Secondary Ion Mass Spectrometry Analysis Research Articles

Instrumental mass fractionation during sulfur isotope analysis by secondary ion mass spectrometry in natural and synthetic glasses

Sulfur isotope ratios are among the most commonly studied isotope systems in geochemistry. While sulfur isotope ratio analyses of materials such as bulk rock samples, gases, and sulfide grains are routinely carried out, in-situ analyses of silicate glasses such as those formed in magmatic systems are relatively scarce in the literature. Despite a number of attempts in recent years to analyse sulfur isotope ratios in volcanic and experimental glasses by secondary ion mass spectrometry (SIMS), the effects of instrumental mass fractionation (IMF) during analysis remain poorly understood. In this study we use more than 600 sulfur isotope analyses of nine different glasses to characterise the matrix effects that arise during sulfur isotope analysis of glasses by SIMS. Samples were characterised for major element composition, sulfur content, and sulfur isotope ratios by independent methods. Our glasses contain between 500 and 3400 ppm sulfur and cover a wide compositional range, including low-silica basanite, rhyolite, and phonolite, allowing us to investigate composition-dependent IMF. We use SIMS in multi-collection mode with a Faraday cup/electron multiplier detector configuration to achieve uncertainty of 0.3‰ to 2‰ (2σ) on measured δ34S. At high sulfur content, the analytical error of our SIMS analyses is similar to that of bulk analytical methods, such as gas-source isotope ratio mass spectrometry. We find IMF causes an offset of −12‰ to +1‰ between bulk sulfur isotope ratios and those measured by SIMS. Instrumental mass fractionation correlates non-linearly with glass sulfur contents and with a multivariate regression model combining glass Al, Na, and K contents. Both ln(S) and Al-Na-K models are capable of predicting IMF with good accuracy: 84% (ln(S)) and 87% (Al-Na-K) of our analyses can be reproduced within 2σ combined analytical uncertainty after a correction for composition-dependent IMF is applied. The process driving IMF is challenging to identify. The non-linear correlation between glass S content and IMF in our dataset resembles previously documented correlation between glass H2O abundance and IMF during D/H ratio analyses by SIMS, and could be attributed to changes in 32S− and 34S− ion yields with changing S content and glass composition. However, a clear correlation between S ion yields and S content cannot be identified in our dataset. We speculate that accumulation of alkalis at the SIMS crater floor may be the principal driving force of composition-dependent IMF. Nonetheless, other currently unknown factors could also influence IMF observed during S isotope ratio analyses of glasses by SIMS. Our results demonstrate that the use of multiple, well-characterised standards with a wide compositional range is required to calibrate SIMS instruments prior to sulfur isotope analyses of unknown silicate glasses. Matrix effects related to glass Al-Na-K contents are of particular importance for felsic systems, where alkali and aluminium contents can vary considerably more than in mafic magmas.

Tracing sulfur sources in the crust via SIMS measurements of sulfur isotopes in apatite

We present a refined approach for acquiring sulfur (S) isotope compositions (33S/32S, 34S/32S) in apatite by secondary ion mass spectrometry (SIMS), including the characterisation of new reference materials. In order to test the method, we analyzed potential apatite reference samples for their S isotope ratios via three different bulk methods. The investigated apatite samples contain S concentrations between ~160 μg/g and 3100 μg/g and their 34S/32S (δ34S) ratios deviate by more than 25‰ from the Vienna-Canyon Diablo Troilite (VCDT) standard. We identified four candidates as new primary reference materials for routine SIMS S isotope measurements of apatite. Based on ICP-MS, EA-IRMS, and fluorination analyses, recommended S isotope values are +12.27± 0.22 (2σ) ‰ δ34S for SAP1, +14.02 ± 0.22 (2σ) ‰ δ34S for Big1, −1.06 ± 0.80 (2σ) ‰ δ34S for Durango-A, and −1.39 ± 0.48 (2σ) ‰ for Durango-B. By selecting one of those four primary standards for SIMS analysis, the S isotope values of the other reference materials and additional tested apatite specimens can be reproduced to within 1‰. Under optimized SIMS conditions, single spot uncertainty for δ34S that combines the within-spot precision and the repeatability of measurements of the primary apatite reference material during an analytical session is ±0.4‰ (95% CI). We also show that in apatite with S > 1000 μg/g, SIMS analysis permits the detection of mass-independent S isotope signatures (i.e., Δ33S) that are larger than ~1.0‰ if an average of multiple grains is used, and larger than ~1.5‰ for a single analytical point. Furthermore, our study shows that apatite can record S isotope signatures from extremely diverse environments, making this near-ubiquitous mineral a key candidate for tracing S source reservoirs and to track the pathway of magmatic-hydrothermal fluids in a wide range of geological settings.

Method for Evaluating Hydrogen Embrittlement of High-Strength Steel Sheets Considering Press Formation and Hydrogen Existence State in Steel

High strength steel sheets are increasingly being used due to the growing need to improve fuel efficiency by reducing vehicle weight. Steel sheets are usually used as automotive parts formed by pressing, etc., and complicated strain is generated in the steel sheet after forming. This strain is thought to affect the occurrence of hydrogen embrittlement. In this study, a new hydrogen embrittlement evaluation method using a forming limit diagram was devised. A forming limit diagram of a steel sheet with a strength level adjusted to 1470 MPa was prepared for uniaxial, plane strain and biaxial modes, and stress and hydrogen were applied to the specimens formed with respective strain modes to evaluate the occurrence of fracture. In order to examine the relationship between the hydrogen content and the cracking, evaluation of the hydrogen content by Thermal Desorption Analysis, visualization of hydrogen by Secondary Ion Mass Spectrometry and microstructure analysis by Electron BackScatter Diffraction were carried out. It was found that cracks are generated in the strain mode in which hydrogen accumulates locally in the steel even when the apparent hydrogen content is small, and it was clarified experimentally that evaluation of local hydrogen concentration is important for the evaluation of hydrogen embrittlement.

Techniques of Tracer Diffusion Measurements in Metals, Alloys and Compounds

Tracer diffusion is one of most reliable techniques for providing basic kinetic data in solids. In the present review, selected direct methods, in particular the radiotracer measurements as a superior technique due to its high sensitivity, Secondary-Ion-Mass-Spectroscopy (SIMS) profiling, X-Ray Diffraction measurements and Rutherford Backscattering Spectrometry are presented and discussed. Special attention is put on the radiotracer technique describing the currently used sectioning techniques in detail with a focus on the experimental applications and complications. The relevant experimental results are exemplary shown. Furthermore, the most recent developments and advances related to the combined tracer/inter-diffusion measurements are highlighted. It is shown that this approach offers possibilities to provide the concentration-dependent tracer diffusion coefficients of the constituting elements in multi-component alloys in high-throughput experiments. Possibilities of estimating the tracer diffusion coefficients following different types of diffusion couple methods in binary and multicomponent systems are briefly introduced. Finally, specificity of SIMS analysis of diffusion in fine-grained materials are carefully analyzed. If applicable, a direct comparison of the results obtained by different techniques is given.

Wide bandgap tunability of N-alloyed ZnGa2O4 thin films

ZnGa2O4 films with different nitrogen impurity concentrations were deposited using radio frequency magnetron sputtering in an ammonia (NH3)/Ar gas mixture and were post-annealed at different temperatures, ranging from 600 °C to 900 °C, in NH3 atmosphere. The influence of ammonia partial pressure ratio and nitridation temperature on the microstructure, surface morphology, nitrogen doping profile, and optical properties has been investigated. The optical band gap of ZnGa2O4, under in-situ nitrogen-doping, decreases from 4.6 to 4.1 eV but the primitive ZnGa2O4 crystalline structure does not change. On nitridation, the optical band gap gradually decreases from 4.6 to 2.1 eV and the ZnGa2O4 changes into a zinc gallium oxynitride quaternary alloy structure. Secondary ion mass spectrometry analysis revealed that nitrogen atoms were uniformly distributed in the film. The narrowing, by more than 40%, of the optical band gap is attributed to the hybridization of Zn3d and N2p orbits promote p-d repulsion in the top of the valence band, and the formation of hexagonal wurtzite phase.

Influence of microstructure on replacement and porosity generation during experimental dolomitization of limestones

Replacement reactions commonly alter the multiscale pore structures of rocks during fluid-rock interactions. Analysis of these processes in various model fluid-rock systems during controlled laboratory experiments provides insights into the origins of microstructures found in natural materials. This study focused on understanding the effects of initial starting material permeability and resultant differences in transport pathways on porosity and mineralogical changes during limestone dolomitization.A series of replacement experiments (32–317 days in duration) have been conducted in which 1.59 cm (5/8 in.) diameter cores of two different limestones were reacted with saturated MgCl2 solutions at 200 °C. The Texas Cream (Austin Chalk) is a high-porosity, high-permeability limestone, whereas both the porosity and permeability of the Carthage Marble (Burlington Limestone) are relatively low. Altered limestones were imaged using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), Time-of-Flight Secondary Ion Mass Spectrometry (ToF–SIMS) and electron microprobe analysis (EMPA). A representative grain boundary of the low-porosity limestone was targeted for a focused ion beam (FIB) lift-out and characterized using transmission electron microscopy (TEM). These results were coupled with analyses of radial changes in the porosity distribution of the core derived from X-ray and neutron small- and ultra-small angle scattering ((U)SANS/(U)SAXS).The high-porosity/permeability limestone showed a four times faster bulk replacement rate than the lower-porosity/permeability material, and a different mechanism of porosity development. For the low-porosity limestone, a two-stage replacement occurred, with the reacted region of the core consisting of an inner rim in which the limestone was replaced by two calcite-dolomite solid solutions, and an outer rim in which the dolomite was replaced by magnesite. Elongated pores formed along grain boundaries at the initial limestone/dolomite reaction interface, and additional nanometer-scale porosity was formed at the secondary magnesite replacement rim. Grain boundaries were identified as preferential pathways for transport leading to dolomitization and a grain boundary diffusion rate was calculated based on microstructural characterization. In contrast, replacement in the high-porosity limestone was accompanied by porosity generation through replacement of individual grains by dolomite throughout the sample and, in longer runs, magnesite in outer parts of the core. These observations emphasize that both the mechanisms of the replacement reaction and the microstructure and chemistry of the replaced product are contingent on the initial structure of the starting material.

Supercritical Extraction of Biomass—A Green and Sustainable Method to Control the Pyrolysis Product Distribution

This research demonstrates that supercritical extraction of the biomass has a remarkable and complex influence on Scots pine tree fractions changing the surface concentration of water, lipids, and metals simultaneously. Surprisingly, this surface composition modification makes a considerable impact on the pyrolysis of the bulk biomass mechanism, leading to the alternation of the volatile and inorganic matter composition. The unique combination of time-of-flight secondary-ion mass spectrometry analysis and utilization of pyrolysis gas chromatography-mass spectrometry data on the thermal behavior of woody biomass demonstrates, for the first time, the extraordinary influence of surface adsorbed metals on the composition of pyrolysis products. ScCO2 could extract the surface metals in the form of fatty acid salts, demonstrating a sustainable and environmentally friendly pretreatment method for controlling the pyrolysis products.

Interfacial Leveler-Accelerator Interactions in Cu Electrodeposition

We investigate the effect of amine-based leveler additives on the catalytic function of the accelerator at the Cu-electrolyte interface. In the presence of the bis-(sodium sulfopropyl)-disulfide (SPS) accelerator, chronopotentiometric measurements show the potential changes from inhibition of the levelers increased with molecular weight and were greater to those of glycol-based suppressors. In situ surface-enhanced Raman spectroscopy (SERS) revealed significant conformational changes of the surface-adsorbed SPS in the presence of the amine-based levelers. This leveler-induced conformational perturbation of SPS diminishes the activity of SPS. SERS also revealed decreased coverages of surface-adsorbed SPS in the presence of the high molecular weight amine-based levelers at negative potentials, indicating that the leveler limits direct contact of SPS with the surface. Decreased coverages were also found for adsorbed chloride in the presence of all levelers considered, likely contributing to the deactivation of the accelerative effect of SPS. Secondary-ion mass spectrometry (SIMS) analysis of Cu electrodeposited from solutions comprised of a linear polyethyleneimine (PEI), SPS, and Cl– show increased S, Cl, and C content in the deposit relative to solutions absent PEI, indicating the presence of PEI results in co-incorporation of these additives. This leveler-assisted incorporation of SPS and Cl– also serves to mitigate SPS acceleration.

Effect of ALD- and PEALD- Grown Al2O3 Gate Insulators on Electrical and Stability Properties for a-IGZO Thin-Film Transistor

This study investigated the electrical and stability characteristics of Al2O3 as a gate insulator, which was deposited by various atomic layer deposition methods in top-gate staggered amorphous InGaZnO (a-IGZO) thin film transistors. A trimethylaluminum precursor was used as an Al source, and H2O gas (H2O device) and O2 plasma with a long plasma time (O2 LP device) and a short plasma time (O2 SP device) were used as oxidants. The initial electrical characteristics, including the hysteresis, on–off current ratio, and subthreshold swing, were superior in the H2O device compared to the O2 LP and O2 SP devices. In the positive bias stress (PBS) results, the degradation characteristics showed a tendency similar to the transfer properties. However, under the negative bias illumination stress (NBIS), the stability of the H2O device was significantly reduced compared to the O2 LP and O2 SP devices. In this paper, the mechanism of instability, which has opposite results in terms of the PBS and NBIS for the three devices, was identified using capacitance–voltage, three-terminal charge pumping as electrical analysis techniques and secondary ion mass spectroscopy (SIMS) as a physical analysis technique. It was confirmed that the surface oxidation of a-IGZO deteriorates the interfacial properties, causing the transfer characteristics to degrade. The carbon of the Al2O3 film identified via SIMS analysis acts as a trap layer, causing deterioration in the PBS. Alternatively, in the NBIS, it was observed that the carbon acts as a capture site for photo-excited holes, thereby promoting device stability.

Dynamics of the6Li/7Li Exchange at a Graphite–Solid Electrolyte Interphase: A Time of Flight–Secondary Ion Mass Spectrometry Study

The isotopic Li-ion exchange occurring in the solid electrolyte interphase (SEI) of a graphite electrode is studied by time of flight secondary ions mass spectrometry analysis (ToF-SIMS) of Li isot...

Oxidation of reaction-bonded silicon carbide-boron carbide in air

The oxidation behaviour of reaction-bonded silicon carbide-boron carbide (RBSBC) in air for durations of 5–96 was investigated in the temperature range of 1250–1350 °C. Scanning electron microscopy observations showed that the oxide layer became uniform after 48 h, with a thickness of 3–5 μm. Transmission electron microscopy, Raman spectroscopy, and secondary ion mass spectroscopy analyses showed that the addition of 7 wt% B4C and a (SiC + Si)/B4C ratio of ∼13 resulted in an amorphous silica-rich borosilicate layer with no phase segregation and random mixing of the borates in the silica network. The oxidation kinetics profile was parabolic, where the transport of ionic oxygen is the rate-controlling step for oxide growth. The oxidation kinetics and activation energy of 353 kJ mol‒1 are close to those reported for CVD-SiC and siliconised-SiC, suggesting that the oxide behaves like pure silica. RBSBC with 7% B4C can provide a more economical alternative to SiC materials for oxidation-resistant applications, with a lower density.

Highly volatile element (H, C, F, Cl, S) abundances and H isotopic compositions in chondrules from carbonaceous and ordinary chondrites

The partial pressures and isotopic compositions of volatiles present during chondrule formation can be constrained by the highly volatile element or HVE (H, C, F, Cl, and S) abundances and isotopic compositions in chondrules. Here we present the results of high spatial resolution and low background secondary ion mass spectroscopy (SIMS) analyses of the HVE concentrations and H isotopic compositions in type I and II chondrules in primitive ordinary chondrites Semarkona (LL3.00) and Queen Alexandra Range (QUE) 97008 (L3.05), and the primitive carbonaceous chondrite Dominion Range (DOM) 08006 (CO3.00). The HVEs in the chondrules primarily reside in the mesostases, in which the HVE contents and H isotopic compositions vary significantly (H2O: 8–10,200 ppm, CO2: 2.4–1170 ppm, F: 0.3–30 ppm, Cl: 0.07–175 ppm, S: 0.38–4400 ppm, δD: 77–15,000‰). To dissolve such HVE contents in a silicate melt requires significantly higher total pressures (up to 1900 bars), and in some cases requires anomalous gas compositions (CO dominated), compared to those expected from canonical conditions of chondrule formation (∼10−3 bars, H2 + H2O dominated). Rather, the enrichments of H2O, CO2, Cl, and F in the mesostases at the edges of some chondrules suggest that there were secondary influxes of HVEs into the chondrule mesostases from the surrounding matrix during parent body processes. Consistent with this, melt inclusions sealed in olivine phenocrysts have significantly lower HVE contents than the mesostases in contact with the surrounding matrix material. Further, the calculated diffusion distances of H2O in silicate glasses under the relevant conditions are comparable to the radii of the chondrules. The high δD values in the mesostases could have been generated through isotopic Rayleigh fractionation as a result of the loss of very D-poor H2 generated from Fe metal oxidation by H2O in the parent bodies. Based on these results, we hypothesize that the bulk of the HVEs in the chondrules are secondary in origin. However, a small portion of the HVEs in chondrules could be primary, as there are low but measurable amounts of HVEs in the melt inclusions that are sealed in phenocrysts. Further, measured S contents in some chondrule mesostases agree with those predicted in a sulfide saturated silicate melt based on an experimentally calibrated thermodynamic model. We constrain the upper limits of primary HVEs in the chondrules based on the lowest measured HVE contents to minimize the effects of the secondary influx of HVEs (type I H2O: 7–11 ppm, CO2: 0.3–0.6 ppm, F: 0.1–0.2 ppm, Cl: 0.01–0.03 ppm, S: 0.3–60 ppm, and type II H2O: 50–85 ppm, CO2: 0.4–3 ppm, F: 0.04–2 ppm, Cl: 0.04–2 ppm, S: 190–260 ppm).

Surface galvanic formation of Co-OH on Birnessite and its catalytic activity for the oxygen evolution reaction

Low-cost, high-efficient catalysts for water splitting can be potentially fulfilled by developing earth-abundant metal oxides. In this work, surface galvanic formation of Co-OH on K0.45MnO2 (KMO) was achieved via the redox reaction of hydrated Co2+ with crystalline Mn4+. The synthesis method takes place at ambient temperature without using any surfactant agent or organic solvent, providing a clean, green route for the design of highly efficient catalysts. The redox reaction resulted in the formation of ultrathin Co-OH nanoflakes with high electrochemical surface area. X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the changes in the oxidation state of the bulk and surface species on the Co-OH nanoflakes supported on the KMO. The effect of the anions, such as chloride, nitrate and sulfate, on the preparation of the catalyst was evaluated by electrochemical and spectrochemical means. XPS and Time of flight secondary ion mass spectrometry (ToF-SIMS) analysis demonstrated that the layer of CoOxHy deposited on the KMO and its electronic structure strongly depend on the anion of the precursor used during the synthesis of the catalyst. In particular, it was found that Cl- favors the formation of Co-OH, changing the rate-determining step of the reaction, which enhances the catalytic activity towards the OER, producing the most active OER catalyst in alkaline media.

The Interface Characterization of 2-Mercapto-1-methylimidazole Corrosion Inhibitor on Brass

This work presents a detailed surface analytical study and surface characterization, with an emphasis on the X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses of 2‑mercapto‑1‑methylimidazole (MMI) as a corrosion inhibitor for brass. First, the electrochemical measurements demonstrated a corrosion inhibition effect of MMI in a 3 wt.% NaCl solution. Next, the formation of the MMI surface layer and its properties after 1 month of immersion was analyzed with attenuated total reflectance–Fourier-transform infrared spectroscopy, atomic force microscopy, field-emission scanning electron microscopy, and contact angle analysis. Moreover, to gradually remove the organic surface layer, a gas cluster ion beam (GCIB) sputtering source at different accelerated voltages and cluster sizes was employed. After each sputtering cycle, a high-resolution XPS analysis was performed. Moreover, an angle‑resolved XPS analysis was carried out for the MMI-treated brass sample to analyze the heterogeneous layered structure (the interface of the MMI organic/inorganic brass substrate). The interface properties were also investigated in detail using ToF-SIMS for spectra measurements and 2D imaging. Special attention was devoted to the possible spectral interferences for MMI‑related species. The thermal stability of different MMI-related species using molecular-specific signals without possible spectral interferences was determined by performing a cooling/heating experiment associated with ToF-SIMS measurements. It was shown that these species desorbed from the brass surface in the temperature range of 310–370 °C.

Temperature control on high-resolution SIMS oxygen isotopic compositions in Porites coral skeletons

Oxygen isotope composition (δ18O) in Porites coral skeletons at the micrometer scale has been proposed to be uninfluenced by temperature in previous studies. Considering that temperature is the main controlling factor of coral δ18O at the macro scale, the effect of temperature on the δ18O variations at the micrometer scale should be evaluated carefully. To better understand the climatic and biological significance of high-resolution δ18O in coral skeletons, in situ δ18O values were analyzed in three modern Porites corals from the South China Sea and the Great Barrier Reef by a Cameca IMS 1280-HR secondary ion mass spectrometry (SIMS). A twice vacuum impregnation procedure for sample mount preparation and a subsection calibration method based on multiple controlling points for coral matrix effect correction were used for SIMS analysis. The derived SIMS coral δ18O time series exhibit consistent long-term variations with the monthly δ18O (measured by conventional gas isotope ratios mass spectrometry), monthly Sr/Ca, and daily sea surface temperature, first highlighting the dominant temperature control on micrometer-scale coral δ18O. The 1.5‰ fluctuation amplitude of SIMS coral δ18O at the scales of 400–800 μm can be explained by the combined SST effects of ~10-day variation and day–night fluctuation, whereas the effects of seawater δ18O and growth rate on SIMS coral δ18O seem not dominant. Some abnormally negative δ18O values possibly resulted from the primary ion bombardment on indistinguishable centers of calcification.

Practical Aspects of Focused Ion Beam Time-of-Flight Secondary Ion Mass Spectrometry Analysis Enhanced by Fluorine Gas Coinjection

The interest in using high vacuum-compatible time-of-flight secondary ion mass spectrometry (TOF-SIMS) detectors integrated within focused ion beam instruments (FIB) has increased due to the possibility of conducting correlative and/or complementary studies with other techniques such as scanning electron microscopy, energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy, electron backscatter diffraction, atomic force microscopy, and Raman spectroscopy without breaking vacuum conditions. This work discusses the practical aspects of FIB-TOF-SIMS analysis enhanced by fluorine gas. A series of systematic experiments with high-purity Al and Cu single crystals was conducted. We demonstrate that fluorine-assisted FIB-TOF-SIMS analysis yields up to several orders of magnitude higher SIMS signals due to chemically improved ionization probability of elements. The potential of fluorine gas-assisted FIB-TOF-SIMS analysis and the correlated benefits are demonstrated on a real-life sample based on comparing the results to EDS and TOF-SIMS experiments conducted without any gas. Our studies indicate that the presence of fluorine gas reduces the negative effect of preferential reoxidation of the sample surface. This enables high lateral resolution FIB-TOF-SIMS mapping because the secondary ion signals are not dominated by elements with strongly oxygen-enhanced ionization probability.

Application of μRBS/ERDA system in microstructured devices

This paper reports on the application of Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA) using the microbeam system at Tohoku University. The first microbeam RBS/ERDA spectra in this beam line were successfully obtained for microstructured semiconductor devices. The results indicate a clear difference in stoichiometry and thickness after annealing. In addition, a comparison with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analysis is presented.

Charging Compensation Layer on Polyimide for Enhanced Device Stability in Flexible Technology

In this paper, we propose a structure that prevents the charging effects that occur in devices fabricated on polyimide (PI) substrates. In general, when fabricating a device on a PI substrate, an inorganic barrier layer is first deposited to prevent penetration of oxygen and moisture. In this study, we confirmed that fluorine ions were induced from PI by bias stress and proposed a SiOCH/SiO2 double layer as a barrier to prevent charging. Then, Al/PI/SiO2/Al and Al/ PI/SiOCH/SiO2/Al metal–insulator–metal capacitors were manufactured. The capacitor characteristics before and after application of bias stress were verified through current–voltage (I–V) and capacitance–voltage (C–V), which are electrical characterization methods, and secondary ion mass spectrometry (SIMS), which is a physical analysis method. As the voltage increased, the capacitance and current of the Al/PI/SiO2/Al capacitor varied, but those of the Al/PI/SiOCH/SiO2/Al device did not change. Finally, SIMS analysis confirmed that the PI-derived fluorine ions replaced the Si–CH3 bonds within the SiOCH film with Si–F bonds, thereby preventing capacitance and current fluctuations.

Effect of temperature on tribological performance of organic friction modifier and anti-wear additive: Insights from friction, surface (ToF-SIMS and EDX) and wear analysis

Tribological performance of an organic friction modifier (glycerol monooleate – GMO), an anti-wear additive (zinc dialkyldithiophosphate – ZDDP) and its combination was studied using a ball-on-disc tribometer equipped with optical interferometry at 90 °C and 140 °C. Higher temperatures were needed for the formation of additive layers and chemically reactive anti-wear protective layers. Comparison of Stribeck curves obtained after different rubbing durations showed that GMO reduced friction at low speed sliding-rolling contact. Despite notable decrease in the base oil viscosity with increase in temperature — in turn, increasing the severity of asperity contact — GMO exhibited enhanced frictional performance. The presence of ZDDP alone in the formulation led to significant increase in friction at both low and high temperatures, with the thickness of tribofilm unaffected after prolonged rubbing. The addition of friction modifier to ZDDP-based formulation reduced the friction in the boundary lubrication regime where longer rubbing aided in effective friction reduction at higher temperature. For the binary additive system, the friction coefficient was found to lie between the values corresponding to the single additives. The observed tribological response is attributed to preferential adsorption of the friction modifier over ZDDP and/or ZDDP decomposition products. This notion was corroborated by the results obtained from static and dynamic time-of-flight secondary ion mass spectrometry (ToF-SIMS) and energy-dispersive X-ray spectroscopy (EDX) analysis of the disc surface post tribological measurement. The concentration gradient of different chemical species detected in the tribofilm correlated with the frictional performance of the additives. Analysis of surface roughness and wear scar width showed an improvement in wear performance at higher temperature suggesting the friction modifier and anti-wear additive adsorbed on the surface providing a mechanical barrier. A synergistic effect on the wear performance was observed for GMO + ZDDP-based formulations, which resulted in a smaller wear scar compared to the individual additives.

Cell Cycle, Filament Growth and Synchronized Cell Division in Multicellular Cable Bacteria.

Cable bacteria are multicellular, Gram-negative filamentous bacteria that display a unique division of metabolic labor between cells. Cells in deeper sediment layers are oxidizing sulfide, while cells in the surface layers of the sediment are reducing oxygen. The electrical coupling of these two redox half reactions is ensured via long-distance electron transport through a network of conductive fibers that run in the shared cell envelope of the centimeter-long filament. Here we investigate how this unique electrogenic metabolism is linked to filament growth and cell division. Combining dual-label stable isotope probing (13C and 15N), nanoscale secondary ion mass spectrometry, fluorescence microscopy and genome analysis, we find that the cell cycle of cable bacteria cells is highly comparable to that of other, single-celled Gram-negative bacteria. However, the timing of cell growth and division appears to be tightly and uniquely controlled by long-distance electron transport, as cell division within an individual filament shows a remarkable synchronicity that extends over a millimeter length scale. To explain this, we propose the “oxygen pacemaker” model in which a filament only grows when performing long-distance transport, and the latter is only possible when a filament has access to oxygen so it can discharge electrons from its internal electrical network.