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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Volumetric Shaping of Nanoparticle-DNA Crystals by Light-Induced Milling

DNA-programmable self-assembly enables the formation of nanoparticle crystals with controlled lattice symmetry. While this approach offers the formation of complexly ordered nanostructures for optical, mechanical, and biological applications, a mesoscale control over such nanomaterials is limited. Directing the material formation process through the assembly pathway or external fields allows for modulating crystal morphology, but achieving arbitrary morphology remains challenging. Here, we present a photothermal method for shaping 3D DNA-programmable crystals of gold nanoparticles. Through local heating of nanoparticles due to plasmonic light absorption, we induce targeted volumetric dissolution of specifically defined crystal areas with micron-scale accuracy. This technique effectively prescribes crystal shaping and creates arbitrarily shaped voids within crystals. We further investigate both computationally and experimentally the key factors governing volumetric material subtraction. The developed automated light-milling platform enables the fabrication of nanomaterials exhibiting both DNA-programmable nanoscale order and custom-designed mesoscale architecture.

36 MATERIALS SCIENCE↗
DOE OSTI2024

3D Printing ofThermally Responsive Shape Memory LiquidCrystalline Epoxy Networks

Abstract A two-component liquid crystalline epoxy network (LCEN) with shape memory behavior was developed and evaluated as a candidate material for 3D printing. The cure kinetics of the uncured material and the shape memory properties of the cured LCEN were investigated by using parallel plate rheology and dynamic mechanical analysis, respectively. A commercially available fumed silica additive was introduced to the neat, uncured material to improve the rheological properties for 3D printing. The addition of fumed silica was found to increase the yield stress, shear-thinning behavior, and toughness of the uncured epoxy ink. Polarized light microscopy, differential scanning calorimetry, and wide-angle X-ray scattering measurements between the neat and additive-modified LCEN suggested a reduction in liquid crystalline alignment in the modified LCEN, owing to interactions between crystalline domains and fumed silica, which in turn influenced the mechanical behavior. Overall, the additive was found to be successful in preserving the shape memory properties of LCEN while improving its printability.

Chemistry↗
DOE OSTI2021

Enabling the Application of Large Footprint Open-Bottom Permeameters through New Shape Factors

Open-bottom permeameters (OBP) are commonly used for estimating the hydraulic properties of sediment beds under water bodies and fluxes across the sediment-water interface. The specific shape factor for an OBP flow situation is necessary for data interpretation. It is determined by the ratio of the permeameter tube radius to the tube's penetration depth within the sediment. Previous permeameter designs favored small radii which allowed for deeper penetration and stability of the tube. The shape factor is provided here for large footprint OBPs that allows for shallow penetration and greater radius. Through a numerical and analytical modeling study of the OBP hydrodynamics, previous knowledge on the OBP shape factor is generalized to the entire range of radius-to-penetration ratios that might be practically applied. The results reveal the advantages of the large footprint design, including better sensitivity due to the ability to impose larger discharge over a shorter test duration.

42 ENGINEERING↗
DOE OSTI2024

Flower-shaped 2D crystals grown in curved fluid vesicle membranes

Abstract The morphologies of two-dimensional (2D) crystals, nucleated, grown, and integrated within 2D elastic fluids, for instance in giant vesicle membranes, are dictated by an interplay of mechanics, permeability, and thermal contraction. Mitigation of solid strain drives the formation of crystals with vanishing Gaussian curvature (i.e., developable domain shapes) and, correspondingly, enhanced Gaussian curvature in the surrounding 2D fluid. However, upon cooling to grow the crystals, large vesicles sustain greater inflation and tension because their small area-to-volume ratio slows water permeation. As a result, more elaborate shapes, for instance, flowers with bendable but inextensible petals, form on large vesicles despite their more gradual curvature, while small vesicles harbor compact planar crystals. This size dependence runs counter to the known cumulative growth of strain energy of 2D colloidal crystals on rigid spherical templates. This interplay of intra-membrane mechanics and processing points to the scalable production of flexible molecular crystals of controllable complex shape.

36 MATERIALS SCIENCE↗
DOE OSTI2024

In-beam spectroscopy reveals competing nuclear shapes in the rare isotope 62 Cr

In recent decades, rareisotope facilities have enabled the study of short-lived, neutron-rich nuclei. Their measured properties indicate that shell structure changes in the regime of unbalanced neutron-to-proton ratios compared to that of stable nuclei. In the so-called islands of inversion in the nuclear chart – around the neutron-rich nuclei 32 Mg, 42 Si and 64 Cr, for example – the textbook shell-model picture predicts the presence of spherical shapes due to the respective magic neutron numbers of 20, 28, and 40 of these nuclei. However, nuclei in these regions turn out to be deformed in their ground states. Another hallmark of these islands is shape coexistence, where a nucleus assumes different shapes with excitation energy. Furthermore, we present evidence for this phenomenon from the observation of an excited 0 + state in 62 Cr, two neutrons away from the heart of the island of inversion around neutron number N = 40. We use large-scale shell-model calculations to interpret the results and report extrapolations for the doubly-magic nucleus 60 Ca.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Shape-anisotropy inverses the behavior of emergent vortices in active chiral fluids

Active colloidal fluids exhibit spontaneous emergence of correlated states, characterized by complex collective dynamics and self-organization. In geometrically confined systems, activity modulations trigger robust polar state reversals of a macroscopic vortex formed by colloidal rollers. Here, we reveal that the shape anisotropy of dielectric rollers transforms the system into a chiral active fluid comprised of rollers of arbitrary handedness. The chiral rollers self-assemble into multiple freestanding vortices with a spontaneously selected sense of rotation. We demonstrate that upon reactivation of the system after a complete cessation of activity beyond all relevant timescales, the vortices simultaneously restore their previous chiral states in striking contrast to the chiral state reversals demonstrated by spherical rollers. The analysis reveals that shape-anisotropy modifies the collective state memory of the ensemble. The findings provide insights into the emergence of complex collective behavior in chiral colloidal fluids governed by an interplay between shape anisotropy, chiral motion, and activity modulations.

Colloids↗
DOE OSTI2022

Ion beam-induced bending of TiO 2 nanowires with bead-like and prismatic shapes

Ion beam irradiation is a promising method to manipulate the composition and shape of nanowires. It causes the formation of crystal defects like vacancies and dislocations, and consequently, a volume expansion within the irradiated region, giving rise to the nanowire bending. The bending effect has been extensively discussed within nanowires with different diameters under ion beams with varying energies and ion fluences. However, the behaviors of nanowires with complicated shapes, which may have non-uniform irradiated regions due to the changing angle of incidence and shadowing effect, have remained largely unknown. Herein, the structural changes and bending of TiO 2 nanowires with both bead-like and prismatic shapes are investigated under a Ga + ion beam. The multi-faceted morphology, and consequently, varying angles of incidence, result in inhomogeneous irradiation and volume expansion. As a result, significant bending is only observed in prismatic nanowires. Since irradiation is confined within the half of nanowires facing the ion beam, the bending of nanowires is reversible by changing the direction of the ion beam. In order to provide insights into the tailoring composition and morphology of nanowires, we anticipate that this finding can establish the beam analog at the nanoscale, the bending of which can be tuned by ion irradiation.

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

Understanding the Effect of Chiral NN Parametrization on Nuclear Shapes From an Ab Initio Perspective

The ab initio symmetry-adapted no-core shell model naturally describes nuclear deformation and collectivity, and is therefore well-suited to studying the dynamics and coexistence of shapes in atomic nuclei. For the first time, we analyze how these features in low-lying states of 6 Li and 12 C are impacted by the underlying realistic nucleon-nucleon interaction. We find that the interaction parametrization has a notable but limited effect on collective shapes in the lowest 6 Li and 12 C states, while collective structures in the excited 2 + state of 12 C are significantly more sensitive to the interaction parameters and exhibits emergent shape coexistence.

Becker, Kevin S. [Louisiana State University, Bato↗
DOE OSTI2020

Gunn threshold voltage characterization in GaAs devices with wedge-shaped tapering

Here, we fabricate gallium arsenide-based devices with a wedge-shaped tapering region connected to a rectangular-shaped region and measure the threshold voltage required to trigger the Gunn effect. The threshold voltage reduction is attributed to the focusing of the electric field toward the narrower end of the device and is effective when the device has a steep enough tapering. We also model the electric field profile for the tapered devices using an intuitive graphical approach and the finite element method and provide estimates for the threshold voltages of tapered devices. Finally, we compare the estimates to the measured values and provide possible reasons for the discrepancies. We believe the capability of threshold voltage reduction with the wedge-shaped tapering design could be useful in device applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Temporal pre-pulse shaping in dual pulse laser produced plasma for the optimization of the EUV source in tin microdroplet system

Dual-laser beams interacting with small droplets of liquid tin are currently the most efficient systems for producing the 13.5 nm EUV photon radiation source required for the next generation microchips. Usually, EUV light is produced during the second main-pulse stage, while the pre-pulse (PP) is used for target preparation, i.e., droplet preheating, vaporization, and target deformation. However, the PP laser energy can be utilized more efficiently if the EUV producing plasma is being developed during the PP stage as well. In this work, we study the ways of optimization of the PP laser temporal shape to achieve conditions for maximum EUV output during the pre-pulse. The size of the deformed droplet is kept optimized for the following main laser pulse. Our simulations showed a significant increase in the EUV output at the pre-pulse stage when a ramping profile is used for the laser temporal shape. Using the ramped square pre-pulse produces 24% gain in the EUV output in comparison with the standard Gaussian temporal profile (i.e., regular Nd:YAG shape) for the same energy of the laser pulse.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Effect of penetrant–polymer interactions and shape on the motion of molecular penetrants in dense polymer networks

The diffusion of dilute molecular penetrants within polymers plays a crucial role in the advancement of material engineering for applications such as coatings and membrane separations. The potential of highly cross-linked polymer networks in these applications stems from their capacity to adjust the size and shape selectivity through subtle changes in network structures. In this paper, we use molecular dynamics simulation to understand the role of penetrant shape (aspect ratios) and its interaction with polymer networks on its diffusivity. We characterize both local penetrant hopping and the long-time diffusive motion for penetrants and consider different aspect ratios and penetrant–network interaction strengths at a variety of cross-link densities and temperatures. The shape affects the coupling of penetrant motion to the cross-link density- and temperature-dependent structural relaxation of networks and also affects the way a penetrant experiences the confinement from the network meshes. The attractive interaction between the penetrant and network primarily affects the former since only the system of dilute limit is of present interest. These results offer fundamental insights into the intricate interplay between penetrant characteristics and polymer network properties and also suggest future directions for manipulating polymer design to enhance the separation efficiency.

Chemistry↗
DOE OSTI2024

First look at neutron emission shape characteristics of ignition hotspots at the National Ignition Facility (invited)

The nuclear imaging system has been capturing neutron images of inertial confinement fusion (ICF) driven implosions for over a decade at the National Ignition Facility. This imaging system has evolved from one to three nearly orthogonal lines-of-sight, allowing for the study of three-dimensional shape characteristics of ignition shots. Limited-view tomography algorithms help visualize the burning hotspot in 3D and assess neutron source geometry using Legendre mode parameters. With its neutron, gamma-ray, and x-ray image reconstruction capabilities, NIS has provided critical insight into mechanisms that have limited implosion performance, such as fill tube diameter for ignition-type targets. This comprehensive diagnostic suite opens a window into the shape characteristics of ignition shots and how symmetry affects ICF implosion performance. In more recent ignition shots, neutron yields have visibly increased. Analyzing the shape and size of the reconstructed neutron source has shown an expansion of the burn volume, which is indicative of more efficient alpha heating during the implosion process.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2024

Harnessing complexity: Nonlinear optical phenomena in L-shapes, nanocrescents, and split-ring resonators

Here, we conduct systematic studies of the optical characteristics of plasmonic nanoparticles that exhibit C 2v symmetry. In particular, we analyze three distinct geometric configurations: an L-type shape, a crescent, and a split-ring resonator shaped like the Greek letter π. Optical properties are examined using the finite-difference time-domain method. It is demonstrated that all three shapes exhibit two prominent plasmon modes associated with the two axes of symmetry. This is in addition to a wide range of resonances observed at high frequencies corresponding to quadrupole modes and peaks due to sharp corners. Next, to facilitate nonlinear analysis, we employ a semiclassical hydrodynamic model, where the electron pressure term is explicitly accounted for. This model goes beyond the standard Drude description and enables capturing nonlocal and nonlinear effects. Employing this model enables us to rigorously examine the second-order angular resolved nonlinear optical response of these nanoparticles in each of the three configurations. Two pumping regimes are considered, namely, continuous wave (CW) and pulsed excitations. For CW pumping, we explore the properties of the second harmonic generation (SHG). Polarization and angle-resolved SHG spectra are obtained, revealing strong dependence on the nanoparticle geometry and incident wave polarization. The C 2v symmetry is shown to play a key role in determining the polarization states and selection rules of the SHG signal. For pulsed excitations, we discuss the phenomenon of broadband terahertz (THz) generation induced by the difference-frequency generation . It is shown that the THz emission spectra exhibit unique features attributed to the plasmonic resonances and symmetry of the nanoparticles. The polarization of the generated THz waves is also examined, revealing interesting patterns tied to the nanoparticle geometry. To gain deeper insight, we propose an analytical theory that agrees very well with the numerical experiments. The theory shows that the physical origin of the THz radiation is the mixing of various frequency components of the fundamental pulse by the second-order nonlinear susceptibility. An expression for the far-field THz intensity is derived in terms of the incident pulse parameters and the nonlinear response tensor of the nanoparticle. The results presented in this work offer new insights into the linear and nonlinear optical properties of nanoparticles with C 2v symmetry. The demonstrated strong SHG response and efficient broadband THz generation hold great promise for applications in nonlinear spectroscopy, nanophotonics, and optoelectronics. The proposed theoretical framework also provides a valuable tool for understanding and predicting the nonlinear behavior of other related nanostructures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Shape effects on the local dynamics of suspensions of spheroidal particles

The effect of shape on the dynamics of suspensions of non-spherical heavy particles is examined by fully resolved numerical simulations of oblate and prolate spheroids, as well as spheres, for a density ratio of ten, volume fractions ranging from 0.5% to 5%, and Reynolds numbers between 20 and 30. The dynamics is determined both by the interactions of the particles with the fluid as well as by collisions, with the number and importance of collisions increasing with volume fractions. A single isolated oblate or prolate spheroid falling under gravity generally falls broadside on, for the governing parameters examined here, and at low-volume fractions, the majority of particles in a suspension fall that way. At higher-volume fractions, the orientation is more random. The slip velocity decreases as the volume fraction increases for all shapes, as expected, but the effect of the shape is much less than seen for a single particle. Furthermore, this seems to be due to two effects. For all volume fractions, the most deformed particles cluster more than spheres and less deformed particles, which increases their slip velocity. As the concentration increases, the increased particle interactions also causes more particles to fall short side-on, which reduces the frontal area and the resulting drag, increasing the slip velocity. This second effect is, of course, absent for spherical particles.

42 ENGINEERING↗
DOE OSTI2025

Effect of particle shape on stratification in drying films of binary colloidal mixtures

The role of particle shape in evaporation-induced auto-stratification in polydisperse colloidal suspensions is explored with molecular dynamics simulations of mixtures of spheres and aspherical particles. A unified framework based on the competition between diffusion and diffusiophoresis is proposed to understand the effects of shape and size dispersity. In general, particles diffusing more slowly (e.g., larger particles) tend to accumulate more strongly at the evaporation front. However, larger particles have larger surface areas and therefore greater diffusiophoretic mobility. Hence, they are more likely to be driven away from the evaporation front via diffusiophoresis. For a rapidly dried bidisperse suspension containing small and large spheres, the competition leads to “small-on-top” stratification. Here, we employ a computational model in which the diffusion coefficient is inversely proportional to particle mass. For a mixture of spheres and aspherical particles with similar mass, the diffusion contrast is reduced, and the spheres are always enriched at the evaporation front as they have the smallest surface area for a given mass and, therefore, the lowest diffusiophoretic mobility. Furthermore, for a mixture of solid and hollow spheres that have the same outer radius and thus the same surface area, the diffusiophoretic contrast is suppressed, and the system is dominated by diffusion. Consequently, the solid spheres, which have a larger mass and diffuse more slowly, accumulate on top of the hollow spheres. Finally, for a mixture of thin disks and long rods that differ significantly in shape but have similar mass and surface area, both diffusion and diffusiophoresis contrasts are suppressed, and the mixture does not stratify.

Classical molecular dynamic simulations↗
DOE OSTI2022

Introduction to spectral line shape theory

Spectral line-shape models are an important part of understanding high-energy-density (HED) plasmas. Models are needed for calculating opacity of materials and can serve as diagnostics for astrophysical and laboratory plasmas. However, much of the literature on line shapes is directed toward specialists. This perspective makes it difficult for non-specialists to enter the field. We have two broad goals with this topical review. First, we aim to give information so that others in HED physics may better understand the current field. Additionally, this first goal may help guide future experiments to test different aspects of the theory. Second, we provide an introduction for those who might be interested in line-shape theory, and enough materials to be able to navigate the field and the literature. We give a high-level overview of line broadening process, as well as dive into the formalism, available methods, and approximations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

A method to test the coupling strength of the linear and nonlinear contributions to higher-order flow harmonics via event shape engineering

A Multi-Phase Transport (AMPT) model is used to study the efficacy of shape-engineered events to delineate the degree of coupling between the linear and nonlinear contributions to the higher-order flow harmonics v 4 and v 5 . Here, the study shows that the nonlinear contributions are strongly shape-dependent while the linear contributions are shape-independent, indicating little if any, coupling between the linear and nonlinear flow coefficients. The experimental verification of such patterns could be an invaluable tool for robust extraction of the linear and mode-coupled flow coefficients, especially for beam energies where the charged particle multiplicity and the event statistics precludes the use of current methods to establish the coupling strength.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Equilibrium shapes of facetted 3D metal nanoclusters intercalated near the surface of layered materials

Experimental studies indicate that 3D crystalline metal nanoclusters (NCs) intercalated under the surface of graphite have flat-topped equilibrated shapes. In this work, we characterize the shapes of these facetted NCs sandwiched between a blanketing graphene layer and the underlying graphite substrate. Specifically, we focus on the cases of fcc Cu and hcp Fe NCs. Furthermore, the analysis involves numerical minimization of the system energy for a specified NC volume and NC height, the latter corresponding to the separation between parallel top and bottom facets. Our numerical analysis quantifies how the distance of the side facet planes from center of the nanocluster varies linearly with a natural characteristic linear dimension of the nanocluster. Calculated shapes of fcc Cu and hcp Fe NCs are consistent with the hexagonal footprints observed in scanning tunneling microscopy studies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗