STXM 5.3.2 User Manual
In Scanning Transmission X-ray Microscopy (STXM) a micro focused soft x-ray beam is generated by a zone plate, illuminates the sample and the transmitted x-rays are detected. Transmission images are obtained by a raster scan of the sample. Spectra are obtained in point, line or image mode by acquiring signal at multiple photon energies. The 5.3.2STXM is an interferometrically controlled device mounted on a dedicated bending magnet beamline. The user controls both the beamline and the microscope from a single computer.
The primary signal measured in STXM is transmitted intensity (I) as a function of energy (spectra), or position (images). This signal, when converted to optical density (OD), is sensitive to sample thickness, density and composition, according to the following equation. (Io: incident photon flux intensity) where σ is the linear absorption coefficient, t is the thickness, µ is the mass absorption coefficient and ρ is the density. The useful range of OD is from 0.1 to 3. If there is too little absorption (sample too thin) the signal is lost in the noise. If the absorption is too great, then various artifacts dominate the observed signal, which is no longer quantitative. For organic material with a density of 1 samples need to be between 50 and 300 nm. At higher energy edges or lower density samples, somewhat thicker samples are optimum.
Measuring a raster scanned set of pixels and converting with the incident flux (measured through a hole), gives an x-ray OD image at a single photon energy. Changing the photon energy and taking images with other photon energies gives an image sequence (stack), which includes chemical information as well as topographical information. Analyzing the data with suitable reference model spectra can provide chemical maps with sub-100 nm spatial resolution.
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