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Title: Optical column design with liquid metal ion sources

Abstract

We have applied the results of our studies of fundamental properties of liquid metal ion (LMI) sources to the design of an optical system which exploits their unique characteristics. A gun with a beam current regulating system, a three-element asymmetric electrostatic lens, and an einzel lens were incorporated into an optical column with a six-pole electrostatic stigmator and post-lens deflection. A design consideration with LMI sources is that material sputtered from apertures near the source can ''poison'' it, leading to source instability and short life. This problem can be avoided by large source-lens spacing, but we have chosen to place the source close enough to the lens aperture that virtually no ion current strikes it, resulting in stable operation. While close source-lens aperture spacing normally requires an undesirably low (approx.5 kV) voltage on the source to achieve the conditions for ion emission, we have overcome the problem by surrounding the source with a grid (similar to a Wehnelt) maintained near source potential. The shielding action of the grid allows source operation at voltages in the range 15--20 kV with a 2-mm spacing between source and lens aperture. In addition, by biasing the grid with respect to the source, the ionmore » current can be varied while maintaining constant ion beam energy. The beam voltage can then be varied by using the variable voltage properties of the asymmetric lens. A LMI Ga source has been operated with low total current I/sub t/<3 ..mu..A, corresponding to an angular intensity dI/drroughly-equal20 A sr/sup -1/ and a beam energy spread Eroughly-equal5 eV. With a beam energy of 16 keV, 2-nA current was focused into 4000 A at a working distance of roughly-equal80 mm from the final lens.« less

Authors:
;
Publication Date:
Research Org.:
Oregon Graduate Center, 19600 N.W. Walker Road, Beaverton, Oregon 97006
OSTI Identifier:
5971747
Resource Type:
Journal Article
Journal Name:
J. Vac. Sci. Technol.; (United States)
Additional Journal Information:
Journal Volume: 19:4
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ELECTRON GUNS; DESIGN; LIQUID METALS; ION SOURCES; BEAM OPTICS; GALLIUM IONS; KEV RANGE 10-100; OPTICAL SYSTEMS; CHARGED PARTICLES; ELEMENTS; ENERGY RANGE; FLUIDS; IONS; KEV RANGE; LIQUIDS; METALS; 640301* - Atomic, Molecular & Chemical Physics- Beams & their Reactions

Citation Formats

Orloff, J, and Swanson, L W. Optical column design with liquid metal ion sources. United States: N. p., 1981. Web. doi:10.1116/1.571232.
Orloff, J, & Swanson, L W. Optical column design with liquid metal ion sources. United States. doi:10.1116/1.571232.
Orloff, J, and Swanson, L W. Sun . "Optical column design with liquid metal ion sources". United States. doi:10.1116/1.571232.
@article{osti_5971747,
title = {Optical column design with liquid metal ion sources},
author = {Orloff, J and Swanson, L W},
abstractNote = {We have applied the results of our studies of fundamental properties of liquid metal ion (LMI) sources to the design of an optical system which exploits their unique characteristics. A gun with a beam current regulating system, a three-element asymmetric electrostatic lens, and an einzel lens were incorporated into an optical column with a six-pole electrostatic stigmator and post-lens deflection. A design consideration with LMI sources is that material sputtered from apertures near the source can ''poison'' it, leading to source instability and short life. This problem can be avoided by large source-lens spacing, but we have chosen to place the source close enough to the lens aperture that virtually no ion current strikes it, resulting in stable operation. While close source-lens aperture spacing normally requires an undesirably low (approx.5 kV) voltage on the source to achieve the conditions for ion emission, we have overcome the problem by surrounding the source with a grid (similar to a Wehnelt) maintained near source potential. The shielding action of the grid allows source operation at voltages in the range 15--20 kV with a 2-mm spacing between source and lens aperture. In addition, by biasing the grid with respect to the source, the ion current can be varied while maintaining constant ion beam energy. The beam voltage can then be varied by using the variable voltage properties of the asymmetric lens. A LMI Ga source has been operated with low total current I/sub t/<3 ..mu..A, corresponding to an angular intensity dI/drroughly-equal20 A sr/sup -1/ and a beam energy spread Eroughly-equal5 eV. With a beam energy of 16 keV, 2-nA current was focused into 4000 A at a working distance of roughly-equal80 mm from the final lens.},
doi = {10.1116/1.571232},
journal = {J. Vac. Sci. Technol.; (United States)},
number = ,
volume = 19:4,
place = {United States},
year = {1981},
month = {11}
}