On the SIMS Ionization Probability of Organic Molecules
- The Pennsylvania State University, Department of Chemistry (United States)
- Universität Duisburg-Essen, Fakultät für Physik (Germany)
The prospect of improved secondary ion yields for secondary ion mass spectrometry (SIMS) experiments drives innovation of new primary ion sources, instrumentation, and post-ionization techniques. The largest factor affecting secondary ion efficiency is believed to be the poor ionization probability (α{sup +}) of sputtered material, a value rarely measured directly, but estimated to be in some cases as low as 10{sup −5}. Our lab has developed a method for the direct determination of α{sup +} in a SIMS experiment using laser post-ionization (LPI) to detect neutral molecular species in the sputtered plume for an organic compound. Here, we apply this method to coronene (C{sub 24}H{sub 12}), a polyaromatic hydrocarbon that exhibits strong molecular signal during gas-phase photoionization. A two-dimensional spatial distribution of sputtered neutral molecules is measured and presented. It is shown that the ionization probability of molecular coronene desorbed from a clean film under bombardment with 40 keV C{sub 60} cluster projectiles is of the order of 10{sup −3}, with some remaining uncertainty arising from laser-induced fragmentation and possible differences in the emission velocity distributions of neutral and ionized molecules. In general, this work establishes a method to estimate the ionization efficiency of molecular species sputtered during a single bombardment event. .
- OSTI ID:
- 22776998
- Journal Information:
- Journal of the American Society for Mass Spectrometry, Vol. 28, Issue 6; Other Information: Copyright (c) 2017 American Society for Mass Spectrometry; http://www.springer-ny.com; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-0305
- Country of Publication:
- United States
- Language:
- English
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