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Dynamic reactive ionization with cluster secondary ion mass spectrometry

Tian, Hua, Wucher, Andreas and Winograd, Nicholas (2015) Dynamic reactive ionization with cluster secondary ion mass spectrometry. Journal of The American Society for Mass Spectrometry. ISSN 1879-1123


Gas cluster ion beams have been tuned to enhance secondary ion yields by doping
small gas molecules such as CH4, CO2 and O2 into an Ar cluster projectile, Arn+
(n=1000-10000) to form a mixed cluster. Enhanced sensitivity has the potential to
expand the application of secondary ion mass spectrometry for two and three
dimensional molecular specific imaging. Here, we examine the possibility of further
enhancing the ionization by doping HCl into the Ar cluster. The water is also
introduced to the surface of the sample to help with the disassociation of HCl. This
concerted effect, occurring only at the impact site of the cluster, arises since the HCl is
chemically induced to ionize to H+ and Cl-, allowing improved protonation of neutral
molecular species. This idea is confirmed by depth profiling through a trehalose thin
film exposed to D2O vapor, resulting in ~20-fold increase in ions consisting of
[Mn*+H/D]+ (Mn* (n=1-8), where n H atoms in trehalose molecule have been replaced
by D atoms. The use of D2O allows us to monitor exchange of H and D in the trehalose
molecule). Moreover, it is possible to dynamically maintain the optimum ionization
conditions during depth profiling by proper adjustment of water vapor pressure. For
example, the [Mn*+H/D]+ ion increased by ~10-fold under optimized conditions. In
general, we discuss the role of surface chemistry and dynamic reactive ionization of
organic molecules in increasing the secondary ion yield.

Item Type: Article
Date Deposited: 28 Apr 2016 23:45
Last Modified: 28 Apr 2016 23:45


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