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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Quantum kinetic modeling of KEEN waves in a warm-dense regime

We report the first fully kinetic, quantum study of kinetic electrostatic electron nonlinear (KEEN) waves, showing that quantum diffraction systematically erodes the classical trapping mechanism, narrows harmonic locking to the fundamental, and hastens post-drive decay. Electrons are evolved with a second-order Strang-split 1D1V Wigner–Poisson solver that couples conservative semi-Lagrangian WENO advection to an analytic Fourier space update for the non-local Wigner term, while ions remain classical. We focus on collisionless dynamics in a weakly coupled regime, providing a controlled baseline before collisional extensions. Short, frequency-tuned ponderomotive pulses drive KEEN formation in a uniform Maxwellian plasma; as the dimensionless quantum parameter H rises from the classical limit to values relevant to warm-dense matter, doped semiconductors, and 2D electron systems, the drive threshold increases, higher harmonics are damped, trapped electron vortices diffuse, and the subplasma electrostatic energy relaxes to a lower stationary level, as confirmed by continuous wavelet analysis. These microscopic changes carry macroscopic weight. Ignition-scale capsules now compress matter to regimes where the electron de Broglie wavelength rivals the Debye length, making classical kinetic descriptions insufficient. By extending KEEN physics into this quantum domain, our results offer a potential diagnostic of non-equilibrium electron dynamics for next-generation inertial-confinement designs and high-energy-density platforms, indicating that predictive fusion modeling may benefit from the integration of kinetic fidelity with quantum effects.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Solution-Processed Ultrafast, Room-Temperature Single-Photon Source at 1550 nm

Single photons are cornerstones of quantum technologies. The need for an ultrafast, bright, and stable photon source emitting in the telecom-band at ∼1550 nm, ideally operating at room temperature, has resulted in a decades-long quest. However, to date, telecom sources are hampered by inherently long radiative lifetimes that severely limit brightness and speed, material instability, or the need for cryogenic operation. Here, in this study, stable colloidal PbS/CdS quantum dots emitting at 1550 nm (C-band) or 1350 nm (O-band) are embedded in a solution-synthesized nanoparticle-on-mirror cavity. Single cavity-coupled quantum dots experience extreme Purcell factors up to 10,700, resulting in ultrafast emission lifetimes of 65 ps, along with near-complete blinking suppression. As a result, 12 million single photons are emitted per second affording a single photon source at 1550 nm that is more than two orders of magnitude brighter than previously possible at room-temperature. These telecom-band single photon sources are solution-processable and lithography-free and may leverage mature colloidal fabrication technologies for future quantum applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Excitation of Bloch Surface Waves in Zero-Admittance Multilayers for High-Sensitivity Sensor Applications

The growing need for classical as well as quantum optical sensing places increasingly stringent requirements upon the desired characteristics of the engendered fields. Specifically, achieving superior field enhancement plays a critical role in applications ranging from chem-bio sensing, Raman and infrared spectroscopies to ion trapping and qubit control in emerging quantum-information science. Due to their low optical losses and ability to exhibit resonant field enhancements, all dielectric multilayers are emerging as an optical material system not only useful to classical photonics and sensing but also of potential to be integrated with quantum materials and quantum sensing. The recently introduced concept of zero-admittance layers [1] within dielectric multilayer materials, enables the creation and control of resonant fields orders of magnitude larger than the exciting field. Here, invoking the zero-admittance concept, we design, fabricate, and characterize an all-dielectric nonabsorbing stack and demonstrate the engendered huge field enhancement. Describing the fields in terms of Bloch surface waves, we connect the surface field to the semiperiodicity in the dielectric domains of the stack. As a specific application of the resonant field, we propose and demonstrate refractive-index sensing for the detection of trace amounts of an analyte. The results include a quantification of the sensitivity of the device with respect to the profile of the exciting field. The experimental results are shown to be in good agreement with theoretical calculations.

47 OTHER INSTRUMENTATION↗
DOE OSTI2021

Broadband Plasmonic Photocurrent Enhancement from Photosystem I Assembled with Tailored Arrays of Au and Ag Nanodisks

Plasmonic interactions between metal nanostructures and fluorophores have been increasingly employed to alter photoexcitation pathways in multichromophore photosynthetic proteins like photosystem I (PSI). Our recent experimental studies demonstrated a sixfold plasmon-enhanced photocurrent from PSI assembled on Fischer patterns of Ag nanopyramids. However, lack of control over the specific resonance modes limited the magnitude and selectivity of the plasmonic enhancement. To this end, the present study investigates the excitation wavelength-dependent plasmon-enhanced photocurrents from PSI immobilized around highly ordered Au (AuND) and Ag (AgND) nanodisks with dipolar plasmon resonances that are tuned to ~680 and 560 nm, respectively. Specifically, we report plasmon-induced photocurrent enhancements of ~6.8 and 17.5 for excitation wavelengths of ~680 and 565 nm, respectively, as compared to PSI assembled on planar ITO substrates. We also report the action spectra for photocurrent enhancements recorded over wavelengths of 395–810 nm with nine discrete LED light sources. The results indicate the following: (1) concurrence between the photocurrent-enhancement spectra from PSI assemblies and the plasmonic resonances for the respective nanopatterned substrates, and (2) broadband photocurrent enhancements due to plasmon-coupled photoactivation in the otherwise blind chlorophyll regions of the native PSI absorption spectra. Lastly, these intriguing findings pave the path for rational assembly of future biohybrid structures composed of natural light-harvesting antennae and plasmonic metal nanostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Chiral induction at the nanoscale and spin selectivity in electron transmission in chiral methylated BEDT-TTF derivatives

Great efforts have been made in the last few decades to realize electronic devices based on organic molecules. A possible approach in this field is to exploit the chirality of organic molecules for the development of spintronic devices, an applicative way to implement the chiral-induced spin selectivity (CISS) effect. In this work we exploit enantiopure tetrathiafulvalene (TTF) derivatives as chiral inducers at the nanoscale. The aim is to make use of TTF's well-known and unique semiconducting properties, to be expressed in the fields of enantio-selectivity and the chiral-induced spin selectivity (CISS) effect. Further, the experimental results shown in this paper further demonstrate how chirality and spin are deeply interrelated, as foreseen within the CISS effect theory, paving the way for the application of TTF derivatives in the field of spintronics. In this work, we demonstrate that tetramethyl-bis(ethylenedithio)-tetrathiafulvalene (TM-BEDT-TTF) (1) behaves as an efficient spin filter, as evidenced by magneto-atomic force microscopy (mc-AFM) measurements. Additionally, it is shown to be effective in transferring chirality to CdS/CdSe core–shell nanoparticles, as inferred from the analysis of circularly resolved photoluminescence spectra. This makes 1 a promising candidate for a variety of applications, ranging from plasmonics to quantum computing.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Revealing quasi-excitations in the low-density homogeneous electron gas with model exchange–correlation kernels

Time-dependent density functional theory within the linear response regime provides a solid mathematical framework to capture excitations. The accuracy of the theory, however, largely depends on the approximations for the exchange–correlation (xc) kernels. Away from the long-wavelength (or q = 0 short wave-vector) and zero-frequency (ω = 0) limit, the correlation contribution to the kernel becomes more relevant and dominant over exchange. The dielectric function, in principle, can encompass xc effects relevant to describe low-density physics. Furthermore, besides collective plasmon excitations, the dielectric function can reveal collective electron–hole excitations, often dubbed “ghost excitons.” Besides collective excitons, the physics of the low-density regime is rich, as exemplified by a static charge-density wave that was recently found for r s > 69, and was shown to be associated with softening of the plasmon mode. These excitations are seen to be present in much higher density 2D homogeneous electron gases of r s ≳ 4. Here, in this work, we perform a thorough analysis with xc model kernels for excitations of various nature. The uniform electron gas, as a useful model of real metallic systems, is used as a platform for our analysis. We highlight the relevance of exact constraints as we display and explain screening and excitations in the low-density region.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Engineering the radiative dynamics of thermalized excitons with metal interfaces

As a platform for optoelectronic devices based on exciton dynamics, monolayer transition metal dichalcogenides (TMDCs) are often placed near metal interfaces or inside planar cavities. While the radiative properties of point dipoles at metal interfaces has been studied extensively, those of excitons, which are delocalized and exhibit a temperature-dependent momentum distribution, lack a thorough treatment. Here, we analyze the emission properties of excitons in TMDCs near planar metal interfaces and explore their dependence on exciton center-of-mass momentum, transition dipole orientation, and temperature. Defining a characteristic energy scale k B T c = ($\hbar k$) 2 /2m (k being the radiative wavevector and m the exciton mass), we find that at temperatures T $\gg$ T c and low densities where the momentum distribution can be characterized by Maxwell-Boltzmann statistics, the modified emission rates (normalized to free space) behave similarly to point dipoles. This similarity in behavior arises due to the broad nature of wavevector components making up the exciton and point dipole emission. On the other hand, the narrow momentum distribution of excitons for T < T c can result in significantly different emission behavior as compared to point dipoles. These differences can be further amplified by considering excitons with a Bose Einstein distribution at high phase space densities, such as in a condensate phase. We find suppression or enhancement of emission relative to the point dipole case by several orders of magnitude. These insights can help optimize the performance of optoelectronic devices that incorporate 2D semiconductors near metal electrodes and can inform future studies of exciton radiative dynamics at low temperatures. Additionally, these studies show that nanoscale optical cavities are a viable pathway to generating long-lifetime exciton states in TMDCs.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Tunable plasmon-enhanced second-order optical nonlinearity in transition metal dichalcogenide nanotriangles

The development of nanomaterials with a large nonlinear susceptibility is essential for nonlinear nanophotonics. Here we show that transition metal dichalcogenide (TMD) nanotriangles have a large effective second-order susceptibility [χ (2) ] at midinfrared to near-infrared frequencies owing to their broken centrosymmetry. χ (2) is calculated within the density-matrix formalism that accounts for dissipation and screening. χ (2) peaks in the vicinity of both two-photon resonances (specified by the geometry) and plasmon resonances (tunable via the carrier density). Aligning the resonances yields the values of χ (2) as high as 10 –6 m/V. These findings underscore the potential of TMD nanotriangles for nonlinear nanophotonics, particularly second-harmonic generation.

0-dimensional systems↗
DOE OSTI2023

Plasmon-enhanced optical nonlinearity in graphene nanomeshes

Using the density-matrix formalism, here we show that graphene nanomeshes (GNMs)—graphene sheets patterned with antidots—have large plasmon-enhanced nonlinear optical response. GNMs can be designed to behave as quasi-one-dimensional plasmonic crystals in which plasmons with large propagation lengths are efficiently excited. The associated third-order Kerr and third-harmonic-generation susceptibility can be as high as 10 –7 and 10 –9 m 2 V –2 , respectively, over the mid-to-near-infrared frequency range. Furthermore, carrier-density tuning in GNMs can flip the propagation direction of plasmonic waves and enables bidirectional switching of optical signals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Reversible plasmonic switching in a graphene nanoresonator loaded with a core – shell quantum dot

A model of an all-plasmonic switch based on a graphene waveguide integrated with a stub nanoresonator loaded with a quantum dot is considered. Using the full-wave numerical simulation, it is shown that successive on/off switching of the control surface plasmon – polariton wave at the input of the waveguide leads to a change in the phase of the signal plasmon – polariton wave in the nanoresonator by π. This causes reversible switching of the device operation regime – from almost complete blocking to stable transmission of the signal plasmon – polariton wave through the waveguide. The effect is implemented at rates of ∼0.5 THz for infrared electromagnetic waves localised in a device with a switching region of 40 × 20 nm. (paper)

36 MATERIALS SCIENCE↗
DOE OSTI2022

Entangled two-plasmon generation in carbon nanotubes and graphene-coated wires

Here, we investigate the two-plasmon spontaneous decay of a quantum emitter near single-walled carbon nanotubes (SWCNTs) and graphene-coated wires (GCWs). We demonstrate efficient, enhanced generation of two-plasmon entangled states in SWCNTs due to the strong coupling between tunable guided plasmons and the quantum emitter. We predict two-plasmon emission rates more than twelve orders of magnitude higher than in free space, with average lifetimes of a few dozen nanoseconds. Given their low dimensionality, these systems could be more efficient for generating and detecting entangled plasmons in comparison to extended graphene. Indeed, we achieve a tunable spectrum of emission in GCWs, where sharp resonances occur precisely at the plasmons' minimum excitation frequencies. We show that by changing the material properties of the GCW's dielectric core, one could tailor the dominant modes and frequencies of the emitted entangled plasmons while keeping the decay rate ten orders of magnitude higher than in free space. By unveiling the unique properties of two-plasmon spontaneous emission processes in the presence of low-dimensional carbon-based nanomaterials, our findings set the basis for a novel material platform with applications to on-chip quantum information technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Highly Efficient Plasmon Induced Hot-Electron Transfer at Ag/TiO 2 Interface

Plasmon induced hot carrier transfer is a promising novel approach for solar energy conversion, but its practical application is often hindered by its low efficiency. This work demonstrates an unprecedented quantum efficiency of plasmonic hot-electron transfer of up to 53 ± 2% from 1.7 nm silver nanoparticles to anatase nanoporous TiOsub>2 films at 400 nm excitation. This efficient hot-electron transfer consists of contributions of both hot electrons generated by plasmon decay through exciting Ag intraband transitions and Ag-to-TiO 2 interfacial charge-transfer transitions. The efficiencies of both pathways increase at smaller Ag particle sizes from 5.9 to 1.7 nm, suggesting that decreasing particle sizes is a promising way toward efficient plasmonic hot-carrier extraction.

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

Optical Extinction-Based 3D Nano-Imaging of WS 2 on Gold

Broad band nano-extinction images recorded in the tip-enhanced optical spectroscopy geometry track the 3D topography of a single layer of WS 2 on Au substrate. The described nano-optical method is complementary to conventional AFM and offers additional information about the buried material-metal interface that is not accessible using conventional topographic imaging. Beyond 3D optical imaging, we observe large variations in the junction plasmon resonance on the nanoscale. The latter is important to understand and account for in tip-enhanced Raman and photoluminescence studies that target low-dimensional materials specifically. Further, our observations and (coherent) optical scattering-based method are also relevant to emerging efforts aimed at exploring strong coupling and Fano interferences in hybrid plasmonic-low dimensional quantum material systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

High power edge-cum-surface emitting terahertz laser arrays phased locked by vacuum guided plasmon waves

Terahertz semiconductor quantum-cascade lasers (QCLs) are widely implemented with metallic cavities that support low-loss plasmonic optical modes at long wavelengths. However, resonant optical modes in such cavities suffer from poor radiative characteristics due to their subwavelength transverse dimensions. Consequently, single-mode terahertz QCLs with metallic cavities and large (>100 mW) output power have only been realized in the surface-emitting configuration that affords a large radiating surface. Here, we demonstrate a method to enhance radiative outcoupling from such plasmonic lasers for high-power emission in the edge-emitting (end-fire or longitudinal) direction. Single-sided plasmon waves propagating in vacuum are resonantly excited in surrounding medium of metallic cavities with the QCL semiconductor medium. The vacuum guided plasmon waves with a large wavefront phase-lock multiple metallic cavities longitudinally, which leads to intense radiation in multiple directions, including that in the longitudinal direction in a narrow single-lobed beam. The multicavity array radiates predominantly in a single spectral mode. A peak-power output of 260 mW and a slope efficiency of 303 mW/A are measured for the end-fire beam from a 3.3 THz QCL operating at 54 K in a Stirling cooler. Finally, single-mode operation and lithographic tuning across a bandwidth of ~150 GHz are demonstrated.

42 ENGINEERING↗
DOE OSTI2022

Near–Band–Edge Enhancement in Perovskite Solar Cells via Tunable Surface Plasmons

Plasmonic perovskite solar cells (PSCs) using core-shell type plasmonic particles are designed, which possess the plasmon resonance in the near-infrared range. This can selectively strengthen the interaction of the perovskite layer with low-energy photons. The mesoporous PSCs employing the plasmonic particles have delivered a 10%-15% enhancement of external quantum efficiency in the plasmonic resonance range. This surface-plasmonic effect has been analyzed using complementary techniques, including selective wavelength excitation and time-dependent photoluminescence. Here it is shown that the metal-based core-shell-type plasmonic structures in PSCs optimize the scattering and absorption of incident light and the dynamics of photogenerated carriers. Furthermore, both optical and electronic effects increase the power conversion efficiency of PSCs from 17.49% to 19.88%, paving a way toward controlling the thickness of the photoactive layer for advanced devices such as tandem solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Long-Range Dipole–Dipole Interactions in a Plasmonic Lattice

Spontaneous emission of quantum emitters can be enhanced by increasing the local density of optical states, whereas engineering dipole-dipole interactions requires modifying the two-point spectral density function. Here, we experimentally demonstrate long-range dipole-dipole interactions (DDIs) mediated by surface lattice resonances in a plasmonic nanoparticle lattice. Using angle-resolved spectral measurements and fluorescence lifetime studies, we show that unique nanophotonic modes mediate long-range DDI between donor and acceptor molecules. We observe significant and persistent DDI strengths for a range of densities that map to similar to 800 nm mean nearest-neighbor separation distance between donor and acceptor dipoles, a factor of similar to 100 larger than free space. Here, our results pave the way to engineer and control long-range DDIs between an ensemble of emitters at room temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Towards a quantum fluid theory of correlated many-fermion systems from first principles

Correlated many-fermion systems emerge in a broad range of phenomena in warm dense matter, plasmonics, and ultracold atoms. Quantum hydrodynamics (QHD) complements first-principles methods for many-fermion systems at larger scales. We illustrate the failure of the standard Bohm potential central to QHD for strong perturbations when the density perturbation is larger than about 10^{-3} 10 − 3 of the mean density. We then extend QHD to this regime via the many-fermion Bohm potential from first-principles. This may lead to more accurate QHD simulations beyond their common application domain in the presence of strong perturbations at scales unattainable with first-principles methods.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗