Static Secondary Ion Mass Spectrometry Research Articles

Argon Cluster Ion Source Evaluation on Lipid Standards and Rat Brain Tissue Samples

Argon cluster ion sources for sputtering and secondary ion mass spectrometry use projectiles consisting of several hundreds of atoms, accelerated to 10-20 keV, and deposit their kinetic energy within the top few nanometers of the surface. For organic materials, the sputtering yield is high removing material to similar depth. Consequently, the exposed new surface is relatively damage free. It has thus been demonstrated on model samples that it is now really possible to perform dual beam depth profiling experiments in organic materials with this new kind of ion source. Here, this possibility has been tested directly on tissue samples, 14 μm thick rat brain sections, allowing primary ion doses much larger than the so-called static secondary ion mass spectrometry (SIMS) limit and demonstrating the possibility to enhance the sensitivity of time-of-flight (TOF)-SIMS biological imaging. However, the depth analyses have also shown some variations of the chemical composition as a function of depth, particularly for cholesterol, as well as some possible matrix effects due to the presence or absence of this compound.

Experimental study of the organic ion intensity distribution in the ion imaging of coated polymer fibres with S-SIMS

Time-of-Flight Static Secondary Ion Mass Spectrometry excels in probing the molecular composition of the outer monolayer of flat samples with a lateral resolution in the sub-μm range. However, the method faces significant methodological problems in the case of non-conducting samples with high topography or surface curvature, such as fibres, yarns or fabrics. Specifically, the useful secondary ion yield in a given spot on the fibre depends on the local incidence angle, the height above the earthed sample holder, the position relative to the axis of the mass analyser and the extent of the local surface charging. This study has focused on the empiric reduction of the useful ion yield variations observed in the ion images of fibres with diameter of 25 and 100μm. Up to now, most literature data consider the analysis of fibres positioned along or perpendicular to the projection of the projectile beam in the plane of the sample surface because these specific geometries facilitate the interpretation of the ion images. However, it has been discovered that the diagonal orientation of the fibre in the field-of-view largely reduces the ion yield variations for fibres with a small diameter (25μm). The situation is different for fibres with a diameter of 100μm. In that case, the ion images contain no secondary ion counts for the pixels referring to a significant part of the fibre. In particular, the resulting lack of delineation between the shadow zone in the front of the fibre and the boundary of the fibre hampers the practical use of the ion images A fourfold decrease of the extraction voltage or a 20% increase of the distance between sample holder and extraction electrode is found to improve the detection of secondary ions from the part of the fibre facing towards the impinging primary ion beam. These observations have been tentatively related to the mass analyser acceptance and its dependence on the delicate balance between conflicting effects such as field strength and curvature of the field lines, secondary ion emission angle and initial kinetic energy and difference in local surface potential due to the position in the extraction field and charge build-up during analysis.

Excimer laser patterning of PEDOT:PSS thin-films on flexible barrier foils: A surface analysis study

Selective laser patterning of thin organic films is an important aspect in the roll-to-roll production of organic electronic devices such as organic light emitting diodes (OLEDs). An excimer laser is well suited for the patterning and structuring of polymer thin films as their UV absorption is significant. Selective removal of a transparent conducting polymer PEDOT:PSS (poly(3,4-ethylene dioxythiophene):polystyrene sulfonate) on a multilayered (inorganic–organic–inorganic) barrier and a flexible PEN (polyethylene napthalate) substrate has been studied using a KrF excimer laser. The ablation craters were characterized with electron microscopy and profilometry. For the first time, chemical surface analysis of the patterned area was performed with Time-Of-Flight Static Secondary Ion Mass Spectrometry (TOF-S-SIMS), providing a detailed insight of the surface composition after laser ablation and plasma post-treatments.

Lysophosphatidic acid triggers mast cell-driven atherosclerotic plaque destabilization by increasing vascular inflammation

Lysophosphatidic acid (LPA), a bioactive lysophospholipid, accumulates in the atherosclerotic plaque. It has the capacity to activate mast cells, which potentially exacerbates plaque progression. In this study, we thus aimed to investigate whether LPA contributes to plaque destabilization by modulating mast cell function. We here show by an imaging mass spectrometry approach that several LPA species are present in atherosclerotic plaques. Subsequently, we demonstrate that LPA is a potent mast cell activator which, unlike other triggers, favors release of tryptase. Local perivascular administration of LPA to an atherosclerotic carotid artery segment increases the activation status of perivascular mast cells and promotes intraplaque hemorrhage and macrophage recruitment without impacting plaque cell apoptosis. The mast cell stabilizer cromolyn could prevent intraplaque hemorrhage elicited by LPA-mediated mast cell activation. Finally, the involvement of mast cells in these events was further emphasized by the lack of effect of perivascular LPA administration in mast cell deficient animals. We demonstrate that increased accumulation of LPA in plaques induces perivascular mast cell activation and in this way contributes to plaque destabilization in vivo. This study points to local LPA availability as an important factor in atherosclerotic plaque stability.

ToF-SIMS depth profiling of organic solar cell layers using an Ar cluster ion source

Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) is a very powerful technique for analyzing the outermost layers of organic and biological materials. The ion fluence in static SIMS is usually kept low enough to prevent decomposition of the organic/molecular species and as a result ToF-SIMS is able to detect and image high mass molecular species, such as polymer additives. Depth profiling, in contrast, uses a high ion fluence in order to remove material between each analysis cycle. Unfortunately, the high ion fluence results in not only erosion but also decomposition of the organic species. Recently, high mass Ar cluster ion sources have become available and are enabling depth profiling through organic layers. In this paper, the authors demonstrate that they can obtain and maintain molecular information throughout an organic solar cell test layer when erosion is performed using an Ar1500+ cluster ion source for material removal. Contrary they show that they cannot maintain molecular information when low energy monoatomic ion beams are used for material removal.

Characterization of oxygen and titanium diffusion at the anatase TiO2(001) surface

The diffusion of intrinsic defects in a single crystal anatase TiO2(001) film was explored by isotopic labeling and static secondary ion mass spectrometry. Using both 46Ti and 18O as isotopic labels, we show that the anatase surface responds to redox imbalances by diffusion of both Ti and O into the bulk under vacuum reduction and (at least) Ti from the bulk to the surface during oxidation. The diffusion of Ti between the bulk and surface in anatase TiO2(001) closely resembles what was observed in the literature for the rutile TiO2(110) surface, however the latter is not known to have oxygen diffusion between the bulk and surface under typical ultrahigh vacuum conditions. We speculate that the open lattice of the anatase bulk structure may facilitate independent diffusion of both point defects (Ti interstitials and O vacancies) or concerted diffusion of “TiO” subunits.

ToF-S-SIMS molecular 3D analysis of micro-objects as an alternative to ion beam erosion at large depth: application to single inkjet dots

Molecular depth profiling is needed to develop high-tech materials optimised to the μm or even up to the nm scale. Recent progress in time-of-flight static secondary ion mass spectrometry (ToF-S-SIMS) offers perspectives to molecular depth profiling. However, at this moment, the methodology is not yet capable to deal with a range of materials science applications because of the limited depth range, the loss of intensity in the subsurface and the loss of depth resolution at large distances from the original surface. Therefore, the purpose of this paper is to develop a complementary approach for the molecular 3D analysis at large depth, using a combination of ultra-low angle microtomy (ULAM) and surface analysis of the sectioned material with ToF-S-SIMS. Single inkjet dots with a diameter of 100 μm and height of 22 μm on a PET substrate have been used as a test system for the methodology. It is demonstrated that the use of a diamond knife allows the molecular composition and distribution of components within the microscopic feature to be probed with a lateral resolution of 300 nm. Hence the methodology approaches the physical limit for ion imaging of organic components with local concentrations in the % range. In practice, the achievable depth resolution with ULAM-S-SIMS is ultimately limited by the surface roughness of the section. Careful optimisation of the ULAM step has resulted in a surface roughness within 6 nm (R(a) value) at a depth of 21 μm. This offers perspective to achieve 3D analysis with a depth resolution as good as 18 nm at such a large distance from the surface. Furthermore, the ULAM-S-SIMS approach is applicable to materials unamenable to ion beam erosion. However, the method is limited to dealing with, for instance, Si or glass substrates that cannot be sectioned with a microtomy knife. Furthermore, sufficient adhesion between stacked layers or between the coating and substrate is required. However, it is found that the approach is applicable to a wide variety of industrially important (multi)layers of polymers on a polymer substrate.

Atmospheric pressure plasma modified surfaces for immobilization of antimicrobial nisin peptides

In the field of antimicrobial surfaces, the development of environmentally-friendly surface treatments and industrially viable processes remains a challenging research objective. The use of atmospheric plasma treatments, especially dielectric barrier discharge (DBD) plasma deposition, is a promising technological approach to confer a thin antibacterial coating to a surface. The aim of this work is to investigate the potentiality of atmospheric plasma polymer organosilicon-based coatings as a reactive layer for the immobilization of biologically active molecules on stainless steel surfaces. In this context, an atmospheric-pressure DBD afterglow is used for the first time to functionalize a steel surface with chemical groups in order to attach biomolecules and this process is compared with a direct DBD discharge. The organosilicon-containing plasma interlayer confers a silica-like skeleton to the coatings for adhesion and stability. Composition of the plasma films before and after peptide immobilization has been characterized by Fourier transform infrared spectroscopy (FTIR), static secondary ion mass spectrometry (TOF-SIMS) and X-ray photoelectron spectroscopy (XPS).It is shown that the covalent immobilization of the antibacterial nisin peptides onto the organosilicon interlayer leads to adherent and protective antibacterial coatings on stainless steel as demonstrated against Gram+ bacteria using ISO 12296 antibacterial test. Nearly 4 log10 reduction of Gram+ strain was obtained compared to uncoated stainless steel. Importantly the antibacterial surfaces were resistant to several cleaning conditions. The later is significant as the stability of such antibacterial surfaces in close to real life conditions is a major concern.

The Storing Matter technique applied to Alq3: influence of the collector material and the sputter‐deposition energy on fragmentation

The Storing Matter technique is derived from secondary ion mass spectrometry (SIMS) and consists in decoupling the sputtering of the specimen from the analysis step. In a dedicated prototype instrument, the sample surface is bombarded by an ion beam, and the sputtered particles are deposited at sub‐monolayer level onto a collector. In a second step, this deposit is analyzed by SIMS (static or dynamic). In this work, we applied the Storing Matter technique to tris(8‐hydroxyquinolinato)aluminum (Alq3), a common component of organic light‐emitting diodes. Alq3 was sputter‐deposited onto Ag and Si collectors with different impact energies ranging from 3.75 keV to 10 keV. Positive mass spectra of these deposits and of an Alq3 reference sample were acquired under static SIMS conditions with 10‐keV impact energy. The intensity ratios of the characteristic Alq3 peaks are very similar for the Alq3 reference spectrum and the Storing Matter deposit with 10 keV, which indicates that most of the organic fragments deposited on the collector do not undergo a second fragmentation during the analysis step. This is however not the case for the same deposit on a Si collector. As the impact energy used for the sputter‐deposition step decreases, the peak distribution is shifted in favor of the smaller fragments, indicating a higher level of fragmentation. Copyright © 2012 John Wiley & Sons, Ltd.

The Adsorption of n-Octanohydroxamate Collector on Cu and Fe Oxide Minerals Investigated by Static Secondary Ion Mass Spectrometry

The feasibility of investigating the adsorption of n-octanohydroxamate collector on copper and iron oxide minerals with static secondary ion mass spectrometry has been assessed. Secondary ion mass spectra were determined for abraded surfaces of air-exposed copper metal, malachite, pseudomalachite and magnetite that had been conditioned in aqueous potassium hydrogen n-octanohydroxamate solution, as well as for the corresponding bulk CuII and FeIII complexes. In each case, the chemical species present at the solid/vacuum interface of a similarly prepared surface were established by X-ray photoelectron spectroscopy. The most abundant positive and negative metal-containing fragment ions identified for the bulk complexes were also found to be diagnostic secondary ions for the collector adsorbed on the oxide surfaces. The relative abundances of those diagnostic ions varied with, and could be rationalised by, the monolayer or multilayer coverage of the adsorbed collector. However, the precise mass values for the diagnostic ions were not able to corroborate the different bonding in the copper and iron hydroxamate systems that had been deduced from photoelectron and vibrational spectra. Parent secondary ions were able to provide supporting information on the co-adsorption of hydroxamic acid at each conditioned surface.

Effect of Cosputtering and Sample Rotation on Improving C60+ Depth Profiling of Materials

In the past decade, buckminsterfullerene (C(60))-based ion beams have been utilized in surface analysis instruments to expand their application to profiling organic materials. Although it had excellent performance for many organic and biological materials, its drawbacks, including carbon deposition, carbon penetration, continuous decay of the sputtering rate, and a rough sputtered surface, hindered its application. Cosputtering with C(60)(+) and auxiliary Ar(+) simultaneously and sample rotation during sputtering were proposed as methods to reduce the above-mentioned phenomena. However, the improvement from these methods has not been compared or studied under identical conditions; thus, the pros and cons of these methods are not yet known experimentally. In this work, a series of specimens including bulk materials and thin films were used to explore the differences between cosputtering and sample rotation on the analytical results. The results show that both of these methods can alleviate the problems associated with C(60)(+) sputtering, but each method showed better improvement in different situations. The cosputtering technique better suppressed carbon deposition, and could be used to generally improve results, especially with continuous spectra acquisition during sputtering (e.g., dynamic secondary ion mass spectrometry (SIMS) depth profiling). In contrast, for the scheme of sputter-then-acquire (e.g., alternative X-ray photoelectron spectrometry or dual-beam static SIMS depth profiling), a better result was achieved by sample rotation because it resulted in a flatter sputtered surface. Therefore, depending on the analytical scheme, a different method should be used to optimize the experimental conditions.

In situ study of activation and de-activation of LSM fuel cell cathodes – Electrochemistry and surface analysis of thin-film electrodes

The activation mechanism of the (ORR) on lanthanum strontium manganite (LSM) thin-film electrodes is investigated by examining the electrochemical behavior with impedance spectroscopy. To clarify whether surface segregation processes induced by electrochemical polarization are responsible for the change in catalytic activity of the perovskite electrode, in situ investigations with X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS) were performed. The surfaces of the as-prepared thin-film electrodes, which were annealed at elevated temperatures during the preparation process, show an increased strontium surface concentration. The segregated SrO surface layer has a detrimental effect on the ORR reaction. Cathodic polarization decreases the strontium surface concentration while anodic polarization causes strontium accumulation at the electrode surface, which is proven by both SIMS and XPS in situ. A mechanism based on the incorporation of poorly conductive SrO from the electrode surface into the LSM lattice under cathodic polarization is suggested to be responsible for the observed activation process.

Particle–Particle Chemistry between Micrometer-Sized PbSO4 and CaCO3 Particles in Turbulent Flow Initiated by Liquid Water

A mixture of natural and anthropogenic particles is ubiquitous in the troposphere and exerts an important influence on air quality. This work reports the study of mixing and heterogeneous chemistry of particles of natural-like mineral dust (CaCO(3)) and anthropogenic-like microparticle (PbSO(4)) in turbulent air flow under varying relative humidity. Sparse monolayers of laboratory-generated particles were collected on substrates using impaction. The grain size distribution and chemistry of micrometer-sized particles were determined as CaCO(3)-PbSO(4) internal and external mixtures by Raman imaging, scanning electron microscopy, and time-of-flight static secondary ionization mass spectrometry. The condensation of a thin water layer on mixed aggregates initiates the formation of complex internal mixtures of Pb(3)(CO(3))(2)(OH)(2), PbCO(3), CaSO(4)·2H(2)O, CaCO(3), and PbSO(4) fine particles. These heterogeneous chemistry processes which may occur in ambient air can increase dramatically the amounts of hazardous breathable particles.

Reduction of Matrix Effects in Polystyrene/Poly(methylene methacrylate) Blends by Metal-Assisted Secondary Ion Mass Spectrometry

Secondary ion mass spectrometry (SIMS) is a very surface sensitive analysis technique with low detection limits. The main drawback of SIMS is its inherent incapability of providing quantitative information about sample compositions due to the frequent occurrence of ionization- and sputter-induced matrix effects. Metal-assisted SIMS (MetA-SIMS) is an experimental approach that consists in covering an organic sample with a minute amount of a noble metal prior to a static SIMS analysis, the main objective being an increase of the characteristic secondary ion intensities. We show in this article that MetA-SIMS is also a simple and efficient tool for reducing matrix effects in a set of polymer blend samples containing different relative concentrations polystyrene (PS) and poly(methylene methacrylate) (PMMA). These findings can be explained by diffusion processes leading to a sample surface configuration consisting of individual polymer chains embedded in a common Ag matrix.

Insights into the yield enhancement and ion emission process in metal‐assisted SIMS

Although nowadays the use of cluster ion sources seems to enhance the secondary ion emission for nearly all materials, the technique of metal‐assisted SIMS can still give further insights in the secondary ion emission process. In this study, the metallization for static SIMS analysis was performed in situ. The combination of a detailed morphology study by SEM, TEM and the secondary yield enhancements in time‐of‐flight SIMS allows to develop a model explaining the secondary yield enhancement in metal‐assisted SIMS. Copyright © 2012 John Wiley & Sons, Ltd.

Organic ion yield enhancement in secondary ion mass spectrometry using water vapour injection

The effects of water (H2O) and deuterated water (D2O) vapour, injected closely to the analyzed surface at relatively high pressure, on the enhancement of the ion yield in secondary ion mass spectrometry (SIMS) was investigated for a set of organic samples. The results show that the same signal enhancements occurred either upon Ga+ or C60+ bombardment. In addition, the increase of H2O vapour pressure during the bombardment causes a specific enhancement of the protonated ion intensity. For instance, the presence of H2O vapour induces an enhancement by one order of magnitude of the [M + H]+ static SIMS intensity for the antioxidant Irgafos 168 and by more than two times for the amino acids. Copyright © 2012 John Wiley & Sons, Ltd.

Correlation between molecular secondary ion yield and cluster ion sputtering for samples with different stopping powers

In static SIMS, the secondary ion yield, defined as detected ions per primary ion, can be increased by altering several primary ion parameters. For many years, no quantitative predictions could be made for the secondary ion yield enhancement of molecular ions. For thick samples of organic compounds, a power dependency of the secondary ion yield on the sputtering yield was shown. For this article, samples with thick molecular layers and (sub-)monolayers composed of various molecules were prepared on inorganic substrates such as silicon, silver, and gold, and subsequently analyzed. For primary ion bombardment, monoatomic (Ne+, Ar+, Ga+, Kr+, Xe+, Bi+) as well as polyatomic (Bin+, Bin++) primary ions were used within an energy range of 10–50keV. The power dependency was found to hold true for the different samples; however, the exponent decreased with increasing stopping power. Based on these findings, a rule of thumb is proposed for the prediction of the lower limit of the secondary ion yield enhancement as a function of the primary ion species. Additionally, effects caused by the variation of the energy deposition are discussed, including the degree of molecular fragmentation and the non-linear increase of the secondary ion yield when polyatomic primary ions are used.

Static SIMS study on surfaces of chalcogenide glasses modified by an organic layer

Chalcogenide glasses are useful optic materials that find applications in infrared spectroscopy, sensors and thermal imaging. A route for direct surface modification of such glasses with organic layers has been investigated by static Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The GAS (germanium–arsenic–selenium) glasses are modified by deposition followed by UV-irradiation of disulfide- or/and silane-functionalized organic molecules. SIMS analysis shows the characteristic fragments of the grafted molecules and organic–inorganic fragments which prove unambiguously the binding mode to the surface: disulfides, after S–S cleavage, are linked to arsenic and selenium; triethoxysilanes bind exclusively to oxidized germanium. The successive grafting of disulfide and silane compounds on the same substrate (IG2 glass with 33% of Ge) affords a “mixed” organic layer on the glass surface. From water contact angle measurements and X-ray Photo-electron Spectroscopy (XPS), the coverage density is not significantly improved comparatively to the “non-mixed” layers. However, the grafting of both types of molecules allows to reach a more homogeneous coverage.

Surface Measurement of GLSI Wafer with Copper Interconnects after CMP

Chemical mechanical polishing (CMP) is the best global planarization technology of GLSI process. After CMP process, there may appear large roughness, micro scratch, dishing pit, erosion pit, with-in-wafer-non-uniformity (WIWNU), organic contamination, particles and metal ions pollution on wafer with copper interconnects. Surface measurement of CMP process on the wafer mainly involves the test of roughness, defects and the contaminations. Atomic force profiler (AFP) combined with the resolution of the AFM and long-range-scan ability of the steps instrument (100 mm), is suitable for CMP process which needs to measure both the planarization of long-range scanning and tungsten plug and copper interconnects with high resolution imaging. Optical detection technology combined with the advantages of dark and bright view detection is suitable for detection of particles, crystal originated pits (COP), defects, etc. The time-of-flight static secondary ion mass spectrometry (TOF-SIMS) and total reflection X-ray fluorescence (TXRF) are applicable to detect metal ions. The selection and use of advanced data analysis theory and method can help to improve the speed of analysis and to find the main factors of influence surface quality. Pareto diagram analysis is very beneficial for study polishing effects and the main reason of the surface state for Cu-CMP wafer. Nine sampling method and five sampling method fit to analysis the uniform surface distribution, on the contrast isometric sampling can reflect the distribution of the surface state along the radius difference.

In situ study of electrochemical activation and surface segregation of the SOFC electrode material La0.75Sr0.25Cr0.5Mn0.5O3±δ

Mixed-conducting perovskite-type electrodes which are used as cathodes in solid oxide fuel cells (SOFCs) exhibit pronounced performance improvement after cathodic polarization. The current in situ study addresses the mechanism of this activation process which is still unknown. We chose the new perovskite-type material La(0.75)Sr(0.25)Cr(0.5)Mn(0.5)O(3±δ) which is a potential candidate for use in symmetrical solid oxide fuel cells (SFCs). We prepared La(0.75)Sr(0.25)Cr(0.5)Mn(0.5)O(3±δ) thin film model electrodes on YSZ (111) single crystals by pulsed laser deposition (PLD). Impedance spectroscopy (EIS) measurements show that the kinetics of these electrodes can be drastically improved by applying a cathodic potential. To understand the origin of the enhanced electrocatalytic activity the surfaces of operating LSCrM electrodes were studied in situ (at low pressure) with spatially resolving X-ray photoelectron spectroscopy (μ-ESCA, SPEM) and quasi static secondary ion mass spectrometry (ToF-SIMS) after applying different electrical potentials in the SIMS chamber. We observed that the electrode surfaces which were annealed at 600 °C are enriched significantly in strontium. Subsequent cathodic polarization decreases the strontium surface concentration while anodic polarization increases the strontium accumulation at the electrode surface. We propose a mechanism based on the reversible incorporation of a passivating SrO surface phase into the LSCrM lattice to explain the observed activation/deactivation process.