Oral Presentation 26th ACMM “2020 Visions in Microscopy”

Focused Ion Beams in Biology: How the Helium Ion Microscope and FIB/SEMs Help Reveal Nature’s Tiniest Structures (#60)

Annalena Wolff 1 , Nico Klingner 2 , William Thompson 3 , Yinghong Zhou 4 , Jinying Lin 5 , Yong Peng 6 , John Ramshaw 7 , Yin Xiao 4
  1. Central Analytical Research Facility, Queensland University of Technology (QUT), Brisbane, QLD, Australia
  2. Ion Beam Center, Helmholtz-Zentrum Dresden-Rossendorf (HZDR), Dresden, Germany
  3. Heelionics LLC, Los Altos, CA, USA
  4. Institute of Health and Biomedical Innovation, Queensland University of Technology (QUT), Brisbane, QLD, Australia
  5. Department of Implantology, Xiamen Stomatological Research Institute, Xiamen Stomatological Hospital, Fujian, China
  6. Manufacturing, CSIRO , Bayview Avenue Clayton, Victoria, Australia
  7. Manufacturing, CSIRO, Clayton, VIC, Australia

Focused Ion Beams (FIB) such as the Helium Ion Microscope (HIM) as well as FIB/SEMs have sparked great interest within the biological sciences in recent years. The HIM allows high resolution imaging of uncoated non-conductive samples while the FIB/SEM allows to prepare TEM lamellae, 3D reconstruct the sample or reveal sub surface structures with nanometre precision. Yet, FIB/SEMs have not been established as a “go to” tool in the biological sciences. This is predominantly due to the heat-induced damage from the ion beam when processing soft materials including biological samples.

 This presentation shows how the HIM as well as FIB/SEMs can be used to reveal nature’s tiniest structures. The presented work then focuses on sample heating induced by ion beams. SRIM and COMSOL simulations as well as numerical modelling methods and a basic and a model, based on the physical principles of Fourier’s law of conductive heat transfer, were used to obtain theoretical results which permit to estimate the ion beam induced temperature increases. The results suggests that the ion beam induced increase in temperature can be reduced by:

  1. Reducing the local dose rate (smaller aperture/ion beam current)
  2. Reducing the local dose (smaller aperture/ion beam current, introducing beam blur, reducing the beam overlap)
  3. Using lower beam energies in combination with higher local dose rates to increase processing speed

The technique was tested on collagen, a soft biological material which is commonly used in biomedical applications. Collagen was chosen as a suitable test sample as it loses its fibrillary structure when denaturated by heat, permitting damage to easily be recognized. A TEM comparison of a microtome prepared lamella and the FIB prepared lamellae shows that the fibrillar structures can be maintained, and heat damage avoided when using suitable parameters.