Optical layout of a beamline for photoemission microscopy

摘要

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 monochromator and the light is deflected and focused by two toroidal mirrors. A light spot of approx 30#mu#m diameter and a photon energy range from 45 to 160eV has been achieved. The light illuminates the sample in the microscope at grazing incidence and chemical contrast is observed in photoemission. Apart from the standard photoemission mode of operation with synchrotron 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 electrons while working in NEXAFS mode. The obliquely incident soft X-rays cause shadows due to topography on the surface, which allows an estimate of the height of features. Three-dimensional islands give rise to Fresnel diffraction and many fringes may be visible. This effect and its consequences for chemical imaging are discussed.