Parts-per-billion detection with electron-gas secondary-neutral mass spectrometry

Post-ionization of sputtered neutral atoms by means of the electron component of a special low-pressure plasma (ʹelectron gasʹ) and detection of these ions in a high-transmission double-focusing mass spectrometer provide a bulk detection efficiency in the low parts-per-billion (ppb = 10 -9) range. This is demonstrated for 12 trace elements in a Cu standard (with concentrations in the low and sub-ppm range) and a Te-doped GaAs specimen. The Te isotope with the lowest natural abundance (12°Te) corresponds to an atomic concentration of 2.85 ppb and is identified at a signal level of ~ 2 counts/s, while the (mass-independent) background amounts to < 0.1 counts/s. For both specimens, measured intensities exhibit a close one-to-one correlation with the atomic concentrations extending over a range of nearly nine orders of magnitude. © 1997 Elsevier Science B.V.