Cold cathode field emitter array on a quadrupole mass spectrometer: Route to miniaturization

We have improved the quadrupole mass spectrometer by substituting the conve ntional hot filament electron source by a field emitter array (FEA). Elimin ation of the hot filament avoids a number of common problems, including the rmal cracking of delicate molecules, outgassing of the filament itself and nearby components, high power requirements for the filament, large size, st ray light, stray magnetic fields, contamination by thoria and tungsten, and a long warm-up time. The advantages are dearest for portable applications where power requirements dominate. Here, the power savings are not just in eliminating the filament supply, but more important in reducing the largest component of the system, the vacuum pump. This comes about because the fil ament is the primary gas load and because chemical reactions taking place o n it require fast pumping to keep the products from interfering with the sp ectra. Comparison between hot filament and cold cathode FEA ionization is m ade using a quadrupole mass spectrometer fitted with both electron sources, independently controlled. The FEA advantage is strongest when the ultrahig h vacuum system is throttled to a low pumping speed, mimicking a portable s ystem with a small pump. FEAs also enable miniaturization and a correspondi ng decrease in pump size. Moreover, with miniaturization, shorter mean free paths and consequently higher working pressures can be tolerated further d ecreasing pump requirements. (C) 1999 American Vacuum Society. [S0734-211X( 99)01905-8].