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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Role of higher order plasmonic modes in one-dimensional nanogratings

By theoretically investigating the optical behavior of one-dimensional gold nanogratings using Fourier Modal Method, we have shown that both integer and non-integer multiples of surface plasmon polariton wavelengths should be taken into consideration in special optical contrast ratio for highly sensitive sensing. The emergence of higher modes is the key factor for the formation of observed plasmonic band gap. Through considering the significant role of grating period and thickness respectively in horizontal and vertical surface resonances, it was demonstrated that for gold thicknesses below 100 nm, the dominant phenomenon is horizontal surface resonances while for increased thicknesses both horizontal and vertical surface resonances mediate. The transmission minima are insensitive to the grating thickness, which confirms that their origins are not vertical surface resonances. This study can open an avenue towards designing highly sensitive sensors with focus not only on the plasmonic resonance wavelength but also on its integer and non-integer multiples whose origins should be investigated in both horizontal and vertical surface resonances.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

A 2 × 1 all-optical multiplexer using Kerr nonlinear nano-plasmonic switch

In this paper, a novel surface plasmon polariton based 2 × 1 multiplexer, which is based on an adder module and an all-optical controllable nano-plasmonic switching module is presented. It is shown that by applying a pump light, the transmissions of the input signals into the output waveguide can be controlled. The operation of the proposed device is investigated through the use of coupled-mode theory and finite-difference time-domain method. In the proposed adder module, the transmissions of the input signals at the working wavelengths are about 0.7. Based on the simulation results, by applying a pump light intensity of 150 KW/cm{sup 2} the transmissions of input signals alter with the extinction ratio of 22.04 dB, which shows a significant switching effect. For a pump light intensity of 150 KW/cm{sup 2} the switching times of input signals are measured about 560 fs. It is expected that the proposed 2 × 1 multiplexer can be used in all-optical signal processing, nano-plasmonic circuits, communication, etc.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

A Time-Dependent Density Functional Theory Study of the Impact of Ligand Passivation on the Plasmonic Behavior of Ag Nanoclusters

We present a detailed study of the impact of ligand passivation on the electronic structures and optical properties of plasmonic Ag nanoclusters using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The clusters studied are A g 13 5 + , A g 25 S H 18 - , A g 25 N H 2 18 - , A g 32 14 + , and A g 44 S H 30 4 - . We find that the highest occupied ligand orbitals from S (3p) and N (2p) appear just above the conduction band, and this leads to significant ligand-to-metal charge transfer transitions at high energies. Dielectric screening associated with ligand passivation results in reduced HOMO–LUMO gaps and in an increased gap between the HOMO and the valence band associated with the Ag 4d orbitals. Ligand field effects result in splitting of plasmonic peaks, leading to reduced mixing between nearby single-particle excitations. The magnitude of these effects is found to decrease when thiolate ligands are replaced with amine ligands. We also find that, in the case of the A g 44 S H 30 4 - cluster, the ligands localize plasmonic excitations into the core of the cluster.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Electric-field-induced plasmon in AA-stacked bilayer graphene

The collective excitations in AA-stacked bilayer graphene for a perpendicular electric field are investigated analytically within the tight-binding model and the random-phase approximation. Such a field destroys the uniform probability distribution of the four sublattices. This drives a symmetry breaking between the intralayer and interlayer polarization intensities from the intrapair band excitations. A field-induced acoustic plasmon thus emerges in addition to the strongly field-tunable intrinsic acoustic and optical plasmons. At long wavelengths, the three modes show different dispersions and field dependence. The definite physical mechanism of the electrically inducible and tunable mode can be expected to also be present in other AA-stacked few-layer graphenes. -- Highlights: •The analytical derivations are performed by the tight-binding model. •An electric field drives the non-uniformity of the charge distribution. •A symmetry breaking between the intralayer and interlayer polarizations is illustrated. •An extra plasmon emerges besides two intrinsic modes in AA-stacked bilayer graphene. •The mechanism of a field-induced mode is present in AA-stacked few-layer graphenes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Plasmonic Ag/Ag2O nanoparticles anchored needle-like Bi2O3 as an efficient visible-light-driven nanocomposite photocatalyst

Highlights: • Deposition of plasmonic Ag/Ag{sub 2}O NPs on the surface of Bi{sub 2}O{sub 3}. • Synthesis of Ag/Ag{sub 2}O@Bi{sub 2}O{sub 3} by thermal-assisted precipitation. • SPR of Ag enhances use of solar energy and transfer of carriers. • Degradation of Reactive Black 5 by CCD model. - Abstract: In this study, a thermal-assisted precipitation method was applied for the uniform deposition of plasmonic Ag/Ag{sub 2}O nanoparticles on the surface of needle-like Bi{sub 2}O{sub 3} to synthesis Ag/Ag{sub 2}O@Bi{sub 2}O{sub 3} nanocomposite. The synthesized nanocomposite was characterized by different techniques including UV–vis spectrophotometry, X-ray diffraction (XRD), scanning electronic microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray mapping, and photoluminescence (PL). The visible-light-driven photocatalytic activities of Ag{sub 2}O@Bi{sub 2}O{sub 3} and Ag/Ag{sub 2}O@Bi{sub 2}O{sub 3} were evaluated on photo-degradation of Reactive Black 5 (RB 5) dye as model pollutant. The effect of process variables including the initial dye concentration, reaction time, and pH on the photo-degradation of RB 5 was studied by Central Composite Design (CCD) methodology. It was found that the photo-degradation rate of Ag/Ag{sub 2}O@Bi{sub 2}O{sub 3} was higher than that of the Ag{sub 2}O@Bi{sub 2}O{sub 3} and Bi{sub 2}O{sub 3}. The highly efficient photocatalytic activity of Ag/Ag{sub 2}O@Bi{sub 2}O{sub 3} nanocomposite is mainly ascribed to enhancing photogenerated electron-hole separation and the surface plasmon resonance (SPR) influence of silver-based nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Surface-plasmon enhanced photoemission of a silver nano-patterned photocathode

Here, nano-patterned photocathodes (NPC) take advantage of plasmonic effects to resonantly increase absorption of light and localize electromagnetic field intensity on metal surfaces leading to surface-plasmon enhanced photoemission. In this paper, we report the status of NPC research at UCLA including in particular the optimization of the dimensions of a nanohole array on a silver wafer to enhance plasmonic response at 800 nm light, the development of a spectrally-resolved reflectivity measurement setup for quick nanopattern validation, and of a novel cathode plug to enable high power tests of NPCs on single crystal substrates in a high gradient radiofrequency gun.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Theory of Plasmonic Hot-Carrier Generation and Relaxation

Hot-carrier (HC) generation from (localized) surface plasmon decay has recently attracted much attention due to its promising applications in physical, chemical, materials, and energy science. However, the detailed mechanisms of plasmonic HC generation, relaxation, and trapping are less studied. In this work, we developed and applied a quantum-mechanical model and coupled master equation method to study the generation of HCs from plasmon decay and their following relaxation processes with different mechanisms treated on equal footing. First, a quantum-mechanical model for HC generation is developed. Its connection to existing semiclassical models and time-dependent density functional theory (TDDFT) is discussed. Second, the relaxation and lifetimes of HCs are investigated in the presence of electron–electron and electron–phonon interactions. A GW-like approximation is introduced to account for the electron–electron scattering. The numerical simulations on the Jellium nanoparticles with a size up to 1.6 nm demonstrate the electron–electron scattering and electron–phonon scattering dominate different time scale in the relaxation dynamics. We also generalize the model to study the extraction of HCs to attached molecules. The quantum yield of extracting HCs for other applications is found to be size-dependent. In general, the smaller size of NP improves the quantum yield, which is in agreement with recent experimental measurements. Even though we demonstrate this newly developed theoretical formalism with Jellium model, the theory applies to any other atomistic models.

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

Visualization of Plasmonic Couplings Using Ultrafast Electron Microscopy

Hybrids of graphene and metal plasmonic nanostructures are promising building blocks for applications in optoelectronics, surface-enhanced scattering, biosensing, and quantum information. An understanding of the coupling mechanism in these hybrid systems is of vital importance to its applications. Previous efforts in this field mainly focused on spectroscopic studies of strong coupling within the hybrids with no spatial resolution. In this study, we report direct imaging of the local plasmonic coupling between single Au nanocapsules and graphene step edges at the nanometer scale by photon-induced near-field electron microscopy in an ultrafast electron microscope for the first time. The proximity of a step in the graphene to the nanocapsule causes asymmetric surface charge density at the ends of the nanocapsules. Computational electromagnetic simulations confirm the experimental observations. The results reported here indicate that this hybrid system could be used to manipulate the localized electromagnetic field on the nanoscale, enabling promising future plasmonic devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

How Light Is Emitted by Plasmonic Metals

The mechanism by which light is emitted from plasmonic metals such as gold and silver has been contentious, particularly at photon energies below direct interband transitions. Using nanoscale plasmonic cavities, blue-pumped light emission is discovered to directly track dark-field scattering on individual nanoconstructs. By exploiting slow atomic-scale restructuring of the nanocavity facets to spectrally tune the dominant gap plasmons, this correlation can be measured from 600 to 900 nm in gold, silver, and mixed constructs ranging from spherical to cube nanoparticles-on-mirror. We demonstrate that prompt electronic Raman scattering is responsible and confirm that “photoluminescence”, which implies phase and energy relaxation, is not the right description. Our model indicates how to maximize light emission from metals.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Differential Wavevector Distribution of Surface-Enhanced Raman Scattering and Fluorescence in a Film-Coupled Plasmonic Nanowire Cavity

Here, we report on the experimental observation of differential wavevector distribution of surface-enhanced Raman scattering (SERS) and fluorescence from dye molecules confined to a gap between plasmonic silver nanowire and a thin, gold mirror. The fluorescence was mainly confined to higher values of in-plane wavevectors, whereas SERS signal was uniformly distributed along all the wavevectors. The optical energy momentum spectra from the distal end of the nanowire revealed strong polarization dependence of this differentiation. All these observations were corroborated by full-wave three-dimensional numerical simulations, which further revealed an interesting connection between out-coupled wavevectors and parameters such as hybridized modes in the gap-plasmon cavity, and orientation and location of molecular dipoles in the geometry. Our results reveal a new prospect of discriminating electronic and vibrational transitions in resonant dye molecules using a subwavelength gap plasmonic cavity in the continuous-wave excitation limit, and can be further harnessed to engineer molecular radiative relaxation processes in momentum space.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Self-assembly of Janus Dumbbell Nanocrystals and Their Enhanced Surface Plasmon Resonance

Self-assembly is a critical process that can greatly expand the existing structures and lead to new functionality of nanoparticle systems. Multicomponent superstructures self-assembled from nanocrystals have shown promise as multifunctional materials for various applications. Despite recent progress in assembly of homogeneous nanocrystals, synthesis and self-assembly of Janus nanocrystals with contrasting surface chemistry remains a significant challenge. Herein, we designed a novel Janus nanocrystal platform to control the self-assembly of nanoparticles in aqueous solutions by balancing the hydrophobic and hydrophilic moieties. A series of superstructures have been assembled by systematically varying the Janus balance and assembly conditions. Janus Au–Fe 3 O 4 dumbbell nanocrystals (<20 nm) were synthesized with the hydrophobic ligands coated on the Au lobe and negatively charged hydrophilic ligands coated on the Fe 3 O 4 lobe. We systematically fine-tune the lobe size ratio, surface coating, external conditions, and even additional growth of Au nanocrystal domains on the Au lobe of dumbbell nanoparticles (Au–Au–Fe 3 O 4 ) to harvest self-assembly structures including clusters, chains, vesicles, and capsules. It was discovered that in all these assemblies the hydrophobic Au lobes preferred to stay together. In addition, these superstructures clearly demonstrated different levels of enhanced surface plasmon resonance that is directly correlated with the Au coupling in the assembly structure. The strong interparticle plasmonic coupling displayed a red-shift in surface plasmon resonance, with larger structures formed by Au–Au–Fe 3 O 4 assembly extending into the near-infrared region. Self-assembly of Janus dumbbell nanocrystals can also be reversible under different pH values. In conclusion, the biphasic Janus dumbbell nanocrystals offer a platform for studying the novel interparticle coupling and open up opportunities in applications including sensing, disease diagnoses, and therapy.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Tailored Plasmons in Pentacene/Graphene Heterostructures with Interlayer Electron Transfer

van der Waals (vdW) heterostructures, which are produced by the precise assemblies of varieties of two-dimensional (2D) materials, have demonstrated many novel properties and functionalities. Here we report a nanoplasmonic study of vdW heterostructures that were produced by depositing ordered molecular layers of pentacene on top of graphene. We find through nanoinfrared (IR) imaging that surface plasmons formed due to the collective oscillations of Dirac Fermions in graphene are highly sensitive to the adjacent pentacene layers. In particular, the plasmon wavelength declines systematically but nonlinearly with increasing pentacene thickness. Further analysis and density functional theory (DFT) calculations indicate that the observed peculiar thickness dependence is mainly due to the tunneling-type electron transfer from pentacene to graphene. Here, our work unveils a new method for tailoring graphene plasmons and deepens our understanding of the intriguing nano-optical phenomena due to interlayer couplings in novel vdW heterostructures.

42 ENGINEERING↗
DOE OSTI2019

Dynamic Tuning of Gap Plasmon Resonances Using a Solid-State Electrochromic Device

Plasmonic antennas and metasurfaces can effectively control light–matter interactions, and this facilitates a deterministic design of optical materials properties, including structural color. However, these optical properties are generally fixed after synthesis and fabrication, while many modern-day optics applications require active, low-power, and nonvolatile tuning. These needs have spurred broad research activities aimed at identifying materials and resonant structures capable of achieving large, dynamic changes in optical properties, especially in the challenging visible spectral range. In this work, we demonstrate dynamic tuning of polarization-dependent gap plasmon resonators that contain the electrochromic oxide WO 3 . Its refractive index in the visible changes continuously from n = 2.1 to 1.9 upon electrochemical lithium insertion and removal in a solid-state device. By incorporating WO 3 into a gap plasmon resonator, the resonant wavelength can be shifted continuously and reversibly by up to 58 nm with less than 2 V electrochemical bias voltage. Lastly, the resonator can remain in a tuned state for tens of minutes under open circuit conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Microscopic Theory of Plasmons in Substrate-Supported Borophene

Here, we compute the dielectric properties of freestanding and metal-supported borophene from first-principles time-dependent density functional theory. We find that both the low- and high-energy plasmons of borophene are fully quenched by the presence of a metallic substrate at borophene–metal distances smaller than ≃9 Å. Based on these findings, we derive an electrodynamic model of the interacting, momentum-dependent polarizability for a two-dimensional metal on a model metallic substrate, which quantitatively captures the evolution of the dielectric properties of borophene as a function of metal–borophene distance. Applying this model to a series of metallic substrates, we show that maximizing the plasmon energy detuning between borophene and substrate is the key material descriptor for plasmonic performance.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Less is More: Improved Thermal Stability and Plasmonic Response in Au Films via the Use of SubNanometer Ti Adhesion Layers

The use of a metallic adhesion layer is known to increase the thermo-mechanical stability of Au thin films against solid-state dewetting, but in turn results in damping of the plasmonic response, reducing their utility in applications such as heat-assisted magnetic recording (HAMR). In this work, 50 nm Au films with Ti adhesion layers ranging in thickness from 0 to 5 nm were fabricated, and their thermal stability, electrical resistivity, and plasmonic response were measured. Subnanometer adhesion layers are demonstrated to significantly increase the stability of the thin films against dewetting at elevated temperatures (>200 °C), compared to more commonly used adhesion layer thicknesses that are in the range of 2-5 nm. For adhesion layers thicker than 1 nm, the diffusion of excess Ti through Au grain boundaries and subsequent oxidation was determined to result in degradation of the film. This mechanism was confirmed using transmission electron microscopy and X-ray photoelectron spectroscopy on annealed 0.5 and 5 nm adhesion layer samples. The superiority of subnanometer adhesion layers was further demonstrated through measurements of the surface-plasmon polariton resonance; those with thinner adhesion layers possessed both a stronger and spectrally sharper resonance. Furthermore, these results have relevance beyond HAMR to all Ti/Au systems operating at elevated temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Tuning Gold Nanoparticle Size with Fixed Interparticle Spacing in Large-Scale Arrays: Implications for Plasmonics and Nanoparticle Etching Masks

Gold nanoparticles play an important role in plasmonic arrays, including, but not limited to, photovoltaic, biomedical, sensing, optical, and catalytic applications. For plasmonic arrays, control over spatial variables of the array, such as nanoparticle size and spacing, must be judiciously cared for. In this work, we present here a multistep deposit/dewet process for nanoparticle ensemble fabrication that exploits thermally driven solid-state diffusional dewetting, coupled with Ostwald ripening, to tune the nanoparticle size or area coverage for a particular particle–particle spacing. The initial dewetting process defines the spatial period of the array, with subsequent dewetting steps growing the nanoparticles while adhering to the “seeded” period from the first dewetting. Following the fifth deposit/dewet cycle, relative to the first cycle, the mean nanoparticle height exhibited a percent increase of 90 and 66% for 5 and 7.5 nm multistep deposit/dewet processes, respectively, while minimally impacting the ensemble period. This provides unprecedented control over the spatial parameters of large-scale nanoparticle ensembles for plasmonic and etching-mask applications where a particular particle size and spacing are desired. Due to the simplicity of the technique and its area scalability, the cyclic deposition/dewetting process is shown here to be a method that can be easily scaled up to apply to large-area (up to meter-size) applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Enhanced Tunability of Gold Nanoparticle Size, Spacing, and Shape for Large-Scale Plasmonic Arrays

Gold nanoparticles are important constituents in plasmonic arrays, lending themselves to electronic, optical, biomedical, sensing, and catalytic applications, among numerous others. Process variables that must be controlled when engineering plasmonic nanoparticle ensembles include nanoparticle size, shape, and spatial distribution on surfaces. The challenge in generating arrays of nanoparticles with control over these three parameters increases dramatically as spatial requirements for uniformity extend to larger processing areas. In this paper, we present a procedure that exploits thermally driven solid-state diffusional dewetting to yield considerable flexibility in generating ensembles of gold nanoparticles. Such submelting dewetting introduces fine control over particle spatial features that are currently difficult to achieve through conventional methods of generating nanoparticle arrays. Because of the simplicity of the process and its area-scalability, solid-state diffusional dewetting is shown here to be a method that could be easily scaled up to apply to large-area plasmonic fabrication processes.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Plasmon-Enhanced Greenhouse Selectivity for High-Temperature Solar Thermal Energy Conversion

The greenhouse effect arises when thermal radiation is forced to undergo absorption and re-emission many times before escaping, while sunlight transmits largely unimpeded. Although this effect is responsible for global warming, it is generally weak in solid-state materials because radiation can be easily overpowered by other modes of heat transfer. Here, we report on the use of infrared plasmonic nanoparticles to enhance the greenhouse effect in transparent mesoporous materials. Local surface plasmon resonances in transparent conducting oxide nanoparticles (TCO NPs) selectively shorten the mean free path of thermal photons while maintaining high solar transmittance. The addition of a small amount of TCO NPs (<0.1% by volume) nearly halves the heat losses at 700 °C. This leads to an experimentally demonstrated effective thermal emittance of ~0.17 at 700 °C, which is the lowest reported value to date, among all selective surfaces and transparent insulating materials measured at 650 °C or above. Furthermore, our results show that plasmon-enhanced greenhouse selectivity (PEGS) is a promising mechanism for spectral control of radiative heat transfer, and more specifically, for conversion of minimally concentrated sunlight into high-temperature heat.

14 SOLAR ENERGY↗