Departmental Seminar

Exploring ion tracks and nanopores using small angle X-ray scattering

Mr Shankar Dutt
PhD Candidate, Materials Physics, ANU

When high-energy ions penetrate organic or inorganic materials, they can create ion tracks, which are narrow and long damage trails. These tracks are often highly susceptible to chemical etching, which can be used to fabricate nanopores with extremely narrow size distributions. To fully comprehend the irradiation damage process and how tracks can be used to engineer nanopores, understanding the track structure and its dependence on ion irradiation parameters and material composition is crucial.

Small angle X-ray scattering (SAXS) is a powerful and non-destructive technique for investigating the structure of ion tracks and nanopores in various organic and inorganic materials. The technique provides highly precise measurements and is a statistically reliable as measured scattering intensities arise from hundreds of thousands of ion tracks or nanopores. In this presentation, I will showcase recent research conducted by our group using synchrotron-based SAXS to explore the morphology of ion tracks and track-etched nanopores. I will discuss new SAXS analysis procedures for characterizing ion tracks in polymers such as polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), and polymethyl methacrylate (PMMA). Furthermore, the dependence of the ion track structure on the concentration of antioxidants in polypropylene foils will also be discussed.

For over 40 years, researchers have noted that trac k-etched nanopores in PC can have a tapered structure towards their surfaces, but the quantification of this shape has remained challenging due to inherent difficulty of imaging nanopores using microscopy methods. I will discuss how using SAXS, we were able to quantitatively measure the structure of these high aspect-ratio nanopores and solve a four-decade old problem.

Lastly, I will also address the characterization of conical-shaped nanopores in freestanding silicon dioxide (SiO 2 ) membranes. Our team has developed innovative fabrication techniques that allow us to produce conical nanopores with lengths between approximately 50 and 3000 nm, featuring pore opening angles ranging from about 3 to 110 degrees. These conical nanopores offer various intriguing applications, such as biosensing for DNA and protein sensing, as well as charge-based protein separation. During the talk, I will explore various strategies for fitting SAXS data and hence characterising the nanopores in these membranes.

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