Oxygen Depth Profiles Research Articles

Seasonal dynamics of the microbial methane filter in the water column of a eutrophic coastal basin.

In coastal waters, methane-oxidizing bacteria (MOB) can form a methane biofilter and mitigate methane emissions. The metabolism of these MOBs is versatile, and the resilience to changing oxygen concentrations is potentially high. It is still unclear how seasonal changes in oxygen availability and water column chemistry affect the functioning of the methane biofilter and MOB community composition. Here, we determined water column methane and oxygen depth profiles, the methanotrophic community structure, methane oxidation potential, and water-air methane fluxes of a eutrophic marine basin during summer stratification and in the mixed water in spring and autumn. In spring, the MOB diversity and relative abundance were low. Yet, MOB formed a methane biofilter with up to 9% relative abundance and vertical niche partitioning during summer stratification. The vertical distribution and potential methane oxidation of MOB did not follow the upward shift of the oxycline during summer, and water-air fluxes remained below 0.6mmol m-2 d-1. Together, this suggests active methane removal by MOB in the anoxic water. Surprisingly, with a weaker stratification, and therefore potentially increased oxygen supply, methane oxidation rates decreased, and water-air methane fluxes increased. Thus, despite the potential resilience of the MOB community, seasonal water column dynamics significantly influence methane removal.

Oxygen inward diffusion and complex reorganization of the reaction layer in ion-exchanged glasses evidenced by Auger electron spectroscopy

Alkali silicate glasses subjected to low-temperature ion exchange in molten salt are being probed by Auger electron spectroscopy (AES). Spot analyses and elemental line scans across fresh fracture surfaces of broken glass specimens reveal oxygen enrichment of reaction layer where Na+-for-K+ ion exchange occurred and exceptional similarity in shapes of concentration depth profiles of potassium and oxygen. The probe provides the first direct evidence that smaller-for-larger ion replacement is accompanied by inward oxygen transport into reaction zone where potassium cations rearrange former sodium sites in accordance with their steric demands. Such chemical and structural rearrangements entail defect formation and glass network depolymerization and fragmentation, which define stress buildup and relaxation, residual stress intensity and profile in the surface layer of chemically strengthened glasses.

Regional and Global Patterns of Apparent Organic Matter Reactivity in Marine Sediments

AbstractOrganic matter (OM) degradation in marine sediments is fundamental to understanding and constraining global biogeochemical cycling, whereby OM reactivity is at its core. Here, we use benthic diffusive oxygen uptake (DOU) rates as a proxy for OM reactivity. We apply an analytical diagenetic model to inversely determine OM reactivities in marine sediments (i.e., Reactive Continuum Model parameters a and ν) using data sets of global DOU, surface sediment OM contents, and seafloor boundary conditions. Simulated oxygen depth profiles show good agreement with observations, increasing confidence in our reactivity estimates. Inversely determined reactivities vary over orders of magnitude between individual sites ranging from high (k = 0.252 year−1) for sediments in the Polar region to extremely low (k = 7.96 ⋅ 10−5 year−1) in South Pacific. Our findings highlight the heterogeneity of OM reactivities, revealing regional patterns that broadly agree with observations and prior assessments. In general, high benthic reactivity can be linked to limited pelagic OM degradation favored by either a rapid vertical or lateral OM transport to the sediment or environmental factors, such as low oxygen concentrations or low temperature, slowing pelagic OM degradation. Finally, we develop a set of transfer functions that allow estimating OM reactivity as a function of DOU, OM content and water depths, and use one to derive the first global maps of benthic OM reactivity based on two global DOU maps. Despite the inherent observational biases in the data sets, our results provide a good first‐order estimate of the apparent benthic OM reactivity agreeing with our current mechanistic understanding and observations.

Versatile methanotrophs form an active methane biofilter in the oxycline of a seasonally stratified coastal basin.

The potential and drivers of microbial methane removal in the water column of seasonally stratified coastal ecosystems and the importance of the methanotrophic community composition for ecosystem functioning are not well explored. Here, we combined depth profiles of oxygen and methane with 16S rRNA gene amplicon sequencing, metagenomics and methane oxidation rates at discrete depths in a stratified coastal marine system (Lake Grevelingen, The Netherlands). Three amplicon sequence variants (ASVs) belonging to different genera of aerobic Methylomonadaceae and the corresponding three methanotrophic metagenome-assembled genomes (MOB-MAGs) were retrieved by 16S rRNA sequencing and metagenomic analysis, respectively. The abundances of the different methanotrophic ASVs and MOB-MAGs peaked at different depths along the methane oxygen counter-gradient and the MOB-MAGs show a quite diverse genomic potential regarding oxygen metabolism, partial denitrification and sulphur metabolism. Moreover, potential aerobic methane oxidation rates indicated high methanotrophic activity throughout the methane oxygen counter-gradient, even at depths with low in situ methane or oxygen concentration. This suggests that niche-partitioning with high genomic versatility of the present Methylomonadaceae might contribute to the functional resilience of the methanotrophic community and ultimately the efficiency of methane removal in the stratified water column of a marine basin.

Reconstructing the Oxygen Depth Profile in the Arabian Sea During the Last Glacial Period

AbstractReconstructing the strength and depth boundary of oxygen minimum zones (OMZs) in the glacial ocean advances our understanding of how OMZs respond to climate changes. While many efforts have inferred better oxygenation of the glacial Arabian Sea OMZ from qualitative indices, oxygenation and vertical extent of the glacial OMZ is not well quantified. Here we present glacial‐Holocene oxygen reconstructions in a depth transect of Arabian Sea cores ranging from 600 to 3,650 m water depths. We estimate glacial oxygen concentrations using benthic foraminiferal surface porosity and benthic carbon isotope gradient reconstructions. Compared to the modern Arabian Sea, glacial oxygen concentrations were approximately 10–15 μmol/kg higher in the shallow OMZ (<1,000 m), and 5–80 μmol/kg lower at greater depths (1,500–3,650 m). Our results suggest that the OMZ in the glacial Arabian Sea was slightly better oxygenated but remained in the upper 1,000 m. We propose that the small increase in oxygenation of the Arabian Sea OMZ during the last glacial period was due to weaker upper ocean stratification induced by stronger winter monsoon winds coupled with an increase in oxygen solubility due to lower temperatures, counteracting the effects of more oxygen consumption resulting from higher primary productivity. Large‐scale changes in ocean circulation may have also contributed to better ventilation of the glacial Arabian Sea OMZ.

Weak Hypoxia Enhanced Denitrification in a Dissimilatory Nitrate Reduction to Ammonium (DNRA)-Dominated Shallow and Eutrophic Coastal Waterbody, Jinhae Bay, South Korea

The effects of seasonal hypoxia on sediment-water interface nitrogen (N) transformations in Jinhae Bay were examined from 2015 to 2019. The rates of benthic denitrification, anaerobic ammonium oxidation (anammox), dissimilatory nitrate reduction to ammonium (DNRA), nutrient exchange, and sediment oxygen consumption were measured seasonally. The oxygen (O2) and hydrogen sulfide (H2S) depth profiles were measured using microelectrodes. Neither penetration nor consumption of oxygen decreased during hypoxia. Denitrification, anammox, and DNRA ranged from 0 to 0.73, 0.13, and 1.09 mmol N m-2 day-1, respectively. Denitrification, the dominant N removal pathway, increased by 75% while anammox ceased, which led to an overall increase of 55% in the total N2 gas production during hypoxia relative to that during normoxia. Enhanced denitrification is the result of increased coupled nitrification–denitrification due to the intermittent supply of oxygen during bottom water hypoxia (“weak hypoxia”). In the hypoxic period, DNRA decreased by 62%, and the relative contribution of DNRA to the total nitrogen reduction process decreased from 81 to 58%, but it still outperformed denitrification as the main nitrate reduction pathway. Sediments were strong sources of ammonium for the water column, both under normoxia and hypoxia, whereas they were a sink of nitrate from the water column during hypoxia. Bioturbation may be important for maintaining oxygen penetration and consumption in sediments. The dominance of DNRA was mainly due to the relatively high content of sulfide and organic-rich sediments. The repressed macrofaunal activity and increased coupling of nitrification and denitrification during hypoxia may have contributed to enhanced denitrification. Taken together, the overall dominance of DNRA might contribute to the development and maintenance of eutrophication and seasonal hypoxia in this system. However, in contrast to the previous results, denitrification was enhanced during “weak hypoxia,” which might be helpful in alleviating eutrophication.

Oxidation behavior of TiCr and TiMo alloys formed by low-energy pulsed electron beam impact

The titanium-based alloys with 2–3 at.% of chromium (TiCr) and molybdenum (TiMo) were produced on the top of titanium samples by means of the high-intense pulsed electron beam impact on the titanium with preliminary deposited Cr and Mo coatings. The TiCr and TiMo alloys were subjected to oxidation in open air atmosphere at temperature 600 °C. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy-disperse X-ray microanalysis (EDX) were used for structure and elemental composition determination in the samples. The analysis of oxygen depth profiles showed the increase in oxygen penetration depth in the case of TiCr alloy in comparable to pure titanium. The oxygen concentration corresponding to stoichiometry of the oxide phase TiO2 was found on the depth equaled to the thickness of the TiCr alloy that shows the enhancement of the diffusion of oxygen in the modified layer. The diffusion of oxygen at the temperature of 600 °C is enhanced by decomposition of the solid solutions based on bcc β-Ti phase with free chromium and molybdenum atoms releasing. The free molybdenum atoms take part in the stabilization of TiO2 anatase phase while the free chromium atoms form intermetallic compound TiCr2 preventing the sample from oxidation.

Influence of nutrient enrichment on temporal and spatial dynamics of dissolved oxygen within northern temperate estuaries

In temperate estuaries of the southern Gulf of St. Lawrence, intermittent seasonal anoxia coupled with phytoplankton blooms is a regular occurrence in watersheds dominated by agricultural land use. To examine the spatial relationship between dissolved oxygen and phytoplankton throughout the estuary to assist in designing monitoring programs, oxygen depth profiles and chlorophyll measurements were taken bi-weekly from May to December in 18 estuaries. In five of those estuaries, dissolved oxygen data loggers were set to measure oxygen at hourly intervals and at multiple locations within the estuary the subsequent year. The primary hypothesis was that dissolved oxygen in the upper estuary (first 10% of estuary area) is predictive of dissolved oxygen mid-estuary (50% of estuary area). The second hypothesis was that hypoxia/superoxia in the estuary is influenced by temperature and tidal flushing. Oxygen depth profiles conducted in the first year of study provided preliminary support that dissolved oxygen in the upper estuary was related to dissolved oxygen throughout the estuary. However, dissolved oxygen from loggers deployed at 10% and 50% of estuary area did not show as strong a correlation as expected (less than half the variance explained). The strength of the correlation declined towards the end of summer. Spatial decoupling of oxygen within the estuary suggested influence of local conditions. Chlorophyll concentration seemed also to be dependent on local conditions as it appeared to be coupled with the presence of sustained anoxia in the upper estuary with blooms typically occurring within 7 to 14 days of anoxia. The practical implication for oxygen monitoring is that one location within the most severely impacted part of the estuary is not sufficient to fully evaluate the severity of eutrophication effects.

Adjusting oxygen vacancy and resistance switching of InWZnO thin films by high-pressure oxidation technique

In this study, the room temperature high-pressure oxidation technique is proposed to exquisitely manipulate the surface morphology and oxygen depth-profile of the tungsten-doped indium zinc oxide (InWZnO) film, and its influence on the switching characteristics is emphasized. Based on the atomic force microscope analysis, the smoother surface morphology of the InWZnO film after the high-pressure oxidation treatment is observed. Moreover, it is observed that the InWZnO film has significantly manipulated the oxygen vacancy depth-profile and improved the chemical properties after high-pressure oxidation treatment, according to the x-ray photoelectron spectroscopy depth profiling results. Compared with the control device, the device with high-pressure oxidation treatment exhibited highly uniform resistance states and set/reset repeatability. Finally, the mechanism of the effect of high-pressure oxidation treatment on the InWZnO film is completely examined according to the in-depth material analysis and physical model discussed.

Determination of Oxide Ion Conductivity in Ba-Doped LaYbO3 Proton-Conducting Perovskites via an Oxygen Isotope Exchange Method

Proton-conducting oxides have garnered much attention as electrolyte materials of electrochemical devices operating at intermediate temperatures ranging 400–700 °C. For the implementation, quantifying the transport number of oxygen ions is crucial to predict the fuel utilization efficiency of solid oxide fuel cells (SOFCs). The acceptor-doped LaYbO3 proton conductors are one of the candidates for the electrolyte material of electrochemical devices such as SOFCs because of their high pure proton conduction. However, the oxide ion conductivity in this material is not quantified yet. Here, we evaluate the tracer diffusion coefficient (D*) of 5 mol % Ba-doped LaYbO3 by the oxygen isotope exchange and depth profile technique using secondary ion mass spectrometry. It is found that the oxygen ion conductivities in this material are lower than 10–4 S cm–1 below 800 °C, less than 2% to the total conductivity. We also visualize the domain of dominant conduction in this material. It reveals that proton conduction is dominant in fairly wide areas of the atmospheric condition, in particular below 600 °C, suggesting that the Ba-doped LaYbO3 is suitable for the SOFC electrolyte in terms of transport number.

Biogeochemical impact of cable bacteria on coastal Black Sea sediment

Abstract. Cable bacteria can strongly alter sediment biogeochemistry. Here, we used laboratory incubations to determine the potential impact of their activity on the cycling of iron (Fe), phosphorus (P) and sulfur (S). Microsensor depth profiles of oxygen, sulfide and pH in combination with electric potential profiling and fluorescence in situ hybridisation (FISH) analyses showed a rapid development (<5 d) of cable bacteria, followed by a long period of activity (>200 d). During most of the experiment, the current density correlated linearly with the oxygen demand. Sediment oxygen uptake was attributed to the activity of cable bacteria and the oxidation of reduced products from the anaerobic degradation of organic matter, such as ammonium. Pore water sulfide was low (< 5 µM) throughout the experiment. Sulfate reduction acted as the main source of sulfide for cable bacteria. Pore water Fe2+ reached levels of up to 1.7 mM during the incubations, due to the dissolution of FeS (30 %) and siderite, an Fe carbonate mineral (70 %). Following the upward diffusion of Fe2+, a surface enrichment of Fe oxides formed. Hence, besides FeS, siderite may act as a major source of Fe for Fe oxides in coastal surface sediments where cable bacteria are active. Using µXRF, we show that the enrichments in Fe oxides induced by cable bacteria are located in a thin subsurface layer of 0.3 mm. We show that similar subsurface layers enriched in Fe and P are also observed at field sites where cable bacteria were recently active and little bioturbation occurs. This suggests that such subsurface Fe oxide layers, which are not always visible to the naked eye, could potentially be a marker for recent activity of cable bacteria.

(Invited) Si-Cap-Free Low-DIT SiGe Gate Stack for High-Performance pFETs

As the continuous physical device scaling is facing increasing challenges in today’s CMOS technology, introduction of high mobility channel material has further increased its potential value as performance booster. Low-Ge-content SiGe is the leading candidate for p-channel devices, as it is process-compatible with state-of-the-art Si CMOS fabrication platform and requires no strain relaxed buffer layer. In order to benefit from the high intrinsic carrier mobility at a low VDD operation, an efficient SiGe channel passivation with low interface state densities (Dit) needs to be developped. However, the presence of GeO is known to increase Dit [1]. One of the effective passivation schemes for SiGe-based channel surface uses an epitaxially-grown ultrathin Si cap [2]. It suppresses the formation of GeO and enables to fabricate a high-k/SiO2 gate stack equivalent to the one in Si devices. The outstanding improvement achieved with this approach was previously highlighted on pure Ge channel devices, where the formation of GeO is inevitable without the use of Si-cap [3]. On the other hand, it poses some concerns such as EOT penalty and process controllability, making the Si-cap-free route the desired option as long as the interface and oxide bulk trap densities can be kept under control. In this contribution, we will review our recent studies towards the realization of a low-Dit Si-cap-free SiGe gate stack [4]. Selective GeO scavenging from Si1-xGexOy interface layer was previously reported as the key process to reduce Dit of SiGe gate stack [1]. Wostyn et al., demonstrated on Si0.75Ge0.25 that the annealing of chemical oxide in inert ambient (i.e. H2) reduces GeO in Si1-xGexOy IL thanks to the conversion of the thermally-unstable GeO into SiO [5]. A MOS capacitor experiment confirmed a clear Dit reduction by H2 anneal, although at an increased EOT. Additional NH3 anneal on IL was found to further reduce the Dit down to 5×1011 cm-2eV-1 while cancelling out the H2-anneal-induced EOT increase (EOT=10.1 Å). We also found that the metal gate deposition process has a strong impact on Dit even for the same metal. While the PVD W/TiN led to low Dit and EOT, both of them increased as the PVD was changed to ALD (or ALD followed by CVD) process. This can be explained by the PVD-TiN-induced additional GeO scavenging from IL [6] and/or oxygen diffusion from ALD-based metal to IL through HfO2 inducing GeO formation. A nitridation of HfO2 was found to suppress the negative impact from ALD-based metal electrode. XPS confirmed that the significant Dit reduction coincides with the nitridation of HfO2. By replacing the HfO2 with other dielectrics in which lower oxygen diffusivity is expected such as SiO2, the Dit of SiGe gate stack became insensitive to the metal deposition process and nitridation, indicating that the high oxygen diffusivity of the HfO2 layer was, together with the GeO formation, the root cause of the process-sensitive Dit. These results emphasize the importance of the oxygen depth profile control for the realization of a low-Dit SiGe gate stack.

Oxygen diffusion in oxide thin films grown on SrTiO3

$\mathrm{SrTi}{\mathrm{O}}_{3}$ thin films were grown on $^{18}\mathrm{O}$-exchanged $\mathrm{SrTi}{\mathrm{O}}_{3}$ single crystalline substrates by pulsed-laser deposition, rf sputtering, and oxide molecular-beam epitaxy to study their oxygen diffusion depth profiles using secondary ion mass spectrometry and elastic recoil detection analysis depth profiling. The oxygen depth profiling shows that $\mathrm{SrTi}{\mathrm{O}}_{3}$ films prepared with the three different deposition techniques will take oxygen from the substrate, even at room temperature. This confirms that the substrate is one possible oxygen source for the growth of oxide thin films independent of the physical vapor deposition technique employed. It was also found that a reactive oxygen environment changes the oxygen composition of the substrate during the growth of a film and partly replaces $^{18}\mathrm{O}$ with $^{16}\mathrm{O}$ up to a depth of several tens of nm. These findings imply that $\mathrm{SrTi}{\mathrm{O}}_{3}$ and therefore other ion conducting oxide substrates, which are commonly used as platforms for thin film growth, can be considered capricious in nature with respect to oxygen chemistry and lattice constants.

Nanocatalyst-induced hydroxyl radical (·OH) slurry for tungsten CMP for next-generation semiconductor processing

Chemical mechanical polishing (CMP) is one of the important steps that involves during fabrication of semiconductor devices. This research highlights the importance of tungsten (W) polishing slurries consisting of a novel nonionic, heat-activated FeSi nanocatalyst on the performance of W chemical mechanical polishing. The results obtained from the polishing data showed a higher W removal rate of 5910 A/min with a slurry consisting of FeSi nanocatalyst at a polishing temperature of 80 °C. The increase in W polishing rate using FeSi slurry was explained on the basis of formation of a thicker oxide layer (WO3) due to the interaction between the W surface and hydroxyl radicals (·OH) generated via the reaction between FeSi and hydrogen peroxide at 80 °C. Higher ·OH generation and increase in oxygen depth profile of W film were confirmed by UV–Vis spectrometer and AES analysis, respectively. Compared to Fe(NO3)3 catalyst, the slurry with FeSi showed a higher static etch rate at 80 °C. Potentiodynamic polarization results obtained using FeSi slurry showed thicker WO3 passivation layer as compared to the slurry with Fe(NO3)3. The increase in the polishing rate of W CMP using slurry with FeSi nanocatalyst can be essentially attributed to the generation of much stronger oxidant ·OH due to its increased catalytic effect at a high polishing temperature of 80 °C.

Sixty years since the creation of Lake Kariba: Thermal and oxygen dynamics in the riverine and lacustrine sub-basins.

The current boom of dam construction at low latitudes endangers the integrity and function of major tropical river systems. A deeper understanding of the physical and chemical functioning of tropical reservoirs is essential to mitigate dam-related impacts. However, the development of predictive tools is hampered by a lack of consistent data on physical mixing and biogeochemistry of tropical reservoirs. In this study, we focus on Lake Kariba (Southern Africa), the largest artificial lake in the world by volume. Kariba Dam forms a transboundary reservoir between Zambia and Zimbabwe, and therefore its management represents a socio-politically sensitive issue because the Kariba Dam operation completely changed the downstream hydrological regime. Although Lake Kariba represents a unique and scientifically interesting case study, there is no consistent dataset documenting its physical and chemical behaviour over time. This limits the scope for quantitative studies of this reservoir and its downstream impacts. To address this research gap, we aggregated a consistent database of in situ measurements of temperature and oxygen depth profiles for the entire 60 years of Lake Kariba’s lifetime and performed a detailed statistical analysis of the thermal and oxygen regime of the artificial lake to classify the different behaviours of the lake’s sub-basins. We demonstrate that the seasonal stratification strongly depends on the depth of the water column and on the distance from the lake inflow. Satellite data confirm these spatiotemporal variations in surface temperature, and reveal a consistent longitudinal warming trend of the lake surface water temperature of about 1.5°C from the inflow to the dam. Finally, our results suggest that the stratification dynamics of the lacustrine sub-basins have the potential to alter the downstream Zambezi water quality. Future research should focus on assessing such alterations and developing strategies to mitigate them.

Investigation of shear-induced physical and chemical transformations of Fe microparticles in hydrocarbon- and fluorocarbon-based magnetorheological fluids

Aging of magnetorheological fluids (MRFs) during the operation of mechanical devices is accompanied by degradation of both the particles and the fluid components. This study has shown that collisions among micron-size magnetic iron particles under shear can result in nanoscale changes to surface topography. Moreover, it has shown that shear-induced collisions can lead to redistributions among different oxidation state species in surface and near sub-surface regions of the particles. The redistributions among oxidation states and chemical species is the result of interfacial reactions that can involve adventitious oxygen, catalysis and other energetic processes that can act on either or both, the host fluid medium and additives introduced to stabilize the MRF. The interfacial chemistry is complex, inviting studies that couple macroscale processes (shear events in a clutch mechanism) with nanoscale inquiry into the effects of such processes. This study examined the chemical and morphological states of MRF particles subjected to continual shear loading in a rotary clutch device over well-defined periods of time for both hydrocarbon and fluorocarbon-based host fluids. New insights into chemical transformations, on and beneath, particle surfaces provide reference for better durability assessment, MRF formulation, and device design in the future. X-ray photoelectron spectroscopy iron, fluorine, oxygen and carbon depth profiles provided insight into the evolving oxidation states of the MRF particles. Over time, fluorine and oxygen insinuate themselves into the particle where they give rise to a host of different oxidized iron species. Simultaneously, the iron content of the surface diminishes. Scanning electron microscopy revealed how the particles transform from nascent nearly spherical shape prior to shear to irregular morphology in the clutch mechanisms. Transmission electron microscopy revealed carbon-rich residues with embedded nanoparticle fragments in aged MRF particle samples, suggesting that MRF particle surfaces may have served as reaction interfaces.

Structural and compositional modification of graphene oxide by means of medium and heavy ion implantation

Graphene and its allotropes belong to the new generation of materials. Due to their extraordinary electrical, mechanical and other properties, their application possibilities are vast. In this work, a study on interactions of graphene oxide (GO) layers using Au and Ga ions with energy of 40 keV was realized. Very shallow layers of GO are modified as low energy ions are depositing energy mostly in the upper layer due to the low projected ion ranges at most of 50 nm. The ion irradiation fluences of 5.0 × 1014 cm−2, 5.0 × 1015 cm−2 and 5.0 × 1016 cm−2 were used. Upon irradiation, the modified GO foils were characterised using nuclear analytical methods – Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection Analysis (ERDA) and various conventional analytical methods such as Raman spectroscopy, Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), and 2-point conductivity measurements. Oxygen species removal was evidenced as the increasing function of the ion implantation fluence and oxygen depth profiles exhibited complex behaviour connected to implanted ion specie. The deep oxygen depletion in the broad surface layer accompanied by Ga diffusion into the depth was observed in Ga irradiated GO compared to Au irradiated samples which exhibited a narrow oxygen depleted layer at GO surface. XPS evidenced strong increase of CC bonds compared to CO bonds on the irradiated GO surface with increasing ion fluence, which was comparable for both ion species. Raman spectroscopy shows the modification of main phonon modes identified in GO. The D peak slight decrease and broadening was observed for GO irradiated with ion fluence above 5 × 1015 cm−2 and mainly for Au ion irradiation. FTIR analysis proved the oxygen containing functional group release with the increased ion fluence, mainly CO group release after Au ion irradiation was observed. Simultaneously HO stretching absorption peak is in FTIR spectrum reduced more significantly for Ga irradiated GO which is in accordance with RBS elemental analysis exhibiting the more pronounced hydrogen depletion. Electrical conductivity measurement shows the linear I-V characteristics for the GO irradiated using both ion species and all ion fluences; the surface layer exhibited conductive behaviour comparing to pristine GO non-linear I-V characteristics.

Multiscale analysis of autotroph-heterotroph interactions in a high-temperature microbial community

Interactions among microbial community members can lead to emergent properties, such as enhanced productivity, stability, and robustness. Iron-oxide mats in acidic (pH 2–4), high-temperature (> 65 °C) springs of Yellowstone National Park contain relatively simple microbial communities and are well-characterized geochemically. Consequently, these communities are excellent model systems for studying the metabolic activity of individual populations and key microbial interactions. The primary goals of the current study were to integrate data collected in situ with in silico calculations across process-scales encompassing enzymatic activity, cellular metabolism, community interactions, and ecosystem biogeochemistry, as well as to predict and quantify the functional limits of autotroph-heterotroph interactions. Metagenomic and transcriptomic data were used to reconstruct carbon and energy metabolisms of an important autotroph (Metallosphaera yellowstonensis) and heterotroph (Geoarchaeum sp. OSPB) from the studied Fe(III)-oxide mat communities. Standard and hybrid elementary flux mode and flux balance analyses of metabolic models predicted cellular- and community-level metabolic acclimations to simulated environmental stresses, respectively. In situ geochemical analyses, including oxygen depth-profiles, Fe(III)-oxide deposition rates, stable carbon isotopes and mat biomass concentrations, were combined with cellular models to explore autotroph-heterotroph interactions important to community structure-function. Integration of metabolic modeling with in situ measurements, including the relative population abundance of autotrophs to heterotrophs, demonstrated that Fe(III)-oxide mat communities operate at their maximum total community growth rate (i.e. sum of autotroph and heterotroph growth rates), as opposed to net community growth rate (i.e. total community growth rate subtracting autotroph consumed by heterotroph), as predicted from the maximum power principle. Integration of multiscale data with ecological theory provides a basis for predicting autotroph-heterotroph interactions and community-level cellular organization.

Oxygen reduction reaction process of LaNi0.6Fe0.4O3 − δ film – porous Ce0.9Gd0.1O1.95 heterostructure electrode

Relevant factors affecting an oxygen reduction reaction (ORR) in a heterostructure electrode comprising a Ce0.9Gd0.1O1.95 porous layer on LaNi0.6Fe0.4O3−δ film electrode were evaluated using electrochemical impedance spectroscopy and isotope depth profile analyses. Despite the LaNi0.6Fe0.4O3−δ film – porous Ce0.9Gd0.1O1.95 electrode having higher interfacial conductivity,σE, compared to a bare LaNi0.6Fe0.4O3−δ film electrode, σEbehavior as a function of p(O2) was similar to each measured temperature. This exhibits a good correlation with the isotopic oxygen depth profile analysis where the evaluated surface oxygen exchange coefficient, k*, showed enhancement compared to bare LaNi0.6Fe0.4O3−δ film and exhibited the same behavior on p(O2). Based on the analyses, there are two plausible reasons for this enhancement: (a) the formation of triple phase boundaries at the junction of LaNi0.6Fe0.4O3−δ film, porous Ce0.9Gd0.1O1.95, and gas phase, where the incorporation process during an ORR process takes place via the porous Ce0.9Gd0.1O1.95; and (b) a modification of the subsurface layer just below the film surface where the presence of diffused Ce and Gd appears to accelerate the ORR process.

Influence of oxygen concentration on the optoelectronic properties of hydrogenated polymorphous silicon thin films

Hydrogenated polymorphous silicon (pm-Si:H) is a suitable candidate for application in silicon-based thin film solar cells because it exhibits improved electronic transport properties and stability with respect to conventional hydrogenated amorphous silicon (a-Si:H). The use of chlorinated precursors to grow pm-Si:H thin films in a plasma enhanced chemical vapor deposition systems increases photoconductivity and photo-stability, which is one of the most desired aspects for modern solar cell applications. However, the effects of chlorine and hydrogen chemistry should be more extensively studied because it may lead to the generation of a secondary SiOx phase, after exposure to the ambiance and/or during the growth processes. In the present work, X-Ray photoelectron spectroscopy results showed the depth profile of oxygen in the polymorphous silicon thin film. Finally, we have analyzed the effect of different concentrations and profile of oxygen on the electronic transport properties by means of dark and photoconductivity analysis. Sample with high crystalline fraction and oxygen concentration showed an increase in photo-stability and conductivity due to the passivation of free terminal bonds with oxygen. Understanding chemical and structural properties of pm-Si: H thin films based on chlorine, with additional oxygen incorporation to the films, is a key towards optimizing their electrical and optical properties for the practical implementation of solar cells.