title: Spherical aberration correction with threefold symmetric line currents.
abstract: It has been shown that N-fold symmetric line current (henceforth denoted as N-SYLC) produces 2N-pole magnetic fields. In this paper, a threefold symmetric line current (N3-SYLC in short) is proposed for correcting 3rd order spherical aberration of round lenses. N3-SYLC can be realized without using magnetic materials, which makes it free of the problems of hysteresis, inhomogeneity and saturation. We investigate theoretically the basic properties of an N3-SYLC configuration which can in principle be realized by simple wires. By optimizing the parameters of a system with beam energy of 5.5keV, the required excitation current for correcting 3rd order spherical aberration coefficient of 400 mm is less than 1AT, and the residual higher order aberrations can be kept sufficiently small to obtain beam size of less than 1 nm for initial slopes up to 5 mrad.
authors.affiliation: Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan; Hitachi High-Technologies Corporation, 882, Ichige, Hitachinaka, Ibaraki 312-8504, Japan.
authors.forename: Shahedul
authors.initials: S
authors.lastname: Hoque
authors.affiliation: Hitachi High-Technologies Corporation, 882, Ichige, Hitachinaka, Ibaraki 312-8504, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ito
authors.affiliation: Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
authors.forename: Ryuji
authors.initials: R
authors.lastname: Nishi
authors.affiliation: Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
authors.forename: Akio
authors.initials: A
authors.lastname: Takaoka
authors.affiliation: Munro's Electron Beam Software Ltd., 14 Cornwall Gardens, London SW7 4AN, UK.
authors.forename: Eric
authors.initials: E
authors.lastname: Munro
keywords: Aberration correction; Hexapole corrector; Magnetic multipole; N-fold symmetric line current; Sextupole corrector; Spherical aberration