Distinguished Speakers Series presents Dr. Harry J. Whitlow: MeV ion microprobes for study of radiation damage

Distinguished Speakers Series

MeV ion microprobes for study of radiation damage
by Dr. Harry J. Whitlow, Uppsala University, Sweden

Friday, October 18, 2024
10:30 AM - 11:30 AM
Room 306 McLaughlin Hall

MeV ion microprobes have a long history in the study of the interactions of energetic ions with materials. Regularly, μm-sized beams can be obtained. These have been widely employed in ion beam analysis e.g. Particle Induced X-Ray Emission (PIXE) imaging. Today, for some special cases super-resolutions of a few nm have been demonstrated. Ion beam modification studies with microprobes generally exploit the extremely high fluxes attainable, for spatial writing of radiation damage in different classes of materials.

This presentation discusses some applications and potential applications of MeV ion microprobes for different aspects of radiation damage studies. What is especially useful is the high fluxes (>1015 ions cm–2 s–1) of MeV ions that can be directed into a small area (~1 μm x 1 μm) leaving surrounding areas pristine. Apart from using the radiation damage as the basis of ion beam lithography aka proton beam writing, the microprobe lens system can be utilised to perform broad beam irradiation with extremely low uniform fluxes in the range 105 – 1010 ions cm–2s–1. The latter is useful for radiation biomedicine as these fluxes correspond to absorbed dose rates in the range 10 mGy s-1. This enables studies of tissue damage and the onset acute radiation syndrome (~10 mGy) and also higher absorbed doses which are important in Ion Beam Cancer Therapy (IBCT).

Space charged-particle and neutron irradiation effects in low earth orbits and long-duration lunar and interplanetary missions are a serious problem. Energetic GeV particles (such as 56Fe ) cause soft-upsets in Metal Oxide Semiconductor (MOS) devices which are detrimental to spacecraft control and data integrity. However, low energy (<200 MeV) protons are about 104 times more abundant and damage bipolar devices, such as power switches and photovoltaic panels, as well as optical coatings as those used on camera lenses.

Hydrogen is the most abundant element and as a constituent of water plays a major role in corrosion, particularly in radiation environments where both electrolysis and radiolysis take place. The ubiquitousness of hydrogen makes it hard to analyse by e.g. mass spectroscopic methods due to contamination signals. Recently, we have developed Off-axis Scanning Transmission Ion Microscopy (OA-STIM) to quantitatively map H concentrations in self-supporting thin films (such as used in electron microscopy). This was developed for measuring C, H, N and O in biological tissue sections. However, the method is quite general and can be applied to measure and map hydrogen contents of e.g. ceramics and/or metal samples.

Speaker profile: 

Harry J. Whitlow (HJW) was born in London, UK in 1954 and was educated in the UK. HJW holds a BSc (hons) and DSc degrees from the University of Bath UK, a MSc from the CNAA and a DPhil from the University of Sussex. He is a docent at the Royal Institute of Technology (KTH) in Stockholm, Sweden.

HJW’s highly international career started as a postdoc at the University of Aarhus Denmark. It includes periods working at the Universities of Helsinki and Jyväskylä in Finland, Uppsala, KTH and Malmö universities in Sweden, Haute Ecole Arc Ingénierie, University of Applied Sciences of Western Switzerland and University of Louisiana at Lafayette USA and the University of Oslo.

HJW was appointed to professorships in Lund University in 2000, Jyväskylä in 2004 and Lafayette in 2016. Today, he holds adjunct professorships at Uppsala University Sweden and Kasetsart University in Thailand and is a guest researcher in Oslo University, Norway. He has supervised 13 PhD students, his scientific production approaches 300 publications. His notable research contributions cover a wide range of topics and include surface segregation during sputtering, Monte Carlo and Molecular dynamics studies of collision cascade anisotropies, Multi-dispersive ToF-E elastic recoil detection analysis, stopping measurements, Programable proximity aperture lithography, low flux irradiation with MeV ion microprobes and more recently a quantitative microprobe method for measuring ex-vivo trace element molarity is biomedical tissues.