High-resolution microscopy - marriage of lenseless imaging and X-ray nano beam technology

Scanning diffraction microscopy, or ptychography, was first developed for the scanning transmission electron microscope (STEM). In the same way, by using an X-ray nano beam, one can use a STXM. The X-ray beam is focused onto the sample via a lens, and the transmission is measured. The image is obtained by plotting the transmission as a function of the sample position, as it is rastered across the beam. The analysis is straightforward, but its resolution is limited by the beam size. On the other hand, coherent diffractive imaging (CDI) now reaches resolutions below 10 nm, but the reconstruction procedures are not always easy due to the influences of data quality, sample conditions etc. A Swiss research group led by Drs. C. David and F. Pfeiffer (Paul Scherrer Institut) recently demonstrated a ptychographic imaging method that bridges the gap between STXM and CDI by measuring complete diffraction patterns at each point of a STXM scan. The group employed an advanced large-area pixel detector, Pilatus, to obtain the diffraction pattern efficiently. These diffraction data were then treated with an image reconstruction algorithm developed by the team. Several tens of thousands of diffraction images were processed to obtain one super-resolution X-ray image. The algorithm not only reconstructs the sample but also the exact shape of the light probe resulting from the X-ray beam. The 6.8 keV X-ray beam was focused using a zone plate, and the beam size was 300 nm. The spatial resolution achieved was about five times higher. For more information, see the paper, "High-Resolution Scanning X-ray Diffraction Microscopy", P. Thibault et al., Science, 321, 379 - 382 (2008).