CLEAN ULTRAHIGH-VACUUM SYSTEM WITH SINGLE-STRUCTURE DIFFUSION PUMPS

A practical example of the use of single-structure diffusion pumping g roups in an experiment requiring hydrocarbon-free, ultrahigh vacuum is presented. With the use of proper vacuum procedures and careful forel ine design and operation, but with no exotic hardware or liquid nitrog en, we have demonstrated that such a pump could provide vacuum that wa s ''clean,'' i.e., which had no residual pump-oil contamination to a p artial pressure below 10(-8) mbar. Their use is thus compatible, at le ast in peripheral vacuum chambers, with standard ''UHV-surface science '' processes. We discuss our vacuum system in detail, and present a re view of the literature on the production of clean vacua with diffusion pumps.