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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Strong-Field Control of Plasmonic Properties in Core–Shell Nanoparticles

Utilization of the plasmonic response in nanosystems is a key component of nanophotonics that is typically altered by varying the incident optical frequency or the material configuration. However, in this work we demonstrate that employing intense, femtosecond laser fields unlock nonlinear light–matter interactions such that precise control of the optical response is achieved solely by adjusting the incident intensity. The plasmonic properties of Au/SiO 2 nanoshells are manipulated by exploiting the nonlinear index of refraction of gold and experimentally observed by employing photoelectrons emitted during the interaction as a sensitive, sub-wavelength probe. A striking transition seen in the photoelectron energy spectrum between the weak and strong-field regime is verified by a modified Mie theory simulation that incorporates the nonlinear dielectric nanoshell response. The exhibited intensity-dependent optical control of the plasmonic response in prototypical core–shell nanoparticles paves the way toward ultrafast switching and opto-electronic signal modulation with more complex nanostructures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Purcell-enhanced quantum yield from carbon nanotube excitons coupled to plasmonic nanocavities

Single-walled carbon nanotubes (SWCNTs) are promising absorbers and emitters to enable novel photonic applications and devices but are also known to suffer from low optical quantum yields. Here we demonstrate SWCNT excitons coupled to plasmonic nanocavity arrays reaching deeply into the Purcell regime with Purcell factors (F P ) up to F P = 180 (average F P = 57), Purcell-enhanced quantum yields of 62% (average 42%), and a photon emission rate of 15 MHz into the first lens. The cavity coupling is quasi-deterministic since the photophysical properties of every SWCNT are enhanced by at least one order of magnitude. Furthermore, the measured ultra-narrow exciton linewidth (18 ueV) reaches the radiative lifetime limit, which is promising towards generation of transform-limited single photons. Furthermore, to demonstrate utility beyond quantum light sources we show that nanocavity-coupled SWCNTs perform as single-molecule thermometers detecting plasmonically induced heat at cryogenic temperatures in a unique interplay of excitons, phonons, and plasmons at the nanoscale.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Slow light in a 2D semiconductor plasmonic structure

Spectrally narrow optical resonances can be used to generate slow light, i.e., a large reduction in the group velocity. In a previous work, we developed hybrid 2D semiconductor plasmonic structures, which consist of propagating optical frequency surface-plasmon polaritons interacting with excitons in a semiconductor monolayer. Here, we use coupled exciton-surface plasmon polaritons (E-SPPs) in monolayer WSe 2 to demonstrate slow light with a 1300 fold decrease of the SPP group velocity. Specifically, we use a high resolution two-color laser technique where the nonlinear E-SPP response gives rise to ultra-narrow coherent population oscillation (CPO) resonances, resulting in a group velocity on order of 105 m/s. Our work paves the way toward on-chip actively switched delay lines and optical buffers that utilize 2D semiconductors as active elements.

42 ENGINEERING↗
DOE OSTI2023

Plasmon mediated coherent population oscillations in molecular aggregates

The strong coherent coupling of quantum emitters to vacuum fluctuations of the light field offers opportunities for manipulating the optical and transport properties of nanomaterials, with potential applications ranging from ultrasensitive all-optical switching to creating polariton condensates. Often, ubiquitous decoherence processes at ambient conditions limit these couplings to such short time scales that the quantum dynamics of the interacting system remains elusive. Prominent examples are strongly coupled exciton-plasmon systems, which, so far, have mostly been investigated by linear optical spectroscopy. Here, we use ultrafast two-dimensional electronic spectroscopy to probe the quantum dynamics of J-aggregate excitons collectively coupled to the spatially structured plasmonic fields of a gold nanoslit array. We observe rich coherent Rabi oscillation dynamics reflecting a plasmon-driven coherent exciton population transfer over mesoscopic distances at room temperature. This opens up new opportunities to manipulate the coherent transport of matter excitations by coupling to vacuum fields.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2023

Observation of hydrodynamic plasmons and energy waves in graphene

Thermally excited electrons and holes form a quantum-critical Dirac fluid in ultraclean graphene and their electrodynamic responses are described by a universal hydrodynamic theory. The hydrodynamic Dirac fluid can host intriguing collective excitations distinctively different from those in a Fermi liquid. Here we report the observation of the hydrodynamic plasmon and energy wave in ultraclean graphene. In this study, we use the on-chip terahertz (THz) spectroscopy technique to measure the THz absorption spectra of a graphene microribbon as well as the propagation of the energy wave in graphene close to charge neutrality. We observe a prominent high-frequency hydrodynamic bipolar-plasmon resonance and a weaker low-frequency energy-wave resonance of the Dirac fluid in ultraclean graphene. The hydrodynamic bipolar plasmon is characterized by the antiphase oscillation of massless electrons and holes in graphene. The hydrodynamic energy wave is an electron-hole sound mode with both charge carriers oscillating in phase and moving together. The spatial–temporal imaging technique shows that the energy wave propagates at a characteristic speed of $V_f$ / $ \sqrt2$ near the charge neutrality. Our observations open new opportunities to explore collective hydrodynamic excitations in graphene systems.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structural color printing based on plasmonic metasurfaces of perfect light absorption

Subwavelength structural color filtering and printing technologies employing plasmonic nanostructures have recently been recognized as an important and beneficial complement to the traditional colorant-based pigmentation. However, the color saturation, brightness and incident angle tolerance of structural color printing need to be improved to meet the application requirement. Here we demonstrate a structural color printing method based on plasmonic metasurfaces of perfect light absorption to improve color performances such as saturation and brightness. Thin-layer perfect absorbers with periodic hole arrays are designed at visible frequencies and the absorption peaks are tuned by simply adjusting the hole size and periodicity. Near perfect light absorption with high quality factors are obtained to realize high-resolution, angle-insensitive plasmonic color printing with high color saturation and brightness. Moreover, the fabricated metasurfaces can be protected with a protective coating for ambient use without degrading performances. The demonstrated structural color printing platform offers great potential for applications ranging from security marking to information storage.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Plasmons in graphene on uniaxial substrates

Placing graphene on uniaxial substrates may have interesting application potential for graphene-based photonic and optoelectronic devices. Here, we analytically derive the dispersion relation for graphene plasmons on uniaxial substrates and discuss their momentum, propagation length, and polarization as a function of frequency, propagation direction, and both ordinary and extraordinary dielectric permittivities of the substrate. We find that the plasmons exhibit an anisotropic propagation, yielding radially asymmetric field patterns when a point emitter launches plasmons in the graphene layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Simulations of the spontaneous emission of a quantum dot near a gap plasmon waveguide

In this paper, we modeled a quantum dot at near proximity to a gap plasmon waveguide to study the quantum dot-plasmon interactions. Assuming that the waveguide is single mode, this paper is concerned about the dependence of spontaneous emission rate of the quantum dot on waveguide dimensions such as width and height. We compare coupling efficiency of a gap waveguide with symmetric configuration and asymmetric configuration illustrating that symmetric waveguide has a better coupling efficiency to the quantum dot. We also demonstrate that optimally placed quantum dot near a symmetric waveguide with 50 nm × 50 nm cross section can capture 80% of the spontaneous emission into a guided plasmon mode.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Laser-ablative engineering of phase singularities in plasmonic metamaterial arrays for biosensing applications

By using methods of laser-induced transfer combined with nanoparticle lithography, we design and fabricate large-area gold nanoparticle-based metamaterial arrays exhibiting extreme Heaviside-like phase jumps in reflected light due to a strong diffractive coupling of localized plasmons. When employed in sensing schemes, these phase singularities provide the sensitivity of 5 × 10{sup 4} deg. of phase shift per refractive index unit change that is comparable with best values reported for plasmonic biosensors. The implementation of sensor platforms on the basis of such metamaterial arrays promises a drastic improvement of sensitivity and cost efficiency of plasmonic biosensing devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

High-Q band edge mode of plasmonic crystals studied by cathodoluminescence

We have investigated the quality factor (Q-factor) of the band edge modes in the plasmonic crystal by a cathodoluminescence technique. We have found that the Q-factor at the Γ point depends on the terrace width (D)/period (P) ratio of the plasmonic crystal. The finite-difference time-domain methods predict that the band edge mode at D/P = 3/4 has a high-Q-factor (Q ∼ 250 by Palik's permittivity data and Q ∼ 530 by Johnson and Christy's data). The beam-scan spectral images allowed us to visualize the standing surface plasmon polariton waves at the band edge energies, and a high-Q-factor of ∼200 was observed at D/P ∼ 3/4.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Regular arrays of Al nanoparticles for plasmonic applications

Optical properties of aluminium nanoparticles deposited on glass substrates are investigated. Laser interference lithography allows a quick deposition of regular, highly periodic arrays of nanostructures with different sizes and distances in order to investigate the shift of the surface plasmon resonance for, e.g., photovoltaic, plasmonic or photonic applications. The variation of the diameter of cylindrical Al nanoparticles exhibits a nearly linear shift of the surface plasmon resonance between 400 nm and 950 nm that is independent from the polarization vector of the incident light. Furthermore, particles with quadratic or elliptic base areas are presented exhibiting more complex and polarization vector dependent transmission spectra.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

ZnO/Ag composite nanorod arrays for surface-plasmon-enhanced emission study

The surface plasmon resonance enhanced emission through coupling of surface plasmons and exciton band energies is studied in hybrid ZnO/Ag nanostructure. The catalytic growth of ZnO nanorods is controlled in seed mediated growth by altering size distribution of Ag nanoislands. X-ray diffraction shows a predominant (002) crystal plane confirming the preferential growth of ZnO nanorods on as-deposited Ag. Increase of surface roughness in Ag film by post deposition annealing process enhances the light emission due to momentum matching between surface plasmons and excitons as well as a red shift of 32 meV occurs due to multi phonon and phonon-exciton interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Systematic approach of nanoparticle design to enhance the broadband plasmonic scattering effect

To overcome low conversion efficiency of thin film solar cells, using the localized surface plasmon effect caused by the interaction between the incident beam and metallic nanoparticles inserted in or on the absorbing layer can be a promising alternative to overcome the low efficiency problem. Detail shape and size of nanoparticles are directly related with the localized surface plasmon effect as well as optical properties; however, their detail shape and size are hard to be determined depending only on the theoretical or experimental approach. Therefore, the method focusing on defining structural boundaries would be a useful method for nano or microscale design to generate simple and clear shape. In this study, we adopted the structural optimization scheme based on the phase field method to determine the optimal shape of a silver (Ag) nanoparticle positioned on the upper surface of the absorbing layer. We carried out the design process for broadband wavelength to be taken into account and verified the plasmonic scattering effect enhancement in the absorbing layer by numerical simulations.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2014

Plasmon-polariton and ⟨n⟨ = 0 non-Bragg gaps in 1D Cantor photonic superlattices

We have used the transfer-matrix approach for one-dimensional Cantor photonic superlattices, and studied the plasmon-polariton modes for a multilayered system composed by alternating layers of positive and dispersive materials. Results indicate that the corresponding plasmon-polariton modes, which show up for oblique incidence, strongly depend on the Cantor step, and the plasmon-polariton subbands are associated with the number of metamaterial layers contained in the elementary cell. Moreover, we have studied the ⟨n⟩ = 0 non-Bragg gap in such fractal photonic superlattices and characterized its behavior as function of the steps of the Cantor series.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Role of electron carriers on local surface plasmon resonances in doped oxide semiconductor nanocrystals

Optical properties of carrier-dependent local surface plasmons (LSPs) were studied using dopant-controlled In{sub 2}O{sub 3}:Sn nanocrystals (NCs). From a systematic correlation between LSP excitations and electron carriers, electron-impurity scattering contributed towards plasmon damping as one of a factor that is absent in metal NCs. A threshold electron density (n{sub e}) from a damping dominated regime to a quenched damping regime appeared at around 10{sup 20} cm{sup −3}. The validity of Mie theory failed in ITO NCs with high n{sub e} greater than 10{sup 20} cm{sup −3} since the role of electron carriers could enhance LSPs with simultaneous damped plasmonic excitations, which is valuable information for optical applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Tuning the interaction between propagating and localized surface plasmons for surface enhanced Raman scattering in water for biomedical and environmental applications

With a view to biomedical and environmental applications, we investigate the plasmonic properties of a rectangular gold nanodisk array in water to boost surface enhanced Raman scattering (SERS) effects. To control the resonance wavelengths of the surface plasmon polariton and the localized surface plasmon, their dependence on the array period and diameter in water is studied in detail using a finite difference time domain method. A good agreement is obtained between calculated resonant wavelengths and those of gold nanodisk arrays fabricated using electron beam lithography. For the optimized structure, a SERS enhancement factor of 7.8 × 10{sup 7} is achieved in water experimentally.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Cylindrical vector beams of light from an electrically excited plasmonic lens

The production of cylindrical vector beams from a low-energy, electric, microscale light source is demonstrated both experimentally and theoretically. This is achieved by combining a “plasmonic lens” with the ability to locally and electrically excite propagating surface plasmons on gold films. The plasmonic lens consists of concentric circular subwavelength slits that are etched in a thick gold film. The local excitation arises from the inelastic tunneling of electrons from the tip of a scanning tunneling microscope. We report on the emission of radially polarized beams with an angular divergence of less than ±4°.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Positional control of plasmonic fields and electron emission

We report the positional control of plasmonic fields and electron emission in a continuous gap antenna structure of sub-micron size. We show experimentally that a nanoscale area of plasmon-enhanced electron emission can be motioned by changing the polarization of an exciting optical beam of 800 nm wavelength. Finite-difference calculations are presented to support the experiments and to show that the plasmon-enhanced electric field distribution of the antenna can be motioned precisely and predictively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗