Compound refractive lenses (CRLs) have been widely used for more than 20 years on leading synchrotrons and free-electron lasers for hard X-ray beam transport, collimation and focusing [1-2]. The combination of coherent compatible optics and new coherent sources increased opportunities for the development of new research methods.
In this abstract, we demonstrate a new X-ray interferometer based on compound refractive optics (CRL) for thin-film structures study . The idea of a reflecto-interferometer is to use a very simplified experimental setup, where a coherent monochromatic X-ray beam, focused by CRL, impinges on a thin film at a grazing angle. This converging fan of radiation incoming on a sample surface provides a range of grazing angles. For each grazing angle, the rays reflected from the front and rear boundaries of the film will interfere, and as a result, the diffracted intensity in the range of exit angles equal to the angular range of the incident fan will generate an interference pattern representing fringes of equal inclination. The capabilities of the new reflecto-interferometer were demonstrated at the ESRF ID06 beamline using X-rays from 10 to 20 keV. The Si3N4 membranes of thicknesses in the range from 100 to 1000 nm were studied. Experimentally obtained reflecto-interferograms correspond well with calculated ones, and the distance between fringes correspond to the thickness of the tested membranes. While the interference pattern in rather wide angular range is recorded in one shot, the proposed approach has a very good temporal resolution, which is limited to a few milliseconds, depending on the X-ray flux and the sensitivity of the detector. The high spatial resolution of the interferometer was demonstrated on interferograms recorded from an 8 nm-thick gold strip deposited on an Si3N4 membrane. It was shown that the interference pattern is very sensitive even to small deviations in the thickness of the layer.
In addition, this reflecto-interferometer can be easily adapted for use with the MetalJet Excillium micro-focus laboratory source, which has GaKα emission line at 9.25 keV. As a result, a series of interference patterns for test sample - free-standing thin-film membrane thick of 500 um were observed.
The new X-ray reflecto-interferometer opens a wide range of opportunities for the analysis of thin-film and multilayer systems. The recording of the interference pattern in a single shot allows a fast in-situ analysis of solid and liquid materials including organic and biological ﬁlms. The proposed method has significant advantages compared to classical X-ray reflectometry, providing information on the thickness and density of layers or structures in real time which allows research with a fundamentally new spatial and temporal resolution.
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- Lyatun, S., et al. Journal of synchrotron radiation 26.5 (2019).