Optical column design with liquid metal ion sources
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.
- Research Organization:
- Oregon Graduate Center, 19600 N.W. Walker Road, Beaverton, Oregon 97006
- OSTI ID:
- 5971747
- Journal Information:
- J. Vac. Sci. Technol.; (United States), Vol. 19:4
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
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