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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Synthesis of Monomeric Fe(II) and Ru(II) Complexes of Tetradentate Phosphines

rac-Bis[{l_brace}(diphenylphosphino)ethyl{r_brace}-phenylphosphino]methane (DPPEPM) reacts with iron(II) and ruthenium(II) halides to generate complexes with folded DPPEPM coordination. The paramagnetic, five-coordinate Fe(DPPEPM)Cl{sub 2} (1) in CD{sub 2}Cl{sub 2} features a tridentate binding mode as established by {sup 31}P{l_brace}{sup 1}H{r_brace} NMR spectroscopy. Crystal structure analysis of the analogous bromo complex, Fe(DPPEPM)Br{sub 2} (2) revealed a pseudo-octahedral, cis-{alpha} geometry at iron with DPPEPM coordinated in a tetradentate fashion. However, in CD{sub 2}Cl{sub 2} solution, the coordination of DPPEPM in 2 is similar to that of 1 in that one of the external phosphorus atoms is dissociated resulting in a mixture of three tridentate complexes. The chloro ruthenium complex cis-Ru({kappa}{sup 4}-DPPEPM)Cl{sub 2} (3) is obtained from rac-DPPEPM and either [RuCl{sub 2}(COD)]{sub 2} [COD = 1,5-cyclooctadiene] or RuCl{sub 2}(PPh{sub 3}){sub 4}. The structure of 3 in both the solid state and in CD{sub 2}Cl{sub 2} solution features a folded {kappa}{sup 4}-DPPEPM. This binding mode was also observed in cis-[Fe({kappa}{sup 4}-DPPEPM)(CH{sub 3}CN){sub 2}](CF{sub 3}SO{sub 3}){sub 2} (4). Addition of an excess of CO to a methanolic solution of 1 results in the replacement of one of the chloride ions by CO to yield cis-[Fe({kappa}{sup 4}-DPPEPM)Cl(CO)](Cl) (5). The same reaction in CH{sub 2}Cl{sub 2} produces a mixture of 5 and [Fe({kappa}{sup 3}-DPPEPM)Cl{sub 2}(CO)] (6) in which one of the internal phosphines has been substituted by CO. Complexes 2, 3, 4, and 5 appear to be the first structurally characterized monometallic complexes of {kappa}{sup 4}-DPPEPM.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Surface modified, collapsible controlled pore glass materials for sequestration and immobilization of trivalent metal ions.

We report a one-pot method for sequestration, containment, and immobilization of lanthanide (Ln) ions from dilute aqueous waste streams. The approach is based on the use of collapsible, surface modified controlled pore glass (CPG) nanomaterials. We present several approaches for a single-step chemical modification of 3-propylaminated CPGs that yield highly efficient Ln-extracting materials with distribution coefficients exceeding 10000 mL/g. The resulting Ln complexes were studied using X-ray absorption, magnetic resonance, and time-resolved luminescence spectroscopies. One of these CPG materials involving an imidodi(methanediphosphate) moiety demonstrated high extraction efficacy, significant ionic radius sensitivity, and exceptional tolerance to masking agents, which is conducive to its use for removal of traces of radionuclide ions from aqueous TALSPEAK raffinate (trivalent actinide-lanthanide separation by phosphorus reagent extraction from aqueous complexes process used in processing of spent nuclear fuel). The glass loaded with the extracted metal ions can be calcined and sintered at 1100 C, yielding fused material that buries Ln ions in the vitreous matrix. This processing temperature is significantly lower than 1700 C that is required for direct vitrification of lanthanide oxides in high-silica glass. X-ray absorption spectroscopy and acid leaching tests indicate that the immobilized ions are isolated and dispersed in the fused glass matrix. Thus, the method integrates Ln ions into the glass network. The resulting glass can be used for temporary storage or as the source of silica for production of borosilicate waste forms that are used for long-term disposal of high level radioactive waste.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2012

Theoretical analysis of the sequential proton-coupled electron transfer mechanisms for H2 oxidation and production pathways catalyzed by nickel molecular electrocatalysts

The design of electrocatalysts for the oxidation and production of H2 is important for the development of alternative energy sources. This paper focuses on the electrocatalysts, where denotes 1,5-diaza-3,7-diphosphacyclooctane ligands with substituent groups R and R' covalently bound to the phosphorus and nitrogen atoms, respectively. Theoretical methods are used to investigate the mechanism of the step in the catalytic cycle corresponding to – e– → for H2 oxidation and the reverse reaction for H2 production. This step involves electron transfer (ET) between the Ni complex and the electrode as well as proton transfer (PT) between the Ni and the N. The sequential mechanisms, PT–ET and ET–PT, are investigated for the following (R,R’) substituents: (Me,Me), (Ph,Ph), and (Ph,Bz), where Me, Ph, and Bz denote methyl, phenyl, and benzyl substituents. Density functional theory is used to calculate reduction potentials, pKas, and PT pathways, and Marcus theory is used to describe the electrochemical electron transfer, including the effects of solute and solvent reorganization energies. For the (Ph,Ph) and (Ph,Bz) systems, the sequential PT–ET mechanism would require surmounting a large free energy barrier for the initial PT step, followed by thermodynamically favorable or thermoneutral ET. The sequential ET–PT mechanism for these systems would require a relatively large initial applied overpotential, followed by a PT reaction with a relatively low free energy barrier. Consistent with experimental data, the calculated overpotential required for the initial reduction in the ET–PT mechanism is lower for the (Ph,Bz) system than for the (Ph,Ph) system. The concerted mechanism, in which the electron and proton transfer simultaneously without a stable intermediate, may be thermodynamically favorable and is a direction of future research. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under FWP56073.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Multiscale Simulations of Li Ion Conductivity in Solid Electrolyte

Optimizing solid electrolyte design for its application in Li-ion and Li-metal batteries requires a fundamental understanding of the mechanism of ion and electron transport in the material at the nano- to micron-scales. We have performed simulations of Li+ and electron conductivity in lithium phosphorus oxynitride, one of the most widely used solid electrolytes, using novel hierarchical multiscale models. By comparing the results of one- and three-dimensional models we show that for this material with complex non-linear Li+ diffusion pathways three-dimensional description is essential for reproducing experimentally measured conductivity. We also suggest some basic principles to design optimum electrolyte tailored for low and high temperature regimes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2010

Deactivation Mechanisms of Ni-Based Tar Reforming Catalysts As Monitored by X-ray Absorption Spectroscopy

Deactivation mechanisms of alumina-supported, Ni-based catalysts for tar reforming in biomass-derived syngas were evaluated using extended X-ray absorption fine structure (EXAFS) spectroscopy. Catalysts were characterized before and after catalytic reaction cycles and regeneration procedures, which included oxidation by a mixture of steam and air, and reduction in hydrogen. Qualitative analysis of the EXAFS spectra revealed that oxidation of a portion of the Ni in the catalysts to form an oxide phase and/or a sulfide phase were likely scenarios that led to catalyst deactivation with time-on-stream and with increased reaction cycles. Deactivation through carbon deposition, phosphorus poisoning, or changes in particle size were deemed as unlikely causes. Quantitative analysis of the EXAFS spectra indicated sulfur poisoning occurred with time-on-stream, and the contaminating species could not be completely removed during the regeneration protocols. The results also verified that Ni-containing oxide phases (most likely a spinel also containing Mg and Al) formed and contributed to the deactivation. This study validates the need for developing catalyst systems that will protect Ni from sulfur poisoning and oxide formation at elevated reaction and regeneration temperatures.

08 HYDROGEN↗
DOE OSTI2020

Competing effects of soil fertility and toxicity on tropical greening

Tropical forests are expected to green up with increasing atmospheric CO 2 concentrations, but primary productivity may be limited by soil nutrient availability. However, rarely have canopy-scale measurements been assessed against soil measurements in the tropics. Here, we sought to assess remotely sensed canopy greenness against steep soil nutrient gradients across 50 1-ha mature forest plots in Panama. Contrary to expectations, increases in in situ extractable soil phosphorus (P) and base cations (K, Mg) corresponded to declines in remotely sensed mean annual canopy greenness (r 2 = 0.77– 0.85; p < 0.1), controlling for precipitation. The reason for this inverse relationship appears to be that litterfall also increased with increasing soil P and cation availability (r 2 = 0.88–0.98; p < 0.1), resulting in a decline in greenness with increasing annual litterfall (r 2 = 0.94; p < 0.1). As such, greater soil nutrient availability corresponded to greater leaf turnover, resulting in decreased greenness. However, these decreases in greenness with increasing soil P and cations were countered by increases in greenness with increasing soil nitrogen (N) (r 2 = 0.14; p < 0.1), which had no significant relationship with litterfall, likely reflecting a direct effect of soil N on leaf chlorophyll content, but not on litterfall rates. In addition, greenness increased with extractable soil aluminum (Al) (r 2 = 0.97; p < 0.1), but Al had no significant relationship with litterfall, suggesting a physiological adaptation of plants to high levels of toxic metals. Thus, spatial gradients in canopy greenness are not necessarily positive indicators of soil nutrient scarcity. Using a novel remote sensing index of canopy greenness limitation, we assessed how observed greenness compares with potential greenness. We found a strong relationship with soil N only (r 2 = 0.65; p < 0.1), suggesting that tropical canopy greenness in Panama is predominantly limited by soil N, even if plant productivity (e.g., litterfall) responds to rock-derived nutrients. Moreover, greenness limitation was also significantly correlated with fine root biomass and soil carbon stocks (r 2 = 0.62–0.71; p < 0.1), suggesting a feedback from soil N to canopy greenness to soil carbon storage. Altogether, these data point to the potential utility of a remote sensing product for assessing belowground properties in tropical ecosystems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2011

Structure, surface reactivity and physico-chemical degradation of fluoride containing phospho-silicate glasses

We report on the structure, apatite-forming ability and physicochemical degradation of glasses along fluorapatite [FA; Ca5(PO4)3F] - diopside (Di; CaMgSi2O6) join. A series of glasses with varying FA/Di ratio have been synthesised by melt-quenching technique. The amorphous glasses could be obtained only for compositions up to 40 wt.% of FA. The detailed structural analysis of glasses has been made by infra-red spectroscopy (FTIR), Raman spectroscopy and magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR). Silicon was predominantly present as Q2 (Si) species while phosphorus was found in orthophosphate type environment in all the investigated glasses. The apatite forming ability of glasses was investigated by immersion of glass powders in simulated body fluid (SBF) for time durations varying between 1 h – 28 days. An extensive precipitation of calcite (CaCO3) after immersion in SBF was found in all the glasses which considerably masked the formation of hydroxyapatite [HA; Ca5(PO4)3OH] as depicted by X-ray diffraction (XRD) and FTIR. The possible mechanism favouring formation of calcite instead of HA has been explained on the basis of experimental results obtained for structure of glasses, leaching profile of glass powders in SBF solution and pH variation in SBF solution. Further, physico-chemical degradation of glasses has been studied in accordance with ISO 10993-14 “Biological evaluation of medical devices – Part 14: Identification and quantification of degradation products from ceramics” in Tris HCl and citric acid buffer. All the FA containing glasses exhibited a weight gain (instead of weight loss) after immersion in citric acid buffer due to the formation of different crystalline products.

58 GEOSCIENCES↗
DOE OSTI2010

Experiments and simulation on diffusion and activation of codoped with arsenic and phosphorous germanium

We report arsenic and phosphorus diffusion experiments and activation related phenomena in codoped germanium substrates utilizing conventional thermal annealing. Chemical profiles were obtained by secondary ion mass spectroscopy, sheet resistance was estimated by the Van der Pauw method. Our study covers the temperature range from 600 to 750 deg. C. We accurately described the dopant profiles with a quadratic dependence of the dopants diffusion coefficient on the free electron concentration. In our simulations we considered the dopant pile-up near the surface and dopant loss owing to outdiffusion during the annealing. Although the double donor codoping technique exhibited no advantage over monodoping with P concerning the level of activation and junction depth, it was interesting to observe the different diffusion behavior of the two dopants. Whereas the diffusion of As indicates a retardation under codoping the diffusion of P remains either unaffected or is slightly enhanced by codoping. The activation level of the codoped samples remains lower compared to the respective monodoped samples, except for the highest annealing temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Auger electron spectroscopy for the determination of sex and age related Ca/P ratio at different bone sites

The Ca/P ratio of normal cortical and trabecular rat bone was measured by Auger electron spectroscopy (AES). Semiquantitative analysis was carried out using ratio techniques to draw conclusions on how age, sex and bone site affect the relative composition of calcium and phosphorus. Results show that Ca/P ratio is not sex dependent; quite the opposite, bone sites exhibit variations in elemental stoichiometry where femoral sections demonstrate higher Ca/P ratio than rear and front tibias. Age-related changes are more distinct for cortical bone in comparison with the trabecular bone. The latter's Ca/P ratio remains unaffected from all the parameters under study. This study confirms that AES is able to successfully quantify bone mineral main elements when certain critical points, related to the experimental conditions, are addressed effectively.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2011

Ribbon and Spot Beam Process Performance of the Dual Mode iPulsar High Current Ion Implanter

Low energy implant process data are presented from a dual mode high current ion implanter. The iPulsar is a flexible single wafer implanter capable of running both ribbon beams with one-dimensional mechanical scan of the wafer and spot beams with two-dimensional wafer scan. The main components of the implanter are described and their operation explained. Boron concentration profiles in Ge pre-amorphized substrates, measured by secondary ion mass spectroscopy (SIMS) are presented before and after anneal with drift and decelerated beams. In addition, spot and ribbon beam as-implanted phosphorus and carbon profiles are presented and the characteristics of each mode of operation are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2011

SEN Ultra-High Energy Implanter (UHE) Developed for Next Generation Image Sensors

The UHE is an ultra-high energy implanter developed by SEN Corporation. It was derived from the NV-GSD-HE3 by adding six RF resonators to the beam line. This extends performance so that singly charged boron ions can reach 2 MeV with beam current of 0.75 mA. The maximum energy for triple charged boron is 5 MeV with beam current of 1p{mu}A. For phosphorus ions, the UHE can accelerate doubly charged ions up to 4.4 MeV with beam current of 0.35 mA and quadruply charged ions up to 8 MeV with beam current of 1 p{mu}A. The primary application of the UHE is the image sensor market where it is used to increase the depth of CCD photodiodes into the surface of the wafer and thereby permit higher pixel density for image sensors. The second purpose is to improve productivity for relatively high boron doses at energies around 3 MeV. In order to address certain CCD defects, the system includes a state-of-the-art beam profile controller which allows optimization of implant damage and micro-uniformity. The ULE is currently used in production of high-end CCD's.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Process Performance of Optima XEx Single Wafer High Energy Implanter

To meet the process requirements for well formation in future CMOS memory production, high energy implanters require more robust angle, dose, and energy control while maintaining high productivity. The Optima XEx high energy implanter meets these requirements by integrating a traditional LINAC beamline with a robust single wafer handling system. To achieve beam angle control, Optima XEx can control both the horizontal and vertical beam angles to within 0.1 degrees using advanced beam angle measurement and correction. Accurate energy calibration and energy trim functions accelerate process matching by eliminating energy calibration errors. The large volume process chamber and UDC (upstream dose control) using faraday cups outside of the process chamber precisely control implant dose regardless of any chamber pressure increase due to PR (photoresist) outgassing. An optimized RF LINAC accelerator improves reliability and enables singly charged phosphorus and boron energies up to 1200 keV and 1500 keV respectively with higher beam currents. A new single wafer endstation combined with increased beam performance leads to overall increased productivity. We report on the advanced performance of Optima XEx observed during tool installation and volume production at an advanced memory fab.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Use of Xenon Difluoride to Clean Hazardous By-Products in Ion Implanter Source Housings, Turbo Pumps, and Fore-Lines

This paper describes the use of xenon difluoride to clean deposits in the source housing, source turbo pump, and source turbo pump fore-line of ion implanters. Xenon difluoride has previously been shown to be effective in increasing the lifetime of the ion source{sup 1,2} and this paper presents an extension of the technology to other areas within the tool. Process by-products that are deposited in the source housing, turbo pump, and turbo pump fore-line can not only pose productivity issues, in the case of coatings on insulators, but can also be flammable and toxic in the case of deposits formed within the turbo pump and fore-line. The results presented in this paper detail the initial successful examples of using xenon difluoride to clean these deposits.ATMI has shown that xenon difluoride is capable of cleaning an insulator in an ion implanter. Typically during use an insulator will become increasingly coated with deposits that could lead to productivity problems. By introducing xenon difluoride into the source housing the insulator residues were effectively cleaned in-situ, thereby extending the maintenance interval and resulting in significant consumable savings.Similar deposits that form in the turbo pump and fore-line could not only lead to production problems due to turbo pump failure or fore-line build-up, but pose significant health risks during the ex-situ cleaning process. Through internal testing ATMI has shown that xenon difluoride is able to clean phosphorus and germanium deposits located within a turbo pump. Additionally, testing has demonstrated that the turbo pump fore-line can be cleaned in-situ without the need to remove these components, thereby virtually eliminating the possibility of fires. The cleaning reaction progress and by-products were monitored using FTIR spectrometry and thermocouples.In order to efficiently clean the source housing, turbo pump, and turbo pump fore-line xenon difluoride delivery must be optimized. This paper also details a hardware concept that maximizes xenon difluoride delivery and allows the clean to be done in a way that is viable for production ion implanters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

A method to characterize the sheet resistance of a laser doped line on crystalline silicon wafers for photovoltaic applications

A theory is presented that correlates the different sheet resistance (R{sub sh}) values of the same phosphorus laser doped (LD) line approximated by two different methods: the LD box and transfer length measurement (TLM) methods. By modeling the LD line junction profile, an effective R{sub sh} value using the LD box method is obtained and used to derive the R{sub sh} upper limit (R{sub sh.UL}) of the LD line. This value matches within {+-}10% of the R{sub sh.UL} value obtained using the TLM method across four lasing speeds. Subsequently, a LD box method is introduced to determine the LD line R{sub sh.UL} easily without modeling work.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Iron distribution in silicon after solar cell processing: Synchrotron analysis and predictive modeling

The evolution during silicon solar cell processing of performance-limiting iron impurities is investigated with synchrotron-based x-ray fluorescence microscopy. We find that during industrial phosphorus diffusion, bulk precipitate dissolution is incomplete in wafers with high metal content, specifically ingot border material. Postdiffusion low-temperature annealing is not found to alter appreciably the size or spatial distribution of FeSi{sub 2} precipitates, although cell efficiency improves due to a decrease in iron interstitial concentration. Gettering simulations successfully model experiment results and suggest the efficacy of high- and low-temperature processing to reduce both precipitated and interstitial iron concentrations, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Advanced non-destructive assessment technology to determine the aging of silicon containing materials for generation IV nuclear reactors

To create an in-situ, real-time method of monitoring neutron damage within a nuclear reactor core, irradiated silicon carbide samples are examined to correlate measurable variations in the material properties with neutron fluence levels experienced by the silicon carbide (SiC) during the irradiation process. The reaction by which phosphorus doping via thermal neutrons occurs in the silicon carbide samples is known to increase electron carrier density. A number of techniques are used to probe the properties of the SiC, including ultrasonic and Hall coefficient measurements, as well as high frequency impedance analysis. Gamma spectroscopy is also used to examine residual radioactivity resulting from irradiation activation of elements in the samples. Hall coefficient measurements produce the expected trend of increasing carrier concentration with higher fluence levels, while high frequency impedance analysis shows an increase in sample impedance with increasing fluence.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Sintering Effects on Morphology, Thermal Stability and Surface Area of Sol-Gel Derived Nano-Hydroxyapatite Powder

Hydroxyapatite (HAP) ceramics have been recognized as substitute materials for bone and teeth in orthopedic and dentistry field due to their chemical and biological similarity to human hard tissue. The nanosized and nanocrystalline forms of HAP have great potential to revolutionize the hard tissue-engineering field, starting from bone repair and augmentation to controlled drug delivery systems. This paper reports the synthesis of biomimetic nano-hydroxyapatite (HAP) by sol-gel method using calcium nitrate tetrahydrate (CNT) and potassium dihydrogen phosphate (KDP) as calcium and phosphorus precursors, respectively to obtain a desired Ca/P ratio of 1.67. Deionized water was used as a diluting media for HAP sol preparation and ammonia was used to adjust the pH to 11. After aging, the HAP gel was dried at 55 deg. C and sintered to different temperatures (200 deg. C, 400 deg. C, 600 deg. C, 800 deg. C, 1000 deg. C and 1200 deg. C). The dried and sintered powders were characterized for phase composition using Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The particle size and morphology was studied using transmission electron microscopy (TEM). The thermal behavior of the dried HAP nanopowder was studied in the temperature range of 55 deg. C to 1000 deg. C using thermal gravimetric analyser (TGA). The BET surface area of absorbance was determined by Nitrogen adsorption using Brunauer-Emmett-Teller (BET) method. The presence of characteristic peaks of the phosphate and OH groups in FTIR spectrums confirmed the formation of pure HAP in dried as well as sintered powders. XRD results also confirmed the formation of stoichiometric nano-HAP. Sintering revealed that with increase in temperature, both the crystallinity and crystallite size of nano-HAP particles increased. The synthesized nano-HAP powder was found to be stable upto 1000 deg. C without any additional phase other than HAP, whereas peak of {beta}-TCP (tricalcium phosphate) was observed at 1200 deg. C. Photomicrograph of TEM showed that the nanopowder sintered at 600 deg. C is composed of hydroxyapatite nanoparticles (26.0-45.6 nm), which is well in agreement with the crystallite size calculated using XRD data. TGA study showed the thermal stability of the synthesized nano-HAP powder. The BET surface area decreased with increase in sintering temperature.

36 MATERIALS SCIENCE↗