Multiphysical mechanisms in geological formations associated with subsurface energy activities.
Abstract not provided.
Chang, Kyung Won↗
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Multiphysics-driven geomechanical instability: Implications for subsurface energy activities.
Abstract not provided.
Chang, Kyung Won↗
Multiphysics-driven Instability along Geological Discontinuities: Implications for subsurface energy activities.
Abstract not provided.
Chang, Kyung Won↗
Native Defects Hybridization and Electronic Transport in Cu 2 Se–CuGaSe 2 Hierarchical Composites
Engineering the energy distribution of electronic defects in semiconductors can afford the coexistence of degenerate and nondegenerate transport behavior. By leveraging native defects in Cu 2 Se and CuGaSe 2 phases, the tunability of the concentration and energy distribution of active electronic defects in hierarchical (1-x)Cu 2 Se-(x)CuGaSe 2 composites is demonstrated. This study found that the electrical conductivity of various composites decreases with rising temperature indicating degenerate semiconducting behavior, whereas the carrier density increases with temperature, which is consistent with non-degenerate semiconductivity. Remarkably, this study found that while the carrier density and electrical conductivity drop with the increasing CuGaSe 2 content for samples with x ≤ 0.45 is consistent with an increase in the activation energy of “active” electronic defects, the sudden increase by 140% in the electrical conductivity and by 109% in the carrier density for near equimolar composition suggests the formation of a large density of electronic defects with lower activation energy. This unusual behavior is understood within the context of the hybridization of coexisting native electronic defects to form degenerate hybrid acceptor states with lower activation energy. The reported unique electronic transport can be leveraged for the development of more versatile electronic and optoelectronic devices with superior performance.
36 MATERIALS SCIENCE↗
Redox chemistry at liquid/liquid interfaces
The interface between two immiscible liquids with immobilized photosynthetic pigments can serve as the simplest model of a biological membrane convenient for the investigation of photoprocesses accompanied by spatial separation of charges. As it follows from thermodynamics, if the resolvation energies of substrates and products are very different, the interface between two immiscible liquids may act as a catalyst. Theoretical aspects of charge transfer reactions at oil/water interfaces are discussed. Conditions under which the free energy of activation of the interfacial reaction of electron transfer decreases are established. The activation energy of electron transfer depends on the charges of the reactants and dielectric permittivity of the non-aqueous phase. This can be useful when choosing a pair of immiscible solvents to decrease the activation energy of the reaction in question or to inhibit an undesired process. Experimental interfacial catalytic systems are discussed. Amphiphilic molecules such as chlorophyll or porphyrins were studied as catalysts of electron transfer reactions at the oil/water interface.
Non-NASA Center↗
Surface stability and H adsorption and diffusion near surfaces of W borides: a first-principles study
Abstract Understanding the behavior of tungsten boride (W x B y ) surfaces in a fusion reactor environment is an important topic since boronization is a common wall conditioning method used in fusion Tokamaks. We report the results of density functional theory calculations that investigate the surface stability of W x B y (tetragonal I4 1 /amd -WB, hexagonal P 6 3 / mmc -WB 2 and tetragonal I4/m- W 2 B) with low-index orientations, as well as hydrogen (H) energetics near W x B y surfaces. For single element terminated W x B y surfaces, B terminated surfaces are more energetically stable than W terminated as a result of significant reconstruction of B. The H surface adsorption energy and activation energy of H diffusion penetration below W x B y surfaces are mainly related to the outer termination. Specifically, the WB(001) surface terminated with two B layers, referred to as WB(001)-T BB , has higher H adsorption affinity and lower H diffusivity on this surface than other terminations, which is controlled by the significant charge transfer from B to H. However, B atoms on the WB 2 (0001)-T BB surface decrease both H adsorption and diffusivity on the surface, but enhance H diffusion below the surface in comparison to W terminated WB 2 (0001) surface. H would be trapped and diffuse within atomic surface gaps on the WB 2 ( 2 1 ˉ 1 ˉ 0 ) surface, while H below the surface layer would jump along the [0001] direction rather than diffuse into bulk. The surface diffusion activation energy of H on the W 2 B(001) surface slightly varies with terminations. Once H crosses the surface layer of W 2 B(001) with either termination, it prefers to diffuse into the bulk, or back towards the surface, rather than move parallel to the surface. Interestingly, WB 2 (0001) and WB 2 ( 2 1 ˉ 1 ˉ 0 ) surfaces will have relatively higher H retention than the other W x B y surfaces evaluated in this work.
Yang, L. (ORCID:0000000322166071)↗
A Study of Oxidation of Hydrogen Based on Flashback of Hydrogen-Oxygen-Nitrogen Burner Flames
The flashback of hydrogen-oxygen-nitrogen flames was studied as a function of pressure, burner diameter, equivalence ratio, and oxidant strength. The results were treated on the assumption that the product of the critical boundary velocity gradient for flashback and the initial concentration of that reactant which is not in excess is proportional to a mean reaction rate associated with the flame zone. It was further assumed that this reaction rate can be expressed in terms of initial concentrations and flame temperature. Measurements at constant flame temperature yield orders of reaction with respect to hydrogen and oxygen. These do not vary with flame temperature. Measurements in which pressure is varied for several values of oxidant strength at constant equivalence ratio yield a total order of reaction and a function describing the dependence of the mean reaction rate on flame temperature. The total reaction order is independent of flame temperature and equal to the sum of the orders for hydrogen and oxygen. The dependence of the reaction rate on flame temperature cannot be described by a constant activation energy. The activation energy obtained apparently increases with flame temperature. Flashback results can be described by a single rate constant which is independent of equivalence ratio. Values were estimated for this rate constant as a function of flame temperature.
Fine, Burton D.↗
Electrical characterization of 6H crystalline silicon carbide
Crystalline silicon carbide (SiC) substrates and epilayers, undoped as well as n- and p-doped, have been electrically characterized by performing Hall effect and resistivity measurements (van der Pauw) over the temperature range of approximately 85 K to 650 K (200 K to 500 K for p-type sample). By fitting the measured temperature dependent carrier concentration data to the single activation energy theoretical model: (1) the activation energy for the nitrogen donor ranged from 0.078 eV to 0.101 eV for a doping concentration range of 10(exp 17) cm(exp -3) to 10(exp 18) cm(exp -3) and (2) the activation energy for the aluminum acceptor was 0.252 eV for a doping concentration of 4.6 x 10(exp 18) cm(exp -3). By fitting the measured temperature dependent carrier concentration data to the double activation energy level theoretical model for the nitrogen donor: (1) the activation energy for the hexagonal site was 0.056 eV and 0.093 eV corresponding to doping concentrations of 3.33 x 10 (exp 17) cm(exp -3) and 1.6 x 10(exp 18) cm(exp -3) and (2) the activation energy for the cubic site was 0.113 and 0.126 eV corresponding to doping concentrations of 4.2 x 10(exp 17) cm(exp -3) and 5.4 x 10(exp 18) cm(exp -3).
Lempner, Stephen E.↗
Reconstruction and Measurement of $\mathcal{O}$(100) MeV Energy Electromagnetic Activity from $\pi^0 \rightarrow \gamma\gamma$ Decays in the MicroBooNE LArTPC
We present results on the reconstruction of electromagnetic (EM) activity from photons produced in charged current νμ interactions with final state π0s. We employ a fully-automated reconstruction chain capable of identifying EM showers of &calO;(100) MeV energy, relying on a combination of traditional reconstruction techniques together with novel machine-learning approaches. These studies demonstrate good energy resolution, and good agreement between data and simulation, relying on the reconstructed invariant π0 mass and other photon distributions for validation. The reconstruction techniques developed are applied to a selection of νμ + Ar → μ + π0 + X candidate events to demonstrate the potential for calorimetric separation of photons from electrons and reconstruction of π0 kinematics.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Analysis of differential scanning calorimetry data for aged plutonium
Differential scanning calorimetry data for samples of a 52 year old plutonium alloy with 3.3 at. % Ga that were heated beyond the melting point is analyzed using transition state theory to find activation energies for the δ to ε and ε to liquid phase transitions. A Bayesian statistical method involving a Gaussian process model is used to find mean values and confidence intervals for the activation energies. The activation energy for the δ to ε phase transition increases by 3.3 ± 3.8% per decade, relative to the case when all age related plutonium lattice point defects have been removed through annealing. The corresponding increase in activation energy for the ε to liquid transition is shown to be 7.1 ± 1.8% per decade. It is postulated that the change in activation energy with age for both phase transitions is caused, in part, by the accumulation of the same type of lattice point defects associated with the observed increase in elastic bulk modulus over time.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Long-Term Degradation of Passivated Emitter and Rear Contact Silicon Solar Cell under Light and Heat
Advanced designs enable high-efficiency solar cells; however, more complex structures create new long-term stability concerns. Herein, the long-term degradation processes affecting advanced silicon solar cells using laboratory-based illumination and heating over hundreds of hours are investigated. The activation energy for the degradation of voltage is estimated and the degradation rates to normal solar cell operating temperature ranges are extrapolated. The cell degradation observed at high temperatures in the lab is kinetically similar to the process affecting field-deployed modules contributing to 0.37% year-1 of annualized degradation. Electroluminescence and photoluminescence mapping show that the degradation is dominated by minority carrier lifetime reduction. Suns-open-circuit voltage and light beam-induced current results indicate that the degradation could result from passivation degradation at the surface or defect formation in the near-subsurface region, leading to increased minority carrier recombination. This work highlights a long-term degradation process under elevated temperature and illumination that may continue to affect cells in an irreversible manner that is separate from recoverable light-induced degradation and light- and elevated temperature-induced degradation.
14 SOLAR ENERGY↗
Impact of the LiPF6 Concentration on the Interfacial Charge Transfer and Fast-charging Capabilities of Lithium-Ion Batteries
Fast-charging lithium-ion batteries (LIB) demand optimized electrolyte formulations to balance ionic conductivity, viscosity, and interfacial charge transfer kinetics. This study examines how LiPF 6 concentration shapes solvation structure, desolvation energy, charge transfer activation energy, and solid electrolyte interphase (SEI) properties, which are critical for fast-charging performance. Using Raman spectroscopy, electrochemical cycling, X-ray photoelectron spectroscopy, and atomistic modeling, we analyze how varying LiPF 6 concentrations impact interfacial and bulk transport properties. Our findings show that increasing LiPF 6 concentration alters lithium solvation structures, reduces desolvation energy, and accelerates charge transfer at the electrode interface. Higher concentrations lower the activation energy for charge transfer and suppress excessive SEI growth, improving interfacial kinetics. However, concentrations above a certain threshold increase viscosity and reduce ionic conductivity, limiting transport efficiency. These results offer insights into electrolyte solvation and interfacial charge transfer mechanisms, providing guidelines for designing next-generation fast-charging LIB electrolytes with enhanced efficiency, stability, and longevity.
Son, Seoung-Bum [Argonne National Laboratory (ANL)↗
Membrane hydrophobicity determines the activation free energy of passive lipid transport
The collective behavior of lipids with diverse chemical and physical features determines a membrane's thermodynamic properties. Yet, the influence of lipid physicochemical properties on lipid dynamics, in particular interbilayer transport, remains underexplored. Here, we systematically investigate how the activation free energy of passive lipid transport depends on lipid chemistry and membrane phase. Through all-atom molecular dynamics simulations of 11 chemically distinct glycerophospholipids, we determine how lipid acyl chain length, unsaturation, and headgroup influence the free energy barriers for two elementary steps of lipid transport: lipid desorption, which is rate limiting, and lipid insertion into a membrane. Consistent with previous experimental measurements, we find that lipids with longer, saturated acyl chains have increased activation free energies compared to lipids with shorter, unsaturated chains. Lipids with different headgroups exhibit a range of activation free energies; however, no clear trend based solely on chemical structure can be identified, mirroring difficulties in the interpretation of previous experimental results. Compared to liquid-crystalline phase membranes, gel phase membranes exhibit substantially increased free energy barriers. Overall, we find that the activation free energy depends on a lipid's local hydrophobic environment in a membrane and that the free energy barrier for lipid insertion depends on a membrane's interfacial hydrophobicity. Both of these properties can be altered through changes in lipid acyl chain length, lipid headgroup, and membrane phase. Thus, the rate of lipid transport can be tuned through subtle changes in local membrane composition and order, suggesting an unappreciated role for nanoscale membrane domains in regulating cellular lipid dynamics.
59 BASIC BIOLOGICAL SCIENCES↗
The kinetics of the Au-InP interaction
An analysis of the reaction of Au and Au-In alloys with InP has permitted the identification of the mechanisms occurring during the first two stages of the Au-InP interaction. The first stage of the interaction, during which the Au is converted to a saturated Au (In) solution, is controlled by the vacancy-generation rate at the free surface of the metallization. The activation energy for this process is the activation energy for Au self-diffusion. Evidence is presented for the existence of large localized variations in this value due to surface related effects. At the completion of stage I stage II becomes active and continues until the metallization is converted to Au3In. This process, proceeding via an interstitial interchange mechanism, is many orders of magnitude slower than stage I. The rate-limiting step, with an activation energy of 2.8 eV, is shown to be the diffusion of In from the InP-metal interface. The P atoms that are released when In enters the metallization during stage I leave the system without reacting, whereas in stage II they form a compound (Au2P3) at the InP-metal interface. The presence of the Au2P3 severely retards the stage II interaction rate.
Fatemi, Navid S.↗
Final-stage densification kinetics of direct current–sinteredZrB2
Final-stage sintering was analyzed for nominally phase pure zirconium diboride synthesized by borothermal reduction of high-purity ZrO2. Analysis was conducted on ZrB2 ceramics with relative densities greater than 90% using the Nabarro–Herring stress–directed vacancy diffusion model. Temperatures of 1900°C or above and an applied uniaxial pressure of 50 MPa were required to fully densify ZrB2 ceramics by direct current sintering. Ram travel data were collected and used to determine the relative density of the specimens during sintering. Specimens sintered between 1900 and 2100°C achieved relative densities greater than 97%, whereas specimens sintered below 1900°C failed to reach the final stage of sintering. The average grain size ranged from 1.0 to 14.7 μm. The activation energy was calculated from the slope of an Arrhenius plot that used the Kalish equation. The activation energy was 162 ± 34 kJ/mol, which is consistent with the activation energy for dislocation movement in ZrB2. The diffusion coefficients for dislocation motion that controls densification were 5.1 × 10−6 cm2/s at 1900°C and 5.1 × 10−5 cm2/s at 2100°C, as calculated from activation energy and average grain sizes. This study provides evidence that the dominant mechanism for final-stage sintering of ZrB2 ceramics is dislocation motion.
36 MATERIALS SCIENCE↗
The Limit of Free Magnetic Energy in Active Regions
By measuring from active-region magnetograms a proxy of the free energy in the active region fs magnetic field, it has been found previously that (1) there is an abrupt upper limit to the free energy the field can hold that increases with the amount of magnetic field in the active region, the active region fs magnetic flux content, and (2) the free energy is usually near its limit when the field explodes in a CME/flare eruption. That is, explosive active regions are concentrated in a main-sequence path bordering the free-energy ]limit line in (flux content, free-energy proxy) phase space. Here, from measurement of Marshall Space Flight Center vector magnetograms, we find the magnetic condition that underlies the free ]energy limit and the accompanying main sequence of explosive active regions. Using a suitable free ]energy proxy measured from vector magnetograms of 44 active regions, we find that (1) in active regions at and near their free ]energy limit, the ratio of magnetic-shear free energy to the non ]free magnetic energy the potential field would have is approximately 1 in the core field, the field rooted along the neutral line, and (2) this ratio is progressively less in active regions progressively farther below their free ]energy limit. This shows that most active regions in which this core-field energy ratio is much less than 1 cannot be triggered to explode; as this ratio approaches 1, most active regions become capable of exploding; and when this ratio is 1 or greater, most active regions are compelled to explode. From these results we surmise the magnetic condition that determines the free ]energy limit is the ratio of the free magnetic energy to the non-free energy the active region fs field would have were it completely relaxed to its potential ]field configuration, and that this ratio is approximately 1 at the free-energy limit and in the main sequence of explosive active regions.
Moore, Ron↗
Structural trends in the dehydrogenation selectivity of palladium alloys
Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior. To provide molecular-level insights into these effects, a series of Pd intermetallic alloy catalysts with Zn, Ga, In, Fe and Mn promoter elements was synthesized, and the structures were determined using in situ X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (XRD). The alloys all showed propane dehydrogenation turnover rates 5–8 times higher than monometallic Pd and selectivity to propylene of over 90%. Moreover, among the synthesized alloys, Pd 3 M alloy structures were less olefin selective than PdM alloys which were, in turn, almost 100% selective to propylene. This selectivity improvement was interpreted by changes in the DFT-calculated binding energies and activation energies for C–C and C–H bond activation, which are ultimately influenced by perturbation of the most stable adsorption site and changes to the d-band density of states. Furthermore, transition state analysis showed that the C–C bond breaking reactions require 4-fold ensemble sites, which are suggested to be required for non-selective, alkane hydrogenolysis reactions. These sites, which are not present on alloys with PdM structures, could be formed in the Pd 3 M alloy through substitution of one M atom with Pd, and this effect is suggested to be partially responsible for their slightly lower selectivity.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Elevated Temperature Creep Deformation in Solid Solution <001> NiAL-3.6Ti Single Crystals
The 1100 to 1500 K slow plastic strain rate compressive properties of <001> oriented NiAl-3.6Ti single crystals have been measured, and the results suggests that two deformation processes exist. While the intermediate temperature/faster strain rate mechanism is uncertain, plastic flow at elevated temperature/slower strain rates in NiAl-3.6Ti appears to be controlled by solute drag as described by the Cottrell-Jaswon solute drag model for gliding b = a(sub 0)<101> dislocations. While the calculated activation energy of deformation is much higher (approximately 480 kJ/mol) than the activation energy for diffusion (approximately 290 kJ/mol) used in the Cottrell-Jaswon creep model, a forced temperature compensated - power law fit using the activation energy for diffusion was able to adequately (greater than 90%) predict the observed creep properties. Thus we conclude that the rejection of a diffusion controlled mechanism can not be simply based on a large numerical difference between the activation energies for deformation and diffusion.
Whittenberger, J. Daniel↗