Molecular ions in cluster bombardment: what clues do the molecular dynamics simulations provide?

Garrison, Barbara J.

doi:10.1002/sia.3502

Cited by 8 publications

(9 citation statements)

References 14 publications

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“…This allows D‐rich fragments from the enriched layer to come into contact with PHE molecules in lower layers. This is a process in support of DCPI proposed recently . Alternatively, in the case where the enriched film is on the bottom, the width of the [M PHE + D] + peak is half the size as in the preceding case.…”

Section: Resultssupporting

confidence: 76%

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Evidence for the formation of dynamically created pre‐formed ions at the interface of isotopically enriched thin films

Lerach

Winograd

2012

Surface & Interface Analysis

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A novel approach to elucidate the ionization mechanism for the [M + H]+ molecular ion of organic molecules is investigated by molecular depth profiling of isotopically enriched thin films. Using a model bi-layer film of phenylalanine (PHE) and PHE-D8, the results show formation of an [M + D]+ molecular ion for the non-enriched PHE molecule attributed to rearrangements of chemical damage due to successive primary ion impacts. The [M + D]+ ion is observed at the interface for 19.9nm in the enriched-on-top system and 9.9nm for the enriched-on-bottom system. This ion formation is direct evidence for dynamically created pre-formed ions as a result of chemical damage rearrangement induced by previous primary ion bombardment events.

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Section: Resultssupporting

confidence: 76%

“…Thus, the possibility of exchange not due to primary ion impact is negligible. Molecular depth profiling is performed, and exchange of a deuteron from fragmented PHE‐D 8 molecules is observed in the form of the [M PHE + D] + molecule, yielding strong evidence for dynamically created pre‐formed ions (DCPI) …”

Section: Introductionmentioning

confidence: 99%

Evidence for the formation of dynamically created pre‐formed ions at the interface of isotopically enriched thin films

Lerach

Winograd

2012

Surface & Interface Analysis

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“…The picture of the energetic collisions in the first hundreds of femtoseconds of the interaction allows us to speculate about the reasons of the observed discrepancy between the sputtering yield and the ion yield enhancements when going from atomic Bi projectiles to clusters. In addition to the possibility of preformed ions, 66,67 it has long been thought, 68,69 and also shown in previous simulation works, 70 that significant ionization occurs in the energetic collision cascade, at the beginning of the interaction. It seems very difficult to explain the aforementioned discrepancy with the concept of preformed ions, because in that case, the sputtering and ion yields should, in principle, be proportional to each other.…”

Section: Resultsmentioning

confidence: 88%

Computer Simulations of the Sputtering of Metallic, Organic, and Metal–Organic Surfaces with Bi_n and C₆₀ Projectiles

et al. 2013

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This study focuses on the microscopic modeling of 0–25 keV Bi1–3–5 and C60 cluster impacts on three different targets (Au crystal, adsorbed Au nanoparticle, and organic solid), using molecular dynamics simulations, and on the comparison of the calculated quantities with recent experimental results, reported in the literature or obtained in our laboratory. The sputtering statistics are reported, showing nonlinearity of the sputtering yields with the number of cluster atoms at the same incident velocity for Bi1–5 bombardment. They are compared to experiments (especially for the organic target), and the microscopic explanation of the observations is analyzed. The results show that the respective behaviors and performances of the different projectiles are strongly dependent on the target, with clusters of heavy Bi atoms being more efficient at sputtering gold and, conversely, fullerene clusters inducing the largest sputtering yields of the organic material (mass matching). For organic targets, some important and novel conclusions of this work are the following: (i) The increase of the sputtering yield when going from Bi atoms to Bi clusters is insufficient to explain the much larger increase of characteristic ion yields, suggesting a projectile-dependent ionization probability. (ii) The extent of molecular fragmentation follows the order of Bi > Bi3 > Bi5 > C60, that is, softer emission with larger clusters. (iii) Even 5–10 keV Bi atoms create collective molecular motions and craters in the polymeric solid, though the collision cascades are rather dilute. Finally, a second series of simulations performed at low energies predict that 0.1–1 keV Bi n clusters should not provide better results for sputtering and depth profiling than isoenergetic single atoms.

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“…A systematic study varying the salt content of the samples would be required to clarify this issue. However, MD studies have shown that preformed protonated ions can be expected to be emitted from the low energy periphery of a high energy primary ion impact site. , It is envisaged that some protons formed during high-energy fragmentation during the initial impact flow out to the periphery and encounter intact molecules. Protonated molecular ions are formed and emitted, possibly during a subsequent primary impact.…”

Section: Resultsmentioning

confidence: 99%

Enhancing Ion Yields in Time-of-Flight-Secondary Ion Mass Spectrometry: A Comparative Study of Argon and Water Cluster Primary Beams

et al. 2015

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Following from our previous Letter on this topic, this Article reports a detailed study of time-of-flight-secondary ion mass spectrometry (TOF-SIMS) positive ion spectra generated from a set of model biocompounds (arginine, trehalose, DPPC, and angiotensin II) by water cluster primary ion beams in comparison to argon cluster beams over a range of cluster sizes and energies. Sputter yield studies using argon and water beams on arginine and Irganox 1010 have confirmed that the sputter yields using water cluster beams lie on the same universal sputtering curve derived by Seah for argon cluster beams. Thus, increased ion yield using water cluster beams must arise from increased ionization. The spectra and positive ion signals observed using cluster beams in the size range from 1,000 to 10,000 and the energy range 5-20 keV are reported. It is confirmed that water cluster beams enhance proton related ionization over against argon beams to a significant degree such that enhanced detection sensitivities from 1 μm(2) in the region of 100 to 1,000 times relative to static SIMS analysis with Ar2000 cluster beams appear to be accessible. These new studies show that there is an unexpected complexity in the ionization enhancement phenomenon. Whereas optimum ion yields under argon cluster bombardment occur in the region of E/n ≥ 10 eV (where E is the beam energy and n the number of argon atoms in the cluster) and fall rapidly when E/n < 10 eV; for water cluster beams, ion yields increase significantly in this E/n regime (where n is the number of water molecules in the cluster) and peak for 20 keV beams at a cluster size of 7,000 or E/n ∼3 eV. This important result is explored further using D2O cluster beams that confirm that in this low E/n regime protonation does originate to a large extent from the water molecules. The results, encouraging in themselves, suggest that for both argon and water cluster beams, higher energy beams, e.g., 40 and 80 keV, would enable larger cluster sizes to be exploited with significant benefit for ion yield and hence analytical capability.

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Molecular ions in cluster bombardment: what clues do the molecular dynamics simulations provide?

Cited by 8 publications

References 14 publications

Evidence for the formation of dynamically created pre‐formed ions at the interface of isotopically enriched thin films

Evidence for the formation of dynamically created pre‐formed ions at the interface of isotopically enriched thin films

Computer Simulations of the Sputtering of Metallic, Organic, and Metal–Organic Surfaces with Bi_n and C₆₀ Projectiles

Enhancing Ion Yields in Time-of-Flight-Secondary Ion Mass Spectrometry: A Comparative Study of Argon and Water Cluster Primary Beams

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Molecular ions in cluster bombardment: what clues do the molecular dynamics simulations provide?

Cited by 8 publications

References 14 publications

Evidence for the formation of dynamically created pre‐formed ions at the interface of isotopically enriched thin films

Evidence for the formation of dynamically created pre‐formed ions at the interface of isotopically enriched thin films

Computer Simulations of the Sputtering of Metallic, Organic, and Metal–Organic Surfaces with Bin and C60 Projectiles

Enhancing Ion Yields in Time-of-Flight-Secondary Ion Mass Spectrometry: A Comparative Study of Argon and Water Cluster Primary Beams

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Computer Simulations of the Sputtering of Metallic, Organic, and Metal–Organic Surfaces with Bi_n and C₆₀ Projectiles