Journal
ANALYTICAL CHEMISTRY
Volume 81, Issue 16, Pages 6676-6686Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ac900746x
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Funding
- Belgian Fonds National pour la Recherche Scientifique (FNRS)
- National Science Foundation of America (NSF) [CHE-0456514]
- UK Engineering and Physical Sciences Research Council (EPSRC)
- University of Surrey
- FSR
- French Community of Belgium via the Concerted Research Action programme (ARC NANHYMO) [07/12-003]
- Services and Emerging technologies (ASET)
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The present theoretical study explores the interaction of various energetic molecular projectiles and clusters with a model polymeric surface, with direct implications for surface analysis by mass spectrometry. The projectile sizes (up to 23 kDa) are intermediate between the polyatomic ions (SF5, C-60) used in secondary ion mass spectrometry and the large organic microdroplets generated, for example, in desorption electrospray ionization. The target is it model of amorphous polyethylene, already used in a previous study [Delcorte, A.; Garrison, B. J. J. Phys. Chem. C 2007, 111, 15312]. The chosen method relies on classical molecular dynamics (MD) simulations, using it coarse-grained description of polymeric samples for high energy or long time calculations (20-50 ps) and a full atomistic description for low energy or short time calculations (< 1 ps). Two regions of sputtering or desorption are observed depending on the projectile energy per nucleon (i.e., effectively the velocity). The transition, occurring around 1 eV/nucleon, is identified by a change of slope in the curve of the sputtering yield per nucleon vs energy per nucleon. Beyond 1 eV/nucleon, the sputtering yield depends only on the total projectile energy and not on the projectile nuclearity. Below 1 eV/nucleon, i.e., around the sputtering threshold for small projectiles, yields are influenced by both the projectile energy and nuclearity. Deposition of intact molecular clusters is also observed at die lowest energies per nucleon. The transition in the sputtering curve is connected to a change of energy deposition mechanisms, from atomistic. and mesoscopic processes to hydrodynamic flow. It also corresponds to a change in terms of fragmentation. Below 1 eV/nucleon, the projectiles are not able to induce bond scissions in the sample. This region of molecular emission with minimal fragmentation offers new analytical perspectives, out of reach of smaller molecular clusters such as fullerenes.
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