MEX µProbe (µMEX)

The terminal endstation on the MEX1 beamline is a scanning X-ray fluorescence (XRF) µProbe, termed µMEX.

Scanning XRF µProbes provide element-specific mapping of the distributions and associations between elements within heterogeneous, structured, and even dynamic systems. Measurements are usually minimally destructive and (often) require little in the way of specific sample preparation.

The figure below highlights the types of chemical detail that scanning µProbe XRF can reveal;

Figure 2 | Distribution of elements with nematodes. The greyscale image on the left shows the ultrastructure of two freeze-dried adult C. elegans. The image on the right displays the distribution of calcium, manganese and copper within the same animals. These animals were placed on a silicon nitride window before being snap-frozen and desiccated.

Image courtesy of Dr Gawain McColl - The Florey - and Dr Simon James - ANSTO. These data were collected at Australian Synchrotron's XFM beamline.

Alongside XRF mapping, µMEX will offer X-ray microspectroscopy capabilities throughout an energy range (~2.1 – 13.6 keV) and with a spatial resolution unique within the facility and uncommon worldwide. The instrument design enables studies of a wide range of elements and edges, including K-edges of first-row transition metals and s-block elements like sulfur, L-edges for rare earth elements and M-edges for high Z elements like lead and uranium. Though the primary analytical purpose of µMEX is X-ray microspectroscopy, access to energies below 5 keV makes this instrument useful for mapping the distribution of low Z species like chlorine or phosphorous.

Figure 2 | Distribution of copper within adherent cells. A) Map of copper distribution in cells treated with Cu(II)Cl₂. These cells were grown on a silicon nitride window and snap-frozen in place by a 100 K N₂ gas stream. B) Mapping the same region of the sample at different incident energies allows the speciation of copper within the cells to be estimated. Here, we observed a mixture of cuprous and cupric copper.

Image courtesy of Dr Alejandra Ramirez Munoz, Dr Carlos Opazo, Prof Ashley Bush - The Florey - and Dr Simon James - ANSTO. These data were collected at Australian Synchrotron's XFM beamline.

µMEX sits alongside existing (XFM) and planned (NANO) scanning XRF µProbes available at the Australian Synchrotron. The figure below provides a view of how the different capabilities of these instruments complement each other.

µMEX has been installed at the MEX1 beamline (Sept 2023). Updates will (slowly) appear as we commission the instrument.

For those curious about what EXAFS can tell you about your sample, here is a series of complicated plots ;)

The data above all come from a thin metallic copper foil measured at the MEX1 beamline. Many excellent papers/textbooks describe EXAFSs in detail, so that we won't get into it here. Briefly, the leftmost column shows the types of plots one may encounter in the literature. These data summarise how a photo-electron scatters off the neighbouring atoms and, in the process, reveals the chemical environment of the absorbing atom in atomic detail. The rightmost column (attempts) to show how the multitude of scattering paths available to the ejected photo-electron contribute (sum) to the total signal. Ultimately, we hope to collect these data types from tiny regions of natural samples courtesy of µMEX’s microfocussed beam of X-rays.