Optical layout of a beamline for photoemission microscopy

An optical layout for performing photoemission microscopy using synchrotron light from the storage ring Elettra is described. The microscope, property of the Technical University of Clausthal, was installed on an existing mon ochromator and the light is deflected and focused by two toroidal mirrors. A light spot of similar to 30 mu m diameter and a photon energy range from 45 to 160 eV has been achieved. The light illuminates the sample in the mic roscope at grazing incidence and chemical contrast is observed in photoemis sion. Apart from the standard photoemission mode of operation with synchrot ron radiation, surface NEXAFS spectra from microspot areas can be measured, and an example is shown. Images can also be obtained with variable kinetic energies (and therefore variable surface sensitivity) of the secondary ele ctrons while working in NEXAFS mode. The obliquely incident soft X-rays cau se shadows due to topography on the surface, which allows an estimate of th e height of features. Three-dimensional islands give rise to Fresnel diffra ction and many fringes may be visible. This effect and its consequences for chemical imaging are discussed.