Design parameters of an unconventional probe-forming lens

Abstract

The design parameters of an electron probe-forming lens with a zero-bore flat-face single pole piece have been considered under nonsaturation conditions. From the measured axial flux density distribution of an experimental single-pole-piece lens, the maximum flux density, the spherical and chromatic aberration coefficients, the focal length and the object position have been investigated in terms of the diameter of the pole's flat face, which is the effective geometrical parameter. Empirical equations relating the geometrical electron-optical parameters have been put forward and compared with those of a different experimental lens reported in the literature. The focal properties of the probe-forming lens have also been investigated in the telescopic mode of operation. The results should be useful for preliminary design considerations of an unconventional electron probe-forming lens with zero-bore flat-face single pole piece for various types of electron-optical instruments according to the operational requirements.