Localized Surface Plasmon Effect Research Articles

Montmorillonite-Supported Ag/TiO2 Nanoparticles: An Efficient Visible-Light Bacteria Photodegradation Material

Montmorillonite (MMT)-supported Ag/TiO(2) composite (Ag/TiO(2)/MMT) has been prepared through a one-step, low-temperature solvothermal technique. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveal that the Ag particles coated with TiO(2) nanoparticles are well-dispersed on the surface of MMT in the composite. As a support for the Ag/TiO(2) composite, the MMT prevents the loss of the catalyst during recycling test. This Ag/TiO(2)/MMT composite exhibits high photocatalytic activity and good recycling performance in the degradation of E. coli under visible light. The high visible-light photocatalytic activity of the Ag/TiO(2)/MMT composite is ascribed to the increase in surface active centers and the localized surface plasmon effect of the Ag nanoparticles. The Ag/TiO(2)/MMT materials with excellent stability, recyclability, and bactericidal activities are promising photocatalysts for application in decontamination.

Localized surface plasmon enhanced photoluminescence from ZnO films: Extraction direction and emitting layer thickness

The light emission from ZnO films is enhanced by localized surface plasmon (LSP) of Ag island films. The dependence of LSP coupled emission on light-extracting direction and the thickness of ZnO films is investigated. It is found that the photoluminescence (PL) enhancement factors for upward extraction are much smaller than those for downward extraction. This is ascribed to the low transmittance and nonradiative absorption loss of Ag films. The near-field effect of LSP results in the dependence of the PL enhancement of ZnO films on the film thickness. A maximum PL enhancement factor of more than 15 is obtained when the thickness of ZnO was about 40 nm.

Metallic nanoparticle array on GaN by microsphere lithography

AbstractThe optical characteristics of GaN blue‐light (peak wavelength at 440 nm) light‐emitting diode (LED) under the effect of localized surface plasmon (LSP) have been studied. Hexagonal arrays of triangular metallic nanoparticles deposited through a self‐assembled silica microsphere mask have been fabricated using vertical deposition. By comparing the PL spectra of samples coated with Au, Al and Ag nanoparticles, it is found that Ag nanoparticles offer the most pronounced PL enhancement. The resonance wavelength was determined from optical transmission and verified by theoretical calculations. These results provide a cost‐effective solution for improving the efficiency of LEDs. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of localized surface plasmon on the photocurrent of silicon nanocrystal photodetectors

We report on the photocurrent of silicon nanocrystal (Si NC) photodetectors (PDs) that contain silver (Ag) islands. Here, a larger increase in the photocurrent of Si NC PDs was observed with increasing Ag island size. The maximum increase occurred at the wavelength of the Ag surface plasmon resonance and redshifted as the size of the Ag islands increased. As a result, a 97% increase in photocurrent generation was observed and this was attributed mostly to the coupling of Si NC with the localized surface plasmon of the Ag islands in Si NC PDs.

A method to assess modifications of fluorophore radiative rate by plasmonic structures

We present a method for assessing radiative emission rates of the fluorophores by plasmonic metal structures by using fluorescence lifetime and cathodoluminescence measurements. By using this approach we identified and quantified the increased radiative rate of a Deep Purple fluorophore in inverted pyramidal pits of gold nanostructured arrays (Klarite) compared with the radiative rate of the same fluorophore on planar gold. This increased rate is attributed to the effect of localized surface plasmons preferentially concentrated in the pits of these arrays.

Sensitivity Enhancement by Au Nanoparticles in Surface Plasmon Resonance Chemical Sensors

We investigated the sensitivity enhancement in chemical sensors by coupling Au nanoparticles that have the specific size and surface density on sensor chips as those found in label-free detection systems. The Au particles with 10, 30, 60 nm diameter were conjugated by amine groups of cystamine modified chips. The surface density of Au particles was controlled by the reaction time and the concentration of the solution containing the particles. In order to investigate the sensitivity enhancement, we compared the resonance angle shifts with or without Au particles in a methanol aqueous solution. We know that the sensitivity depends on the size and surface density of particles. The sensitivity increased by 57% with the adsorption of 30 nm diameter particles and low surface density due to the coupling effect of localized surface plasmon derived by the size and density of specific Au nanoparticles and surface plasmon waves.

Optical tunneling effect of localized surface plasmon: A simulation study using particle-in-cell method

Optical tunneling through thin metal films with periodic Gaussian-shaped grooves was studied using the particle-in-cell method. For a normally incident TM-polarized wave, the transmission coefficients are maximal in the localized surface plasmon (LSP) modes, which is similar to the predictions of the Drude model, but with lower transmission coefficients. The plasma-plasma interactions partially smear out the LSP modes, which has not been addressed in previous studies that involved the Drude model. Although various heating and cooling processes occur at the air-plasma interface, the temperature of the plasma only slightly affects the transmission coefficients.

Near-field optical microscopy of strongly scattering microporous metal/polymer membranes

Optical properties of microporous polymer membranes coated with metal have been studied using scanning near-field optical microscopy. The electromagnetic field distribution close to pores of various sizes ranging from 35 to 750 nm has been investigated in the different illumination configurations. Individual pores as small as 35 nm were seen in the near field. For directly illuminated membranes the field distribution is related mainly to the pores themselves. However, when surface plasmon polaritons were excited, the field distribution exhibited much more complex structure related to the interaction of surface polaritons with the ensemble of randomly distributed pores and metal surface roughness as well as localized surface plasmon effects. The results will be of importance for the understanding of optical properties of subwavelength apertures in strongly scattering films as well as optics of randomly structured metal films.