Secondary Ion Research Articles

Secondary metal ion-induced electrochemical reduction of U(VI) to U(IV) solids

Recent studies have shown that aqueous U(VI) ions can be transformed into U(VI) precipitates through electrocatalytic redox reactions for uranium recovery. However, there have been no reports of U(IV) solids, such as UO2, using electrochemical methods under ambient conditions since low-valence states of uranium are typically oxidized to U(VI) by O2 or H2O2. Here we developed a secondary metal ion-induced strategy for electrocatalytic production of U(IV) solids from U(VI) solutions using a catalyst consisting of atomically dispersed gallium on hollow nitrogen-doped carbon capsules (Ga-Nx-C). This method relies on the presence of secondary metal ions, e.g., alkaline earth metals, transition metals, lanthanide metals, and actinide metals, which promote the generation of UO2 or bimetallic U(IV)-containing oxides through a two-electron transfer process. No U(IV) solid products were generated in the presence of alkali metal ions. Mechanistic studies revealed that the strong binding affinity between U(IV) and alkaline earth metals (Ca2+/Mg2+/Sr2+/Ba2+), transition metals (Ni2+/Zn2+/Pb2+/Fe3+, etc.) and lanthanide/actinide metals (Ce4+/Eu3+/Th4+/La3+) suppressed re-oxidation of U(IV) to U(VI), leading to the generation of U(IV)O2 and Mx(M = Ce, Eu, Th, La)U(IV)yO2. This work provides fundamental insights into the electrochemical behavior of uranium in aqueous media, whilst guiding uranyl capture from nuclear waste and contaminated water.

Studying microbially induced corrosion on glass using ToF-SIMS.

Microbially induced corrosion (MIC) is an emerging topic that has huge environmental impacts, such as long-term evaluation of microbial interactions with radioactive waste glass, environmental cleanup and disposal of radioactive material, and weathering effects of microbes. Time-of-flight secondary ion mass spectrometry (ToF-SIMS), a powerful mass spectral imaging technique with high surface sensitivity, mass resolution, and mass accuracy, can be used to study biofilm effects on different substrates. Understanding how to prepare biofilms on MIC susceptible substrates is critical for proper analysis via ToF-SIMS. We present here a step-by-step protocol for preparing bacterial biofilms for ToF-SIMS analysis, comparing three biofilm preparation techniques: no desalination, centrifugal spinning (CS), and water submersion (WS). Comparisons of two desalinating methods, CS and WS, show a decrease in the media peaks up to 99% using CS and 55% using WS, respectively. Proper desalination methods also can increase biological signals by over four times for fatty acids using WS, for example. ToF-SIMS spectral results show chemical compositional changes of the glass exposed in a Paenibacillus polymyxa SCE2 biofilm, indicating its capability to probe microbiologically induced corrosion of solid surfaces. This represents the proper desalination technique to use without significantly altering biofilm structure and substrate for ToF-SIMS analysis. ToF-SIMS spectral results showed chemical compositional changes of the glass exposed by a Paenibacillus bacterial biofilm over 3-month inoculation. Possible MIC products include various phosphate phase molecules not observed in any control samples with the highest percent increases when experimental samples were compared with biofilm control samples.

Oceanic and Sedimentary Microbial Sulfur Cycling Controlled by Local Organic Matter Flux During the Ediacaran Shuram Excursion in the Three Gorges Area, South China.

The increased difference in the sulfur isotopic compositions of sedimentary sulfate (carbonate-associated sulfate: CAS) and sulfide (chromium-reducible sulfur: CRS) during the Ediacaran Shuram excursion is attributed to increased oceanic sulfate concentration in association with the oxidation of the global ocean and atmosphere. However, recent studies on the isotopic composition of pyrites have revealed that CRS in sediments has diverse origins of pyrites. These pyrites are formed either in the water column/shallow sediments, where the system is open with respect to sulfate, or in deep sediments, where the system is closed with respect to sulfate. The δ34S value of sulfate in the open system is equal to that of seawater; on the contrary, the δ34S value of sulfate in the closed system is higher than that of seawater. Therefore, obtaining the isotopic composition of pyrites formed in an open system, which most likely retain microbial sulfur isotope fractionation, is essential to reconstruct the paleo-oceanic sulfur cycle. In this study, we carried out multiple sulfur isotope analyses of CRS and mechanically separated pyrite grains (>100 μm) using a fluorination method, in addition to secondary ion mass spectrometry (SIMS) analyses of insitu δ34S values of pyrite grains in drill core samples of Member 3 of the Ediacaran Doushantuo Formation in the Three Gorges area, South China. The isotope fractionation of microbial sulfate reduction (MSR) in the limestone layers of the upper part of Member 3 was calculated to be 34ε = 55.7‰ and 33λ = 0.5129 from the δ34S and Δ33S' values of medium-sized pyrite grains ranging from 100 to 300 μm and the average δ34S and Δ33S' values of CAS. Model calculations revealed that the influence of sulfur disproportionation on the δ34S values of these medium-sized pyrite grains was insignificant. In contrast, within the dolostone layers of the middle part of Member 3, isotope fractionation was determined to be 34ε = 47.5‰. The 34ε value in the middle part of Member 3 was calculated from the average δ34S values of the rim of medium-sized pyrite grains and the average δ34S values of CAS. This observation revealed an increase in microbial sulfur isotope fractionation during the Shuram excursion at the drill core site. Furthermore, our investigation revealed correlations between δ34SCRS values and CRS concentrations and between CRS and TOC concentrations, implying that organic matter load to sediments controlled the δ34SCRS values rather than oceanic sulfate concentrations. However, these CRS and TOC concentrations are local parameters that can change only at the kilometer scale with local redox conditions and the intensity of primary production. Therefore, the decreasing δ34SCRS values likely resulted from local redox conditions and not from a global increase in the oceanic sulfate concentration.

New diagenetic constraints for the interpretation of Neoarchaean stromatolitic dolostone geochemical composition and their palaeoenvironmental significance

Abstract The stromatolitic dolostones of the Ramonnedi Formation in the Lower Transvaal Supergroup of Botswana formed along a shallow carbonate platform during the transition between the Archaean and Proterozoic eons. These dolostones are bound to reveal more details of the mechanisms and timing of Earth oxygenation and particularly the role of microbial communities in the formation of carbonate platforms in the Archaean; but only if we are able to discriminate what signature is pristine and what is due to diagenetic overprinting. Here, the focus is on the isotopic composition of stromatolitic dolostone, pyrite grains and chert laminations found within the Ramonnedi Formation. Oxygen and carbon isotopes were investigated from the Ramonnedi Formation stromatolitic dolostones in order to constrain chemo-physical conditions at the time of deposition and, eventually, evaluate to what extent the system was re-set during diagenetic processes. In situ δ34S and δ18O compositions were determined by secondary ionisation mass spectrometry (SIMS) from pyrite and chert, respectively. These novel results complement previous analyses and reveal that: (i) the pyrite grains are not common in the dolostones and when present have sulphur isotope compositions that point toward abiotic formation; (ii) dolostone δ13CVPDB values between -1.2 and -0.7‰ are close to marine values and might reflect pristine Archaean signature; (iii) the dolostone δ18OVPDB values, between -9 and -11‰, on the other hand, might reflect diagenetic resetting or very warm Archaean seawater, in line with the δ18O values from the chert laminae in the upper Ramonnedi Formation. (iv) The correct interpretation of these results has important implications in the interpretation of the geochemical proxies coming from the lower Transvaal Supergroup carbonate platform and for the interpretation of the onset of the Great Oxidation Event (GOE). Aim of this work is to complement the existing data on the Lower Transvaal Supergroup of Botswana and assess to what extent the geochemistry of these dolostone was overprinted during diagenesis/metasomatism. These results indicate that a multi-analytical approach is required to ensure the correct interpretation of geochemical proxy data related to the onset of the GOE.

Footwall refrigeration versus footwall hydration: Reassessing steep thermal gradients below detachment faults with in situ SIMS oxygen isotope analysis

The extensional detachment systems of metamorphic core complexes (MCC) have the potential to facilitate significant fluid movement between Earth's surface and the warm, ductile middle crust. One long-standing and influential detachment fault-fluid interaction model called the “footwall refrigeration hypothesis” (Morrison and Anderson, 1998) postulates that cool meteoric fluids circulating downward along a detachment can facilitate large-scale heat loss at depth before rocks are exhumed by faulting. Stable isotopes of oxygen and hydrogen have long been recognized as potentially useful tracers of surface-to-depth fluid flow in core complexes; however, typical sampling methods and the competing effects between temperature and fluid composition have made oxygen isotope signatures of meteoric fluid infiltration difficult to detect and/or interpret in the rock record.Here, we use in situ δ18O measurements by secondary ion mass spectrometry (SIMS) to address the rock record of meteoric fluid interactions and temperature variation within the Whipple Mountains MCC footwall beneath the Whipple detachment fault (WDF). The micro-scale sampling of SIMS (10 µm diameter x 1–2 µm deep pits) allows investigation of isotope variability as a function of mineral geochemistry and microstructure and enables more accurate interpretation of the causes of isotope variability. In the Whipple footwall mylonites, quartz and epidote show grain-to-grain oxygen-isotope variability within samples and as a function of distance from the main detachment. Approaching the WDF, both quartz and epidote show increasing spread toward low δ18O values. The lowest SIMS-measured δ18O epidote values require exchange with a low δ18O, meteoric fluid at high temperature. However, SIMS data also reveal that meteoric fluid-rock interactions were spatially heterogeneous at the scale of individual grains, resulting in local preservation of metamorphic quartz-epidote oxygen isotope equilibrium unaffected by infiltrating meteoric fluid. Within preserved metamorphic domains at all investigated structural levels of the WDF footwall, quartz and epidote δ18O values are tightly clustered and yield similar fractionations (∆18Oqz-ep). For samples from the longest footwall traverse, these ∆18Oqz-ep values are 4.0 ± 0.4‰, consistent with δ18O equilibrium at 521+43/-37 °C. We conclude that there is no evidence of a large paleo-thermal gradient associated with the Whipple Detachment Fault (i.e., no evidence for footwall refrigeration).

NST3 induces ectopic transdifferentiation, forming secondary walls with diverse patterns and composition in Arabidopsis thaliana.

The master transcription factor NAC SECONDARY WALL THICKENING PROMOTING FACTOR3 (NST3), also known as SND1, plays a pivotal role in regulating secondary cell wall (SCW) development in interfascicular and xylary fibers in Arabidopsis thaliana. Despite progress in understanding SCW assembly in xylem vessel-like cells, the mechanisms behind its assembly across different cell types remain unclear. Overexpressing NST3 or its homolog NST1 leads to reduced fertility, posing challenges for studying their impact on secondary wall formation. This study aimed at developing a tightly regulated dexamethasone (DEX)-inducible expression system for NST3 and NST1 to elucidate the structure and assembly of diverse SCWs. Using the DEX-inducible system, we characterized ectopically formed SCWs for their diverse patterns, mesoscale organization, cellulose microfibril orientation, and molecular composition using spinning disk confocal microscopy, field emission scanning electron microscopy (FESEM), vibrational sum-frequency generation (SFG) spectroscopy and, histochemical staining and time-of-flight secondary ion mass spectrometry (ToF-SIMS), respectively. Upon DEX treatment, NST3 and NST1 transgenic hypocotyls underwent time-dependent transdifferentiation, progressing from protoxylem-like to metaxylem-like cells. NST3-induced plants exhibited normal growth but had rough secondary wall surfaces with delaminating S2 and S3 layers. Mesoscale examination of induced SCWs in epidermal cells revealed that macrofibril thickness and orientation were comparable to xylem vessels, while wall thickness resembled that of interfascicular fibers. Additionally, induced epidermal cells formed SCWs with altered cellulose and lignin contents. These findings suggest NST3 and/or NST1 induce SCWs with shared characteristics of both xylem and fiber-like cells forming loosely arranged cell wall layers and cellulose organized at multiple angles relative to the cell growth axis and with varied cellulose and lignin abundance. This inducible system opens avenues to explore ectopic SCWs for bioenergy and bioproducts, offering valuable insights into SCW patterning across diverse cell types and developmental stages.

Chain forming diatoms use different strategies to avoid diffusion limited N assimilation

AbstractFormation of large colonies by phytoplankton is considered a disadvantage during low nutrient and non‐turbulent conditions because of diffusion limitation and competition by neighboring cells. This is assumed by diffusion models and not empirical measurements. Here, we measured cell‐specific dissolved inorganic carbon (DIC) and nitrate () assimilation in two chain‐forming Skeletonema marinoi strains by combining secondary ion mass spectrometry with stable isotopic tracer incubations. The pelagic strains were recently germinated from resting stages and thus not adapted to high nutrient regimes of laboratory cultures. During the exponential phase, the cells assimilated excess relative to DIC. The DIC and assimilation varied with chain length or the position of the cell within chains but did not follow any consistent trend. Solitary cells were rare and did not exceed 6% of all cells. During the nitrogen‐limited stationary phase, assimilation was lower than modeled by mass transfer theory at diffusion limitation. assimilation rates were apparently limited by the biological uptake rate at nitrate concentrations < 0.46 μmol L−1. We conclude that S. marinoi is adapted to high nutrient concentrations and may seldom be diffusion limited in coastal waters with ambient concentrations > 0.46 μmol L−1. These findings contrast those previously reported in larger chain forming diatoms, for example, Chaetoceros, which appear to circumvent diffusion limitation at low ambient concentrations and succeed S. marinoi during spring blooms.

Active site requirements for bio-alcohol dehydration: Effect of chemical structure and site proximity

Synthesis-structure-activity relations are reported, describing how interzeolite conversion (IZC) allows synthesis of ZSM-5 (MFI framework) with fixed physicochemical properties, except the variable local acid site (Al) arrangement, by variation of the synthesis time. Local confinement and acidity effects are probed by applying both H-ZSM-5 and Na-ZSM-5 samples in alcohol dehydration. Pyridine and divalent cobalt ion probing are used to quantify the amount of accessible acid sites and of Al in close proximity. Al in close proximity shows a strong influence on n-butanol dehydration turnover rates. The turnover rates are also strongly dependent on local confinement: in Na-form, ZSM-5 synthesized with more Al present as isolated species is a factor of 3–7 times more active than Na-ZSM-5 with fewer isolated Al. However if the zeolites are in proton form, ZSM-5 with more proximate sites show a higher activity compared to ZSM-5 with more isolated sites. Linear butene selectivity increases in Na-ZSM-5 compared to H-ZSM-5, caused by a suppressed dibutyl ether formation. The selectivity towards 1-butene is enhanced to a greater extent on proximate sites, likely due to a local/steric constraint at the active site. Decomposition of DBE over Na-ZSM-5 is more active compared to n-butanol dehydration, independent of acid site proximity. Also for 2-propanol dehydration, Na-ZSM-5 is less active than H-ZSM-5, yet the activity difference is attenuated compared to n-butanol dehydration. Essentially, due to the intrinsic higher reactivity of 2-propanol, the acid site requirement is less stringent. These findings highlight the importance of local confinement and Al proximity in acid-catalyzed conversion of oxygenated compounds.

Investigations into the Impact of Deposition or Growth Techniques on the Field Oxide TID Response for 4H-SiC Space Applications

The total ionising dose (TID) reliability of a phosphorous pentoxide (P2O5) treated SiO2 (silicon dioxide) layer is compared for the first time to other industrially relevant oxides formed on 4H-silicon carbide (SiC). Metal-oxide-semiconductor capacitors (MOSCAPs) are characterised before and after irradiation to ascertain changes in flat band voltage shift, leakage current, and dielectric breakdown (BV). Secondary ion mass spectrometry (SIMS) profiling reveals a significant phosphorus concentration near the SiO2/SiC interface, which led to improved TID resistance. The P2O5 treated oxide had the lowest leakage current at high voltage bias due to the high-temperature (1,000°C) anneal, though it had a significantly negative flat band voltage due to the high concentration of deposited phosphorus atoms. The thermal and P2O5 oxides demonstrated a TID resistance, suffering only minor shifts in flat band voltage, while the P2O5 oxide suffered the smallest decrease in its BV and the smallest leakage current rise, post-irradiation.

Synthesis and Characterization of Metallic (Fe‐Ni, Fe‐Ni‐Si) Reference Materials for SIMS 34S/32S Measurements

Secondary ion mass spectrometry (SIMS) is often used to determine the sulfur contents and isotope ratios of metallic alloys in meteorites or high‐pressure experimental samples. However, SIMS analyses involve calibration and the determination of instrumental mass fractionation in reference materials with a matrix composition similar to that of the unknown samples. To provide metallic reference materials adapted to S measurements via SIMS, we synthesised a series of twenty‐eight alloys comprising four FeNi(±Si) compositions (Fe95Ni5, Fe90Ni10, Fe80Ni20, and Fe80Ni15Si5) with S contents varying from 100 μg g−1 to 4 g/100g using the “melt spinning” method, which guarantees that the metal alloys are rapidly quenched at ~ 106 K s−1. Sulfur contents were determined at the Service d'Analyse des Roches et Minéraux at the CRPG and absolute δ34S values were determined by multi‐collector ICP‐MS (MC‐ICP‐MS, ThermoScientific Neptune) and isotope ratio mass spectrometry (Thermoscientific Delta V). A δ34S value of 16.01 ± 0.31‰ was consistently obtained using the MC‐ICP‐MS, which was indistinguishable of the δ34S value of the FeS starting material (15.95 ± 0.08‰). It suggests that S did not undergo isotopic fractionation during the melting process. Of fifteen samples containing ≤ 5000 μg g−1 S, SIMS measurements with 15‐μm‐diameter spots were repeatable to within 10% relative (1 standard deviation, 1s) for S contents and 2‰ for δ34S values. However, samples containing > 5000 μg g−1 S showed FeNi–FeS immiscibility, leading to minor dispersion of the S mass fractions and δ34S values. No matrix effect was observed for Fe‐Ni, Si, or S contents in terms of the calibration curves and instrumental mass fractionation. We ultimately recommend eight samples as reliable reference materials for S isotopic measurements by SIMS, which we can share worldwide with other laboratories.

Extensive hydrogen incorporation is not necessary for superconductivity in topotactically reduced nickelates

A key open question in the study of layered superconducting nickelate films is the role that hydrogen incorporation into the lattice plays in the appearance of the superconducting state. Due to the challenges of stabilizing highly crystalline square planar nickelate films, films are prepared by the deposition of a more stable parent compound which is then transformed into the target phase via a topotactic reaction with a strongly reducing agent such as CaH2. Recent studies, both experimental and theoretical, have introduced the possibility that the incorporation of hydrogen from the reducing agent into the nickelate lattice may be critical for the superconductivity. In this work, we use secondary ion mass spectrometry to examine superconducting La1−xXxNiO2 / SrTiO3 (X = Ca and Sr) and Nd6Ni5O12 / NdGaO3 films, along with non-superconducting NdNiO2 / SrTiO3 and (Nd,Sr)NiO2 / SrTiO3. We find no evidence for extensive hydrogen incorporation across a broad range of samples, including both superconducting and non-superconducting films. Theoretical calculations indicate that hydrogen incorporation is broadly energetically unfavorable in these systems, supporting our conclusion that extensive hydrogen incorporation is not generally required to achieve a superconducting state in layered square-planar nickelates.

Characterization of Growth Sectors in Gallium Nitride Substrate Wafers

During crystal growth processes, growth sectors are formed due to growth along different crystallographic directions. Although the crystal structure in the different growth sectors is unchanged, strain induced topography contrast is observed by synchrotron X-ray topography. In this study, synchrotron monochromatic beam X-ray topography (SMBXT), synchrotron X-ray plane wave topography (SXPWT), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and secondary ion mass spectrometry (SIMS) are used to characterize growth sectors in gallium nitride (GaN) substrate wafers grown by patterned hydride vapor phase epitaxy (HVPE). The SMBXT images reveal the boundaries of {0001} and {1122} type growth sectors. Strain maps generated from SXPWT shows that the out-of-plane strains in different growth sectors have a difference of the order of 10-5. SEM images from SE2 signal shows no contrast of growth sector boundaries while images from Robinson detector (RBSD) show different growth sectors as different grey scale contrast, indicating a strain effect. SIMS analysis shows that the different oxygen impurity levels in the growth sectors, which is the origin of the strain. A formation mechanism of growth sectors in patterned HVPE grown GaN wafers is proposed.

Hydrogenation by catalytically generated atomic hydrogen for passivating contacts in crystalline silicon solar cells

Hydrogenation employing catalytically generated atomic hydrogen (Cat-H) is implemented on stacks of n-type polycrystalline silicon (poly-Si)/Si oxide (SiOx) to enhance passivation quality. The utilization of Cat-H demonstrates a substantial enhancement in surface passivation quality on crystalline Si (c-Si), resulting in an increase of the effective minority carrier lifetime (τeff) from 2.0 to 3.9 ms. The investigation reveals a dependency of τeff on the duration of Cat-H treatment: an initial rise followed by a plateau or slight decline. Secondary ion mass spectrometry (SIMS) measurements revealed the diffusion of H atoms into poly-Si and c-Si, which accumulate at the poly-Si/c-Si interface. This accumulation terminates dangling bonds in the poly-Si layer on the c-Si surface. Furthermore, the presence of an ultra-thin thermal Si oxide layer on the poly-Si layer formed during high-temperature annealing is crucial for protecting the film against etching induced by Cat-H.

An alternative chlorine-assisted optimization of CdS/Sb2Se3 solar cells: Towards understanding of chlorine incorporation mechanism

The current strategies in the development of Sb2Se3 thin film solar cells involve fabrication and optimization of superstrate and substrate device architectures, with the preferable choice for TiO2 and CdS heterojunction layers. For CdS-based superstrate cells, several studies reported the necessity to apply CdCl2 or other metal halide-based post-deposition treatment (PDT), highlighting improvement of CdS/Sb2Se3 device efficiency. However, the need, effect, and mechanism of such PDT are very often not described. Additionally, the fact that many groups have not succeeded in demonstrating its benefits suggests that this strategy is not straightforward, requiring a deeper understanding towards a more unified concept. The present study proposes an alternative approach to the challenging CdCl2 PDT of CdS in CdS/Sb2Se3 device, involving controllable Cl incorporation in CdS films by systematically varying the concentration of NH4Cl in the CBD precursor solution from 1 to 8 mM. Structural and electrical characterizations are correlated with advanced measurements of Scanning Kelvin Probe, surface photovoltage, and atomic force microscopy to understand the impact of Cl incorporation on the properties of CdS films and CdS/Sb2Se3 devices. The validity of Cl incorporation in the CdS lattice and interdiffusion processes at the CdS-Sb2Se3 interface is confirmed by secondary ion mass spectrometry analysis. It is demonstrated that incorporation of 1 mM of NH4Cl, as a Cl source in CBD CdS, can boost the PCE of CdS/Sb2Se3 by ∼20 %. With this approach, we offer new perspectives on the optimization methodology for Cl-based CdS/Sb2Se3 device processing and complementary understanding of the physiochemistry behind these processes.

Nanoparticle Diffusion in Crowded Polymer Nanocomposite Melts.

This study examines nanoparticle diffusion in crowded polymer nanocomposites by diffusing small Al2O3 nanoparticles (NPs) in SiO2-loaded P2VP matrices. Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) measures Al2O3 NP diffusion coefficients within a homogeneous PNC background of larger, immobile SiO2 NPs. By developing a geometric model for the average interparticle distance in a system with two NP sizes, we quantify nanocomposite confinement relative to the Al2O3 NP size with a bound layer. At low SiO2 concentrations, Al2O3 NP diffusion aligns with the neat polymer results. In more crowded nanocomposites with higher SiO2 concentrations where the interparticle distance approaches the size of the mobile Al2O3 NP, the 6.5 nm Al2O3 NPs diffuse faster than predicted by both core-shell and vehicular diffusion models. Relative to our previous studies of NPs diffusing into polymers, these findings demonstrate that the local environment in crowded systems significantly complicates NP diffusion behavior and the bound layer lifetimes.

Gradient conducting polymer surfaces with netrin-1-conjugation promote axon guidance and neuron transmission of human iPSC-derived retinal ganglion cells

Major advances have been made in utilizing human-induced pluripotent stem cells (hiPSCs) for regenerative medicine. Nevertheless, the delivery and integration of hiPSCs into target tissues remain significant challenges, particularly in the context of retinal ganglion cell (RGC) restoration. In this study, we introduce a promising avenue for providing directional guidance to regenerated cells in the retina. First, we developed a technique for construction of gradient interfaces based on functionalized conductive polymers, which could be applied with various functionalized ehthylenedioxythiophene (EDOT) monomers. Using a tree-shaped channel encapsulated with a thin PDMS and a specially designed electrochemical chamber, gradient flow generation could be converted into a functionalized-PEDOT gradient film by cyclic voltammetry. The characteristics of the successfully fabricated gradient flow and surface were analyzed using fluorescent labels, time of flight secondary ion mass spectrometry (TOF-SIMS), and X-ray photoelectron spectroscopy (XPS). Remarkably, hiPSC-RGCs seeded on PEDOT exhibited improvements in neurite outgrowth, axon guidance and neuronal electrophysiology measurements. These results suggest that our novel gradient PEDOT may be used with hiPSC-based technologies as a potential biomedical engineering scaffold for functional restoration of RGCs in retinal degenerative diseases and optic neuropathies.

Comparative analysis of feature annotation methods for SESI-HRMS in exhaled breath analysis

Secondary electrospray ionization coupled to high-resolution mass spectrometry (SESI-HRMS) is a powerful method for the analysis of exhaled breath in real time. However, feature annotation is challenging due to the flow-injection nature of the technique. To evaluate alternative methods for enhancing feature annotation, a study was conducted where the exhaled breath of sixteen subjects was condensed and analyzed using dynamic headspace vacuum in-trap extraction gas chromatography-mass spectrometry (DHS-V-ITEX-GC–MS) and liquid chromatography coupled to mass spectrometry (LC-MS) using polar and reverse-phase conditions along with a data-independent MS2-acquisition method based on multiple injections. The annotation results obtained from these methods were compared to those from SESI-HRMS. The use of these techniques on breath condensate is unprecedented. The GC–MS method primarily detected compounds of exogenous origin, particularly additives in oral hygiene products like menthol. On the other hand, LC-MS detected a vast number of features, especially with the utilized data-independent acquisition method. Chemical classes to these features were assigned in-silico. In positive ion mode, mostly amino acids and amines were detected, while the largest group in negative ion mode consisted of carboxylic acids. Approximately 25% and 5% of SESI features had a corresponding match with LC-MS and GC–MS. While both GC–MS and LC-MS methods partially overlapped with the SESI features, there was limited overlap of both in the mass-to-charge range from 150 to 200. In conclusion, both GC–MS and LC-MS analysis of breath condensate can serve as supplementary tools for annotating features obtained from SESI-MS. However, to increase confidence in the annotation results, combining these methods with additional on-line fragmentation techniques is recommended.

Revealing the role of oxygen on the defect evolution of electron-irradiated tungsten: A combined experimental and simulation study

The evolution of Frenkel pairs has been studied experimentally and theoretically in tungsten, a Body-Centered Cubic metal. We used positron annihilation spectroscopy to characterize vacancy defects induced by electron irradiation in two sets of polycrystalline tungsten samples at room temperature. Doppler Broadening spectrometry showed that some positrons were trapped at pure single vacancies with a lower concentration than expected. At the same time, positron annihilation lifetime spectroscopy revealed that positrons are annihilated in unexpected states with a lifetime 1.44–1.64 times shorter than that of single vacancy (200 ps), namely unidentified (X) defects. Secondary ions mass spectrometry detected a significant concentration of oxygen in these samples, of the same order of magnitude as electron-induced single vacancy. In addition, Cluster dynamics simulated defect behaviors under experimental conditions, and Two-component density functional theory was used to calculate defect annihilation characteristics that are difficult to obtain in experiments. Finally, by combining the theoretical data, we simulated the positron signals and compared them with the experimental data. This enabled us to elucidate the interactions between oxygen and Frenkel Pairs. The X defects were identified as oxygen-vacancy complexes formed during irradiation, as oxygen is mobile in tungsten at room temperature, and can be trapped in a vacancy, while its binding to self-ion atoms leads to their immobilization thus reducing defect recombination. Therefore, we anticipate oxygen to play an important role in the evolution of tungsten microstructure under irradiation.

High-temperature atomic layer deposition of silicon oxide films using Tris(dimethylamino)silane and ozone

Atomic layer deposition (ALD) benefits from high process temperatures when the substrate is not temperature-sensitive because the films deposited at higher temperatures exhibit better electrical properties. In this study, we investigated the ALD process of silicon oxide films by alternating injections of tris(dimethylamino)silane (tris-DMAS) and O3/O2 at temperatures ranging from 400 to 700 °C. The saturation dose of tris-DMAS was 1.5 × 106 L at 400 °C. Self-limiting growth with a growth rate of approximately 0.9 Å/cycle was observed up to 600 °C, allowing excellent step coverage. However, at 700 °C, the growth rate increased significantly to 4.6 Å/cycle, carbon and nitrogen impurities were detected by secondary ion mass spectrometry, and step coverage was poor, supporting the thermal decomposition of tris-DMAS at this temperature. Therefore, the optimum temperature for ALD SiO2 using tris-DMAS is 600 °C for application as an insulating film on high aspect ratio patterns. At this temperature, the leakage current density was 0.58 nA/cm2, and the oxide-trapped charge density was 4.0 × 1010 cm−2.

Quench-condensed hydrogen films studied by cryogenic time-of-flight secondary ion mass spectrometry

Quench-condensed hydrogen films studied by cryogenic time-of-flight secondary ion mass spectrometry