"Simulation of A Mirror Corrector for PEEM3"

W. Wan, J. Feng, H. A. Padmore and D. S. Robin


A third generation aberration-corrected photoemission electron
microscope (PEEM3) is being designed at the Advanced Light Source. 
An electron mirror is used for the correction of the lowest order 
spherical and chromatic aberrations. Two very different methods, 
one using finite-element method and ray-tracing technique and the 
other using charge ring method and differential algebra (DA) technique, 
have been employed to simulate the electrostatic field and the behavior 
of the electron beam. Good agreement has been obtained between the two 
methods and a tetrode mirror has been found to effectively correct the
spherical and chromatic aberrations. Operating at 20 kV, the point
resolution for 100% transmission reaches 50 nm with the mirror corrector, 
a significant reduction from that of 440 nm without correction. 
The highest resolution achieved is 4 nm at 2% transmission, as opposed 
to 20 nm at 1% transmission without correction.