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At least 163 records · Page 9

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DOE OSTI2018

Surface-optimized core–shell nanocomposites (Fe 3 O 4 @Mn x Fe y O 4 ) for ultra-high uranium sorption and low-field separation in water

Multifunctional manganese ferrite-coated superparamagnetic magnetite (core–shell) nanocrystals, surface stabilized by a (organic) phosphate functionalized bilayer, have been simultaneously optimized here for ultra-high uranium sorption capacity, colloidal stability under elevated ionic strengths, and susceptibility to low magnetic fields, which are critical for subsequent separation processes.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Emerging investigator series: kinetics of diopside reactivity for carbon mineralization in mafic–ultramafic rocks

The ongoing use of fossil fuels to supply modern energy demands has necessitated research on combating carbon dioxide (CO 2 ) emissions and climate change. Carbon storage via mineral trapping in basalt and related rocks is a promising strategy. However, mineralization rates depend on the variable minerology that makes up these rock formations. Diopside (CaMgSi 2 O 6 ) is a common pyroxene mineral in ultramafic and mafic rocks including basalt, but relatively little work has been done to understand its carbon mineralization kinetics using hydrated supercritical CO 2 , which induces the formation of reactive nanoscale interfacial water films. Here, in situ XRD experiments at 50–110 °C and 90 bar indicate that diopside transforms into a myriad of Mg/Ca carbonates, including huntite [Mg 3 Ca(CO 3 ) 4 ] and very high magnesium calcite (VHMC, i.e., protodolomite). Through ex situ characterization, we were able to constrain reaction pathways for the dissolution–precipitation transformation process including metastable intermediate precipitates. Experiments performed at variable temperatures enabled Avrami-derived rate constants and an apparent activation energy of 97 ± 16 kJ mol –1 , implying the dissolution of diopside is the rate-limiting step. Density functional theory (DFT) calculations, used to gain molecular insight into the surface stability of the diopside during dissolution, suggest that exposed calcium cations are susceptible to dissolution when put in contact with water given their coordination environment. The collective results point to the high CO 2 mineralization potential of diopside in basalts, which could help guide parameterization of reactive transport models needed to design and permit commercial-scale subsurface carbon storage operations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

First-principles insights into chromium-induced oxide phases in NiO

The high-temperature oxidation of Ni–Cr alloys leads to complex oxide scales comprising Ni(Cr)O solid solutions, NiCr 2 O 4 spinel, and Cr 2 O 3 corundum within the NiO matrix. Understanding the atomic-scale mechanisms of Cr segregation and precipitate formation is crucial for enhancing oxidation resistance. Here, we employ density functional theory calculations to investigate Cr behavior on NiO(100), (110), and (111) surfaces and in the bulk. Our results reveal that isolated Cr atoms preferentially segregate to the surfaces, stabilizing Ni(Cr)O solid solutions via strong Cr–O bonding, whereas Cr pairs and clusters favor subsurface migration and bulk aggregation, promoting nucleation of NiCr 2 O 4 and Cr 2 O 3 phases. These findings elucidate a size-dependent segregation mechanism linking Cr coordination environments to oxide phase evolution. This atomic-scale insight informs strategies to tailor oxide microstructures and enhance the high-temperature oxidation resistance of Ni–Cr alloys.

Chromium Segregation↗

DOE OSTI2015

Optical functions of silicon from reflectance and ellipsometry on silicon-on-insulator and homoepitaxial samples

The optical properties of silicon have been determined from 0.2 to 6.5 eV at room temperature, using reflectance spectra of silicon-on-insulator (SOI) and ellipsometric spectra of homoepitaxial samples. Optimized Fabry-Perot-type SOI resonators exhibit high finesse even in near ultraviolet. Very high precision values of the real part of the refractive index are obtained in infrared up to a photon energy of 1.3 eV. The spectra of the extinction coefficient, based on observations of light attenuation, extend to 3.2 eV due to measurements on SOI layers as thin as 87 nm. These results allowed us to correct spectroellipsometric data on homoepitaxial samples for the presence of reduced and stabilized surface layers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2021

Precipitation of dopants on acceptor-doped LaMnO3±δ revealed by defect chemistry from first principles

Perovskite oxides degrade at elevated temperatures while precipitating dopant-rich particles on the surface. A knowledge-based improvement of surface stability requires a fundamental and quantitative understanding of the dopant precipitation mechanism on these materials. We propose that dopant precipitation is a consequence of the variation of dopant solubility between calcination and operating conditions in solid oxide fuel cells (SOFCs) and electrolyzer cells (SOECs). To study dopant precipitation, we use 20% (D = Ca, Sr, Ba)-doped LaMnO3+δ (LDM20) as a model system. We employ a defect model taking input from density functional theory calculations. The defect model considers the equilibration of LDM20 with a reservoir consisting of dopant oxide (DO), peroxide (DO2), and O2 in the gas phase. The equilibrated non-stoichiometry of the A-site and B-site as a function of temperature, T, and oxygen partial pressure, p(O2), reveals three regimes for LDM20: A-site deficient (oxidizing conditions), A-site rich (atmospheric conditions), and near-stoichiometric (reducing conditions). Assuming an initial A/B non-stoichiometry, we compute the dopant precipitation boundaries in a p–T phase diagram. Our model predicts precipitation both under reducing (DO) and under highly oxidizing conditions (DO2). We found precipitation under anodic, SOEC conditions to be promoted by large dopant size, while under cathodic, SOFC conditions precipitation is promoted by initial A-site excess. The main driving forces for precipitation are oxygen uptake by the condensed phase under oxidizing conditions and oxygen release assisted by B-site vacancies under reducing conditions. Possible strategies for mitigating dopant precipitation under in electrolytic and fuel cell conditions are discussed.

Hess, Franziska (ORCID:000000024460643X)↗

DOE OSTI2022

Plateau–Rayleigh instability with a grain boundary twist

We demonstrate using theoretical, computational, and experimental studies a morphological instability, in which a polycrystalline nanorod breaks up at grain boundaries (GBs) into an array of isolated domains. Our theoretical model is used to establish a neutral stability surface demarcating stable and unstable perturbations. It is shown that GBs play a destabilizing role in which the critical wavelength for the instability decreases with the increase in the GB energy. We carry out phase field simulations, which reveal accelerated pinch-off kinetics with the increase in the GB energy and predict temporal evolution of interfacial profiles in quantitative agreement with experimental observations.

Hussein, Omar↗

DOE OSTI2021

Effects of Ink Formulation on the Structure and Performance of PGM-Free Catalyst Layer in PEMFCs

Platinum group metal (PGM) catalysts are the major electrocatalysts for oxygen reduction reaction (ORR) in the polymer electrolyte membrane fuel cells (PEMFCs). The cost becomes unaffordable if the PEMFC is in massive application. The PGM-Free catalyst shows very promising activity in rotation disk electrode (RDE) testing. The half-wave potential could reach 0.91 V versus standard hydrogen electrode (SHE). However, in a membrane electrode assembly (MEA), the performance of PGM-Free catalysts is not good enough to replace the PGM catalysts. Since the PGM-free catalysts are so different from the PGM catalysts in terms of catalytic activity, stability, surface conditions, particle size, etc., the fabrication of PGM-Free catalyst MEA cannot simply copy the method of making PGM MEA. Here we proposed a novel method of fabricating PGM-Free catalyst MEA, so that the intrinsic catalyst activity from RDE can be translated into MEA performance. The method is based on the catalyst coated membrane (CCM) method using optimized ionomer to carbon (I/C) ratio and solvent mixture of catalyst ink. Using this method, the PGM-free catalyst MEA achieved the current density 44.9 mA cm -2 at 0.9 V iR-free in H 2 /O 2 and 150 mA cm -2 at 0.8 V in H 2 /air, which surpassed the performance targets of US Department of Energy (DOE)for PGM-Free catalyst MEA. The property (solvent composition, dispersion of catalyst and ionomer in an ink), structure (pore structure) and the MEA performance have been characterized using, mercury intrusion porosimetry (MIP), MEA testing. A property-structure-performance relationship has been established.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Spectral interferometry-based microwave-frequency vibrometry for integrated acoustic wave devices

Microwave phononics is a promising platform for sensing, computing, and quantum information science; thus, sensitive and high-throughput characterization tools are needed not only for device verification and optimization but also for revealing transient and nonlinear dynamics. Existing interferometric optical vibrometers for 2D mapping are challenged by operating point stabilization, surface reflectivity contrast, and long acquisition time. Here, we use spectral interferometry, which is insensitive to these factors and utilizes a continuous raster scanning scheme for vibration mapping with high throughput. We intensity-modulate our broadband light source with an electro-optic modulator to resolve vibrations at microwave frequencies. Our system requires no fast photodetector or digitizer operating in the microwave frequency range. We image the 1 GHz vibration field of a 300 × 150 µm 2 area of an entire surface acoustic wave device in 10 min with simultaneous surface profilometry. Our system has a vibration sensitivity of 120 fm/sqrt(Hz) and a linear throughput of 0.77 mm/s on the chip surface. The technique offers capabilities for characterizing a wide range of acoustic wave and micromechanical devices to better understand their behavior and performance.

47 OTHER INSTRUMENTATION↗

DOE OSTI2017

NMSBA Leveraged Project Interim Status Report

We have investigated the quality of copper particles available on the market today and determined their complete unsuitability to be used for copper inks, since all of them were significantly oxidized: there was only 50% of metallic copper in each batch and the rest was Cu 2 O and CuO. To date, we have fully identified the challenges and developed the synthesis for large amounts of the copper ink precursor, namely, copper(I) mesityl. Currently, the amounts of tens of grams of the precursor have been obtained. From this precursor, four small batches of copper nanoparticles (50 mg each) have been synthesized to investigate the possibility of decreasing particle sensitivity to oxygen. These particles have been treated with different surface-stabilizing agents (namely, octylamine, oleylamine, pyridine, benzotriazole, and dodecanethiol) in order to investigate their influence on particle oxygen sensitivity. A batch of copper nanoparticles in the amount of 2 grams has also been synthesized in order to start preparation of test ink batches with different solvents, surfactants, and stabilizers.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Breaking the Limit of Size-Dependent CO2RR Selectivity in Ag Nanoparticle Electrocatalysts through Electronic Metal-Carbon Interactions: Insights from Computational Hydrogen Electrode Calculations

This poster highlights the use of computational hydrogen electrode approach to explain the improved activity and selectivity of Ag nanoparticle catalysts for CO2 to CO conversion observed in the experiments. The calculations predict a charge transfer from the Ag nanoparticle to a defective carbon surface, stabilizing the *COOH intermediate through reduced antibonding orbital overlap, significantly reducing the *COOH formation energy barrier, and improving CO2-to-CO conversion selectivity compared with Ag nanocluster on defect-free carbon. These results provide new insights into carbon-supported electrocatalysts for CO2RR and introduce a new approach for creating active and selective nanocatalysts.

electrocatalysis↗

DOE OSTI2026

Hofmann Stability Charts Revisited for PIP-II: From Classical Theory to Assumption-Free and ML-Driven Maps

The Hofmann stability chart remains a standard for visualizing parametric resonances in space-charge–dominated linacs, but its use typically relies on non-oscillatory Vlasov dispersion relations with simplifying assumptions (continuous focusing, KV phase space, linear optics, limited transverse–longitudinal coupling). We revisit the chart for the PIP-II linac along three tracks. (1) We reproduce the conventional maps in the (νz/νx, νx/ν0x) plane for relevant εz/εx, providing a validated reference. (2) We remove key assumptions by deriving stability surfaces directly from multi-particle tracking with realistic lattice discreteness, RF defocusing, solenoid/quad optics, and bunched-beam dynamics; local tunes and early-time growth rates are estimated from envelope oscillations and projected to the same coordinates. These assumption-reduced maps recover the canonical stopbands while revealing shifts and broadenings driven by tune modulation, non-KV distributions, and transverse–longitudinal coupling at PIP-II intensities. (3) We train a compact machine-learning surrogate that emulates the growth surface from zero-current optics, tune depression, emittance ratio, bunching factor, and selected lattice descriptors, enabling rapid scans and online working-point selection. We compare the three representations on representative PIP-II sections and discuss implications for commissioning guard bands, resonance avoidance, and routine operations.

Pathak, Abhishek [Fermilab] (ORCID:000000021704208↗

DOE OSTI2016

Surface protected lithium-metal-oxide electrodes

A lithium-metal-oxide positive electrode having a layered or spinel structure for a non-aqueous lithium electrochemical cell and battery is disclosed comprising electrode particles that are protected at the surface from undesirable effects, such as electrolyte oxidation, oxygen loss or dissolution by one or more lithium-metal-polyanionic compounds, such as a lithium-metal-phosphate or a lithium-metal-silicate material that can act as a solid electrolyte at or above the operating potential of the lithium-metal-oxide electrode. The surface protection significantly enhances the surface stability, rate capability and cycling stability of the lithium-metal-oxide electrodes, particularly when charged to high potentials.

25 ENERGY STORAGE↗

DOE OSTI2014

Surface protected lithium-metal-oxide electrodes

Thackeray, Michael M.↗

DOE OSTI2017

Characterization and Remediation of the Hanford 618-10 Burial Ground Vertical Pipe Units - 17121

The 618-10 Burial Ground is approximately 148 m by 143 m (485 feet by 470 feet) and consists of 12 trenches and 94 Vertical Pipe Units (VPU's). It is located approximately 8.1 km (5 miles) north of Richland, Washington in the 600 Area of the Hanford Site. The 618-10 Burial Ground received low- to high-activity waste (e.g., fission products and some plutonium-contaminated waste). Most of the waste originated at the 300 Area laboratory facilities. Lower activity radioactive material and shielded drums were disposed in trenches, while laboratory wastes with higher levels of radiation were disposed in Vertical Pipe Units (VPUs). There are different variants of VPUs. Some VPUs are simply corrugated culverts or standard pipes, 36 cm (14 in.) diameter and 3.1 m to 4.6 m (10- to 15-ft) long, buried vertically. Some VPUs are carbon steel pipes 25 to 61 cm (10 to 24 in.) in diameter and up to 4.6 m (15 ft) in length. The final design of the VPUs is 56 cm (22-in) diameter, 4.4 m (14.4 ft) long waste receptacles constructed by welding five 208 L (55-gallon) bottomless drums together end-to-end and burying them vertically, separated by approximately 3.1 m (10 feet) on center in rows approximately 7.6 m (25 feet) apart. The 618-10 Burial Ground contains approximately 94 VPUs. Historical documents indicate that shielding materials (e.g., concrete or soil) may have been added to the VPUs to reduce dose rates over the openings, and that each VPU was backfilled with sand and capped with concrete at the end of its service life. Historical documents also indicate that the VPUs were covered with approximately 0.6 m (2-ft) of soil when they were closed, and an additional 0.6 m (2-ft) of topsoil was later added for surface stabilization. In general, the process for VPU remediation was as follows: - Installed four cone penetrometers (CPTs) around the exterior of each individual VPU and sent radiation detection probes down the interior of the CPTs to get initial radiation data in order to calculate the overall curie content and create maps showing the dose rate distribution throughout the VPU. - Removed the CPTs and installed a 122 cm (48-in) diameter, 1.3 cm (0.5-in) thick steel over-casing using a vibrating hammer suspended from a crane that encompassed the VPU with some surrounding soil. - Using a Bauer BG-30 drill rig with a specifically designed augur bit and a specially designed confinement system the auger process was used to stabilize and size reduce the contents. - Once the auger reached a depth of 8.5 m (28 feet) the BG-30 drill stem was separated and additional characterization was completed by sending a radiation probe down the center of the drill stem to gather radiological data. - Once auguring and characterization was completed the waste was removed using a specially designed extended clamshell retrieval bucket and placed into individual 2.7 m x 1.5 m x 1.2 m (9-ft x 5-ft x 4-ft) metal boxes. - After the waste was placed into the metal waste boxes a low strength grout was added and the grout and waste material was mixed using a large rake device attached to an excavator. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2016

Role of porosity on the stiffness and stability of (001) surface of the nanogranular C–S–H gel

We present here a nanoscale modeling of the bulk and surface states of the nanogranular Calcium Silicate Hydrate (C–S–H) gel. Regarding the mechanical properties as well as porosity, we identify two main phases: a ductile one, for a porosity from 12.4% to 27% and a brittle phase for a porosity lower than 12.4% or higher than 27%. Particularly, our calculations show that 20% of gel porosity gives a better structural stability to C–S–H and a higher stiffness. Besides, we have explored the (001) surface of C–S–H gel at the nanoscale level and have proved that more water on the surface will stabilize thermodynamically the nanostructure. This means that adsorbed H{sub 2}O molecules lead to the coexistence of Si–OH and Ca–OH groups on the surface. The calcium-terminated plane is a polar and unstable surface, and will either reconstruct to neutralize the dipole moment or adsorb ions to remove it. Our results also show that the (001) surface of low density C–S–H tends to be more stable than the surface of high density phase since the obtained surface energy decreases with increasing gel porosity.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Stability at the surface

Metal oxides are ubiquitous as minerals in the terrestrial environment, as well as in a variety of technologically important structures such as electronic devices and heterogeneous catalysts. Within these various contexts, interfaces between oxides and gases, liquids and solids drive many critically important phenomena ranging from the uptake of contaminants in groundwater by redox-active minerals to the switching of the millions of transistors found in every cell phone and computer. Function is tied to structure. Therefore, fundamental understanding of the structure of oxide surfaces and interfaces is of crucial importance to the comprehension of a plethora of phenomena involving this broad class of materials.

N06266↗

DOE OSTI2014

Ab initio density functional theory study of non-polar (101{sup ¯}0), (112{sup ¯}0) and semipolar (202{sup ¯}1) GaN surfaces

The atomic structures of non-polar GaN(101{sup ¯}0), (112{sup ¯}0) and semipolar GaN(202{sup ¯}1), (202{sup ¯}1{sup ¯}) surfaces were studied using ab initio calculations within density functional theory. The bulk-like truncated (1 × 1) structure with buckled Ga-N or Ga-Ga dimers was found stable on the non-polar GaN(101{sup ¯}0) surface in agreement with previous works. Ga-N heterodimers were found energetically stable on the GaN(112{sup ¯}0)-(1 × 1) surface. The formation of vacancies and substitution site defects was found unfavorable for non-polar GaN surfaces. Semipolar GaN(202{sup ¯}1)-(1 × 1) surface unit cells consist of non-polar (101{sup ¯}0) and semipolar (101{sup ¯}1) nano-facets. The (101{sup ¯}1) nano-facets consist of two-fold coordinated atoms, which form N-N dimers within a (2 × 1) surface unit cell on a GaN(202{sup ¯}1) surface. Dimers are not formed on the GaN(202{sup ¯}1{sup ¯}) surface. The stability of the surfaces with single (101{sup ¯}0) or (101{sup ¯}1) nano-facets was analyzed. A single non-polar (101{sup ¯}0)-(1 × 1) nano-facet was found stable on the GaN(202{sup ¯}1) surface, but unstable on the GaN(202{sup ¯}1{sup ¯}) surface. A single (101{sup ¯}1) nano-facet was found unstable. Semipolar GaN surfaces with (202{sup ¯}1) and (202{sup ¯}1{sup ¯}) polarity can be stabilized with a Ga overlayer at Ga-rich experimental conditions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2017

Slippery liquid-infused porous surfaces having improved stability

Methods and articles disclosed herein relate to liquid repellant surfaces having selective wetting and transport properties. An article having a repellant surface includes a substrate comprising surface features with re-entrant curvature and an immobilized layer of lubricating liquid wetting over the surface features. The surface features with re-entrant curvature can be designed to provide high repellency even after failure or removal of the immobilized layer of lubricating liquid under certain operating conditions.

36 MATERIALS SCIENCE↗