Presence Of Surface Plasmons Research Articles

CO2 adsorption and activation on Ag(1 1 1) surfaces in the presence of surface charge density: A static gas phase DFT study

The CO2 reduction reaction on Ag in the presence of surface plasmons are of strong interest in photocatalysis. Here, two Density Functional Theory (DFT) approaches are proposed to localize charges at the Ag surface to mimic surface plasmon excitation. These calculations predict charge localization at the outermost surface layer, a result confirmed via light excitation at the plasmon resonance modeled by Density Functional Tight Binding Hamiltonian (DFTB) theory. The CO2(gas) reduction initial steps are studied by DFT models showing that bonded species can be created on top of an Ag-atom in the presence of extra charges. A second CO2 molecule can assist the first molecule, decreasing the charge carrier density requirement for CO2 reduction bonded species. A Molecular Dynamics (MD) study shows a possible interaction among CO2 molecule. These results show that a static DFT simulation can mimic charge localization resulting from surface plasmon effects, thus enabling studies on surface plasmon-enhanced chemical reactions, paving the way for future time-dependent (TD) studies.

Extreme Ultraviolet Beam Enhancement by Relativistic Surface Plasmons.

The emission of high-order harmonics in the extreme ultraviolet range from the interaction of a short, intense laser pulse with a grating target is investigated experimentally. When resonantly exciting a surface plasmon, both the intensity and the highest order observed for the harmonic emission along the grating surface increase with respect to a flat target. Harmonics are obtained when a suitable density gradient is preformed at the target surface, demonstrating the possibility to manipulate the grating profile on a nanometric scale without preventing the surface plasmon excitation. In support of this, the harmonic emission is spatiotemporally correlated to the acceleration of multi-MeV electron bunches along the grating surface. Particle-in-cell simulations reproduce the experimental results and give insight on the mechanism of high harmonic generation in the presence of surface plasmons.

Three-dimensional hot electron photovoltaic device with vertically aligned TiO2 nanotubes

Titanium dioxide (TiO2) nanotubes with vertically aligned array structures show substantial advantages in solar cells as an electron transport material that offers a large surface area where charges travel linearly along the nanotubes. Integrating this one-dimensional semiconductor material with plasmonic metals to create a three-dimensional plasmonic nanodiode can influence solar energy conversion by utilizing the generated hot electrons. Here, we devised plasmonic Au/TiO2 and Ag/TiO2 nanodiode architectures composed of TiO2 nanotube arrays for enhanced photon absorption, and for the subsequent generation and capture of hot carriers. The photocurrents and incident photon to current conversion efficiencies (IPCE) were obtained as a function of photon energy for hot electron detection. We observed enhanced photocurrents and IPCE using the Ag/TiO2 nanodiode. The strong plasmonic peaks of the Au and Ag from the IPCE clearly indicate an enhancement of the hot electron flux resulting from the presence of surface plasmons. The calculated electric fields and the corresponding absorbances of the nanodiode using finite-difference time-domain simulation methods are also in good agreement with the experimental results. These results show a unique strategy of combining a hot electron photovoltaic device with a three-dimensional architecture, which has the clear advantages of maximizing light absorption and a metal–semiconductor interface area.

The surface plasmon-induced hot carrier effect on the catalytic activity of CO oxidation on a Cu2O/hexoctahedral Au inverse catalyst.

The intrinsic correlation between an enhancement of catalytic activity and the flow of hot electrons generated at metal-oxide interfaces suggests an intriguing way to control catalytic reactions and is a significant subject in heterogeneous catalysis. Here, we show surface plasmon-induced catalytic enhancement by the peculiar nanocatalyst design of hexoctahedral (HOH) Au nanocrystals (NCs) with Cu2O clusters. We found that this inverse catalyst comprising a reactive oxide for the catalytic portion and a metal as the source of electrons by localized surface plasmon resonance (localized SPR) exhibits a change in catalytic activity by direct hot electron transfer or plasmon-induced resonance energy transfer (PIRET) when exposed to light. We prepared two types of inverse catalysts, Cu2O at the vertex sites of HOH Au NCs (Cu2O/Au vertex site) and a HOH Au NC-Cu2O core-shell structure (HOH Au@Cu2O), to test the structural effect on surface plasmons. Under broadband light illumination, the Cu2O/Au vertex site catalyst showed 30-90% higher catalytic activity and the HOH Au@Cu2O catalyst showed 10-30% higher catalytic activity than when in the dark. Embedding thin SiO2 layers between the HOH Au NCs and the Cu2O verified that the dominant mechanism for the catalytic enhancement is direct hot electron transfer from the HOH Au to the Cu2O. Finite-difference time domain calculations show that a much stronger electric field was formed on the vertex sites after growing the Cu2O on the HOH Au NCs. These results imply that the catalytic activity is enhanced when hot electrons, created from photon absorption on the HOH Au metal and amplified by the presence of surface plasmons, are transferred to the reactive Cu2O.

Excitation of atoms by single-photon pulses in the presence of surface plasmons

Plasmons on the surface of a metal increase the light intensity by several orders of magnitude. To quantify the consequences of this phenomenon in quantum processes, we calculate the excitation probability for atoms near the surface, which are excited by a single-photon pulse. Using quantum electrodynamics in the presence of absorbing dielectrics, we predict that nonradiative decay in the metal will limit the excitation probability to about one-half of the maximum that could be achieved in the absence of such losses.

Surface plasmons and magneto-optic activity in hexagonal Ni anti-dot arrays

The influence of surface plasmons on the magneto-optic activity in a two-dimensional hexagonal array is addressed. The experiments were performed using hexagonal array of circular holes in a ferromagnetic Ni film. Well pronounced troughs are observed in the optical reflectivity, resulting from the presence of surface plasmons. The surface plasmons are found to strongly enhance the magneto-optic response (Kerr rotation), as compared to a continuous film of the same composition. The influence of the hexagonal symmetry of the pattern on the coupling between the plasmonic excitations is demonstrated, using optical diffraction measurements and theoretical calculations of the magneto-optic and of the angular dependence of the optical activity.

Enhanced photoluminescence of conjugated polymer thin films on nanostructured silver

Photoluminescence of a conjugated polymer in the presence of surface plasmons on metallic nanoparticles is studied. A layered device structure was constructed that enabled control over nanoparticle diameter and separation between the polymer and nanoparticles layers. The dependence of the surface plasmon evanescent field and energy transfer has been investigated with the largest enhancement in photoluminescence observed at a 40 nm distance separation between the fluorophore and the surface plasmon. A spectrum of surface plasmon resonances ranging from the emission to the absorption energies of the conjugated polymer revealed largest enhancements when the resonance was tuned to the conjugated polymer emission energy. At peak photoluminescence the maximum photoluminescent enhancement was found to be 5.6 times of the photoluminescence of the control structure and the total integrated enhancement was 5.9 times.

Fundamental behavior of electric field enhancements in the gaps between closely spaced nanostructures

We demonstrate that the electric field enhancement that occurs in a gap between two closely spaced nanostructures, such as metallic nanoparticles, is the result of a transverse electromagnetic waveguide mode. We derive an explicit semianalytic equation for the enhancement as a function of gap size, which we show has a universal qualitative behavior in that it applies irrespective of the material or geometry of the nanostructures and even in the presence of surface plasmons. Examples of perfect electrically conducting and Ag thin-wire antennas and a dimer of Ag spheres are presented and discussed.

Magneto-optic behaviour in the presence of surface plasmons

Insight into the mechanism responsible for the enhanced level of magneto-optical (MO)activity observed from magnetic surfaces when supporting propagating surface plasmons(SPs) is provided by studies of ferromagnetic Ni and Co gratings where SPs are generatedand interact magneto-optically at the air/ferromagnetic interface. These ferromagneticgratings were subsequently coated with semi-transparent Ag layers. In these systems onlysome 30% of the light incident on the air/Ag interface is reflected; most is converted tosurface plasmons whilst the remainder propagates to reflect off the ferromagneticsurface where it undergoes a MO interaction before returning through the Ag. Theprecise nature of the beam returned from the ferromagnetic and the MO signatureimprinted on it depends on the relative magnitude of two driving sources: theE-field of the lightwave and the E-field associated with SPs penetrating through the Ag to the ferromagnetic. Evidence isobtained indicating that the degree of MO enhancement correlates strongly with themagnitude of the intense electric field associated with the presence of SPs at theferromagnetic surface, confirming previous experimental studies postulating that enhancedMO effects are not solely a consequence of the reduction in reflection that is experienced atsurface plasmon resonance.

Near- to far-field imaging of free-space and surface-bound waves emanating from a metal nanoslit

The authors report the radiation pattern (radial and angular distribution of light intensity) of a silver nanoslit measured in the near- to far-field regimes. In most far fields, the 1∕r dependence of intensity distribution, expected from a cylindrical wave emanating from a line source, is clearly observed. The glancing angle regime is found to be governed by the presence of surface plasmons, showing higher intensity closer to the metal surface. From the radiation patterns measured with a tilted-probe, radial-scan method, a branching ratio is quantitatively determined for the free-space radiation and surface plasmon components, emerging from the nanoslit.

Photoacoustic determination of the plasmon enhanced electric field at a corrugated metal interface

The intensity of the optical electric field in the vicinity of a corrugated Ni interface is evaluated in the presence of surface plasmons. A photoacoustic technique is used to measure the energy absorbed by the sample which together with a simultaneous conventional measurement of reflectance allows determination of the total energy flow into and out of the interface. The value of the optical electric field is then evaluated on the basis of energy conservation and found to be intensified by a factor of 2.5 as surface plasmons are resonantly generated.

Image resolution of surface-plasmon-mediated near-field focusing with planar metal films in three dimensions using finite-linewidth dipole sources

We study the role of surface plasmons in the near-field focusing of a finite-linewidth point dipole by a planar silver film using three-dimensional finite element calculations. We find that the intensity distribution in the image plane at a distance of 60 nm from the source is narrowed by a factor of 1.4 in the presence of a 30-nm-thick silver film. The lateral field components are found to be focused significantly better. We show that the difference is caused by unavoidable stray fields normal to the lens surface due to the interface charge distribution induced by the presence of surface plasmons.

Hexagonal Lattice Photonic Crystal in Active Metallic Microcavity

ABSTRACTA hexagonal lattice photonic crystal was fabricated inside the metallic microcavity. And a thin film of Alq3 was incorporated inside the textured cavity as an active medium. The microcavity is designed such that the modified photonic modes due to the textured structure can couple to the excited electronic states of Alq3. This leads to changes in the emission characteristics of Alq3. From the angle-resolved transmission (ARTR) results, the photonic bandgap was observed at all angles from normal incident to 60°. The presence of surface plasmon (SP) was observed in both TM and TE modes of the transmission. Compare to the bulk Alq3 photoluminescence spectrum, significant modification of the photoluminescence (PL) spectrum was observed in the angle-resolved photoluminescence (ARPL). The photoluminescence spectra showed clear suppression in luminescence intensity for the range inside the photonic bandgap. We use decouple approximation for the standing wave modes and derive the photonic waveguide characteristics for two-dimensional textured metallic microcavities. The theoretical result is in good agreement to the experimental result.

Electronic response of aligned multishell carbon nanotubes

We report calculations of the effective electronic response of aligned multishell carbon nanotubes. A local graphitelike dielectric tensor is assigned to every point of the multishell tubules, and the effective transverse dielectric function of the composite is computed by solving Maxwell's equations. Calculations of both real and imaginary parts of the effective dielectric function are presented, for various values of the filling fraction and the ratio of the internal and external radii of hollow tubules. Our full calculations indicate that the experimentally measured macroscopic dielectric function of carbon nanotube materials is the result of a strong electromagnetic coupling between the tubes, which cannot be accounted for with the use of simplified effective medium theories. The presence of surface plasmons is investigated, and both optical absorption cross sections and energy-loss spectra of aligned tubules are calculated.

Speckle Pattern Intensification in Highly Conducting Microrough Gratings

Abstract The scattering of a plane wave by a rough interface between a vacuum and a metal is computed for the case of a boundary constructed as the sum of two contributions: a perfectly periodic sinusoidal roughness representing an ideal grating and a statistically varying roughness representing the defects of a real diffraction grating. We restrict ourselves to the case of highly conducting shallow gratings, so that Rayleigh expansions and a surface impedance boundary condition can be used as an approximation. The speckle patterns obtained for p-polarized light show intensification at angular positions that do not depend on the incidence. We show that the presence of surface plasmons propagating on the grating is related to this intensification.