Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films

Calculation of postionization probabilities as a function of plasma parameters in electron gas secondary neutral mass spectrometry

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Using the semiempirical cross-section functions for electron impact ionization developed by Lotz, we calculated the ionization rate constants for most elements as a function of the electron temperature in a low-pressure noble gas plasma typically employed in electron gas secondary neutral mass spectrometry (SNMS). After first-order corrections accounting for (a) the different mean energies of sputtered neutral particles and (b) signal losses due to heavy particle scattering by discharge gas particles (e.G., Ar), the neutral-to-ion conversion factors are α0x calculated for the Leybold INA 3 system for most elements X across the Periodic Table. Assuming uniform (mass independent) transmission in the detection system the ratios a£eA,x are equivalent with the relative sensitivity factors D%c/D in SNMS. © 1988, American Vacuum Society. All rights reserved.