Oxygen Flooding Research Articles

Parametric Modeling Study of PEM Fuel Cell with Platinum Group Metal -Free Cathode Catalyst Layer

Polymer electrolyte fuel cells offer zero-emissions energy conversion but are commercially limited by cost and durability. Stack cost can be reduced by using platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR). PGM-free catalysts have lower volumetric activity relative to PGM catalysts and consequently require thicker catalyst layers. Thicker catalyst layers result in increased oxygen transport resistance and flooding in the cathode, which must be considered to accurately model PGM-free fuel cells and quantify the distinct transport resistance. For this purpose, we have developed a well validated model to elucidate relative contributions to oxygen transport resistance. This two-phase, transient, non-isothermal, channel-to-channel model contains cathode catalyst layer morphology informed by plasma-focused ion beam (P-FIB) SEM. Furthermore, the model includes agglomerate treatment of volumetrically active catalyst primary particles coated by ionomer. The structure of the agglomerate model is well suited for describing the catalyst layers containing metal organic framework (MOF) derived metal-nitrogen-carbon catalysts that are roughly spherical and volumetrically active for ORR. The MOF-derived Fe-N-C catalyst used in this study’s experiments contains atomically dispersed active sites and uniform, tunable primary particle size. In this presentation, we will report on our investigation of the performance sensitivity to a wide variety of operating conditions and MEA design specificiation, including cell temperature, gas pressures, cathode thickness, hydrophobic pore fractions and wettability, catalyst primary particle size, ionomer content, and ionomer equivalent weight. Non-dimensional characteristic parameter analysis on the model results is used to distinguish the transition between proton conductivity limited and oxygen transport limited performance, and indicate critical values that affect the the through plane ultilization of the catalyst. This information and studies on the impact of active site density help us set catalyst-specific targets for meeting fuel cell performance goals. With highly active PGM-free catalysts, we can model the impact of parameter changes on transport with experimental validation.DOE ACKNOWLEDGEMENTThis material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office (FCTO) under award number DE-EE0008076. The authors gratefully acknowledge research support from the Electrocatalysis Consortium (ElectroCat), established as part of the Energy Materials Network under the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, under contract number DEEE0008076.

Suppression of self-organized surface nanopatterning on GaSb/InAs multilayers induced by low energy oxygen ion bombardment by using simultaneously sample rotation and oxygen flooding

Time of flight secondary ion mass spectrometry (ToF-SIMS) is a well-adapted analytical method for the chemical characterization of concentration profiles in layered or multilayered materials. However, under ion beam bombardment, initially smooth material surface becomes morphologically unstable. This leads to abnormal secondary ion yields and depth profile distortions. In this contribution, we explore the surface topography and roughening evolution induced by O2+ ion bombardment on GaSb/InAs multilayers. We demonstrate the formation of nanodots and ripples patterning according to the ion beam energy. Since the latter are undesirable for ToF-SIMS analysis, we managed to totally stop their growth by using simultaneously sample rotation and oxygen flooding. This unprecedented coupling between these two latter mechanisms leads to a significant enhancement in depth profiles resolution.

SIMS depth profiling of ‘frozen’ samples: in search of ultimate depth resolution regime

We have performed secondary ion mass spectrometry depth profiling analysis of III–V based hetero-structures at different target temperatures and found that both the surface segregation and surface roughness caused by ion sputtering can be radically reduced if the sample temperature is lowered to −150 °C. The depth profiling of ‘frozen’ samples can be a good alternative to sample rotation and oxygen flooding used for ultra-low-energy depth profiling of compound semiconductors. Copyright © 2016 John Wiley & Sons, Ltd.

Comparing depth profiling of oxide scale on SOFC interconnect-materials using ToF-SIMS with 69Ga+, Bi3+/Cs+ and C60+/C602+ as primary and sputter ions

Oxide scale cross-sections of CeO2 coated FeCr based solid oxide fuel cell interconnect materials were examined using secondary ion mass spectrometry (SIMS) depth profiling. A duplex spinel∶chromia scale was formed after 1 h at 850°C. Ti and ceria were observed between these layers. Additionally, minor concentrations of Mn, Si and Nb were observed at the oxide/metal interface. Furthermore, Al and Ti were concentrated primarily in the metal surface close to the oxide/metal interface. Secondary ion mass spectrometry sputter depth profiles using different ion sources; 69Ga+, Bi3+/Cs+ and C60+/C602+ were compared with TEM oxide scale cross-section and field emission gun–Auger electron spectroscopy depth profiling. Secondary ion mass spectrometry depth profiling with 69Ga+, Bi3+/Cs+ showed decreased secondary ion yields in the metallic matrix. This decrease could be avoided using oxygen flooding. The C60 cluster ion depth profiles were less sensitive to type of matrix and gave the best correspondence to the TEM cross-section. However, the impact energy has to be high enough to avoid carbon deposition.

The development of uranium isotopic ratio analysis for uranium‐bearing particles by using oxygen flooding technique with SIMS

The isotopic ratio of uranium‐bearing particles could be used to detect undeclared nuclear activities. How to strengthen the analyzing ability of secondary ion mass spectrometry (SIMS) was important to get certain information. For this purpose, the oxygen flooding technique was studied to enhance the ability of measuring isotopic ratio in uranium particles. The influence of oxygen flooding on the sensitivity of U+, UO+ and UO2+ was checked by using uranium metal and uranium particle (CRM U200) samples. The major and minor isotopic ratios of uranium bearing particles were measured by U+, UO+ and UO2+. The result shows that the use of oxygen flooding technique has no effect on the sensitivity of U+ and the isotopic ratio 234U/238U and 235U/238U. However, the intensity of UO+ and UO2+ increased several times with the oxygen flooding. Besides, the accuracy and precision of major isotopic ratio measured by uranium–oxygen ions were better than that measured by U+. For the minor isotopic ratio (234U/238U), it cannot be measured by uranium–oxygen ions because of the interference of polyatomic ions on carbon mat. After changing sample mat, for example, silicon mat, it can be measured by UO+ and get better results with oxygen flooding technique. Copyright © 2014 John Wiley & Sons, Ltd.

Storing matter technique performed in the analytical chamber of a quadrupole SIMS analyser

The storing matter technique is applied in quadrupole type SIMS analyser. Its analytical chamber is additionally equipped with a special magnetically driven x, Θ, UHV manipulator applied for transfer of the metal ring collector. The sample holder, horizontally positioned, carries the analysed sample as well as a watch like rotation mechanism carrying a continuously rotating collector of 1 inch diameter at a rate of 1 rev. per hour. The procedure includes cleaning of the collector with the ion beam, the collector reverse, sputter deposition of the analysed material from the sample onto the clean surface of the collector, reversal of the sample and analysis of the stored material. The whole procedure is performed in one analytical chamber, using a Physical Electronics 06‐350E sputter ion gun and QMA‐410 Balzers quadrupole mass analyser. The procedure is tested on pure chromium and is applied to an inconel alloy implanted with 120 keV Cr2+ and 145 keV Y2+. The SIMS results are obtained using 5 and 3 keV Ar+ ion beam at 45° incidence angle. As the collector, we use high purity titanium. The obtained depth profile analysis of the inconel alloy shows that the ‘matrix effect’ is largely reduced when compared with standard SIMS analysis. The storing matter procedure was performed with the use of oxygen flooding (during sputter deposition and during SIMS analysis). Results show significant improvement with respect to the use of this technique without oxygen flooding. Copyright © 2014 John Wiley & Sons, Ltd.

Estimating Effects of Tidal Power Projects and Climate Change on Threatened and Endangered Marine Species and Their Food Web

Marine hydrokinetic power projects will operate as marine environments change in response to increased atmospheric carbon dioxide concentrations. We considered how tidal power development and stressors resulting from climate change may affect Puget Sound species listed under the U.S. Endangered Species Act (ESA) and their food web. We used risk tables to assess the singular and combined effects of tidal power development and climate change. Tidal power development and climate change posed risks to ESA-listed species, and risk increased with incorporation of the effects of these stressors on predators and prey of ESA-listed species. In contrast, results of a model of strikes on ESA-listed species from turbine blades suggested that few ESA-listed species are likely to be killed by a commercial-scale tidal turbine array. We applied scenarios to a food web model of Puget Sound to explore the effects of tidal power and climate change on ESA-listed species using more quantitative analytical techniques. To simulate development of tidal power, we applied results of the blade strike model. To simulate environmental changes over the next 50 years, we applied scenarios of change in primary production, plankton community structure, dissolved oxygen, ocean acidification, and freshwater flooding events. No effects of tidal power development on ESA-listed species were detected from the food web model output, but the effects of climate change on them and other members of the food web were large. Our analyses exemplify how natural resource managers might assess environmental effects of marine technologies in ways that explicitly incorporate climate change and consider multiple ESA-listed species in the context of their ecological community. Estimación de los Efectos de Proyectos de Energía de las Mareas y el Cambio Climático sobre Especies Marinas Amenazadas y en Peligro y su Red Alimentaria.

Optimal fallow area and location for multifunctional benefits of a paddy field during drought periods

Paddy fields not only serve to produce food but also have a variety of important ecological functions. Apart from the internal benefit (i.e., crop production), there are external benefits (i.e., reduction of greenhouse gases, oxygen generation, reduction of biological oxygen demand, flood mitigation, and other functions that are difficult to quantify). In the present study, the optimal fallow locations and areas were determined for evaluating the multifunctional benefits of paddy fields during drought periods, by using an optimization model for fallow fields under different exceedance probabilities of river inflows. For each time step, the appropriate probability distributions for river inflows to the Chi-Chi Weir (range 50–90 %) for generating system inflows were obtained. The optimization model for fallow fields was solved using Lingo. It was observed that the external benefits of paddy fields accounted for 76 % of total benefits, with the production benefit accounting for the remainder. The total benefits decreased as the exceedance probability of river discharges increased. Our findings indicate that fallow areas increase as irrigation areas shift downstream.

Towards secondary ion mass spectrometry on the helium ion microscope: An experimental and simulation based feasibility study with He+ and Ne+ bombardment

The combination of the high-brightness He+/Ne+ atomic level ion source with secondary ion mass spectrometry detection capabilities opens up the prospect of obtaining chemical information with high lateral resolution and high sensitivity on the Zeiss ORION helium ion microscope. The analytical performance in terms of sputtering yield, useful yield, and detection limit is studied and subsequently optimized by oxygen and cesium flooding. Detection limits down to 10−6 and 10−5 can be obtained for silicon using Ne+ and He+, respectively. A simulation based study reveals furthermore that a lateral resolution <10 nm can be obtained.

Dramatically Enhanced Oxygen Uptake and Ionization Yield of Positive Secondary Ions with C60+ Sputtering

To explore C(60)(+) sputtering beyond low-damage depth profiling of organic materials, X-ray photoelectron spectrometry (XPS) and secondary ion mass spectrometry (SIMS) were used to examine metallic surfaces during and after C(60)(+) sputtering. During C(60)(+) sputtering, XPS spectra indicated that the degrees of carbon deposition were different for different metallic surfaces. Moreover, for some metals (e.g., Al, W, Ta, Ti, and Mo), the intensity of the O 1s photoelectron increased significantly during C(60)(+) sputtering, even though the instrument was under ultrahigh vacuum (<5 × 10(-7) Pa). This result indicated that the rate of oxygen uptake was greater than the rate of C(60)(+) sputtering. This behavior was not observed with the commonly used Ar(+) sputtering. To measure the oxygen uptake kinetics, pure oxygen was leaked into the chamber to maintain a 5 × 10(-6) Pa oxygen environment. The C(60)(+)-sputtered surface had a clearly increased rate of oxygen uptake than the Ar(+)-sputtered surface, even for moderately reactive metals such as Fe and Ni. For relatively nonreactive metals such as Cu and Au, a small amount of carbon was implanted and no oxygen uptake was observed. High-resolution XPS spectra revealed the formation of metal carbides on these reactive metals, and the carbon deposition and enhanced uptake of oxygen correlated to the carbide formation. Because oxygen enhances the secondary ion yield through surface passivation, the enhanced oxygen uptake due to C(60)(+) sputtering could be beneficial for SIMS analysis. To examine this hypothesis, C(60)(+) and Ar(+) were used as primary ions, and it was found that the intensity enhancement (because of the oxygen flooding at 5 × 10(-6) Pa) was much higher with C(60)(+) than with Ar(+). Therefore, oxygen flooding during C(60)(+) sputtering has a great potential for enhancing the detection limit due to the enhanced oxygen uptake.

Strategies for improving the sensitivity of FIB‐SIMS

AbstractSecondary ion yields need to be enhanced to provide higher sensitivity in the SIMS technique in order to meet the demands for high performance in surface analysis of ever‐decreasing analytical volumes. In this work, we investigated how the ionization probability could be improved by changing the surface chemistry prior to analysis by oxygen implantation and flooding. The ion‐induced altered layer was analyzed with the FIB‐SIMS and oxygen flooding was carried with the ION‐TOF IV. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Cesium retention during sputtering with low energy Cs+ and oxygen flooding

AbstractAccurate knowledge of the stationary Cs retention during Ultra Low Energy (ULE; &lt; 150 eV) Cs+ sputtering (of semiconductor substrates) is the first step towards understanding the basics of SIMS. We have investigated the effect of oxygen on the retention capacity for cesium on silicon and germanium targets. The amount of cesium that is retained was directly measured using Inductively Coupled Plasma Mass Spectrometry (ICP‐MS). Even a very small partial pressure of oxygen (in the 10−9 to 10−8 mbar range) will tremendously increase the dose of cesium that is retained at the sample surface. Concurrent with this increased retention (due to Cs‐oxide formation) strong variations in the target sputtering yield and the ionization degree of silicon can be observed.These data combined support the model that the observed target sputtering yield is directly linked to the Cs‐surface coverage and that a cap layer containing a very high amount of Cs can be formed by the ion beam. The sensitivity to oxygen becomes stronger as the primary ion energy decreases, and implies that SIMS measurements with Cs aimed at a very high depth resolution will suffer from drastically reduced erosion rates due to the deposition process.1 Copyright © 2010 John Wiley &amp; Sons, Ltd.

Evaluation of ionization yields under gallium bombardment

AbstractThe Cameca NanoSIMS 50 is known to provide high resolution chemical mapping for negatively charged secondary ions (50–100 nm). Nevertheless, concerning positive secondary ions, the resolution is only in the 250‐nm range. In order to obtain a better lateral resolution for positive ions, a Liquid Metal Ion Gun (LMIG, Canion 31+, Orsay‐Physics, Fuveau, France) filled with gallium (Ga+) has been installed on the Cameca IMS‐6F. In the case of this study, we have measured the useful yields in inorganic samples. Limitations in the secondary ion signal intensity, which is inherent to the Gallium bombardment, can be partly balanced by using oxygen flooding, as a method to enhance the ion yield. Examples of applications are presented to demonstrate that the IMS‐6F equipped with a Gallium LMIG fulfills the requirements to be a complementary technique to the NanoSIMS. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Negative ion yield and sputter yield variations for Cs+ bombardment of Si with O2 gas flooding

AbstractWe have investigated whether negative secondary ion yields from Cs+ sputtered silicon might be improved by simultaneous O2 gas flooding, which lowers the sputter yield of the silicon, and thus, might increase the cesium content at the surface. The composition at the sputtered surface is derived from quantitative measurements of the ratios of O/Si and Cs/Si in the total emitted flux using the recently developed oxygen 18 method1 and sputter yield measurements, respectively (with XSi + XCs + XO = 1). The silicon sputter yield, Y, is lowered by adsorbed oxygen by as much as a factor of 2.7 and is found to scale almost linearly with the silicon atom fraction XSi at the surface, resulting in the cesium atom fraction XCs at the surface remaining nearly constant during oxygen flooding. We find that oxidation of the cesiated silicon surface influences differently the useful ion yields (ions detected/atom sputtered) of various elements. The yields of B− and Cs− are enhanced by factors of 3 and 34, respectively, the yield of O− remains roughly constant, and yields of other elements (As−, Cl−, P−, Sb−, Si−) are lowered by a factor of 2 or 3. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Precise U–Pb zircon dating at a scale of &lt;5 micron by the CAMECA 1280 SIMS using a Gaussian illumination probe

Zircon is arguably the best, certainly the most commonly used mineral for U–Pb geochronology. Modern large-geometry secondary ion mass spectrometry (SIMS) has been routinely utilized for precise U–Pb zircon age determination at a lateral resolution of 10–30 μm. However, in situ U–Pb dating at a scale of ca. 5 μm scale or less for fine-grained zircons and/or zircon crystals with complex structural and chemical features is still a challenge to the geoscience community. Here we describe a method of precise U–Pb dating for zircons as young as the Jurassic age at a scale of up to <5 μm using the CAMECA ims-1280 SIMS. Gaussian mode primary O2− and O−probes of ca. 5.2 μm and ca. 4.5 μm in diameter with beam intensities of ∼100 pA were obtained, respectively, by optimizing the primary column. Secondary ion optics was optimized to ensure a high Pb+ sensitivity in zircons, producing ∼21 cps/ppm/nA using O2− and ∼13 cps/ppm/nA using O− (with oxygen flooding technique). As a demonstration of this method, three well-characterized zircon standards with a range of ages, AS3 (1099 Ma), Plesovice (377 Ma) and Qinghu (159.5 Ma), were analyzed. We demonstrate with these zircon standards that their ages could be determined with precision and accuracy of 1–2% using a spot <5 micron. The O− primary beam is preferred over the O2− beam for small-spot U–Pb zircon geochronology, because it has higher density and produces smaller craters on the target surface, with insignificant trade off in precision and accuracy of the final U–Pb ages. For U-poor minerals of younger ages, O2− might be preferred in order to generate sufficient Pb+ ions for measurement with minimal loss of spatial resolution.

Comparative Study of the Usefulness of Low Energy Cs+, Xe+, and O2+ Ions for Depth Profiling Amino-Acid and Sugar Films

This work reports a comparative study on the capability of low energy primary ion beams for depth profiling nonpolymeric molecules including amino-acid and sugar layers. Due to their different behavior regarding depth profiling, phenylalanine and trehalose molecules are chosen as reference systems. Each molecule was dissolved in suitable solvent prior to spin-coating on clean silicon wafer. The film thicknesses were in the order of 70 and 100 nm for phenylalanine and trehalose respectively. Depth profiling feasibility were assessed first using Cs(+) as reactive sputtering ion at various energies. The results obtained under Cs(+) sputtering ions are compared afterward to those obtained under Xe(+) sputtering ions which are inert and have a mass very similar to Cs(+). In order to investigate the effect of oxygen, depth profiling are also performed using either Xe(+) under oxygen flooding or O(2)(+) as sputtering ions. While phenylalanine could be depth profiled successfully using Cs(+) ions, Xe(+) and O(2)(+) ions failed to retain any characteristic signal. The sputtering yields measured as a function of the ion beam energies were higher using Cs(+), in particular at low energies. The chemical reactivity of the cesium atoms being implanted during the sputtering process helps to prevent the loss of the molecular phenylalanine signal. In contrast, depth profiling of trehalose was more successful upon Xe(+) and O(2)(+) compared to Cs(+). In this case the sputtering yields were higher if Xe(+) primary ion is employed instead of Cs(+). The different trends observed in this study are interpreted using arguments involving the reactivity of the sputtering ions.

On the effect of oxygen flooding on the detection of noble gas ions in a SIMS instrument

We have investigated the report by Desgranges and Pasquet (2004) [1] that O2 gas flooding in a secondary ion mass spectrometer could enhance by a factor of about ∼5 the Xe+ ion yield for a Xe implant in UO2 sputtered by O2+ primary ions. For a Xe implant in Si sputtered by O2+ primary ions and for Xe+ sputtering of silicon in steady state, O2 gas flooding reduced the Xe+ ion signal by a factor of about 2, presumably due to loss of Xe+ by resonant charge exchange with gas-phase oxygen molecules. The yield of a Kr co-implant in Si was unaffected by oxygen flooding. However, we demonstrate that for steady-state Ar+ sputtering of uranium, the Ar+ ion yield can be increased by a factor of ∼1.7 by oxygen flooding. This enhancement, predicted by a simple model to be a factor of √3, is attributed to a lowering of the neutral Ar emission velocity and hence increased post-ionization efficiency, caused by the suppression of argon bubble formation in uranium by oxidation of the near-surface region, and re-emission of argon by thermal effusion rather than in supersonic expansions from bursting high-pressure gas bubbles. We show that bubble formation, evidenced by the observation of Xe2+ clusters, also occurs for Xe+-bombarded uranium when the surface is sufficiently sputter-cleaned, and that the bubbles are similarly suppressed by oxygen flooding producing a factor of ∼√3 enhancement in the Xe+ signal.

Towards nanometric resolution in multilayer depth profiling: a comparative study of RBS, SIMS, XPS and GDOES

An increasing amount of effort is currently being directed towards the development of new functionalized nanostructured materials (i.e., multilayers and nanocomposites). Using an appropriate combination of composition and microstructure, it is possible to optimize and tailor the final properties of the material to its final application. The analytical characterization of these new complex nanostructures requires high-resolution analytical techniques that are able to provide information about surface and depth composition at the nanometric level. In this work, we comparatively review the state of the art in four different depth-profiling characterization techniques: Rutherford backscattering spectroscopy (RBS), secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS) and glow discharge optical emission spectroscopy (GDOES). In addition, we predict future trends in these techniques regarding improvements in their depth resolutions. Subnanometric resolution can now be achieved in RBS using magnetic spectrometry systems. In SIMS, the use of rotating sample holders and oxygen flooding during analysis as well as the optimization of floating low-energy ion guns to lower the impact energy of the primary ions improves the depth resolution of the technique. Angle-resolved XPS provides a very powerful and nondestructive technique for obtaining depth profiling and chemical information within the range of a few monolayers. Finally, the application of mathematical tools (deconvolution algorithms and a depth-profiling model), pulsed sources and surface plasma cleaning procedures is expected to greatly improve GDOES depth resolution.

Precise U–Pb and Pb–Pb dating of Phanerozoic baddeleyite by SIMS with oxygen flooding technique

Baddeleyite has long been recognized as one of the most important U-bearing minerals for dating silica undersaturated igneous rocks. Age determination of baddeleyite calls for analysis within small volumes using high-resolution secondary ion mass spectrometry (SIMS) because of its minuscule grain size as well as potential altered domains or micro-inclusions. However, precise SIMS U–Pb dating has been hampered for baddeleyite owing to crystal orientation effects that bias Pb/U ratio measured in baddeleyite. In this study we carried out a series of tests of U–Pb and Pb–Pb measurements on Phanerozoic baddeleyite using a multi-collector Cameca 1280 IMS with oxygen flooding technique. Our results demonstrate that the oxygen flooding can not only enhance secondary Pb+ ion yield by a fact of 7 for baddeleyite, but also depress the baddeleyite U/Pb orientation effect down to ∼2% (1 RSD). Therefore, Phanerozoic (as young as Cenozoic) baddeleyite can be precisely dated by SIMS Pb–Pb and/or U–Pb measurements with precision of 1–3% (2 RSE).

Characteristics of a Metal-Cluster-Complex Ion Beam and Its Application to Secondary Ion Mass Spectrometry (SIMS)

Metal cluster complexes are chemically-synthesized organometallic compounds, which have a wide range of chemical compositions with high molecular weight. Using a metal-cluster-complex ion source, sputtering characteristics of a silicon substrate bombarded with normally incident Ir4(CO)7+ ions were investigated. Experimental results showed that the sputtering yield at 10 keV was 36, which is higher than that with Ar+ ions by a factor of 24. Further, secondary ion mass spectrometry (SIMS) of boron-delta-doped silicon samples and organic films of poly (methyl methacrylate) (PMMA) was performed. Using the Ir4(CO)7+ ion beam, the depth resolution of 0.9 nm was obtained at 5keV, 45o with oxygen flooding of 1.3×10−4 Pa. Additionally, it was confirmed that Ir4(CO)7+ ion beams significantly enhanced secondary ion intensity in high-mass range.