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

Rabbani, Sadia; Razo, Irma Berrueta; Kohn, Taylor P.; Lockyer, Nicholas P.; Vickerman, John C.

doi:10.1021/ac504191m

Cited by 82 publications

(108 citation statements)

References 55 publications

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“…This finding is in agreement with recently published studies in the static SIMS regime, which state that high energy and larger clusters are beneficial for increasing the molecular ion yield of organic materials. 15,18 ■ EXPERIMENTAL SECTION Material and Sample Preparation. Presliced 5 mm × 5 mm Si wafers (Ted Pella Inc., Reading, CA, USA) were used as substrates for all films.…”

Section: ■ Introductionmentioning

confidence: 99%

Molecular Depth Profiling with Argon Gas Cluster Ion Beams

2015

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Argon gas cluster ion beams (Ar-GCIBs) are remarkable new projectiles for secondary ion mass spectrometry (SIMS) depth profiling of organic materials. However, the optimal cluster size and kinetic energy to provide the best quality of depth profiles, in terms of high ionization efficiency of the target molecules, little chemical damage, and short experiment time, for organic materials is not fully understood. Hence, the effect of cluster size and kinetic energy on the quality of molecular depth profiling is investigated on a simple platform composed of trehalose thin films to acquire more fundamental information about the ion/solid interaction. The results suggest that the sputter yield (Y/n) of argon clusters is linearly dependent upon kinetic energy per atom (E/ n). When E/n > 5 eV/atom, normal depth profiles are obtained with relatively high sputter yields. When E/n ≤ 5 eV/atom, however, distorted depth profiles in the steady state region are observed, which exhibit a low sputter yield and variable ionization efficiency. As a consequence of these observations, it was concluded that high kinetic energy increases the useful molecular ion yield of trehalose and that Ar n + clusters with a small E/n value minimize ion beam bombardment induced chemical damage. Hence optimal conditions for molecular depth profiling will be obtained using the highest kinetic energy with the largest clusters while maintaining a value of E/n near a threshold value of 5 eV/atom. In general, this study provides insight into selecting optimal Ar-GCIB characteristics for molecular depth profiling of organic materials. ■ INTRODUCTIONSecondary ion mass spectrometry (SIMS) has been used as an indepth characterization method for inorganic materials, particularly semiconductors, for many years. 1−3 To expand the scope of this technique into the investigation of organic samples, there has been a growing emphasis on the development of cluster ion sources, such as Au 3 , 4,5 Bi 3 , 6 SF 5 , 7 and C 60 . 4 These probes, particularly C 60 , are more effective than the traditional atomic ion sources, because less chemical damage is accumulated during the interaction of the projectiles with the solid. Molecular depth profiling of a variety of organic materials is now possible, 8−11 providing an important new characterization modality for SIMS. Recently, argon gas cluster ion beams (Ar-GCIBs) 12 have generated a great deal of excitement, because they appear to yield better depth resolution and produce less chemical damage than C 60 , 13−16 broadening the scope of this technology even further.There is flexibility associated with the implementation of GCIBs. For example, the nature of the chemical composition of these clusters can be varied, consisting of water clusters 17,18 or Ar clusters doped with other species such as CO 2 15 and CH 4 , 19 or other molecules such as N 2 20 and C 2 H 5 OH. 21,22 The idea behind many of these experiments is to increase the ionization efficiency of the target molecules by providing a source of protons for making [M + H...

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Section: ■ Introductionmentioning

confidence: 99%

Molecular Depth Profiling with Argon Gas Cluster Ion Beams

2015

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“…8,9,[18][19][20] The results indicate that in the singlecomponent samples, the ionization of both molecules is enhanced with the (H 2 O) n þ ion beam, particularly with larger water clusters (Fig. 2).…”

Section: A Analysis Of Single-component Samplesmentioning

confidence: 90%

“…Water cluster ion beams were obtained by generating water steam that effused through a heated GCIB nozzle forming clusters in the jet expansion, which are then ionized by electron impact. 9 The study performed a comparison of secondary ion yield obtained with different ion beams on pure and binary mixtures. Secondary ion yields are defined as number of detected secondary ions per primary ion.…”

Section: Methodsmentioning

confidence: 99%

“…This can be explained as the water cluster facilitating proton donation in the emission zone. 9 ToF-SIMS ion yield does not generally provide a direct quantitative determination of analyte concentration in a sample, as the ionization efficiency of molecules in a heterogeneous sample is affected by neighboring molecules. 10,11 Jones et al showed that where proton exchange was the dominate ionization mechanism, the molecules with a high ionization efficiency suppress the ionization of other molecules with a lower ionization efficiency.…”

Section: Introductionmentioning

confidence: 99%

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Matrix effects in biological SIMS using cluster ion beams of different chemical composition

2016

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The influence of the matrix effect on secondary ion yield presents a very significant challenge in quantitative secondary ion mass spectrometry (SIMS) analysis, for example, in determining the relative concentrations of metabolites that characterize normal biological activities or disease progression. Not only the sample itself but also the choice of primary ion beam may influence the extent of ionization suppression/enhancement due to the local chemical environment. In this study, an assessment of ionization matrix effects was carried out on model systems using C60+, Arn+, and (H2O)n+ cluster ion beams. The analytes are pure and binary mixtures of amino acids arginine and histidine biological standards. Ion beams of 20 keV were compared with a range of cluster sizes n = 1000–10 000. The component secondary ion yields were assessed for matrix effects using different primary ion beams and sample composition. The presence of water in the cluster beam is associated with a reduction in the observed matrix effects, suggesting that chemically reactive ion beams may provide a route to more quantitative SIMS analysis of complex biological systems.

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“…The initial version of this source employs 1M Acetic acid solution which are first generated in atmospheric conditions, and then introduced to vacuum conditions through a series of differential pumping apertures, and postaccelerated to the target plate with ~10 kV 114 shown that water clusters could be generated in a nature similar to argon clusters by employing water vapor instead of argon gas 119 . H2O GCIB has been compared to C60 + and Ar2000 + , providing enhanced intact molecular ion yields in comparison to both of these projectiles 120 .…”

Section: Figure 6 Schematic Of An Iontof Argon Gas Cluster Primary Imentioning

confidence: 99%

Development of a Primary Ion Column for Mass Spectrometry-Based Surface Analysis

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

Cited by 82 publications

References 55 publications

Molecular Depth Profiling with Argon Gas Cluster Ion Beams

Molecular Depth Profiling with Argon Gas Cluster Ion Beams

Matrix effects in biological SIMS using cluster ion beams of different chemical composition

Development of a Primary Ion Column for Mass Spectrometry-Based Surface Analysis

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