On the SIMS Ionization Probability of Organic Molecules

Nicholas J. Popczun, Lars Breuer, Andreas Wucher, Nicholas Winograd

Research output: Contribution to journalArticlepeer-review

15 Scopus citations

Abstract

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 + ) of sputtered material, a value rarely measured directly, but estimated to be in some cases as low as 10 −5 . Our lab has developed a method for the direct determination of α + 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 24 H 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 60 cluster projectiles is of the order of 10 −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. [Figure not available: see fulltext.].

Original languageEnglish (US)
Pages (from-to)1182-1191
Number of pages10
JournalJournal of the American Society for Mass Spectrometry
Volume28
Issue number6
DOIs
StatePublished - Jun 1 2017

All Science Journal Classification (ASJC) codes

  • Structural Biology
  • Spectroscopy

Cite this