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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Experimental evidence of plasmarons and effective fine structure constant in electron-doped graphene/h-BN heterostructure

Electron-electron interaction is fundamental in condensed matter physics and can lead to composite quasiparticles called plasmarons, which strongly renormalize the dispersion and carry information of electron-electron coupling strength as defined by the effective fine structure constant $α$ $^{*}_{ee}$. Although h-BN with unique dielectric properties has been widely used as an important substrate for graphene, so far there is no experimental report of plasmarons in graphene/h-BN yet. Here, we report direct experimental observation of plasmaron dispersion in graphene/h-BN heterostructures through angle-resolved photoemission spectroscopy (ARPES) measurements upon in situ electron doping. Characteristic diamond-shaped dispersion is observed near the Dirac cone in both 0° (aligned) and 13.5° (twisted) graphene/h-BN, and the electron-electron interaction strength $α$ $^{*}_{ee}$ is extracted to be $α$ $^{*}_{ee}$ ≈ 0.9 ± 0.1, highlighting the important role of electron-electron interaction. Our results suggest graphene/h-BN as an ideal platform for investigating strong electron-electron interaction with weak dielectric screening, and lays fundamental physics for gate-tunable nano-electronics and nano-plasmonics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Property Measurements of NaCl-UCl 3 and LiF-NaF-KF Molten Salts Doped with Surrogate Fission Products

Knowing thermophysical and thermochemical property values of salts over the expected range of operating temperatures is essential to modeling and simulation efforts that support the commercialization of molten salt reactor (MSR) technologies. Salt properties being measured at Argonne include thermal transitions, phase behavior, heat capacity, density, surface tension, volumetric thermal expansion, thermal diffusivity, thermal conductivity, and viscosity. The properties of several salts of interest including NaCl-UCl 3 and LiF-NaF-KF (FLiNaK) have been measured at Argonne and reported previously. These property measurements are suitable for use in evaluating reactor performance during startup and the early operating life of the reactor. The physical and chemical behavior of the fuel salt is altered by the buildup of fission products and the resulting changes in heat transfer and other properties must be understood by reactor developers. This report summarizes melting behavior, heat capacity, and thermal diffusivity values that were measured for mixtures of FLiNaK and NaCl-UCl 3 salts that have been doped with surrogate fission products. Additional heat capacity measurements were also performed on a separate mixture of FLiNaK without dopants. Measured properties are suitable for incorporation into the Molten Salt Thermal Properties Database–Thermochemical (MSTDB–TC) and the Molten Salt Thermal Properties Database–Thermophysical (MSTDB–TP) to support the development of MSRs. Salts were prepared by doping eutectic mixtures of NaCl-UCl 3 and FLiNaK with surrogate fission products. These salts were prepared for use in salt spill experiments being performed at Argonne and were subsequently used for thermal property measurements. Thermal transitions and heat capacities were measured by using differential scanning calorimetry (DSC) and thermal diffusivity was measured by using laser flash analysis (LFA) at temperatures spanning the typical MSR operating range. The measured property values of the doped salts were compared to measured property values of salts without fission products to quantify the effects of the doped fission products.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1988

Indentation plasticity and fracture in silicon

Measurements of the ductile-brittle transition temperature of heavily doped silicon were carried out using indentation techniques. Diamond pyramid hardness tests were performed on the (100) face of heavily doped N-type and P-type and intrinsic silicon single crystals. Tests were performed over the range 200 C to 850 C and loads of 100 to 500 g were used. Samples were subsequently etched to reveal dislocation rosettes produced by indentation. Intrinsic silicon underwent a ductile-brittle transition at 660 C, P-type at 645 C and N-type at 625 C. Hardness values varied from 1.1 GPa at 700 C to 11.7 GPa at 200 C. Significant effects of hardness on doping were present only at the highest temperatures. Lower loads generally produced higher hardness but load did not affect the Ductile-Brittle Transition Temperature (DBTT). Fracture toughness values ranged from 0.9 MPa m(1/2) at 200 C to 2.75 MPa m(1/2) near the DBTT. Doping did not affect the fracture toughness of silicon. P-type doping increased the size of dislocation rosettes observed after indentation, but N-type did not, in contradiction of the expected results. Results are discussed in terms of the effect of doping on the dislocation mobility in silicon.

Rybicki, George C.↗
DOE OSTI2022

Sensitivity Effects of Hollow Glass Micro-Balloon Doping on RDX-Based Explosives

Sensitivity to initiation is an important characteristic of high explosives. Many chemical and physical properties are fine-tuned to deliver an energetic material that behaves according to the user’s specifications exactly. In some cases, it is advantageous to study the effects that non energetic additives have on the performance of an explosive material. Following on the promising results obtained in other experiments, a study is conducted on the effects of hollow glass micro-balloons (bubbles, spheres), or HGMB, on a material’s sensitivity. Threshold test data is compared between several formulations of explosives. The control formulation is an RDX-based explosive with a non-energetic binder, and the test formulations are identical in composition, but with the addition of HGMB, up to 6% by volume. Safety testing of the new HGMB-doped explosive formulations is conducted to ensure they can be produced and handled safely prior to intentional detonation. This experiment utilizes an attenuation card of varying thicknesses between the initiator and the test article to attenuate the shock imparted, and a witness plate is analyzed for each test article to determine a GO or NO GO result. The data collected and the conclusions of this study affect how additives like HGMB are utilized in future explosive sensitivity threshold experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Correlation effects on coupled electronic and structural properties of doped rare-earth trihydrides

Rare-earth trihydride (𝑅⁢H 3 ) compounds exhibit intriguing coupled electronic and structural properties as a function of doping, hydrogen vacancies, and thermodynamic conditions. Theoretical studies of these materials typically rely on density functional theory (DFT), including the use of small supercells that may underestimate strong correlation effects and structural distortions which in turn may influence their metallicity. Here, we elucidate the roles of lattice distortions and correlation effects on the electronic properties of pristine and doped 𝑅⁢H 3 compounds by adopting DFT +U and quantum Monte Carlo (QMC) methods. Linear-response constrained DFT (LR-cDFT) methods find Hubbard U ≈ 2 eV for 𝑅 𝑑 orbitals and U ≈ 6 eV for H 𝑠 ⁡/N 𝑝 /O 𝑝 orbitals. The small U on Lu 𝑑 orbitals is consistent with QMC calculations on LuH 3 and LuH 2.875 ⁢N 0.125 . In pure face-centered-cubic (FCC) 𝑅⁢H 3 (𝑅 = Lu,Y) compounds, neither DFT nor DFT +U with the self-consistently determined U is enough to create a band gap, however a supercell with hydrogen distortions creates a small gap whose magnitude increases when performing DFT +U with self-consistently determined U values. Furthermore, correlation effects, in turn, have a moderate influence on the coupled structural and electronic properties of doped 𝑅⁢H 3 compounds and may be important when considering the competition between structural distortions and superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Nonadiabatic Effects on Defect Diffusion in Silicon-Doped Nanographenes

Single atom impurities in graphene, substitutional silicon defects in particular, have been observed to diffuse under electron beam irradiation. However, the relative importance of elastic and inelastic scattering in facilitating their mobility remains unclear. Here, we employ excited-state electronic structure calculations to explore potential inelastic effects, and find an electronically nonadiabatic excited-state silicon diffusion pathway involving “softened” Si–C bonding that presents an ~2 eV lower diffusion barrier than the ground-state pathway. Beam-induced transition rates to this state indicate that the excited-state pathway is accessible through irradiation of the defect site. However, even in the limit of fully elastic scattering, upward nonadiabatic transitions are also possible along the diffusion coordinate, increasing the diffusion barrier and further demonstrating the potential for electronic nonadiabaticity to influence beam-induced atomic transformations in materials. Additionally, we also propose some experimentally testable signatures of such excited-state pathways.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Electron Tunneling and X-Ray Photoelectron Spectroscopy Studies of the Superconducting Properties of Nitrogen-Doped Niobium Resonator Cavities

Scanning tunneling microscopy and spectroscopy and X-ray photoelectron spectroscopy (XPS) have been used to investigate the differences between the surface electronic structures and chemical structure of typically prepared and N-doped Nb cutouts from superconducting radio frequency (SRF) cavities. The goal of this work is to get insights into the fundamental physics and materials mechanisms behind the striking decrease of the surface resistance with the radiofrequency magnetic field, which has been observed by many groups on N-doped Nb cavities. In particular, we address the effects of N-doping on the superconducting properties at the surface of SRF cavities. XPS measurements reveal a significantly more oxidized Nb 3d states on the N-doped Nb surfaces which is confirmed by tunneling spectroscopy measurements. Analysis of the tunneling spectra in the framework of a recent model (A. Gurevich and T. Kubo Phys. Rev. B 96, 184515 (2017)) shows that the N-doping greatly reduces local distribution of superconducting properties on the surface, causes a significant shrinkage of the metallic suboxide and changes the contact resistance between the metallic suboxide and the bulk niobium toward an optimum value, resulting in a lower surface resistance. Combination of these factors enables one to effectively tune the density of states at the surface and to reveal the decrease of the surface resistance with the radio frequency field which follows from the BCS theory. A slightly reduced average gap and a smaller coherence length, revealed by tunneling spectroscopy in the vortex cores, have been found in the N-doped Nb samples compared to typically prepared Nb samples, indicating a stronger impurity scattering caused by nitrogen doping in a moderately disordered material.

Lechner, Eric M.↗
DOE OSTI2025

Magnetostriction and temperature dependent Gilbert damping in boron doped Fe 80 ⁢Ga 20 thin films

Magnetic thin films with strong magnetoelastic coupling and low Gilbert damping are key materials for many magnetoelectric devices. Here, we investigated the effects of boron doping concentration on magnetostriction and temperature dependent Gilbert damping in magnetron sputtered (Fe 80 ⁢Ga 20 ) 1−𝑥 ⁢B 𝑥 films. A crystalline to amorphous structural transition was observed for a boron content near 8% and coincided with a decrease in coercivity from 76 Oe to 3 Oe. A 10% doping concentration is optimal for achieving both large magnetostriction of 48.8 ppm and low Gilbert damping of 6×10 −3 . The temperature dependence of the damping shows an increase at low temperatures with a peak around 40 K, and we associate the relative increase Δ⁢𝛼/𝛼 RT with magnetoelastic contributions to the damping, which has a maximum of 55.7% at 8% boron. An increase in the inhomogeneous linewidth broadening was observed in the structural transition regime at about 8% boron concentration. Furthermore, this study suggests that incorporation of glass forming elements, in this case boron, into Fe 80 ⁢Ga 20 is a practical pathway for simultaneously achieving enhanced magnetoelastic coupling and reduced Gilbert damping.

Cryogenics↗
NASA NTRS1987

Effects of substrate misorientation and background impurities on electron transport in molecular-beam-epitaxial grown GaAs/AlGaAs modulation-doped quantum-well structures

The effects of substrate misorientation off the (001) plane and of background impurities on electron transport in MBE-grown GaAs/AlGaAs modulation-doped superlattice-buffered quantum-well structures were investigated. Low-field transport data were obtained on GaAs/AlGaAs structures grown on substrates oriented 0, 2, 4, and 6.5 deg off the (001) plane towards either (111)A or (111)B. It is shown that the low-field two-dimensional electron gas (2DEG) mobility is a function of the angle and direction of the substrate orientation, and that the 2DEG mobility is a function of the direction of the applied electric field in the GaAs quantum well. The anisotropy in the 2DEG mobility is also a function of the tilt angle and tilt azimuth direction of the substrate from the (001) plane. In addition, it is shown that the amount of interface scattering from the inverted interface is a sensitive function of the amount of background impurities in the MBE machine.

Radulescu, D. C.↗
DOE OSTI2025

Hybrid Doping Strategy with High‐Entropy Cu/Fe Surface Modification and Zr Bulk Incorporation for Ni‐Rich Cathodes

A hybrid doping strategy combining Zr 4+ bulk doping with high-entropy Cu 2+ /Fe 3+ surface doping is developed to enhance the structural and interfacial stability of Ni-rich layered oxide cathodes. Cu and Fe are selectively introduced at the particle surface via a surface-selective ion-exchange process, forming a ≈15 nm Fe-rich layer while preserving the layered framework. Compared to the pristine cathode, the hybrid sample exhibits significantly improved electrochemical performance in both half-cell and full-cell configurations. In half-cells, the hybrid retains 88.5% and 90.2% after 100 cycles at 1C under 4.6 and 4.5 V, respectively. During high-voltage full-cell cycling, the hybrid cathode maintains over 80% capacity retention, whereas the pristine counterpart retains less than 10% under identical conditions over the same cycling period. XPS, EELS, and DEMS analyses confirm improved oxygen retention, suppressed gas evolution, and stable surface chemistry, while DFT calculations indicate enhanced Me–O bonding in the selected Fe 0.75 Cu 0.25 (Mn 1/16 Co 2/16 Ni 13/16 )O 2 surface composition, which is identified through DFT-calculated mixing energy reaching a minimum at this ratio, indicating the most thermodynamically favorable configuration. In conclusion, these results demonstrate the effectiveness of this hybrid doping strategy in mitigating coupled degradation pathways in Ni-rich cathodes.

15 GEOTHERMAL ENERGY↗
DOE OSTI2020

Comparing Experimental Phase Behavior of Ion-Doped Block Copolymers with Theoretical Predictions Based on Selective Ion Solvation

The effects of salt-doping on the morphological behavior of block copolymers are well established but remain poorly understood, partially because of the challenge of resolving electrostatics in a heterogeneous medium with low average permittivity. By employing a recently developed field theory, we analyze the phase behavior of polystyrene-b-poly(ethylene oxide) (SEO) copolymers doped with lithium bis(trifluoromethanesulfonyl)imide salts (LiTFSI). Using a single fitting parameter, the ionic solvation radius, we obtain qualitative agreement between our theory and experimental data over a range of polymer molecular weights and copolymer compositions. Such agreement supports and highlights the need of solvation free energy to accurately describe the self-assembly of ion-doped block copolymers and demonstrates that experimentally observed dependence on molecular weight, not present in neutral block copolymers, can be rationalized by solvation effects. Overall, morphological variations are stronger than those predicted by the leading, linear order theory but can be captured by the full model.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Suppression of hybridization by Cd doping in CeCoIn 5

The interaction between superconductivity and magnetism in heavy fermion compounds has remained a challenge ever since the discovery of unconventional superconductivity in such systems. The heavy fermion Ce T In 5 ( T = Co,Rh,Ir) family offers a good platform to study the relationship between superconductivity and magnetism, whose ground state can be easily tuned by chemical doping, making the ambient-pressure experimental techniques like angle-resolved photoemission spectroscopy possible to address this old but engaging question. By Cd doping, the superconducting state of CeCoIn 5 can be smoothly tuned to an antiferromagnetic ground state, which can be reversed by applying pressure. In this study, we present an electronic structure study of CeCo ( In 0.85 Cd 0.15 ) 5 with an antiferromagnetic ground state and the results are compared with CeCoIn 5 . We found that the hybridization strength between the f electrons and conduction electrons in CeCoIn 5 has been suppressed by Cd doping, but still the Fermi surface includes a significant contribution from the Ce f electrons. Our results find that the electronic tuning effect by Cd doping arises from the change in the hybridization strength between the Ce f electrons and conduction electrons caused by the Cd dopant, and the subtle interplay between itinerancy and localization of the f electrons determines the ground state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

X-ray Nanoimaging of Crystal Defects in Single Grains of Solid-State Electrolyte Li 7–3x Al x La 3 Zr 2 O 12

All-solid-state lithium batteries promise significant improvements in energy density and safety over traditional liquid electrolyte batteries. The Al-doped Li 7 La 3 Zr 2 O 12 (LLZO) solid-state electrolyte shows excellent potential given its high ionic conductivity and good thermal, chemical, and electrochemical stability. Nevertheless, further improvements on electrochemical and mechanical properties of LLZO call for an in-depth understanding of its local microstructure. Here, we employ Bragg coherent diffractive imaging to investigate the atomic displacements inside single grains of LLZO with various Al-doping concentrations, resulting in cubic, tetragonal, and cubic-tetragonal mixed structures. We observe coexisting domains of different crystallographic orientations in the tetragonal structure. We further show that Al doping leads to crystal defects such as dislocations and phase boundaries in the mixed- and cubic-phase grain. This study addresses the effect of Al doping on the nanoscale structure within individual grains of LLZO, which is informative for the future development of solid-state batteries.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS1988

Increased effective barrier heights in Schottky diodes by molecular-beam epitaxy of CoSi2 and Ga-doped Si on Si(111)

Increasing the effective Schottky-barrier height of epitaxial CoSi2/Si(111) diodes by the use of thin, highly doped Si layers in close proximity to the metal-semiconductor interface has been studied. Intrinsic Si, Si doped by coevaporation of Ga, and epitaxial CoSi2 layers have all been grown in the same molecular-beam epitaxy system. Current-voltage and photoresponse characterization yield barrier heights ranging from 0.61 eV for a sample with no p(+) layer to 0.89 eV for a sample with a 20-nm-thick p(+) layer. These results are compared to theoretical values based on a one-dimensional solution of Poisson's equation under the depletion approximation.

Fathauer, R. W.↗
DOE OSTI2023

Absence of mixed valency for Pr in pristine and hole-doped PrNiO 2

Infinite-layer nickelates (𝑅⁢NiO 2 ) exhibit some distinct differences as compared to cuprate superconductors, leading to a debate concerning the role of rare-earth ions (𝑅=La,Pr,Nd) in the low-energy many-body physics. Although rare-earth 4⁢𝑓 orbitals are typically treated as inert “core” electrons in studies, this approximation has been questioned. An active participation of 4⁢𝑓 states is most likely for PrNiO 2 based on an analogy to cuprates where Pr cuprates differ significantly from other cuprates. Here, we adopt density functional plus dynamical mean-field theory to investigate the role of Pr 4⁢𝑓 orbitals and more generally the correlated electronic structure of PrNiO 2 and its hole-doped variant. We find that the Pr 4⁢𝑓 states are insulating and show no evidence for either a Kondo resonance or Zhang-Rice singlet formation as they do not have any hybridization channels near the Fermi energy. The biggest effects of hole doping are to shift the Pr 5⁢𝑑 and 4⁢𝑓 states further away from the Fermi energy whereas enhancing the Ni 3⁢𝑑−O 2⁢𝑝 hybridization, thus, reducing correlation effects as the O 2⁢𝑝 states get closer to the Fermi energy. We again find no evidence for either Kondo or Zhang-Rice physics for the 4⁢𝑓 states upon hole doping. Finally, we conclude by commenting on implications for other reduced valence nickelates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Enhancing Dihydrogen Interaction of a Zirconium Metal–Organic Framework by Metal Doping

Advancing efficient hydrogen storage technologies is essential for enabling a sustainable energy future, especially in onboard applications. While hydrogen offers high gravimetric energy density and zero-emission combustion, its low volumetric energy density presents significant storage challenges. Metal-organic frameworks (MOFs), well known for their tunable porosity and high surface areas, have emerged as promising candidates for adsorption-based hydrogen storage. This study investigated a chemically robust zirconium-based MOF, MOF-808, as a representative platform for hydrogen storage enhancement through metal ion doping. Various divalent metal ions were introduced into MOF-808 via one-pot synthesis or post-synthetic modification (PSM) to evaluate their effects on metal doping efficiency, framework stability, and hydrogen adsorption performance. Our findings demonstrate that metal doping enhanced the hydrogen binding affinity of MOF-808 while preserving its structural integrity and excellent stability. A Mg-doped MOF, MOF-808@Mg 2:1, showed a 59% increase in hydrogen uptake, and a Cu-doped MOF, MOF-808-ZrCu, exhibited a 33% increase in isosteric heat of adsorption for H 2 compared to the pristine MOF-808 activated at the same temperature. This work highlights the potential of metal-functionalized stable MOFs for practical hydrogen storage applications. Furthermore, these materials are also being studied for their potential to enhance CO 2 adsorption.

Adsorption↗
DOE OSTI2023

Diffusion of Brønsted acidic dopants in conjugated polymers

Many semiconductor devices (e.g., light emitting diodes and photovoltaics) utilize heterojunctions of doped and undoped layers or depend on gradients of electronic doping to control charge transport. Understanding of the formation and stability of gradients in doping requires an understanding of diffusion of dopants and the complex changes in polymer properties that arise during doping. Conjugated polymers can be electrically doped by strong acids, but the details of the reaction mechanism and subsequent stability are not understood. Here, we show a clear kinetic isotope effect in the doping of thin films of poly(3-hexylthiophene) (P3HT) by bis(trifluoromethane)sulfonimide (HTFSI) from solution indicating that this doping process is limited by proton transfer to the polymer. Complementary X-ray photoelectron spectroscopy and dynamic secondary ion mass spectrometry (DSIMS) depth profiling of dopant concentrations show definitive evidence of dopant enrichment at the P3HT surface. These surface-limited concentration profiles suggest that diffusivity of dopants vary inversely with dopant concentration due to doping-induced changes to the structure of the conjugated polymer.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗