When X-ray microscopy results are reported a high amount of consideration is given the metric of resolution. Not a single result can be published without indicating the smallest feature size that can be resolved. With a pursuit for resolving ever smaller, and thus thinner, features another metric becomes more and more important, but is so far rarely reported [1,2] : sensitivity, the capability to distinguish between tiny differences in the signal strength.
In the presented work we explore the limits of how little signal can be detected with current setups and approaches. As the demonstration example we chose the hard X-ray ptychographic dichroic signal from 1μm thick Fe/Gd films [3,4] recorded at the NanoMAX beamline [5,6] at MAX IV. The very specific sample was chosen, because the electronic contribution of the homogeneous sample thickness cancels out and the magnetic signal can be arbitrarily small when tuning the probing beams photon energy.
We reliably recovered signals below 1 mrad in relative phase shift, the smallest signals recovered via ptychography reported to date.
Acknowledgments
We acknowledge the MAX IV Laboratory for beamtime on the NanoMAX beamline under proposal 20240988. Research conducted at MAX IV, a Swedish national user facility, is supported by Vetenskapsrådet (Swedish Research Council, VR) under contract 2018-07152, Vinnova (Swedish Governmental Agency for Innovation Systems) under contract 2018-04969 and Formas under contract 2019-02496.
References
[1] Y. Takahashi et al. J. Synchrotron Rad. 30, 989–994 (2023)
[2] N. Okawa et al. Microscopy and Microanalysis 30.5 836-843 (2024)
[3] C. Donnelly et al. Phys. Rev. B 94, 06442 (2016)
[4] J. Neethirajan et al. Phys. Rev. X 14, 031028 (2024)
[5] D. Carbone et al. J. Synchrotron Rad. 29, 876-887 (2022)
[6] U. Johansson et al. J. Synchrotron Rad. 28, 1935-1947 (2021)