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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Ectomycorrhizal Community Structure and Soil Characteristics of Mature Lodgepole Pine (Pinus Contorta) and Adjacent Stands of Old Growth Mixed Conifer in Yellowstone National Park, Wyoming USA

Forest development patterns following disturbance are known to influence the physical and chemical attributes of soils at different points in time. Changes in soil resources are thought to have a corresponding effect on ectomycorrhizal (ECM) community structure. We used molecular methods to compare below-ground ECM species richness, composition, and abundance between adjacent stands of homogenous lodgepole pine and old growth mixed conifer in Yellowstone National Park (YNP). In each stand-type we collected soil cores to both identify mycorrhizae and assess soil chemistry. Although no statistical difference was observed in the mean number of ECM root tips per core between stand types, the total number of species identified (85 versus 35) and the mean number of species per core (8.8 +/- 0.6 versus 2.5 +/- 0.3) were significantly higher in lodgepole pine. Differences between the actual and estimated species richness levels indicated that these forest types support a high number of ECM species and that undersampling was severe. Species compositions were widely disparate between stands where only four species were shared out of a total of 116. Soil analysis also revealed that mixed conifer was significantly lower in pH, but higher in organic matter, potassium, phosphorus, and ammonium when compared to lodgepole pine stands. Species richness per core was correlated with these chemical data, however, analysis of covariance indicated that stand type was the only statistically significant factor in the observed difference in species richness. Our data suggest that ECM fungal richness increases as homogenous lodgepole pine stands grow and mature, but declines after Engelmann spruce and subalpine fir colonize. Despite difficulties linking species composition with soil chemistry, there are a variety of physical and chemical factors that could be influencing ECM community structure. Future field experiments are necessary to test some of the mechanisms potentially operating within this system.

Douglas, Robert B.↗
NASA NTRS2020

The Advanced Spectral Library (ASTRAL): Abundance Analysis of the Chemically Peculiar Star HR 465

This paper presents the results of the spectrum analysis of the B-type magnetic chemically peculiar star HR 465. HR 465 shows unusual abundance patterns that vary with a period of 21.5 yr. Our observations are recorded at ϕ = 0.45, 0.68, and 0.85 of the spectroscopic period, where ϕ = 0 represents the phase of maximum flux in the photometric y-band. Synthetic spectra, computed using an LTE atmosphere model, are fit to high-resolution ultraviolet Hubble Space Telescope (ϕ = 0.45) spectra obtained as part of the Advanced Spectral Library Project: Hot Stars program. The ultraviolet data are supplemented by high-resolution optical spectra (ϕ = 0.68 and 0.85) recorded at the Nordic Optical Telescope with the SOFIN spectrograph. The optical data are used as a complement to the high line-density ultraviolet spectrum to derive accurate abundances for elements without spectral lines in the ultraviolet and to improve the abundance phase coverage for many atoms/ions. This analysis presents abundance results for more than 70 atoms/ions and confirms parts of the abundance characteristics previously reported where elements with high mass numbers show significant abundance enhancements compared with solar values while some of the lighter elements show abundance deficiencies. In addition, our measured abundances are consistent with the periodic variability for chromium and rare-earth elements. Our results are compared with earlier investigations of this peculiar object to constrain stellar abundance and diffusion.

Krister E. Nielsen↗
DOE OSTI2022

Multilevel peel-off patterning of a prototype semitransparent organic photovoltaic module

Semitransparent organic photovoltaics (ST-OPVs) with applications to power generating windows have shown substantial increases in power conversion efficiency (PCE) and average photopic transmission (APT) at the laboratory scale. Here, the demonstration of similarly efficient, large-scale ST-OPV modules with geometric fill factors (GFF) approaching 100%, however, remains a challenge. Here, we employ a multilevel peel-off patterning method that can achieve micron-scale resolution without exposing chemically sensitive organic materials to solvents. Eight, 4 cm × 0.4 cm cells are connected in series to realize a prototype ST-OPV module with GFF = 95.8%, with PCE = 7.3 ± 0.2% under simulated AM 1.5G illumination at 1 sun intensity, APT = 41.8 ± 1.4%, and a light utilization efficiency of LUE = 3.1 ± 0.1%. A neutral color STOPV module is also demonstrated with 1.7 ± 0.1% and International Commission on Illumination (CIE) LAB coordinates of (L*, a*, b*) = (53.7, -1.9, -3.9).

14 SOLAR ENERGY↗
DOE OSTI2020

Continental-scale patterns of extracellular enzyme activity in the subsoil: an overlooked reservoir of microbial activity

Abstract Chemical stabilization of microbial-derived products such as extracellular enzymes (EE) onto mineral surfaces has gained attention as a possibly important mechanism leading to the persistence of soil organic carbon (SOC). While the controls on EE activities and their stabilization in the surface soil are reasonably well-understood, how these activities change with soil depth and possibly diverge from those at the soil surface due to distinct physical, chemical, and biotic conditions remains unclear. We assessed EE activity to a depth of 1 m (10 cm increments) in 19 soil profiles across the Critical Zone Observatory Network, which represents a wide range of climates, soil orders, and vegetation types. For all EEs, activities per mass of soil correlated positively with microbial biomass (MB) and SOC, and all three of these variables decreased logarithmically with depth ( p < 0.05). Across all sites, over half of the potential EE activities per mass soil consistently occurred below 20 cm for all measured EEs. Activities per unit MB or SOC were substantially higher at depth (soils below 20 cm accounted for 80% of whole-profile EE activity), suggesting an accumulation of stabilized (i.e. mineral sorbed) EEs in subsoil horizons. The pronounced enzyme stabilization in subsurface horizons was corroborated by mixed-effects models that showed a significant, positive relationship between clay concentration and MB-normalized EE activities in the subsoil. Furthermore, the negative relationships between soil C, N, and P and C-, N-, and P-acquiring EEs found in the surface soil decoupled below 20 cm, which could have also been caused by EE stabilization. This finding suggests that EEs may not reflect soil nutrient availabilities deeper in the soil profile. Taken together, our results suggest that deeper soil horizons hold a significant reservoir of EEs, and that the controls of subsoil EEs differ from their surface soil counterparts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2003

The Highly Robust Electrical Interconnects and Ultrasensitive Biosensors Based on Embedded Carbon Nanotube Arrays

We report on our recent breakthroughs in two different applications using well-aligned carbon nanotube (CNT) arrays on Si chips, including (1) a novel processing solution for highly robust electrical interconnects in integrated circuit manufacturing, and (2) the development of ultrasensitive electrochemical DNA sensors. Both of them rely on the invention of a bottom-up fabrication scheme which includes six steps, including: (a) lithographic patterning, (b) depositing bottom conducting contacts, (c) depositing metal catalysts, (d) CNT growth by plasma enhanced chemical vapor deposition (PECVD), (e) dielectric gap-filling, and (f) chemical mechanical polishing (CMP). Such processes produce a stable planarized surface with only the open end of CNTs exposed, whch can be further processed or modified for different applications. By depositing patterned top contacts, the CNT can serve as vertical interconnects between the two conducting layers. This method is fundamentally different fiom current damascene processes and avoids problems associated with etching and filling of high aspect ratio holes at nanoscales. In addition, multiwalled CNTs (MWCNTs) are highly robust and can carry a current density of 10(exp 9) A/square centimeters without degradation. It has great potential to help extending the current Si technology. The embedded MWCNT array without the top contact layer can be also used as a nanoelectrode array in electrochemical biosensors. The cell time-constant and sensitivity can be dramatically improved. By functionalizing the tube ends with specific oligonucleotide probes, specific DNA targets can be detected with electrochemical methods down to subattomoles.

Li, Jun↗
DOE OSTI2022

Physiochemical Machine Learning Models Predict Operational Lifetimes of CH3NH3PbI3 Perovskite Solar Cells

Halide perovskites are promising photovoltaic (PV) materials with the potential to lower the cost of electricity and greatly expand the penetration of PV if they can demonstrate long-term stability under illumination in the presence of moisture and oxygen. The solar cell service lifetime as quantified by the T80 (the time required for the power conversion efficiency to drop to 80% of its starting value) is a useful metric to assess stability. The T80 for utility, commercial, or residential PV systems needs to be several decades in order to yield low-cost electricity, and thus it is not practical to directly measure the T80. It would be useful if T80 could be predicted from the initial dynamics of a solar cell’s performance, but until now no models have been developed to forecast T80. In this work, we report the development of machine learning models to predict T80 of ITO/NiOx/CH3NH3PbI3/C60/BCP/Ag solar cells operating at maximum power point under 1-sun equivalent photon flux in air at varying temperatures and relative humidities. Efficiency losses are driven by short-circuit current and fill factor, indicating that chemical decomposition of the perovskite is a major contributor to degradation. Spatial patterns evident from in situ dark field optical microscopy suggest that the electric field gradient at device edges plays a significant role in perovskite decomposition, along with photochemical reactions with O2 and H2O. Models are trained using a menu of features from three distinct categories: (i) features based on measurements of the initial rates of change of device parameters, (ii) features based on the ambient conditions during operation (temperature, & partial pressure of H2O), and (iii) features based on underlying physics and chemistry. We show that a theory-based physiochemical feature derived from a model of the chemical reaction kinetics of the rate of degradation of the CH3NH3PbI3 is particularly valuable for prediction. This physiochemical feature was selected as the first or second most dominant feature in the best performing models. With a dataset consisting of 45 accelerated degradation experiments with T80 that range over a factor of 30, the model predicts T80 with an accuracy of about 40% (|predicted T80 - observed T80| / observed T80) on samples not used in training. This hybrid ML approach should be effective when applied to other compositions, device architectures, and advanced packaging schemes.

14 SOLAR ENERGY↗
DOE OSTI2022

Physiochemical Machine Learning Models Predict Operational Lifetimes of CH3NH3PbI3 Perovskite Solar Cells

Halide perovskites are promising photovoltaic (PV) materials with the potential to lower the cost of electricity and greatly expand the penetration of PV if they can demonstrate long-term stability under illumination in the presence of moisture and oxygen. The solar cell service lifetime as quantified by the T80 (the time required for the power conversion efficiency to drop to 80% of its starting value) is a useful metric to assess stability. The T80 for utility, commercial, or residential PV systems needs to be several decades in order to yield low-cost electricity, and thus it is not practical to directly measure the T80. It would be useful if T80 could be predicted from the initial dynamics of a solar cell’s performance, but until now no models have been developed to forecast T80. In this work, we report the development of machine learning models to predict T80 of ITO/NiOx/CH3NH3PbI3/C60/BCP/Ag solar cells operating at maximum power point under 1-sun equivalent photon flux in air at varying temperatures and relative humidities. Efficiency losses are driven by short-circuit current and fill factor, indicating that chemical decomposition of the perovskite is a major contributor to degradation. Spatial patterns evident from in situ dark field optical microscopy suggest that the electric field gradient at device edges plays a significant role in perovskite decomposition, along with photochemical reactions with O2 and H2O. Models are trained using a menu of features from three distinct categories: (i) features based on measurements of the initial rates of change of device parameters, (ii) features based on the ambient conditions during operation (temperature, & partial pressure of H2O), and (iii) features based on underlying physics and chemistry. We show that a theory-based physiochemical feature derived from a model of the chemical reaction kinetics of the rate of degradation of the CH3NH3PbI3 is particularly valuable for prediction. This physiochemical feature was selected as the first or second most dominant feature in the best performing models. With a dataset consisting of 45 accelerated degradation experiments with T80 that range over a factor of 30, the model predicts T80 with an accuracy of about 40% (|predicted T80 - observed T80| / observed T80) on samples not used in training. This hybrid ML approach should be effective when applied to other compositions, device architectures, and advanced packaging schemes.

14 SOLAR ENERGY↗
DOE OSTI2022

Splitting the Ring: Impact of Ortho and Meta Pi Conjugation Pathways through Disjointed [8]Cycloparaphenylene Electronic Materials

In this report, we describe the synthesis and electronic properties of small-molecule and polymeric [8]cycloparaphenylenes ([8]CPPs) with disjointed pi conjugated substituents. Arylene-ethynylene linkers were installed on opposite sides of the [8]CPP nanohoop as separated by three phenyl units on either side such that the monomer systems have syn (C2 symmetry) and anti (C1 symmetry) conformers with a small energy gap (0.1-0.6 kcal/mol). This disjoined substitution pattern necessarily forces delocalization through and around the CPP radial structure. We demonstrate new electronic states from this radial/linear mixing in both the small molecules and the pi extended polymers. Quantum chemical calculations reveal these electronic processes to arise from multiple operative radial/linear conjugation pathways, as the disjoint pattern results in both ortho and meta connections to the CPP ring. Furthermore, these results affirm the unique nature of hybrid radial and linear pi electron delocalization operative in these new conjugation pathways.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Mechanism of Vapor-Phase Infiltration of Organometallic Hf in Poly(Methyl Methacrylate) for Hybrid Resist Applications

Inorganic–organic hybrid thin films synthesized by vapor-phase infiltration (VPI) of metal oxides into organic photoresists, such as poly(methyl methacrylate) (PMMA), have recently demonstrated their utility in extreme ultraviolet lithography, critical for angstrom-era semiconductor device miniaturization. Hafnium oxide infiltration has been reported recently for this purpose, but its detailed VPI mechanism has remained largely unexplored. In this study, we investigated the VPI characteristics and mechanisms of tetrakis(dimethylamido)hafnium (TDMAHf)─the hafnium precursor predominantly used for VPI in the field─into PMMA and examined its impact on electron-beam lithography (EBL) exposure behavior. VPI was performed at temperatures ranging from 85 to 150 °C, with chemical interactions characterized using infrared reflection-absorption spectroscopy, and resist patterning performance was evaluated through EBL dose-sensitivity assessments. The results indicate that TDMAHf forms a reversible adduct with PMMA at temperatures up to 120 °C, whereas at 150 °C, covalent bond formation occurs, most likely via dealkylation that leads to acetate formation. EBL studies reveal that resist sensitivity is influenced by both infiltration temperature and developer selection, with aqueous isopropyl alcohol development demonstrating enhanced sensitivity compared to organic solvent-based development. The optimized infiltration protocol at 120 °C ensures a uniform inorganic distribution without compromising resist dissolution. These findings not only help refine hybrid resist patterning performance but also offer insights potentially applicable to the VPI of other homoleptic metal-amide organometallic VPI precursors that include TDMA ligands.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Mixed-Flux Techniques for Rational Synthesis and Structural Control in Silver Chalcogenides

The functionality of materials is intrinsically linked to their structures, an axiom encapsulated in the principle of structure-property relationships. The pinnacle of materials design is the tailoring of its structure for a specific function, which requires the ability of rational synthesis and the development of synthesis science. This idea, however, remains elusive for the synthesis of complex extended solids. A major obstacle is the difficulty in using established chemical principles selectively to control reaction paths and favor certain structural patterns over numerous other possible results. In this context, we are developing a synthesis science approach that facilitates the control of the structure and bonding to create new structures. This is achieved by employing a two-component flux consisting of mixed hydroxides and halides as the reaction medium. This enables reaction conditions that allow better control of the structure dimensionality and composition by manipulating the temperature and solvent basicity (via the flux component ratio). Here, we demonstrate the efficacy of this method in controlling their structural motifs to arrive at 23 unreported compositions and 6 unique structure types. These materials are expected to exhibit a broad range of properties, from metallic to semiconducting, with calculations suggesting the potential for emergent phenomena such as Dirac semimetals. The reaction paths afforded by these mixed fluxes establish a direct correlation between the synthetic variables and properties, providing significant insight into a broadly applicable approach for new materials.

Zhou, Xiuquan [Argonne National Laboratory (ANL), ↗
DOE OSTI2020

Single crystal structure and photocatalytic behavior of grafted uranyl on the Zr-node of a pyrene-based metal–organic framework

Accurately characterizing actinide oxides bound to metal–organic frameworks (MOFs) is important for designing MOFs as radioactive waste sorbents and catalytic supports. Here, the zirconium MOF NU-1000 was post-synthetically modified through solvothermal deposition to include the uranyl (UO 2 2+ ) ion and characterized via single-crystal X-ray diffraction. Additonally, bond lengths derived from the diffraction pattern and Raman spectroscopy indicate that UO 2 2+ maintains its chemical properties upon deposition, while alcohol oxidation photocatalysis reveals photo-interactions between the pyrene linkers and the UO 2 2+ ion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

SPRUCE S1 Bog Production of Newly-Grown Fine Roots Assessed Using Root Ingrowth Cores in 2013

This dataset contains data from root ingrowth cores from the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experimental site within the Marcell Experimental Forest in northern Minnesota, USA. Root ingrowth cores were used to capture newly-grown fine roots during the 2013 growing season (June - October) at 20 locations at the southern end of the S1-Bog. Rates of fine root production were measured with root ingrowth cores and fine root traits were measured on roots that grew into ingrowth cores. Traits are reported by plant species and root orders and include nitrogen (N) content, root tissue density, specific root length, average diameter. Ingrowth cores were used to compare species-specific depth distribution patterns with minirhizotron analyses and to obtain newly produced roots for chemical analysis and measurement of morphological traits prior to the construction of the SPRUCE experimental plots. This dataset contains two data files in comma-separate values (*.csv) format. Additional metadata are provided: two data dictionaries and a file-level metadata file in comma-separate values (.csv) format and a user guide in PDF (*.pdf) format.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1977

Genesis of howardites, diogenites, and eucrites

The reported investigation was mainly concerned with the precise determinations of major-, minor-, and trace-element abundances, especially the REE abundances in the bulk howardites in order to establish the bulk rock composition for the future chemical-mineralogical, petrographic studies of different rock types on the chemically unique howardites and diogenites if they exist. From the chemical data for the major-element abundances and the REE patterns of the howardites analyzed, it is evident that these howardites are predominantly composed of eucritic and diogenitic components. The analytical results for howardites and diogenites are shown in two tables together with the results for CRB-1. The chondritic normalized K, Sr, Ba, REE, Hf, and Sc abundances of these howardites are plotted in two graphs.

Fukuoka, T.↗
NASA NTRS1992

Effects on post-glacial rebound from the hard rheology in the transition zone

The effect of an increase of viscosity in the earth-mantle's transition zone between 420 and 670 km on the geophysical signatures induced by postglacial rebound was analyzed using a self-gravitating model consisting of an elastic lithosphere, a three-layer viscoelastic mantle, and an inviscid core. Results show that the horizontal displacements and velocities as well as the stress pattern are extremely sensitive to the viscosity increase and to the chemical stratification of the transition zone. The findings indicate that geodetic data on intraplate deformation can be used to put constraints on the viscosity increase in the transition zone and on the amount of chemical stratification in the mantle.

Spada, Giorgio↗
NASA NTRS1993

Calculating Flows With Interfering Shock Waves

Equilibrium Air Shock Interference, EASI, program takes account of dissociation of air molecules. Revives and updates older computational methods for calculating inviscid flow field and maximum heating from interference of shock waves. Expands methods to solve problems involving six shock-wave interference patterns on two-dimensional cylindrical leading edge with equilibrium, chemically-reacting gas mixture. Written in FORTRAN 77.

Glass, Christopher E.↗
NASA NTRS1994

Cooling rates of chondrules: A new approach

Mineralogy and texture of chondrules have been reproduced experimentally and it was demonstrated that the abundance of heterogeneous nuclei is an important factor controlling chondrule textures. Cooling rates of chondrules were estimated from the zoning patterns of olivine. Low cooling rates (less than 100 C/h) yielded chemically homogeneous olivine crystals, whereas higher cooling rates, between 100 and 2000 C/h, produced olivine compositions similar to those observed in natural chondrules. We present a new approach to determining cooling rates of chondrules based on the microstructure of chondrule clinopyroxene and plagioclase. All observations were made on Allende chondrules. Two independent processes (Ca and Mg diffusion in pyroxene and Al/Si ordering in plagioclase) yield similar cooling rates on the order of 10-1 C/h for granular olivine pyroxene (GOP) chondrules in Allende. Our cooling rates are at least one order of magnitude lower than those derived from dynamic crystallization experiments.

Weinbruch, S.↗