Sputtering yields of metal ion beams on polycrystalline films for energies below 1 keV were measured in situ using crystal microbalance techniques. Self-sputtering yields were determined for Au, Cu, Ag, Cr, and Al for energies from 10 to 500 eV. These yields were consistent with some previous noble-gas sputtering yields when only the difference in ionic mass was taken into account. Residual oxygen significantly lowered the self-sputtering yields of Al and Cr for all energies from 0 to 1 keV and the collection rate of oxygen was apparently greater for ions of about 10 eV. Sputtering yields of films by dissimilar metal ions were most strongly influenced by the type of metal in the beam, rather than by the target material, even for high ion energies.
Low pressure measurements by Bayard-Alpert gauges are limited by x-ray photoelectric currents at the ion collector, equivalent to a pressure reading of about 1×10−11 Torr. Through efforts to reduce this x-ray current, the Bayard-Alpert structure has been modified, whereby a beam of ions is extracted from the grid and bent around a corner to a remote collector. By this geometry the collector is shielded from the x-ray source at the grid, and the photoelectric current is reduced by a factor of 100, without incurring a loss in gauge sensitivity. Bending of the ion beam is accomplished by a cylindrical, electrostatic field, in which the ion trajectories are independent of e/m. 100% modulation of the ion beam intensity is achieved by turning off the bending field, thereby permitting pressure measurements as low as 1×10−14 Torr. A total pressure of 5×10−13 Torr, nitrogen equivalent, has been measured in a stainless steel vacuum system employing ion sputtering and titanium sublimation as the means of evacuation.
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