Low-energy foil aberration corrector

• Published in: Ultramicroscopy 2002-12, Vol.93 (3), p.321-330
• Main Authors: van Aken, R.H, Hagen, C.W, Barth, J.E, Kruit, P
• Format: Article
• Language: English
• Subjects: Aberration correction; Aberrations; Beam optics; Chromatic aberration; Chromatic and geometrical aberrations; Electromagnetism; electron and ion optics; Electron, positron and ion microscopes, electron diffractometers and related techniques; Exact sciences and technology; Foil; Fundamental areas of phenomenology (including applications); Geometrical optics; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Optics; Other topics in electromagnetism; electron and ion optics; Physics; Spherical aberration
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/S0304-3991(02)00287-5

A spherical and chromatic aberration corrector for electron microscopes is proposed, consisting of a thin foil sandwiched between two apertures. The electrons are retarded at the foil to almost zero energy, so that they can travel ballistically through the foil. It is shown that such a low-voltage corrector has a negative spherical aberration for not too large distances between aperture and foil, as well as a negative chromatic aberration. For various distances the third- and fifth-order spherical aberration coefficients and the first- and second-order chromatic aberration coefficients are calculated using ray tracing. Provided that the foils have sufficient electron transmission the corrector is able to correct the third-order spherical aberration and the first-order chromatic aberration of a typical low-voltage scanning electron microscope. Preliminary results show that the fifth-order spherical aberration and the second-order chromatic aberration can be kept sufficiently low.