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In the OPINCHARGE Scientific Publications series, we highlight research that advances the methods used to understand materials and interfaces at increasingly small scales. This study explores how X-ray nanobeams can be used to analyse micrometre-sized surface areas, opening new possibilities for highly localised material characterisation.
The publication “X-ray reflectivity from micrometre-scaled surfaces using nanobeams” was authored by Vedran Vonk, Steffen Tober, Steven J. Leake, Breno Rabelo Coutinho Saraiva, Lisa Randolph, Arti Dangwal Pandey, Thomas F. Keller, Hans-Georg Steinrück and Andreas Stierle from DESY, Forschungszentrum Jülich, ESRF, RWTH Aachen University and the University of Hamburg.
Read the publication: https://zenodo.org/records/19908902
X-ray reflectivity (XRR) is a powerful technique for investigating the structure of surfaces and interfaces. It can provide information about properties such as the thickness and density of thin films and multilayers.
Conventionally, however, XRR measurements analyse relatively large surface areas. This can become a limitation when studying heterogeneous materials, because important local differences may be averaged out.
Using highly focused X-ray beams offers a way to overcome this limitation and investigate much smaller individual regions.
Working with nanometre-sized X-ray beams brings a major practical challenge: keeping the exact area of interest inside the beam during the measurement.
In an XRR experiment, both the sample and detector move as the angle changes. Even very small alignment errors or mechanical movements can therefore cause a microscopic target area to move out of the beam.
The researchers developed an alignment approach that compensates for this movement by combining changes in the angle of incidence, detector angle and sample position. This allows the same small area of the surface to remain illuminated throughout the reflectivity measurement.
To demonstrate the approach, the team fabricated microscopic gold islands on a silicon substrate and performed measurements at the European Synchrotron Radiation Facility (ESRF).
A 90 nm X-ray beam was used to investigate structures as small as 10 × 10 µm. The strong contrast between gold and silicon allowed the researchers to accurately track the position of the selected island and keep it inside the beam as the measurement geometry changed.
Using the developed trajectory-based approach, the researchers successfully obtained X-ray reflectivity data from the microscopic gold island.
The analysis determined an island thickness of approximately 8 nm, close to its targeted value of around 10 nm, while the measured density was also consistent with dense bulk gold.
Overall, the method enabled reliable local information about overlayer thickness and density with a lateral resolution of around 10 µm.
Many advanced materials are not perfectly uniform. Their properties can vary between individual grains, interfaces or microscopic surface regions.
Being able to perform X-ray reflectivity on such small areas makes it possible to investigate these local variations instead of averaging them across a much larger surface.
The approach could therefore support future experiments on heterogeneous and polycrystalline materials, including surface grain mapping and increasingly localised studies of material interfaces.
As energy technologies become more sophisticated, understanding materials at smaller spatial scales becomes increasingly important.
By demonstrating how nanometre-sized X-ray beams can be reliably positioned on microscopic surface structures during XRR measurements, this OPINCHARGE-supported research provides a valuable methodological step towards more precise and spatially resolved characterisation of advanced materials and interfaces.
