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A magnetron cold cathode ion source (CCIS) has been developed for ultrahigh vacuum residual gas analysis. The purpose is to eliminate the spurious spectra produced by the conventional hot filament source and to obtain greater sensitivity. A commercial quadrupole mass analyzer was used to evaluate source performance and potential. Resolution equaled that obtained with a hot filament source, giving mass invariant peak separations, with 10% valleys, of 1.0 amu below 150 amu and 0.7 amu below 50 amu. Sensitivities exceeded those obtained with a hot filament source, operated at a 3 mA emission current, by factors of 1.5 to 4.6, depending on pressure and mass. The corresponding CCIS sensitivities, at 1-amu peak separation, were 0.4 mA/Torr for mass 28 at 3×10−9 Torr and 1.2mA/Torr for mass 40 at 1×10−7 Torr. Experiments indicated a potential tenfold further sensitivity improvement if a quadrupole with a higher rf potential were used; by increasing quadrupole dimensions a still greater fraction of the source internal sensitivity, which is in the vicinity of 1 A/Torr, may be realized.

Below 1×10−10 Torr, pressure measurement by means of Bayard-Alpert type ion gauges is complicated by the existence of a current associated with soft ``x-rays.'' The precise measurement of a true ion current requires precise determination of the so-called x-ray limit of each gauge. The present work describes the use of a Bayard-Alpert gauge containing a modulating electrode (after the design of Redhead) to measure pressures below 10−10 Torr. Magnetron-type gauges, which do not have x-ray limitations, were then compared directly with the Bayard-Alpert gauges. In addition, gauge comparisons were carried out in a dynamic system involving pressure ratios across a capillary. Both series of experiments showed that the output current of the magnetron gauge was a power function (exponent 1.6) below approximately 2×10−10 Torr (N2). In the latter work it was possible to make measurements to below 1×10−12 Torr N2 equivalent.

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