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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Correlating structural changes in thermoresponsive hydrogels to the optical response of embedded plasmonic nanoparticles

Stimuli-responsive microgels, composed of small beads with soft, deformable polymer networks swollen through a combination of synthetic control over the polymer and its interaction with water, form a versatile platform for development of multifunctional and biocompatible sensors. The interfacial structural variation of such materials at a nanometer length scale is essential to their function, but not yet fully comprehended. Here, we take advantage of the plasmonic response of a gold nanorod embedded in a thermoresponsive microgel (AuNR@PNIPMAm) to monitor structural changes in the hydrogel directly near the nanorod surface. By direct comparison of the plasmon response against measurements of the hydrogel structure from dynamic light scattering and nuclear magnetic resonance, we find that the microgel shell of batch-polymerized AuNR@PNIPMAm exhibits a heterogeneous volume phase transition reflected by different onset temperatures for changes in the hydrodyanmic radius (R H ) and plasmon resonance, respectively. The new approach of contrasting plasmonic response (a measure of local surface hydrogel structure) with R H and relaxation times paves a new path to gain valuable insight for the design of plasmonic sensors based on stimuli-responsive hydrogels.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Investigation of plasmon relaxation mechanisms using nonadiabatic molecular dynamics

Hot carriers generated from the decay of plasmon excitation can be harvested to drive a wide range of physical or chemical processes. However, their generation efficiency is limited by the concomitant phonon-induced relaxation processes by which the energy in excited carriers is transformed into heat. However, simulations of dynamics of nanoscale clusters are challenging due to the computational complexity involved. Here, in this paper, we adopt our newly developed Trajectory Surface Hopping (TSH) nonadiabatic molecular dynamics algorithm to simulate plasmon relaxation in Au 20 clusters, taking the atomistic details into account. The electronic properties are treated within the Linear Response Time-Dependent Tight-binding Density Functional Theory (LR-TDDFTB) framework. The relaxation of plasmon due to coupling to phonon modes in Au 20 beyond the Born–Oppenheimer approximation is described by the TSH algorithm. The numerically efficient LR-TDDFTB method allows us to address a dense manifold of excited states to ensure the inclusion of plasmon excitation. Starting from the photoexcited plasmon states in Au 20 cluster, we find that the time constant for relaxation from plasmon excited states to the lowest excited states is about 2.7 ps, mainly resulting from a stepwise decay process caused by low-frequency phonons of the Au 20 cluster. Furthermore, our simulations show that the lifetime of the phonon-induced plasmon dephasing process is ~10.4 fs and that such a swift process can be attributed to the strong nonadiabatic effect in small clusters. Our simulations demonstrate a detailed description of the dynamic processes in nanoclusters, including plasmon excitation, hot carrier generation from plasmon excitation dephasing, and the subsequent phonon-induced relaxation process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Plasmonic nanorod probes’ journey inside plant cells for in vivo SERS sensing and multimodal imaging

Nanoparticle-based platforms are gaining strong interest in plant biology and bioenergy research to monitor and control biological processes in whole plants. However, in vivo monitoring of biomolecules using nanoparticles inside plant cells remains challenging due to the impenetrability of the plant cell wall to nanoparticles beyond the exclusion limits (5-20 nm). To overcome this physical barrier, we have designed unique bimetallic silver-coated gold nanorods (AuNR@Ag) capable of entering plant cells, while conserving key plasmonic properties in the near-infrared (NIR). To demonstrate cellular internalization and tracking of the nanorods inside plant tissue, we used a comprehensive multimodal imaging approach that included transmission electron microscopy (TEM), confocal fluorescence microscopy, two-photon luminescence (TPL), X-ray fluorescence microscopy (XRF), and photoacoustics imaging (PAI). We successfully acquired SERS signals of nanorods in vivo inside plant cells of tobacco leaves. On the same leaf samples, we applied orthogonal imaging methods, TPL and PAI techniques for in vivo imaging of the nanorods. This study first demonstrates the intracellular internalization of AuNR@Ag inside whole plant systems for in vivo SERS analysis in tobacco cells. This work demonstrates the potential of this nanoplatform as a new nanotool for intracellular in vivo biosensing for plant biology.

Cupil-Garcia, Vanessa↗
DOE OSTI2024

Resonance plasmonic coupling: selective enhancement of band edge emission over trap state emission of CdSe quantum dots

The photoluminescence properties of quantum dots (QDs) are often enhanced by eliminating surface trap states through chemical methods. Alternatively, a physical approach is presented here for improving photoluminescence purity in QDs by employing frequency-specific plasmon resonance coupling. Emitter-bound plasmonic hybrids are designed by electrostatically binding negatively charged QDs in water to positively charged gold nanoparticles having a thin polymer coating. Herein, two types of QDs are used: (i) bare CdSe, which exhibits both band edge and trap state emission, and (ii) CdSe overcoated with a ZnS shell (CdSe/ZnS) devoid of trap state emission. Tuning the extinction spectrum of the plasmonic system to match the band edge emission of CdSe enables the selective enhancement of band edge emission over trap state emission. Excellent match in the extinction spectrum of the gold nanoparticle with both, experimentally calculated photoluminescence enhancement factor and theoretically calculated radiative rate enhancement signifies the role of frequency-specific plasmon resonance coupling. Plasmon-coupled photoluminescence of CdSe/ZnS is further investigated by varying the number density of emitter on the surface of plasmonic nanoparticle. An enhancement in the photoluminescence is observed at a lower emitter density of CdSe/ZnS and the photoluminescence enhancement factor closely follows the plasmon resonance. However, photoluminescence quenching occurs with an increase in CdSe/ZnS due to plasmon-assisted nonradiative energy transfer between nearby QDs, as indicated by a red shift in the PL maximum. These studies establish that resonance plasmonic coupling is a convenient physical strategy for tuning the intrinsic photoluminescence properties of QDs for various optoelectronic applications.

Paul, Livin↗
DOE OSTI2021

Ambient Tip-Enhanced Photoluminescence with 5 nm Spatial Resolution

We achieve record spatial resolution in ambient tip-enhanced photoluminescence (TEPL) from CdSe/ZnS semiconductor quantum dots (QDs). Our approach only takes advantage of surface roughness at the apex of a sputtered plasmonic gold probe. When irradiated with visible light (633 and 532 nm lasers), nano-corrugated regions of the apex of an Au tip support 5-nm spatial resolution in TEPL imaging of QD aggregates on silicon. The reproducibility of our observations is illustrated using different plasmonic probes and samples. The origin of the observed near-field contrast, underlying the demonstrated high spatial resolution in TEPL, is discussed in the context of field enhancement at the metal tip-fluorophore interface.

Chemical Dynamics Initiative↗
DOE OSTI2021

Strong Coupling Between Plasmons and Molecular Excitons in Metal–Organic Frameworks

This Letter describes strong coupling of densely packed molecular emitters in metal–organic frameworks (MOFs) and plasmonic nanoparticle (NP) lattices. Porphyrin-derived ligands with small transition dipole moments in an ordered MOF film were grown on Ag NP arrays. Angle-resolved optical measurements of the MOF-NP lattice system showed the formation of a polariton that is lower in energy and does not cross the uncoupled MOF Q 1 band. Modeling predicted the upper polariton energy and a calculated Rabi splitting of 110 meV. The coupling strength was systematically controlled by detuning the plasmon energy by changing the refractive index of the solvents infiltrating the MOF pores. Through transient absorption spectroscopy, we found that the lower polariton decays quickly at shorter time scales (<500 ps) and slowly at longer times because of energy transfer from the upper polariton. Furthermore, this hybrid system demonstrates how MOFs can function as an accessible excitonic material for polariton chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

In-plane plasmon coupling in topological insulator Bi 2 Se 3 thin films

The surface states of the 3D topological insulator (TI), Bi 2 Se 3 , are known to host two-dimensional Dirac plasmon polaritons (DPPs) in the terahertz spectral range. In TI thin films, the DPPs excited on the top and bottom surfaces couple, leading to an acoustic mode and an optical plasmon mode. Vertical coupling in these materials is, therefore, reasonably well-understood, but in-plane coupling among localized TI DPPs has yet to be investigated. In this paper, we demonstrate in-plane DPP coupling in TI stripe arrays and show that they exhibit dipole–dipole type coupling. Here, the coupling becomes negligible when the lattice constant is greater than approximately 2.8 times the stripe width, which is comparable to results for in-plane coupling of localized plasmons excited on metallic nanoparticles or graphene plasmon polaritons. This understanding could be leveraged for the creation of TI-based metasurfaces.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Superconducting coherence peak in near-field radiative heat transfer

Enhancement and peaks in near-field radiative heat transfer (NFRHT) typically arise due to surface phonon-polaritons, plasmon-polaritons, and electromagnetic (EM) modes in structured materials. However, the role of material quantum coherence in enhancing near-field radiative heat transfer remains unexplored. Here, we unravel that NFRHT in superconductor-ferromagnetic systems displays a unique peak at the superconducting phase transition that originates from the quantum coherence of Bogoliubov quasiparticles in superconductors. Our theory takes into account evanescent EM radiation emanating from fluctuating currents related to Cooper pairs and Bogoliubov quasiparticles in stark contrast to the current-current correlations induced by free electrons in conventional materials. Our proposed NFRHT configuration exploits ferromagnetic resonance at frequencies deep inside the superconducting band gap to isolate this superconducting coherence peak. Furthermore, we reveal that Cooper pairs and Bogoliubov quasiparticles have opposite effects on near-field thermal radiation and isolate their effects on many-body radiative heat transfer near superconductors. As a result, our proposed phenomenon can have applications for developing thermal isolators and heat sinks in superconducting circuits.

Dipole approximation↗
DOE OSTI2020

Topological Gaseous Plasmon Polariton in Realistic Plasma

Nontrivial topology in bulk matter has been linked with the existence of topologically protected interfacial states. In this work, we show that a gaseous plasmon polariton (GPP), an electromagnetic surface wave existing at the boundary of magnetized plasma and vacuum, has a topological origin that arises from the nontrivial topology of magnetized plasma. Because a gaseous plasma cannot sustain a sharp interface with discontinuous density, one must consider a gradual density falloff with scale length comparable to or longer than the wavelength of the wave. We show that the GPP may be found within a gapped spectrum in present-day laboratory devices, suggesting that platforms are currently available for experimental investigation of topological wave physics in plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Azimuthal Anchoring Strength in Photopatterned Alignment of a Nematic

Spatially-varying director fields have become an important part of research and development in liquid crystals. Characterization of the anchoring strength associated with a spatially-varying director is difficult, since the methods developed for a uniform alignment are seldom applicable. Here we characterize the strength of azimuthal surface anchoring produced by the photoalignment technique based on plasmonic metamsaks. The measurements used photopatterned arrays of topological point defects of strength +1 and −1 in thin layers of a nematic liquid crystal. The integer-strength defects split into pairs of half-integer defects with lower elastic energy. The separation distance between the split pair is limited by the azimuthal surface anchoring, which allows one to determine the strength of the latter. The strength of the azimuthal anchoring is proportional to the UV exposure time during the photoalignment of the azobenzene layer.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Engineering Directionality in Quantum Dot Shell Lasing Using Plasmonic Lattices

In this paper, we report how the direction of quantum dot (QD) lasing can be engineered by exploiting high-symmetry points in plasmonic nanoparticle (NP) lattices. The nanolaser architecture consists of CdSe-CdS core-shell QD layers conformally coated on two-dimensional square arrays of Ag NPs. Using waveguide-surface lattice resonances (W-SLRs) near the Δ point in the Brillouin zone as optical feedback, we achieved lasing from the gain in CdS shells at off-normal emission angles. Changing the periodicity of the plasmonic lattices enables other high-symmetry points (Γ or M) of the lattice to overlap with the QD shell emission, which facilitates tuning of the lasing direction. We also increased the thickness of the QD layer to introduce higher order W-SLR modes with additional avoided crossings in the band structure, which expands the selection of cavity modes for any desired lasing emission angle.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2026

Quantifying the relationship between electric field enhancement and plasmon-driven electron transfer

Plasmonic materials interact strongly with light to create localized, out-of-equilibrium environments with intense electromagnetic fields known as hotspots. After forming, hotspots dissipate energy into their surroundings and can transfer energy and charge carriers to nearby molecules, giving plasmonic materials the potential to drive reactions with sunlight. However, the field needs a better mechanistic understanding of plasmon–molecule interactions and how the local plasmon environment, specifically the electromagnetic field enhancement and spatial distribution of hotspots, impacts the reaction yield. Here, in this work, we mapped plasmon-driven charge transfer across ordered plasmonic substrates using diffraction-limited surface-enhanced Raman spectroscopy (SERS) microscopy to understand the relationship between the average local electric field enhancement and charge transfer reaction yield. We tracked the plasmon-induced electron transfer to buckminsterfullerene (C 60 ) and found that areas with the greatest SERS intensity were not the areas with the greatest ensemble-averaged reduction of C 60 , suggesting that areas with higher electric field enhancement—or “hotter,” more enhancing hotspots—do not improve the charge transfer reaction yield. This work shows that efforts to improve plasmon-driven charge transfer should not merely focus on creating substrates with extremely enhancing regions but also consider how other factors could optimize photoreduction yields.

Koble, MaKenna M. [Univ. of Minnesota, Minneapolis↗
DOE OSTI2022

Neutrino Emissivities as a Probe of the Internal Magnetic Fields of White Dwarfs

Abstract The evolution of white dwarfs (WDs) depends crucially on thermal processes. The plasma in their core can produce neutrinos that escape from the star, thus contributing to the energy loss. While in the absence of a magnetic field the main cooling mechanism is plasmon decay at high temperature and photon surface emission at low temperature, a large magnetic field in the core hiding beneath the surface even of ordinary WDs, and undetectable to spectropolarimetric measurements, could potentially leave an imprint in the cooling. In this paper, we revisit the contribution to WD cooling stemming from neutrino pair synchrotron radiation and the effects of the magnetic field on plasmon decay. Our key finding is that even if observations limit the magnetic field strength at the stellar surface, magnetic fields in the interior of WDs—with or without a surface magnetic field—can be strong enough to modify the cooling rate, with neutrino pair synchrotron emission being the most important contribution. This effect may not only be relevant for the quantification and interpretation of cooling anomalies, but suggests that the internal magnetic fields of WDs should be smaller than ∼ 6 × 10 11 G, slightly improving bounds coming from a stability requirement. While our simplified treatment of the WD structure implies that further studies are needed to reduce the systematic uncertainties, the estimates based on comparing the emissivities illustrate the potential of neutrino emission as a diagnostic tool to study the interior of WDs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Classical vs. quantum plasmon-induced molecular transformations at metallic nanojunctions

Chemical transformations near plasmonic metals have attracted increasing attention in the past few years. Specifically, reactions occurring within plasmonic nanojunctions that can be detected via surface and tip-enhanced Raman (SER and TER) scattering were the focus of numerous reports. In this context, even though the transition between localized and nonlocal (quantum) plasmons at nanojunctions is documented, its implications on plasmonic chemistry remain poorly understood. We explore the latter through AFM-TER-current measurements. We use two molecules: i) 4-mercaptobenzonitrile (MBN) that reports on the (non)local fields and ii) 4-nitrothiophenol (NTP) that features defined signatures of its neutral/anionic forms and dimer product, 4,4′-dimercaptoazobenzene (DMAB). The transition from classical to quantum plasmons is established through our optical measurements: It is marked by molecular charging and optical rectification. Simultaneously recorded force and current measurements support our assignments. In the case of NTP, we observe the parent and DMAB product beneath the probe in the classical regime. Further reducing the gap leads to the collapse of DMAB to form NTP anions. The process is reversible: Anions subsequently recombine into DMAB. Our results have significant implications for AFM-based TER measurements and their analysis, beyond the scope of this work. In effect, when precise control over the junction is not possible (e.g., in SER and ambient TER), both classical and quantum plasmons need to be considered in the analysis of plasmonic reactions

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

Switchable planar chirality and spin texture in highly ordered ferroelectric hybrid perovskite domains

Chiral organic-inorganic hybrid perovskites offer a promising platform for developing non-linear chiro-optical applications and chiral-induced spin selectivity. Here, we show that achiral hybrid perovskites that have highly ordered ferroelectric domains with orthogonal polarization exhibit planar chirality, as manifested by second harmonic generation with strong circular dichroism. Interestingly, the handedness of the second harmonic generation circular dichroism response can be alternatingly switched between orthogonally polarized domains and domain walls. To correlate the origin of planar chirality in these domains, atom-resolved atomic force microscopy is used to reveal distinct arrangements of atomic rows in these ferroelectric crystals that indicate planar symmetry breaking. Remarkably, a large SHG anisotropy factor of 0.41 is measured at the domain wall. Additionally, spatially resolved two-photon photoluminescence excitation measurement provide evidence of larger Rashba spin-splitting in these chiral ferroelectric domains compared to domain-free areas. Our discoveries of domain-dependent planar chirality and spin texture hold great promise for advancement of domain-specific chiro-optical applications.

36 MATERIALS SCIENCE↗
NASA NTRSDate not supplied

Spoof Plasmon Polaritons for NDE Applications an Experimental Demonstration

NASA is exploring the use of microwave spoof plasmon polaritons to detect defects in metallic structures. This work investigates the detection of simulated defects in the form of aluminum wires as small as 1.6 mm diameter and 2mm long that are placed in a grooved aluminum test article. The inclusions simulate manufacturing defects, and the sum of the delta impedance is shown to increase with increasing volume of added metal. A threshold value of 50Ω has been proposed for defect detection. In addition to detecting defects, the technique also estimates the volume of the defect.

Microwave↗
NASA NTRSDate not supplied

Spoof Plasmon Sensing for NDE Application

NASA is exploring the use of microwave spoof plasmon polaritons to detect defects in metallic structures. This work investigates the detection of simulated defects in the form of aluminum wires as small as 1.6 mm diameter and 2 mm long that are placed in a grooved aluminum test article. The inclusions simulate manufacturing defects, and the sum of the delta impedance is shown to increase with increasing volume of added metal. Based on the results, a threshold value of 50Ω has been proposed for defect detection. In addition to detecting defects, the technique also estimates the volume of the defect.

Microwave↗
NASA NTRS1987

Surface characterization in composite and titanium bonding: Carbon fiber surface treatments for improved adhesion to thermoplastic polymers

The effect of anodization in NaOH, H2SO4, and amine salts on the surface chemistry of carbon fibers was examined by X-ray photoelectron spectroscopy (XPS). The surfaces of carbon fibers after anodization in NaOH and H2SO4 were examined by scanning transmission electron microscopy (STEM), angular dependent XPS, UV absorption spectroscopy of the anodization bath, secondary ion mass spectrometry, and polar/dispersive surface energy analysis. Hercules AS-4, Dexter Hysol XAS, and Union Carbide T-300 fibers were examined by STEM, angular dependent XPS, and breaking strength measurement before and after commercial surface treatment. Oxygen and nitrogen were added to the fiber surfaces by anodization in amine salts. Analysis of the plasmon peak in the carbon 1s signal indicated that H2SO4 anodization affected the morphological structure of the carbon fiber surface. The work of adhesion of carbon fibers to thermoplastic resins was calculated using the geometric mean relationship. A correlation was observed between the dispersive component of the work of adhesion and the interfacial adhesion.

Devilbiss, T. A.↗