Ratio-contrast imaging of dual-energy absorption for element mapping with a scanning transmission X-ray microscope

Abstract

The detection of chemical mapping with a spatial resolution of 30 nm has been achieved with a scanning transmission X-ray microscope at the Shanghai Synchrotron Radiation Facility. For each specimen, two absorption images were scanned separately with energies E1 and E2: E1 was focused on the absorption edge of the chosen element and E2 was focused below the edge. A K-edge division method is proposed and applied to obtain the element mapping. Compared with the frequently used K-edge subtraction method, this ratio-contrast method is shown to be more accurate and sensitive in identifying the elements of interest, where the definition of the contrast threshold is simple and clear in physics. Several examples are presented to illustrate the effectiveness of the method. © 2010 International Union of Crystallography.