The influence of the ionizer geometry on the absolute density calibration of reactive neutral species in a molecular beam mass spectrometry

Journal Article · Sun Apr 15 04:00:00 EDT 2012 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.3703305· OSTI ID:22072293

Kraehling, Tobias; Ellerweg, Dirk; Benedikt, Jan ^[1]

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1. Research Department Plasmas with Complex Interactions, Faculty for Physics and Astronomy, Ruhr-University Bochum, Universitaetsstrasse 150, 44780 Bochum (Germany)

Molecular beam mass spectrometry is a powerful diagnostic technique, which can be used for the measurement of absolute number densities of reactive species in non-equilibrium reactive plasmas. However, the calibration of absolute number densities is susceptible to systematic errors. Critical issues are the proper design of the sampling system and the correction of the background signal. Here we discuss the effect of reflections of particles from the molecular beam in an ionizer, formation of additional background particle density in the ionizer, and its effect on the density calibration of reactive particle densities. A Monte Carlo simulation of particle trajectories in the ionizer is used to estimate the detection probability of a beam particle after the collision with the ionizer wall. The simulation shows that as much as two-third of the signal can be due to scattered particles in the commercially available mass spectrometers. This effect leads to systematic underestimation of densities of reactive particles, which are reactive at the surface and, therefore, do not have any background density. A simple change in the ionizer geometry is suggested, which can significantly reduce this problem.

• OSTI ID: 22072293
• Journal Information: Review of Scientific Instruments, Journal Name: Review of Scientific Instruments Journal Issue: 4 Vol. 83; ISSN 0034-6748; ISSN RSINAK
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
BACKGROUND NOISE
CALIBRATION
COMPUTERIZED SIMULATION
CORRECTIONS
DENSITY
DETECTION
IONIZATION
MASS SPECTROMETERS
MASS SPECTROSCOPY
MOLECULAR BEAMS
MONTE CARLO METHOD
PARTICLES
PLASMA
PROBABILITY
SAMPLING