Metal-assisted SIMS and cluster ion bombardment for ion yield enhancement

Heile, Andreas; Lipinsky, D.; Wehbe, Nimer; Delcorte, Arnaud; Bertrand, Patrick; Felten, Alexandre; Houssiau, Laurent; Pireaux, Jean‐Jacques; Mondt, Roel De; Vaeck, Luc Van; Arlinghaus, Heinrich F.

doi:10.1016/j.apsusc.2008.05.007

Cited by 28 publications

(31 citation statements)

References 11 publications

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“…Such sources provide greater ionization efficiency and yields of larger and more indicative fragments [36]. Metal-assisted SIMS could also provide significant improvement [37]. These more informative sources may elude more chemical information regarding the binding mechanisms facilitating the adsorption of organic material in such substrates.…”

Section: Discussionmentioning

confidence: 99%

Use of TOF-SIMS to study adsorption and loading behavior of methylene blue and papain in a nano-porous silicon layer

Kempson

Barnes

Prestidge

2010

J. Am. Soc. Mass Spectrom.

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TOF-SIMS was applied to study the cross-sectional distribution of methylene blue and papain in porous silicon layers. Elemental and molecular information were used to study their distributions in the porous region and the chemistry of their adsorption. Methylene blue (MW ϭ 284 Da) [4], and the delivery of active pharmaceutical ingredients [5,6]. The ongoing interest in pSi for use as a therapeutic delivery system is due to the large internal surface area available, the readily modified surface chemistry [7] and, in particular, the excellent in vivo biodegradation and biocompatibility (low toxicity) of the silicon substrate, hydrolysing to form orthosilicic acid, which is readily excreted [8]. The loading dynamics of molecules into a pSi matrix is dependent on wetting and the size of the pores. Likewise, the interaction between a loaded molecule and the pSi substrate is of interest, particularly in the case of protein based therapeutics, whose bioactivity is dependent on remaining in a specific 3D conformation.TOF-SIMS analysis provides information regarding elemental and molecular species present in a sample surface (i.e., within 1-1.5 nm) with high mass resolution (up to ϳ10,000 m/⌬m) and spatial resolution for imaging (ϳ1 micron). Molecular and elemental information is obtained for organic and inorganic materials providing a powerful technique to image organic compounds associated with inorganic substrates or vice versa [9,10]. This has been demonstrated by imaging solid-state pharmaceutical formulations [11][12][13][14], however, to date this has not been extended to porous silicon substrates.In this study, TOF-SIMS was used to map the distribution of methylene blue and papain across porous silicon layers after loading from aqueous solution. Methylene blue (C 16 H 18 N 3 S ϩ , MW ϭ 284.12 g/mol) is a relatively small organic dye molecule commonly used in adsorption studies and can be considered analogous to therapeutic molecules. A molecular mass of 284 g/mol is within a reasonable mass range for a TOF-SIMS' Ga ϩ primary ion beam and can be easily and uniquely identified without interference or confusion from spectral peaks originating from the silicon substrate or in the instance of organic contamination. This molecule was chosen for its convenience, and to assess the ability to use smaller organic fragments to reflect the distribution of the molecule of interest. This is important to be able to extend this work to studying larger molecules, such as proteins and enzymes of pharmaceutical interest, which will not provide a molecular ion in TOF-SIMS. In contrast to methylene blue, papain is a much larger molecule, detailed elsewhere [15], comprising 212 residue units in two domains, giving a molecular weight of 23,406 g/mol. Papain is a cysteine protease hydrolase enzyme present in papaya. This molecular weight is far greater than can be detected with TOF-SIMS, however, fragmentation products can be detected. Smaller organic fragments can be compared with the distribution of methylene blue to investigate si...

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Section: Discussionmentioning

confidence: 99%

Use of TOF-SIMS to study adsorption and loading behavior of methylene blue and papain in a nano-porous silicon layer

Kempson

Barnes

Prestidge

2010

J. Am. Soc. Mass Spectrom.

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“…On the other hand, the yields increase or decrease continuously with the amount of evaporated gold depending whether Ga ϩ or C 60 ϩ , respectively, are used as projectiles (Figures 2 and 3). An interpretation has already been proposed for this differential effect of the gold metallization in previous papers [7,16,23] [16]. They found that the use of polyatomic ion such as Bi 3 ϩ , SF 5 ϩ , and C 60 ϩ leads to a decrease of the secondary ion yields with increasing gold deposition.…”

Section: Yield Variations As a Function Of The Ps Layer Thicknessmentioning

confidence: 72%

“…The enhancement factor for organic molecules can reach two orders of magnitude and more in some instances [14]. This specific sample preparation protocol, called metal assisted-SIMS (MetA-SIMS), was successfully used for signal enhancement with various materials such as polymers [15,16], organic molecules [17], and, in particular, for a better sensitivity in high-resolution surface imaging [18].…”

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confidence: 99%

Influence of the organic layer thickness in (Metal-Assisted) secondary ion mass spectrometry using Ga⁺ and C₆₀⁺ projectiles

Wehbe

Mouhib

Prabhakaran

et al. 2009

J. Am. Soc. Mass Spectrom.

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This article investigates the influence of the organic film thickness on the characteristic and molecular ion yields of polystyrene (PS), in combination with two different substrates (Si, Au) or gold condensation (MetA-SIMS), and for atomic (Ga ϩ ) and polyatomic (C 60 ϩ ) projectile bombardment. PS oligomer (m/z ϳ 2000 Da) layers were prepared with various thicknesses ranging from 1 up to 45 nm on both substrates. Pristine samples on Si were also metallized by evaporating gold with three different thicknesses (0.5, 2, and 6 nm). Secondary ion mass spectrometry was performed using 12 keV atomic Ga ϩ and C 60 ϩ projectiles. The results show that upon Ga ϩ bombardment, the yield of the fingerprint fragment C 7 H 7 ϩ increases as the PS coverage increases and reaches its maximum for a thickness that corresponds to a complete monolayer (ϳ3.5 nm). Beyond the maximum, the yields decrease strongly and become constant for layers thicker than 12 nm. In contrast, upon C 60 ϩ bombardment, the C 7 H 7 ϩ yields increase up to the monolayer coverage and they remain constant for higher thicknesses. A strong yield enhancement is confirmed upon Ga ϩ analysis of gold-metallized layers but yields decrease continuously with the gold coverage for C 60 ϩ bombardment. Upon Ga ϩ bombardment, the maximum PS fingerprint ion yields are obtained using a monolayer spin-coated on gold, whereas for C 60 ϩ , the best results are obtained with at least one monolayer, irrespective of the substrate and without any other treatment. The different behaviors are tentatively explained by arguments involving the different energy deposition mechanisms of both projectiles. (J Am Soc

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“…The size of the clusters and their dispersion on the surface agrees well with experimental observations, too. [18] The central cluster has a particular importance because it is in the sampled impact zone. It is a quasispherical cluster (Au 555 ) with a diameter of 2.5 nm.…”

Section: Resultsmentioning

confidence: 99%

Molecular dynamics study of metal‐organic samples bombarded by kiloelectronvolt projectiles

Restrepo

Delcorte

2011

Surface & Interface Analysis

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In recent experiments involving metal-assisted secondary ion mass spectrometry (MetA-SIMS), either an increase or a decrease of the sputtered organic ion yield was demonstrated depending whether the incoming projectile was atomic (Ga, In) or polyatomic (Bi 3 , C 60 ). Theoretically, the electronic and molecular processes governing the yield variation are still poorly understood for metal-organic surfaces. To unravel the physics of sputtering, molecular dynamics simulations involving metal-organic samples have been implemented. Two targets mimicking, respectively, a gold/organic vertical interface and a molecular sample covered by gold nanoparticles were designed and bombarded with several projectiles, including Ga and C 60 . The results emphasize the differences of emission and molecular mechanisms induced by these projectiles and explain some of the effects observed in MetA-SIMS.

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Metal-assisted SIMS and cluster ion bombardment for ion yield enhancement

Cited by 28 publications

References 11 publications

Use of TOF-SIMS to study adsorption and loading behavior of methylene blue and papain in a nano-porous silicon layer

Use of TOF-SIMS to study adsorption and loading behavior of methylene blue and papain in a nano-porous silicon layer

Influence of the organic layer thickness in (Metal-Assisted) secondary ion mass spectrometry using Ga⁺ and C₆₀⁺ projectiles

Molecular dynamics study of metal‐organic samples bombarded by kiloelectronvolt projectiles

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Metal-assisted SIMS and cluster ion bombardment for ion yield enhancement

Cited by 28 publications

References 11 publications

Use of TOF-SIMS to study adsorption and loading behavior of methylene blue and papain in a nano-porous silicon layer

Use of TOF-SIMS to study adsorption and loading behavior of methylene blue and papain in a nano-porous silicon layer

Influence of the organic layer thickness in (Metal-Assisted) secondary ion mass spectrometry using Ga+ and C60+ projectiles

Molecular dynamics study of metal‐organic samples bombarded by kiloelectronvolt projectiles

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Influence of the organic layer thickness in (Metal-Assisted) secondary ion mass spectrometry using Ga⁺ and C₆₀⁺ projectiles