Maximum: A scanning photoelectron microscope at Aladdin

Abstract

The recent successful installation of the 30-period undulator on Aladdin, the 1 GeV electron storage ring at the Synchrotron Radiation Center of the University of Wisconsin, opens new possibilities for photoelectron spectroscopy. In particular, the high brightness of the machine, together with innovative optics, make possible the application of photoelectron spectroscopy to high-resolution soft X-ray microscopy. We call this system MAXIMUM (for Multiple Application X-ray IMaging Undulator Microscope). The proposed optical system will have a lateral resolution of better than 1000 Å and a resolving power of better than 200 at 100 eV. After monochromatization, the radiation will be focused on a pinhole that can range in diameter from 1 to 100 μm, and will be prepared by lithographic techniques on a thin nickel film. The image of the pinhole, suitably demagnified, will be relayed to the sample. The image resolution and magnification can be adjusted by changing the pinhole size and the scanning step. A Schwartzschild objective can produce a demagnified image of the pinhole which is diffraction limited even at a wavelength of 40 Å. At 100 Å and at a numerical aperture of 0.2, the objective can produce a 250 Å diameter spot. High flux will be achieved with a Mo-Si multilayer coating, for which preliminary experiments have demonstrated reflectivities near 40% at normal incidence. Other focusing elements (Fresnel zone plates and Kirkpatrick-Baez objectives) will also be implemented.