Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “surface plasmons”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Effective Modulation of Interlayer Excitons in WSe 2 /WS 2 Heterostructures by Plasmon–Exciton Interaction

Effective charge transfer and carrier separation at the interface are paramount for optimizing the performance of devices based on van der Waals heterostructures. In this investigation, surface plasmons generated by gold nanoparticles are employed to modulate the photocarrier dynamics in WSe 2 /WS 2 heterostructures. The results of pump-probe measurements reveal that the efficiency of carrier transfer across the WSe 2 /WS 2 heterostructure interface can be significantly enhanced via energy transfer mechanisms mediated by gold plasmons. Moreover, the electric field engendered by the plasmonic oscillations can modulate the dipole moment of the interlayer exciton. These well-aligned excitons avoid the annihilation and the extension of the lifetime of the excitons with increased pump power is realized by screening effect. The findings presented herein offer valuable insights for the active manipulation of charge transfer and extend our understanding of the integral role played by plasmon-exciton coupling in mediating charge separation in van der Waals heterostructures.

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

Role of Local Conductivities in the Plasmon Reflections at the Edges and Stacking Domain Boundaries of Trilayer Graphene

Here, we employed infrared scattering-type scanning near-field optical microscopy (IR-sSNOM) to study surface plasmon polaritons (SPPs) in trilayer graphene (TLG). Our study reveals systematic differences in near-field IR spectra and SPP wavelengths between Bernal (ABA) and rhombohedral (ABC) TLG domains on SiO 2 , which can be explained by stacking-dependent intraband conductivities. We also observed that the SPP reflection profiles at ABA-ABC boundaries could be mostly accounted for by an idealized domain boundary defined by the conductivity discontinuity. However, we identified distinct shapes in the SPP profiles at the edges of the ABA and ABC TLG, which cannot be solely attributed to idealized edges with stacking-dependent conductivities. Instead, this can be explained by the presence of various edge structures with local conductivities differing from those of bulk TLGs. Our findings unveil a new structural element that can control SPP and provide insights into the structures and electronic states of the edges of few-layer graphene.

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

Elucidating the Roles of Local and Nonlocal Rate Enhancement Mechanisms in Plasmonic Catalysis

Plasmonic metal nanoparticles (e.g., Ag, Au, and Cu) constitute a class of materials that interact with light via the excitation of localized surface plasmon resonance (LSPR). Numerous studies have reported substantial enhancements in the rates of chemical reactions on illuminated plasmonic nanoparticle catalysts compared to corresponding systems in the absence of illumination. There are two mechanisms that have been proposed to explain the LSPR-induced chemical reactivity. One mechanism assumes a local plasmon-induced hot charge-carrier-mediated activation of the reactants, while the other assumes an LSPR-induced equilibrium heating of the catalyst, which leads to energy transfer to and chemical reaction of the adsorbed reactants. Here, in this contribution, we developed a setup amenable to accurate in situ catalyst temperature and kinetic reaction rate measurements. We employed this setup to study the LSPR-induced rate enhancement in a case study of the CO oxidation reaction on plasmonic, monometallic Ag nanoparticle catalysts supported on α-Al 2 O 3 . We explored various Ag loadings and clustering levels. Our data show that the equilibrium heating of the catalyst cannot fully explain the illumination-induced plasmonic rate enhancements. This is the case even for high loading and clustering of Ag nanoparticles, where the equilibrium heating significantly increases. Based on the analysis, we propose that local effects, related to the plasmon-induced activation of adsorbates (reactants) via electronic excitation of the reactant or photothermal heating of the reactants that is highly localized to the individual nanoparticles, play a critical role in driving LSPR-induced chemical reactions.

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

Modulating the Electron Affinity of Small Bipyridyl Molecules on Single Gold Nanoparticles for Plasmon-Driven Electron Transfer

Developing controlled platforms for plasmon-driven chemistry is of great importance in catalytic reactions at the nanoscale. We report anion radical formation for five bipyridyl complexes of varying degrees of electron affinity utilizing optically fo-cused intraband (594 nm) and interband (532 nm) pump excitation of single gold nanoparticles. The surface-enhanced Raman scattering (SERS) of anion radicals for the five non-resonant adsorbed molecules 2,2’-bipyridine (22BPY), 4,4’-bipyridine (44BPY), trans-1,2-bis(4-pyridyl)ethylene (BPE), 1,2-bis(4-pyridyl)acetylene (BPA), and 1,2-bis(4-pyridyl)ethane (BPEt) were detected using localized surface-plasmon resonance (LSPR) excitation with 785 nm. The electron affinity of the five bipyridyl complexes were determined using electrochemistry. Molecules with low electron affinity experienced high-er instances of radical anion formation under a plasmon-coupled intraband electron transfer excitation (594 nm) whereas molecules with high electron affinity showed a preference for anion radical formation under direct interband electron trans-fer excitation (532 nm). The lowest unoccupied molecular orbital (LUMO) energy levels for low electron affinity surface-bound molecules (22BPY, BPEt) are on average ~0.43 eV higher for high electron affinity surface-bound molecules (BPA, BPE, 44BPY) as calculated using time-dependent density functional theory, elucidating the importance of plasmon coupling to energy levels that facilitate charge transfer pathways. We also show the ability to ‘activate’ high vs low electron affinity single nanoparticles with the choice of pump excitation wavelength. The findings show the complex interplay between molecular electron affinity, orbital overlap with the density of states of the plasmonic metal, and excitation energetics of the pump laser wavelength. Potential applications of this work include enhanced control over molecular scale catalysis, biosensor design, and solar energy capture.

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

Activation and Assembly of Plasmonic-Magnetic Nanosurfactants for Encapsulation and Triggered Release

Multifunctional surfactants hold great potentials in catalysis, separation, and biomedicine. Highly active plasmonic-magnetic nanosurfactants are developed through a novel acid activation treatment of Au–Fe 3 O 4 dumbbell nanocrystals. The activation step significantly boosts nanosurfactant surface energy and enables the strong adsorption at interfaces, which reduces the interfacial energy one order of magnitude. Mediated through the adsorption at the emulsion interfaces, the nanosurfactants are further constructed into free-standing hierarchical structures, including capsules, inverse capsules, and two-dimensional sheets. The nanosurfactant orientation and assembly structures follow the same packing parameter principles of surfactant molecules. Furthermore, nanosurfactants demonstrate the capability to disperse and encapsulate homogeneous nanoparticles and small molecules without adding any molecular surfactants. The assembled structures are responsive to external magnetic field, and triggered release is achieved using an infrared laser by taking advantage of the enhanced surface plasmon resonance of nanosurfactant assemblies. Finally, solvent and pH changes are also utilized to achieve the cargo release.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Degenerate parametric down-conversion facilitated by exciton-plasmon polariton states in a nonlinear plasmonic cavity

Abstract We study the effect of degenerate parametric down-conversion (DPDC) in an ensemble of two-level quantum emitters (QEs) coupled via near-field interactions to a single surface plasmon (SP) mode of a nonlinear plasmonic cavity. For this purpose, we develop a quantum driven-dissipative model capturing non-equilibrium dynamics of the system in which incoherently pumped QEs have transition frequency tuned near the second-harmonic response of the SPs. Considering the strong coupling regime, i.e. the SP-QE interaction rate exceeds system dissipation rates, we find a critical SP-QE coupling attributed to the phase transition between normal and lasing steady states. Examining fluctuations above the system’s steady states, we predict new elementary excitations, namely, the exciton-plasmon polaritons formed by the two-SP quanta and single-exciton states of QEs. The contribution of two-SP quanta results in the linear scaling of the SP-QE interaction rate with the number of QEs,  o , as opposed to the  o -scaling known for the Dicke and Tavis–Cummings models. We further examine how SP-QE interaction scaling affects the polariton dispersions and power spectra in the vicinity of the critical coupling. For this purpose, we compare the calculation results assuming a finite ensemble of QEs and the model thermodynamic limit. The calculated power spectra predict an interplay of coherent photon emission by QEs near the second-harmonic frequency and correlated photon-pair emission at the fundamental frequency by the SPs (i.e. the photonic DPDC effect).

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Interplay between gain and loss in arrays of nonlinear plasmonic nanoparticles: toward parametric downconversion and amplification

With the help of a theoretical model and finite-difference time-domain (FDTD) simulations based on the hydrodynamic–Maxwell model, we examine the effect of difference-frequency generation (DFG) in an array of L-shaped metal nanoparticles (MNPs) characterized by intrinsic plasmonic nonlinearity. The outcomes of the calculations reveal the spectral interplay between gain and loss in the vicinity of the fundamental frequency of the localized surface plasmon resonances. Subsequently, we identify different array thicknesses and pumping regimes facilitating parametric amplification and spontaneous parametric downconversion. Our results suggest that the parametric amplification regime becomes feasible on a scale of hundreds of nanometers and spontaneous parametric downconversion on the scale of tens of nanometers, opening up new exciting opportunities for developing building blocks of photonic metasurfaces.

Shah, Syed A.↗
NASA NTRS1993

Infrared photodetectors with tailorable response due to resonant plasmon absorption in epitaxial silicide particles embedded in silicon

Tailorable infrared photoresponse in the 1-2 micron range are demonstrated in a device incorporating electrically floating metal silicide particles. Photons absorbed by excitation of the metallic-particle surface plasmon are shown to contribute to the photoresponse. Quantum efficiencies of roughly 0.2 percent are measured at 77 K, with dark currents of less than 2 nA/sq cm at a reverse bias of 1 V and detectivities of 4 x 10 exp 9 - 8 x 10 exp 9 cm sq rt Hz/W are obtained.

Fathauer, R. W.↗
DOE OSTI2026

Self-Assembly Driven Microlithography via Near-Infrared Light Activation

Current vat photopolymerization (VP) relies on UV or visible light to start the rapid crosslinking of liquid photocurable resins into 3D-printed structures. Here, we develop a self-assembly-driven photopatterning approach to photothermally generate polymeric solids by combining thermoplasmonic nanoparticles and thermoresponsive polymers, in which near-infrared (NIR) light activates thermoplasmonic heating of nanoparticles, triggering the irreversible self-assembly of thermoresponsive polymers into insoluble mesoglobules. A small amount of thermal initiator and crosslinker leads to irreversible self-assembly of polymer nanocomposites. NIR light offers deeper penetration and reduced scattering compared to UV, enabling more uniform curing of thicker or filled materials and expanded process control for composites or opaque systems. Thermoplasmonic heat generation is achieved using surface-modified gold nanorods (AuNRs) with a longitudinal localized surface plasmon resonance peak in the NIR region. Key variables such as polymer composition, molecular weight, physical interactions at the nanoparticle–polymer interface, which can be tuned by surface functionalization, AuNR concentration, and pH can be used to tailor the assembly behavior of these systems, including photothermal effect, flocculation, and cloud point temperature, and the mechanical properties of the final structures. Collectively, these results highlight a platform for photothermally-driven microlithography of polymer solids with diverse, tunable macroscopic properties, enabled by low-energy NIR light-activated self-assembly.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Harnessing Plasmonic Interference for Nanoscale Ultrafast Electron Sources

In this Letter we demonstrate the use of plasmonic focusing in conjunction with nonlinear photoemission to develop geometrically flat nanoscale electron sources with less than 40 pm-rad root mean squared (rms) normalized transverse emittance. Circularly polarized light is incident on a gold Archimedean spiral structure to generate surface-plasmon polaritons that interfere coherently at the center resulting in a 50 nm rms emission area. Furthermore, such a nanostructured flat surface enables simultaneous spatiotemporal confinement of emitted electrons at the nanometer and femtosecond level and can be used as an advanced electron source for high-repetition-rate ultrafast electron diffraction and microscopy experiments as well as the next generation of miniaturized particle accelerators.

43 PARTICLE ACCELERATORS↗
NASA NTRS2008

Nanostructures Exploit Hybrid-Polariton Resonances

Nanostructured devices that exploit the hybrid-polariton resonances arising from coupling among photons, phonons, and plasmons are subjects of research directed toward the development of infrared-spectroscopic sensors for measuring extremely small quantities of molecules of interest. The spectroscopic techniques in question are surface enhanced Raman scattering (SERS) and surface enhanced infrared absorption (SEIRA). An important intermediate goal of this research is to increase the sensitivity achievable by these techniques. The basic idea of the approach being followed in this research is to engineer nanostructured devices and thereby engineer their hybrid-polariton resonances to concentrate infrared radiation incident upon their surfaces in such a manner as to increase the absorption of the radiation for SEIRA and measure the frequency shifts of surface vibrational modes. The underlying hybrid-polariton-resonance concept is best described by reference to experimental devices that have been built and tested to demonstrate the concept. The nanostructure of each such device includes a matrix of silicon carbide particles of approximately 1 micron in diameter that are supported on a potassium bromide (KBr) or poly(tetrafluoroethylene) [PTFE] window. These grains are sputter-coated with gold grains of 40-nm size (see figure). From the perspective of classical electrodynamics, in this nanostructure, that includes a particulate or otherwise rough surface, the electric-field portion of an incident electromagnetic field becomes concentrated on the particles when optical resonance conditions are met. Going beyond the perspective of classical electrodynamics, it can be seen that when the resonance frequencies of surface phonons and surface plasmons overlap, the coupling of the resonances gives rise to an enhanced radiation-absorption or -scattering mechanism. The sizes, shapes, and aggregation of the particles determine the frequencies of the resonances. Hence, the task of designing a nanostructure to exhibit the desired radiation-absorption properties translates, in large part, to selecting particle sizes and shapes to obtain the desired enhanced coupling of energy from photons to plasmons and phonons. To broaden the spectral region(s) of enhanced absorption, one would select a distribution of particle sizes and shapes.

Anderson, Mark↗
DOE OSTI2023

Origin of high optical contrast in zinc-zinc oxide electrodeposits for dynamic windows

The control of solar light and heat emission through windows is an important strategy for increasing the energy efficiency of buildings. Reversible Zn electrodeposition has recently emerged as a promising method for constructing electronically tintable robust dynamic windows. In Zn electrodeposits formed from dimethyl sulfoxide (DMSO) electrolytes during device tinting, we observe extraordinary absorption that is in excess of what is predicted by the Beer-Lambert law for a uniform Zn thin film. Here, the charge required to electroplate these films is abnormally low, significantly less than previously reported dynamic windows based on reversible metal electrodeposition, which facilitates the construction of large-area devices that switch uniformly. Finite-difference time-domain (FDTD) simulations are used to investigate the origin of this enhanced absorption, which arises from plasmonic effects among the Zn nanoparticles and ZnO dendrites in the film. The dielectric ZnO dendrites promote absorption via slit-like Zn-dielectric-Zn structures that from hybrid surface plasmon resonance at metal walls. Through these investigations, we provide design principles to construct low-charge and high-contrast metal and metal oxide-based dynamic windows.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2022

Magnetic and Optical Properties of Au–Co Solid Solution and Phase-Separated Thin Films and Nanoparticles

The chemical composition and morphology of Au x Co 1–x thin films and nanoparticles are controlled via a combination of cosputtering, pulsed laser-induced dewetting (PLiD), and annealing, leading to tunable magnetic and optical properties. Regardless of chemical composition, the as-deposited thin films and as-PLiD nanoparticles are found to possess a face-centered cubic (FCC) Au x Co 1–x solid-solution crystal structure. Annealing results in large phase-separated grains of Au and Co in both the thin films and nanostructures for all chemical compositions. The magnetic and optical properties are characterized via vibrating sample magnetometry (VSM), ellipsometry, optical transmission spectroscopy, and electron energy loss spectroscopy (EELS). Despite the exceptionally high magnetic anisotropy inherent to Co, the presence of sufficient Au (72 atom %) in the Au x Co 1–x solid solution results in superparamagnetic thin films. Among the as-PLiD nanoparticle samples, an increased Co composition leads to a departure from traditional ferromagnetism in favor of wasp-waisted hysteresis caused by magnetic vortices. Phase separation resulting from annealing leads to ferromagnetism for all compositions in both the thin films and nanoparticles. The optical properties of Au x Co 1–x nanostructures are also largely influenced by the chemical morphology, where the Au x Co 1–x intermixed solid solution has significantly damped plasmonic performance relative to pure Au and comparable to pure Co. Phase separation greatly enhances the quality factor, optical absorption, and electron energy loss spectroscopy (EELS) signatures. The enhancement of the localized surface plasmon resonances (LSPRs) scales with the reduction in Co composition, despite EELS evidence that excitation of the Co portions of a nanoparticle can provide a similar, and in some instances enhanced, LSPR resonance compared to Au. This behavior, however, is seemingly limited to the LSPR dipole mode, while higher-order modes are greatly damped by a Co aloof position. As a result, this observed magneto-plasmonic functionality and tunability could be applicable in biomedicine, namely, cancer therapeutics.

annealing (metallurgy)↗
DOE OSTI2024

Unveiling Spatial and Temporal Dynamics of Plasmon-Enhanced Localized Fields in Metallic Nanoframes through Ultrafast Electron Microscopy

Plasmonic nanomaterials, particularly noble metal nanoframes (NFs), are important for applications such as catalysis, biosensing, and energy harvesting due to their ability to enhance localized electric fields and atomic efficiency via localized surface plasmon resonance (LSPR). Yet the fundamental structure-function relationships and plasmonic dynamics of the NFS are difficult to study experimentally and thus far rely predominately on computational methodologies, limiting their utilization. This study leverages the capabilities of ultrafast electron microscopy (UEM), specifically photon-induced near-field electron microscopy (PINEM), to probe the light-matter interactions within plasmonic NF structures. Here, the effects of shape, size, and plasmonic coupling of Pt@Au core-shell NFs on spatial and temporal characteristics of plasmon-enhanced localized electric fields are explored. Importantly, time-resolved PINEM analysis reveals that the plasmonic fields around hexagonal NF prisms exhibit a spatially dependent excitation and decay rate, indicating a nuanced interplay between the spatial geometry of the NF and the temporal evolution of the localized electric field. These results and observations uncover nanophotonic energy transfer dynamics in NFs and highlight their potential for applications in biosensing and photocatalysis.

Plasmonics↗
DOE OSTI2023

Nanoscale Imaging of Optical-Frequency Plasmonic Energy Transfer in Individual Nanoparticles and their Assemblies

The nonradiative transfer of energy from plasmonic metal nanostructures to their neighboring environments is a rapidly expanding research area because of its tremendous potential impact on photovoltaics and photocatalysis. Despite the significant progress achieved via optical spectroscopies, understanding the differing and competing energy transfer pathways available to these systems still presents a major challenge due to a lack of insight into their nanoscale optical responses. With the atom-scale spatial resolving power of the electron microscope and its ability to probe optical transitions, electron spectroscopies like EELS are uniquely suited for these challenges. Our proposal addressed STEM/EELS techniques (Camden) to directly measure and even control energy transfer pathways in hybrid plasmon-resonator systems and leveraged detailed theoretical models combined with simulation (Masiello) to understand the essential underlying physics. In particular, the outcome of our proposed studies deepened the fundamental understanding of how surface plasmons shed energy to their environment and the practical knowledge gained here will influence the design of future high-efficiency solar energy-harvesting devices and photocatalysts capable of operating throughout the visible and the infrared.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2025

Ultrafast Dynamics of Plasmon-Coupled Excitons in Semiconducting Nanoplatelets

Exciton-plasmon coupling in nanomaterials produces many relevant phenomena for photonics applications including increased light-matter interactions, enhanced radiative rates of quantum emitters, and coherent energy exchange. In the case of exciton coupling to surface plasmon polaritons (SPPs), dispersive interactions controlled by the wavevector of optical excitation create the opportunity for tunable optical emission. Strong temporal impacts on exciton lifetimes can also occur in coupled systems, creating the opportunity for ultrafast control of exciton lifetime via changes in electronic coupling magnitude to a dispersive SPP. The coupling strength can be impacted by the morphology of the nanomaterials. Here, in this study, we utilize colloidal semiconductor nanoplatelets deposited onto thin silver plasmonic films, and compare the results to semiconductor quantum dots deposited on the silver films. We map the dispersion of the coupled systems and measure the ultrafast transient absorption response of the coupled systems. Due to the larger interaction areas of the nanoplatelets that lie flat on the silver films, a greater degree of coupling is found for the nanoplatelets, and much faster temporal responses are found as compared to quantum dots. Fresnel theory calculations that incorporate heavy and light hole features can reproduce the dispersion of the nanoplatelet-silver film, and a simple three-state model is developed to provide insights into the nature of the coupling at different photon energies along the dispersion curve.

colloidal semiconductor nanoplatelets↗
DOE OSTI2024

Hybridized magnonic materials for THz frequency applications

The capability of magnons to hybridize and strongly couple with diverse excitations offers a promising avenue for realizing and controlling emergent properties that hold significant potential for applications in devices, circuits, and information processing. In this Letter, we present recent theoretical and experimental developments in magnon-based hybrid systems, focusing on the combination of magnon excitation in an antiferromagnet with other excitations, namely, plasmons in a topological insulator, phonons in a 2D antiferromagnetic (2D AFM), and photons. Here, the existence of THz frequency magnons, plasmons, and phonons makes magnon-based hybrid systems particularly appealing for high-operating-speed devices. In this context, we explore several directions to advance magnon hybrid systems, including strong coupling between a surface plasmon and magnon polariton in a topological insulator /AFM bilayer, a giant spin Nernst effect induced by magnon–phonon coupling in 2D AFMs, and control of magnon–photon coupling using spin torque.

36 MATERIALS SCIENCE↗