X-ray microscopy and spectroscopy

Applications of X-ray nanotomography to materials and biological sciences

Lensless X-ray diffraction microscopy, also called coherent diffraction imaging (CDI) offers extremely high-resolution phase imaging of extended objects. The resolution limits imposed by image-forming optics are avoided and the specific interaction of soft X-rays with matter can be exploited for high elemental or chemical contrast in thick samples.

With our collaborators in the Centre of Excellence for Coherent X-ray Science and at the Advanced Photon Source (USA) we have recently demonstrated tomographic (Fresnel) CDI. Applications of this technique include imaging the ultrastructure of whole unstained biological cells and of the morphology of buried interfaces. In the soft X-ray regime it is particularly important to improve techniques to maximise dose efficiency and for handling noisy diffraction data.

Through the Centre of Excellence for Coherent X-ray Science and the CSIRO we work closely with biologists to develop methods for imaging malaria infectected ethrocytes and yeast cells as models for amyloid beta accumulation. We have recently obtained three-dimensional images of such samples with spatial resolution approaching 50 nm with 2.5 keV X-rays.

With collaborators the ELETTRA Synchrotron Light Laboratory (Italy) we have also demonstrated that comparable resolution with improved intrinsic contrast is possible with X-ray energy in the water-window (between the absorption edges of carbon and oxygen).

Synchrotron instrumentation for X-ray microscopy

 Nanoscale X-ray imaging for materials and biological sciences requires dedicated instrumentation with novel detectors, nanopositioning technology, high bandwidth control systems and very high mechanical and thermal stability control. 

In partnership with the Advanced Photon Source (USA) we have developed an X-ray imaging endstation for various implementations of scanning microscopy and coherent diffractive imaging. We are currently in the progress of relocating the instrument to a dedicated branchline on the SXR beamline at the Australian Synchrotron where it will be further developed for coherent diffractive imaging, scanning transmission microscopy (with phase contrast) and hybrid imaging techniques.

The undulator beamline provides coherent flux of variable polarization in the range 200 eV to 2000 eV, which encompasses the water-window, and is important for biological imaging and absorption edges of the transmission metals.

We are currently developing a multi-axis dynamic stability control system based on laser interferometry. This system will form the basis of the next generation microscope that includes cryogenic sample handling and fast X-ray detectors.

This project is supported by the Australian Research Council (ARC) Centre of Excellence for Coherent X-ray Science and ARC LIEF grants.

Nanomagnetism

Research into the existence, control, and destruction of magnetic order has intensified in recent years following the development of methods to study the evolution of magnetisation on subpicosecond time scales using polarised soft X-rays. Our work addresses the challenge of correlating magnetic structure with three-dimensional morphology of nanostructured systems that are relevant to information storage and sensing applications.

A core part of this work involves modelling nanomagnetic systems and their interaction with coherent, polarised X-ray wavefields. Coherent diffractive imaging with polarised X-rays provides a particularly promising route to understanding magnetisation dynamics due to its potential to deliver very high spatial resolution images in three dimensions, using synchrotron light sources at picosecond time scales. This provides a clear route to femtosecond imaging with X-ray free electron lasers.

Correlated electron pair spectroscopy at surfaces

One of today’s grand challenges for science is to understand the complex correlations and dynamics in the electronic structure of matter and how we can control them. To address this challenge, we investigate electronic structure and correlations at surfaces using two-electron time-coincidence spectroscopy. In one implementation using X-ray excitation, the Auger and photoelectron emitted from the same surface atom are measured, allowing information on the dynamics of electronic excitation and decay to be obtained with exceptional discrimination. 

View Dr van Riessen’s Auger-Photoelectron coincidence spectroscopy page for more information.