Reduction of aberrations in an acceleration lens system to form the gaseous ion nanobeam

Okubo, Takeru; Ishii, Yasuyuki

The acceleration lens system is under development to form a beam diameter of less than 100 nm with a 1 MeV class ion beam. However, chromatic and spherical aberrations are hindrance to form the nanobeam. As used in an optical lens system, a combination of focusing lenses and defocusing lenses can cancel those aberrations. Optics simulations were carried out to show that this aberration cancellation technique is effective to reduce chromatic and spherical aberrations in the acceleration lens system. A deceleration lens which performs like a defocusing lens was added to downstream of the acceleration lens system. As a result, the deceleration energy of 15 keV for the 46 keV hydrogen molecule ion beam reduced the chromatic aberration coefficient by 26% and the spherical aberration coefficient by 17%, and the beam diameter by 17% for the energy spread of 1.5 eV and by 19% for 10 eV.