EVALUATION OF ABERRATION COEFFICIENTS OF PRACTICAL ELECTROSTATIC LENSES FOR X-RAY-ABSORPTION MICRO-SPECTROSCOPY AND IMAGING

A new design of electrostatic optics has been evaluated to improve the performance of the X-ray photoemission microscope (XPEEM) used for micro X-ray-absorption fine-structure imaging. The new optics includes an objective lens with a steep conical shape to allow a larger angle of incidence of the X-ray beam than was possible in the previous design. The objective and projective lenses were designed using the principles outlined by Rempfer, and interpolated from these earlier published tables to meet the design objectives of an energy-filtered XPEEM. These lenses were fabricated with materials compatible with ultrahigh vacuum. The lenses were subsequently evaluated in an electron-optical bench to determine the first-order focussing properties and the spherical and chromatic aberration coefficients. We find that the conically-shaped objective lens has measured aberrations that agree well with the predicted values. The measured aberrations show that the electrostatic objective will contribute less than 10 nm to the resolution limit of an energy-filtered microscope with 1.0 eV electron bandwidth.