralisation by electron flood gun. Investigation of the uncoated wing’s nanotopography using the HIM appeared similar to the Cr coated SEM micrographs but with better overall contrast, depth of field and higher magnification. HIM images show a strong edge effect, which is due to the characteristic scattering dynamics of the ion beam.

The HIM is found to be an important tool to characterise beam sensitive, non-conductive nanotopography of biological samples without metal coating with high precision and causing less beam damage to the surface.

  1. Ivanova, E.P., et al., Bactericidal activity of black silicon. Nat Commun, 2013. 4: p. 2838.
  2. Hasan, J., et al., Selective bactericidal activity of nanopatterned superhydrophobic cicada Psaltoda claripennis wing surfaces. Appl Microbiol Biotechnol, 2012. 97(20): p. 1-6.