Simulation of geometrical aberration and beam shape of scanning X-ray probe

The scanning X-ray probe has been investigated for application to small area X-ray photoelectron spectroscopy (XPS). The aberration due to the ellipsoidal shape of the diffractor has been calculated as a function of position in the image plane. We find the magnitude of this aberration goes linearly with the diffractor size and the distance from the optical axis. It also depends on the tilt angles for the source and image planes. A practical scanning ESCA microprobe is, therefore, a compromise between sensitivity (diffractor area) and spatial resolution. We chose a geometry that makes the ellipsoid aberration comparable in magnitude to the source size and the crystal aberration over a 250 μm scan field. Experimentally, we find that the X-ray beam is under 10 μm at the center of the scan field. The experimental result is compared with the simulation and some of the influencing factors to experimental result are discussed in detail.