A photoemission microscope with a hemispherical capacitor energy filter B.P. Tonner*, D. Dunham, T. Droubay, M. Pauli Dept. of Physics, University of Wisconsin-Milwaukee, P.O. Box 413, Milwaukee, WI 53201, USA Received 19 June 1996; accepted 29 September 1996 Abstract A purely electrostatic photoemission electron microscope with a bandpass energy filter is described. The electron optics are of a hybrid design, incorporating a high-voltage and high-magnification objective and intermediate lens, coupled to a low- voltage hemispherical capacitor configured as an achromatic imaging bandpass filter. The electron optical system design is described, along with initial performance tests. The instrument is used for both imaging X-ray absorption spectroscopy and photoemission spectroscopy.  1997 Elsevier Science B.V. Keywords: Photoemission; Microscopy; Electron spectroscopy; ESCA; PEEM 1. Introduction There are a number of interesting projects under- way today to improve the spatial resolution of surface- sensitive spectroscopic probes. This is a description of one such project, called PRISM, which stands for paraxial ray imaging spectromicroscope[1]. The latter is a type of spectroscopic emission microscope, which combines some characteristics of a photoemission electron microscope (PEEM) with an electron spec- troscopy for chemical analysis (ESCA) spectrometer. It is intended to be used for two types of spectroscopic imaging, based either on X-ray absorption near-edge spectroscopy (XANES) or on X-ray photoemission or Auger electron spectroscopy (XPS). A specific design requirement for this project was the use of synchrotron radiation sources, which pro- vide high-intensity, focused and tunable soft X-ray photon beams. The tunable X-ray source is necessary for XANES, and gives additional flexibility to a photoemission measurement. There are currently two basic approaches to surface electron spectro- scopic imaging. In one, the incident X-ray beam is focused to a small spot which determines the spatial resolution, and the sample is scanned under this beam while detecting emitted electrons with as high a detec- tion solid angle as possible. An image is built up from a sequential record of intensity at different points taken on the sample. Examples of this approach range from the microzone plate scanning photo- emission microscope (SPEM) of beamline X1-A at NSLS [2], to scanning ESCA instruments using Al Ka radiation [3]. In the second approach, the incident X-ray beam illuminates a larger area on the sample, which sets the maximum field of view. The emitted electrons themselves are used to form a magnified image of the sample surface. In this type of microscope, which includes the PRISM as an example, the entire Journal of Electron Spectroscopy and Related Phenomena 84 (1997) 211–229 0368-2048/97/$17.00  1997 Elsevier Science B.V. All rights reserved PII S0368-2048(97)00005-4 * Corresponding author. Tel.: +1 414 229 4626; fax: +1 414 229 5589; e-mail: tonner@csd.uwm.edu