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Soft X-ray microscopy at a spatial resolution better than 15 nm

Abstract

Analytical tools that have spatial resolution at the nanometre scale are indispensable for the life and physical sciences. It is desirable that these tools also permit elemental and chemical identification on a scale of 10 nm or less, with large penetration depths. A variety of techniques1,2,3,4,5,6,7 in X-ray imaging are currently being developed that may provide these combined capabilities. Here we report the achievement of sub-15-nm spatial resolution with a soft X-ray microscope—and a clear path to below 10 nm—using an overlay technique for zone plate fabrication. The microscope covers a spectral range from a photon energy of 250 eV (5 nm wavelength) to 1.8 keV (0.7 nm), so that primary K and L atomic resonances of elements such as C, N, O, Al, Ti, Fe, Co and Ni can be probed. This X-ray microscopy technique is therefore suitable for a wide range of studies: biological imaging in the water window8,9; studies of wet environmental samples10,11; studies of magnetic nanostructures with both elemental and spin-orbit sensitivity12,13,14; studies that require viewing through thin windows, coatings or substrates (such as buried electronic devices in a silicon chip15); and three-dimensional imaging of cryogenically fixed biological cells9,16.

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Figure 1: A diagram of the soft X-ray microscope XM-1.
Figure 2: An illustration of the overlay nanofabrication technique for micro zone plate fabrication.
Figure 3: Scanning electron micrograph of a zone plate with 15 nm outermost zone.
Figure 4: Soft X-ray images of 15.1 nm and 19.5 nm half-period test objects, as formed with zone plates having outer zone widths of 25 nm and 15 nm.
Figure 5: The calculated modulation transfer functions of the microscope with two different zone plates.

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Acknowledgements

The authors acknowledge financial support from the National Science Foundation's Engineering Research Centre Program, the Department of Energy's Office of Science, Office of Basic Energy Sciences, and the Defense Advanced Research Projects Agency.

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Correspondence to Weilun Chao.

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Chao, W., Harteneck, B., Liddle, J. et al. Soft X-ray microscopy at a spatial resolution better than 15 nm. Nature 435, 1210–1213 (2005). https://doi.org/10.1038/nature03719

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