van Riessen - Experimental condensed matter and materials physics, and coherent X-ray imaging development
Our work focuses on the development of novel methods of probing condensed matter and material properties using coherent X-ray imaging methods, electron spectroscopy, and nanofabricated devices.
A key part of this work is concerned with optimising soft X-ray coherent diffractive imaging and related methods for in situ and in operando study of magnetic and functional materials. This work is supported by a dedicated soft X-ray imaging beamline that our group operates at the Australian Synchrotron, together with close collaboration with researchers at international synchrotron radiation facilities.
We make use of modern methods of numerical simulation and nanofabrication techniques to create advanced X-ray optics and nanostructured materials. We also develop synchrotron instrumentation and high-performance computing methods for reconstructing quantitative images from very large datasets.
Research areas
In situ spectroptychography
We have recently developed high-throughput nanoscale imaging techniques based on the combination of soft X-ray ptychography and X-ray absorption spectroscopy. We aim to exploit the chemical-state sensitivity, high lateral resolution and variable probing depth of the technique to investigate in situ the evolving morphological structure and chemical composition of technologically relevant system.
With local and international partners we have developed electrochemical microreactors using MEMS technology. Our current research is centred on optimising the microreactor for the nanoscale in operando study of energy materials.
Magnetic coherent diffraction imaging
Research in modern magnetic materials with applications in sensor technologies and magnetic storage is largely focussed on thin films with lateral patterning. Outstanding questions concerning the relationship between physical properties and mesoscale phases (spin, charge, lattice) can be addressed by coherent imaging techniques using X-rays resonant with inner-shell atomic transitions.
We use coherent diffractive X-ray imaging to visualise magnetism at the nanoscale. In collaboration with researchers from the Australian Synchrotron and Taiwan Photon Source, we are developing methods for coherent diffractive imaging of magnetic systems in reflection-mode.
Our work in this area draws upon a variety of simulation and experimental methods. We undertake micromagnetic modelling using finite-element methods, fabricate patterned magnetic thin-films, and use novel electron spectroscopy to characterise the films we that we prepare. These methods inform developments of our imaging methods and to provide information that will contribute to an understanding of the physics underlying technologically relevant magnetic systems.
X-ray microscopy instrumentation
Our group develops and operates unique instrumentation at a dedicated branch of the soft X-ray beamline at the Australian Synchrotron. We design and implement instrumentation for sub-nanometer positioning and displacement metrology, specimen micro-environment control, X-ray optics, and advanced X-ray detectors. A key part of this work involves modelling and simulation in order to understand and optimise the performance of bespoke instrumentation.
A key component of our X-ray imaging experiments are the diffractive optical elements that are used to produce a nanofocused X-ray beam. The precision of their fabrication limits the size of the X-ray probe that can be formed while a variety of design and fabrication challenges limit their efficiency. With modern coherent x-ray imaging techniques it is ultimately the efficiency that limits future developments in X-ray microscopy using synchrotron radiation and emerging compact light source technologies. Our research projects in this area focus on the design and fabrication of unconventional kineform diffractive soft X-ray optics for producing nanobeams with exceptionally high efficiency.
Group leader