A new aberration-corrected, energy-filtered LEEM/PEEM instrument. I. Principles and design

• Published in: Ultramicroscopy Vol. 110; no. 7; pp. 852 - 861
• Main Authors: Tromp, R.M., Hannon, J.B., Ellis, A.W., Wan, W., Berghaus, A., Schaff, O.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.06.2010
• Subjects: Aberration; Aberration correction; Arrays; Dispersions; Lenses; Low energy electron microscopy; Mathematical analysis; Microscopes; Photo electron emission microscopy; Prisms; Resolution; Retrofitting; Low energy electron microscopy; Aberration correction; Photo electron emission microscopy; Resolution
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/j.ultramic.2010.03.005

We describe a new design for an aberration-corrected low energy electron microscope (LEEM) and photo electron emission microscope (PEEM), equipped with an in-line electron energy filter. The chromatic and spherical aberrations of the objective lens are corrected with an electrostatic electron mirror that provides independent control over the chromatic and spherical aberration coefficients C c and C 3, as well as the mirror focal length, to match and correct the aberrations of the objective lens. For LEEM (PEEM) the theoretical resolution is calculated to be ∼1.5 nm (∼4 nm). Unlike previous designs, this instrument makes use of two magnetic prism arrays to guide the electron beam from the sample to the electron mirror, removing chromatic dispersion in front of the mirror by symmetry. The aberration correction optics was retrofitted to an uncorrected instrument with a base resolution of 4.1 nm in LEEM. Initial results in LEEM show an improvement in resolution to ∼2 nm.