96. Scanning Transmission X-Ray Microscopy

Scanning transmission X-ray microscopy (STXM) is a method to obtain a microscopic image of the raster-scanned sample by detecting the transmission intensity of the focused X-rays. As drawn in Fig. 96.1, a Fresnel zone plate (FZP) is often used to focus the soft X-rays from the synchrotron radiation sources (Attwood in Soft X-rays and Extreme Ultraviolet Radiation: Principles and Applications. Cambridge University Press, 1999 [1]). An order-sorting aperture (OSA) is used to omit the zeroth and higher order diffractions. The photon energy can be tuned around the absorption edge of a specific element. The spatial resolution, i.e. the focusing size of the X-rays in the soft X-ray STXM is typically 20–100 nm. It is in principle determined by the diffraction limit of the lithographically fabricated FZPs (Attwood in Soft X-rays and Extreme Ultraviolet Radiation: Principles and Applications. Cambridge University Press, 1999 [1]). The most important measurement mode in the STXM is an “image stack,” that is, a number of images at different photon energy points to obtain a dataset with space (XY) plus energy (E) dimensions. From the dataset, one can obtain a local spectrum to analyze the near-edge X-ray absorption fine structure (NEXAFS).