Surface Plasmon Resonance Of Ag Research Articles

Enhanced photocatalytic cytotoxic activity of Ag@Fe-doped TiO2 nanocomposites against human epithelial carcinoma cells

Fe-doped TiO2 nanopowders with controlled molar-atomic ratios of iron to titanium oxide (in percentage) ranging from nominal 1 to 10% were synthesized by a new simple sol–gel method. Metallic Ag nanoparticles were successfully deposited on the nanopowder of the Fe-doped TiO2 surface by citrate reduction of AgNO3 in water/CH3CN mixture. The molar ratio of iron to TiO2, phase formation, bandgaps, crystallinity, catalytic and plasmonic properties of the resultant composites were systematically investigated using UV-visible spectroscopy, SEM, TEM, XRD, XPS, EDX, and photoluminescence spectral analyses. The photocatalytic activity of Ag@Fe-doped TiO2 composite nanoclusters was evaluated through photocatalytic killing of cancer cells. For the photocatalytic killing of cancer cells under visible light irradiation, as-prepared Ag@Fe-doped TiO2 nanopowders exhibited higher activity than Fe-doped TiO2. The promoting effect of the Ag nanoparticles deposited on the Fe-doped TiO2 surface showed strong absorption in the visible region due to localized surface plasmon resonance of Ag and inhibited the recombination of photoelectrons and holes rather than only Fe-doped TiO2. The cytotoxic cell killing efficiency depends on the molar ratio of Fe content to TiO2. The optimum Fe content in Fe-doped TiO2 was determined to be 5% due to the Fe/TiO2 molar ratio. Based on the obtained results, a plausible mechanism was also proposed.

Tailoring surface plasmon resonance in Ag:ZrO 2 nanocomposite thin films

Ag:ZrO 2 nanocomposite thin films have been synthesized by a modified sol–gel technique. The effect of post-deposition treatments i.e. thermal annealing and UV irradiation on micro-structural, chemical and optical properties of nanocomposite thin films have been studied by a transmission electron microscope, X-ray photoelectron spectrophotometer and UV–vis spectrophotometer. Films deposited with a polymeric ZrO 2 sol containing Ag + ions when treated with either thermal annealing or with UV irradiation exhibit formation of Ag:ZrO 2 nanocomposite thin films via decomposition of Ag 2O 3 into metallic Ag. The formed Ag nanoparticles are found predominantly in spherical shape and density of Ag nanoparticles increases with increase in annealing duration for a particular concentration of Ag precursor. A protocol is provided to tailor the surface plasmon resonance-induced absorption peak at wavelength from 454 to 586 nm. These nanocomposite thin films show saturable absorption and exhibit high value of non-linear absorption coefficient.

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.

Surface Plasmon-Mediated Energy Transfer in Heterogap Au−Ag Nanowires

We report the observation of energy transfer from a gold (Au) nanodisk pair to a silver (Ag) nanowire across a 120 nm gap via surface plasmon resonance (SPR) excitation. The enhanced electromagnetic (EM) fields generated by Au SPR excitation induce oscillation of the conduction electrons in the Ag segment, transferring energy to it even though the Ag segment has only weak resonant interactions with the incident EM radiation. The induced Ag SPR produces strong EM fields at the position of the Ag segment, leading to a Raman signal approximately 15 times greater than when the Ag segment is alone (not adjacent to the Au nanodisk pair). The Raman intensity is found to depend nonlinearly on the incident laser intensity for laser power densities of 10 kW/cm(2), which is consistent with the results of EM theory calculations which are not able to account for the factor of 15 enhancement based on a linear mechanism. This suggests that energy transfer from the Au disk pair to the Ag segment involves an enhanced nonlinear polarization mechanism such as can be produced by the electronic Kerr effect or stimulated Raman scattering.

Microstructures and Optical Properties of LiNbO3 Sequentially Implanted with Ag and Cu Ions

Microstructures of LiNbO3 sequentially implanted with Ag and Cu ions were investigated in connection with changes in optical properties induced by heat treatment. Ag and Cu ions were implanted into LiNbO3 single crystals at energies of 4.2 and 3.0 MeV, respectively, to ensure an overlap of the depth distribution for both metals. Samples were heated in air for 1 h at temperatures up to 800 °C, and the optical absorption spectra of the samples were measured in the visible region. For the as-implanted samples, two large absorption peaks appeared at 473 and 574 nm, which correspond to absorptions due to the surface plasmon resonance of Ag and Cu nanoparticles, respectively. When the sample was heated at high temperatures, the intensities of the absorption peaks gradually decreased. After being heated at 500 °C, the spectra showed only one peak at 550 nm. For the sample heated at 800 °C, the absorption peak almost disappeared, and the samples became colorless. Changes in the microstructure induced during the annealing processes were examined by scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDX).

Electroless deposition of Au on Ag sol: Oxidation of carbon monoxide and methanol

Ag sols were synthesised by gamma-irradiation of AgNO 3 solution in presence of 2-propanol as OH radical scavenger and PVP as steric stabiliser. Different dose rates were applied to control the size of Ag particles. Ag sol prepared was applied for reduction of AuCl 4 − resulting in the formation of Au–Ag and Au nanoparticles as confirmed by TEM and the red shift of the surface plasmon resonance of Ag. Au–Ag nanoparticles were fixed to Al 2O 3 (ICN alumina N). Following O 2 treatment at 673 K the Au–Ag/Al 2O 3 samples were tested in CO and methanol total oxidation. The increase of Ag activity at low Au concentrations can be attributed to small Au particles decorating Ag causing morphological and ligand effects.

Nonlinear optical properties and surface-plasmon enhanced optical limiting in Ag–Cu nanoclusters co-doped in SiO2 Sol-Gel films

The nonlinear optical properties and the role of the surface-plasmon resonance (SPR) on optical limiting (OL) properties of Ag–Cu nanoclusters co-doped in SiO2 matrix prepared using the sol-gel technique with a Cu∕Ag molar ratio of 1, 2 and 3, respectively, are presented. The studies were made using the second harmonic of high-power nanosecond and picosecond Nd:YAG lasers. These films show a self-defocusing nonlinearity with both nanosecond and picosecond pulses and a good nonlinear absorption behavior with the nanosecond pulse excitation. The nonlinear refractive index decreased with decreasing particle size, whereas the nonlinear absorption increased with an increase in Cu concentration. The observed nonlinear absorption is explained by taking into account the cumulative effect of both the intraband and interband mechanisms. The excitation near the SPR of Cu resulted in an enhanced OL behavior with increasing Cu concentration. No such concentration dependence is observed when the excitation is near the SPR of Ag, however, the limiting threshold is reduced approximately 10–17 times. Excitation at wavelengths far below the SPR of Ag and Cu has not shown any OL behavior. The major contribution toward OL is observed to be from the interband absorption and from a possible energy transfer within the higher unoccupied states of Cu and Ag. Although nonlinear scattering is observed at higher intensities, its contribution is found to be much less than that of the nonlinear absorption assisted by an energy transfer.

Effect of particle shape distribution on the surface plasmon resonance of Ag–SiO2 nanocomposite thin films

Silver–silica nanocomposite thin films were prepared by high pressure d.c. sputtering technique. Films deposited at lower substrate temperature showed a narrow distribution of nanoparticles with nearly spherical shape. Increase in substrate temperature resulted in films with a non-uniform size and shape due to the agglomeration of the nanoparticles. This size and shape distribution has a profound effect on the optical absorbance spectra and results in a broad and asymmetric surface plasmon band. A shape distribution introduced in the Maxwell–Garnett or Bruggeman effective medium theory was found to give a reasonable description of the experimentally observed optical absorption spectra.

Sol-gel synthesis of metal nanoclusters-silica composite films

In a program on the development of metal nanoclusters in sol-gel derived thin films, attempts were made to synthesize pure and mixed metal clusters, control the cluster size and increase the volume fract f the clusters. Thus, Ag, Cu and Ag-Cu nanoclusters were prepared in silica films using dip- and spin-coating techniques. The annealing of Ag/SiO2 films in different atmospheres (air, argon and 5% H2-95% N2 gas) caused modifications of Ag nanoclusters resulting in changes in their surface plasmon resonance (SPR) peak positions. The Cu and Ag-Cu codoped films were annealed in reducing atmosphere (5% H2-95% N2 gas). In order to prepare Cu nanoclusters of different sizes, the concentrations of Cu in Cu/SiO2 composite films were varied from 8 to 30 mol% and annealed at 800°C for different times for growth. The size of the Cu nanoclusters was measured from the half band width of Cu SPR peak (appearing within 570–557 nm range) and X-ray diffraction. In this way Cu-nanoclusters of size ranges from about 3.5 to 10 nm (average diameters) were prepared . The Ag-Cu nanocluster-containing silica films show the existence of both Ag and Cu SPR peaks with some blue shifting in comparison with to their pure analogues depending on the Ag:Cu ratio.