Localized Surface Plasmon Band Research Articles

Study on the Effect of Poly(Styrene 4-Sulfonic Acid-co-Maleic Acid) Toward Metallization and Plasmonic Tuning of Silver Nanoparticle Thin Films

Thin films with tunable optical properties from yellow to metallic were prepared from a monolayer coating of silver nanoparticles (AgNP) onto a polyelectrolyte multilayer (PEM) thin film. The AgNP were synthesized using various concentrations of stabilizing polyelectrolytes leading to a competitive adsorption concept in which AgNP compete with excess polyelectrolytes to coat the cationic PEM top layer. The AgNP were synthesized by chemical reduction of Ag salts using poly(styrene 4-sulfonic acid-co-maleic acid) (PSS-co-MA) as stabilizing agent to produce nanoparticles coated with both a strong acid (sulfonic) and a weak acid (carboxylic) moiety. Although all the nanoparticle solutions displayed a characteristic bright yellow due to the localized surface plasmon band around 420 nm, the monolayer films of nanoparticles obtained after dipping displayed striking different optical properties. When using a high PSS-co-MA content in the solution, a pale-yellow film was obtained which color shifted to orange and metallic when the capping concentration was decreased from 0.25 to 0.001 mM. The optical properties of the AgNP film could be further changed by galvanic replacement of the Ag with gold ions to produce a gold monolayer. These results are interesting to produce surface with tunable catalytic properties, tunable optical properties, or to be used as primer for the metallization of polymeric surfaces.

Latex/AgNPs: Synthesis, and Their Antibacterial Activity

Silver nanoparticles (Ag NPs) coated by an aqueous emulsion of copolymer were elaborated in a short time using polyol process and microwave (MW) heating. This approach is based on reducing AgNO3 powder in the presence of two main components; ethylene glycol as a dispersed medium and an industrial copolymer (latex) as protecting agent. The structural, morphological and optical properties of the prepared silver nanoparticles have been investigated by UV–Vis spectroscopy, Infrared Spectroscopy (IR), X Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). It was found that all these properties are strongly correlated to the latex copolymer concentration and the MW heating process. The absorption band was determined by UV Visible spectra, showing several bands (localized surface Plasmon band) in the visible region at wavelengths between 410 and 430 nm. The TEM analysis of the obtained products indicates the presence of straight nanowires and dispersed, spherical silver nanoparticles with well-controlled size ranging from 7 to 20 nm. The X Ray Diffraction showed that silver nanoparticles synthesized exhibit face centered cubic (fcc) structure. The infrared spectra show the strong coordination between the surface of silver particles and molecules of latex by O–H and C=O groups. Antimicrobial activity of latex/Ag NPs against E. coli, Staphylococcus aureus, and Pseudomonas aeruginosa has been also demonstrated. The results indicated that latex/AgNPs may damage the structure of bacterial cell membrane.

Spectral Nonlinear Optical Response of Ion-Implanted Au and Ag Nanoparticles in Sapphire: A Three-Level Model Description

Nonlinear materials are of great technological interest for the realization of nanophotonic devices able to control and manipulate light. These properties can be specifically engineered by exploiting the surface plasmon resonance of plasmonic nanocomposites, in proximity of which nonlinear absorption and refraction are largely enhanced. An exploration of the spectral, irradiance, and host material dependence of the nonlinear parameters is important to be able to gain a thorough understanding of the nonlinear response. In the present work, we investigate the nonlinear optical response of $\mathrm{Au}$ and $\mathrm{Ag}$ nanoparticles embedded in sapphire by a spectral $z$-scan characterization across the localized surface plasmon band of the samples. We also present a comparison of the results obtained for $\mathrm{Au}$ nanoparticles embedded both in silica and in sapphire, produced under equivalent conditions, to test the influence of the host material. We theoretically describe the spectral trends of both the nonlinear absorption coefficient and nonlinear refractive index by implementing a three-level model, which provides important insights into the main physical parameters controlling the observed spectral features, and the possibility of ab initio composite designs with tailored properties.

Investigation the Nonlinear Optical properties of Silver Nanoparticles Using Femtosecond Laser

In this research, the fabrication of silver nanoparticles and experimental nonlinear response (NLO). The fabrication of the silver nanoparticles has been done using E-Beam evaporation on a glass substrate (Ag-NPs) and investigation of their nonlinear optical response (NLO). The silver nanoparticles was evaluated by optical spectrum (UV-Vis) that shows localized surface Plasmon band at 375 nm. The experiment shows the nonlinear absorption and nonlinear refraction effect of silver nanoparticles, the silver nanoparticles is analysed by Z-Scan technique using a femtoseconds laser with 800 nm wavelength. The result shows the nonlinear absorption (NLA) is at 4.87×10−4cmW−1, while (NLR) is at 7.94×10−9cm2W−1.

Studies of SERS efficiency of gold coated porous silicon formed on rough silicon backside

Starting from a rough backside of silicon wafer, we have formed a porous layer by electrochemical anodization and then coated by a thin film of gold. The morphological characteristics of the porous silicon and in turn the metal film are governed by the anodization process and also by the starting surface. So, in order to investigate the Plasmonic aspect of such rough surface which combines roughness inherent to the porous nature and that due to rough starting surface, we have used a dye target molecule to study its SERS signal using a porous silicon layer obtained on the rough backside surface.The use of unusual backside of silicon wafer could be, beside the others, an interesting way to made SERS effective substrate thanks to reproducible rough porous gold on porous layer from this starting face. The morphological results correspond to the silicon rough surface as a function of the crystallographic orientation showed the presence of two different substrate structure. The optical reflectivity results obtained of gold deposited on oxidized porous silicon showed a dependence of its Localized Surface Plasmon band frequency of the deposit time. SERS results, obtained for a dye target molecule (Rhodamine 6G), show a higher intensities in the case of the 〈110〉 orientation, which characterized by the higher roughness surface. Voici “the most relevant and important aspects of our work”.

2,3-Pyridine dicarboxylic acid functionalized gold nanoparticles: Insight into experimental conditions for Cr3 + sensing

Selectivity of gold nanoparticles (AuNPs) depends upon surface functionality; small changes in structure or concentration bring significant changes in the behavior of AuNPs. In this study, citrate-capped AuNPs were functionalized with ortho-dicarboxylate substituted pyridine (2,3-PDCA) and detailed studies on experimental conditions were carried out to check the stability of AuNPs and response for Cr3+. Stability of PDCA-AuNPs was found sensitive to the pH, ionic strength of buffer and its type. Capping behavior of PDCA on C-AuNPs was examined by FTIR spectroscopy. Surface morphology and size of synthesized AuNPs were confirmed by AFM, XRD, and DLS techniques where particles were found 11nm in size, monodisperse and spherical in shape. Interaction of stabilized AuNPs was tested with various metal ions; where Cr3+ induced the changes in localized surface plasmon band (LSPR) of PDCA-AuNPs which leads to a color change from wine red to violet blue. The phenomenon is explained as cooperative effect of citrate and pyridine nitrogen on surface of AuNPs in contrary to meta-dicarboxylate substituted pyridine derivatives. Further, under optimized and controlled conditions Cr3+ shows linear response with decrease in absorbance at LSPR intensity of AuNPs (518nm). Moreover, to demonstrate the applicability of method, Cr3+ was determined in the presence of Cr (VI) which shows 96% recovery.

Nonlinear optical response of platinum nanoparticles and platinum ions embedded in sapphire.

We report on the fabrication of sapphire samples containing platinum nanoparticles (Pt-NPs) and platinum ions (Pt-ions) and the investigation of their third-order nonlinear (NL) optical properties. The presence of Pt-NPs was confirmed by electronic microscopy and by the linear absorption spectrum that shows a localized surface plasmon band centered at 290 nm. A sample without NPs but containing Pt-ions was also studied. The absorptive and refractive contributions to the nonlinearity were studied using the z-scan technique with 100 fs pulses at 800nm. The experiments revealed a NL refractive index, +3.8×10-13 < n2 < +1.3×10-12cm2/W and NL absorption coefficient (β < 9.3 cm/GW). The results show enhancement of about five orders of magnitude with respect to the NL refractive index of sapphire.

Ultrasensitive Characterization of Mechanical Oscillations and Plasmon Energy Shift in Gold Nanorods.

Mechanical vibrational resonances in metal nanoparticles are intensively studied because they provide insight into nanoscale elasticity and for their potential application to ultrasensitive mass detection. In this paper, we use broadband femtosecond pump-probe spectroscopy to study the longitudinal acoustic phonons of arrays of gold nanorods with different aspect ratios, fabricated by electron beam lithography with very high size uniformity. We follow in real time the impulsively excited extensional oscillations of the nanorods by measuring the transient shift of the localized surface plasmon band. Broadband and high-sensitivity detection of the time-dependent extinction spectra enables one to develop a model that quantitatively describes the periodic variation of the plasmon extinction coefficient starting from the steady-state spectrum with only one additional free parameter. This model allows us to retrieve the time-dependent elongation of the nanorods with an ultrahigh sensitivity and to measure oscillation amplitudes of just a few picometers and plasmon energy shifts on the order of 10(-2) meV.

Nonlinear optical response of platinum nanostructures and application for water detection in transformer oil

We report the fabrication of platinum nanostructures on an ITO substrate (Pt-NSs).

Dependence between the Refractive-Index Sensitivity of Metallic Nanoparticles and the Spectral Position of Their Localized Surface Plasmon Band: A Numerical and Analytical Study

The refractive-index sensitivity of metallic nanoparticles was investigated numerically using the FDTD method as well as analytically. The obtained results show that the sensitivity of nanoparticles situated in a homogeneous host matrix is independent of their shape. Moreover, it exclusively depends on the LSPR band location, the dielectric function of the metal constituting the nanoparticles, and the refractive index of the host matrix. In the case of nanoparticles deposited on a substrate or in close interaction with it, the sensitivity is however dependent on the shape. Additionally, a loss of sensitivity is observed. Different theoretical trails are examined in order to better understand those phenomena. The study emphasizes that the shape-dependent sensitivity can be related to the modification of the depolarization factors of the nanoparticles in the presence of a substrate.

Gold Nanoparticles: Probing Zinc-Protein-Chelant Interactions Using Gold Nanoparticles Functionalized with Zinc-Responsive Polypeptides (Part. Part. Syst. Charact. 11/2014)

A strategy for real-time characterization of zinc-protein-chelant interactions is described by D. Aili and co-workers on page 1127. Gold nanoparticles functionalized with a zinc-responsive protein mimetic polypeptide aggregate extensively in the presence of Zn2+. Small molecular chelants have a significant effect on the aggregation that is reflected in the localized surface plasmon band, and which provides extensive information about the nature of the interactions.

Gold Nanowire Forests for SERS Detection.

Simple wet chemistry has been applied to control the vertical growth of gold nanowires on a glass substrate. As a consequence, the longitudinal localized surface plasmon band position can be tuned from 656 to 1477 nm in a few minutes by simply controlling the growth rate and time. This allowed us to select the optimum conditions for maximum electromagnetic enhancement and performance in surface enhanced Raman scattering (SERS) detection. SERS measurements confirmed the uniform and reproducible distribution of the nanowires on the substrate, with the subsequent high reproducibility of hot spot formation. Detection of malachite green in water and of 1-naphthalenethiol from the gas phase are demonstrated as proof-of-concept applications of these three-dimensional SERS substrates.

Designed Synthesis of Solid and Hollow Cu2–xTe Nanocrystals with Tunable Near-Infrared Localized Surface Plasmon Resonance

Solid and hollow structures of Cu2–xTe nanocrystals are synthesized by the injection of a Te–TOP solution at different reaction times. Both types of Cu2–xTe nanocrystals exhibit an intense absorption peak (localized surface plasmon resonance (LSPR)) in the near-infrared region, arising from excess holes in the valence band, and high molar extinction coefficients of 2.6 × 107 M–1 cm–1 at 1150 nm and 8.1 × 107 M–1 cm–1 at 1200 nm are demonstrated for the solid-type and hollow-type Cu2–xTe nanocrystals, respectively. The experimentally observed extinction spectra and calculated extinction spectra based on the electrostatic approximation are studied. The LSPR responses in the near-infrared (NIR) region for both solid and hollow Cu2–xTe nanocrystals are affected by the refractive index of the medium, whereas the NIR resonance shift is more obvious in the hollow-type Cu2–xTe nanocrystals. Furthermore, the localized surface plasmon band of the Cu2–xTe nanostructures can be tuned by post processing via oxidation ...

Doubly resonant surface-enhanced Raman scattering on gold nanorod decorated inverse opal photonic crystals

We present a novel type of surface-enhanced Raman scattering (SERS) substrate constituted of a 3-dimensinal polymeric inverse opal (IO) photonic crystal frame with gold nanorods (Au-NRs) decorating on the top layer. This substrate employs resonant excitation as well as constructive backward scattering of Raman signals to produce large enhancement of SERS output. For the incoming excitation, Au-NRs with appropriate aspect ratio were adopted to align their longitudinal localized surface plasmon band with the excitation laser wavelength. For the outgoing SERS signal, the spectral position of the photonic band gap was tuned to reflect Raman-scattered light constructively. This SERS substrate produces not only strong but also uniform SERS output due to the well control of Au-NRs distribution by the periodic IO structure, readily suitable for sensing applications.

Dependency of Plasmonic Enhancement on the Refractive Index of the Dielectric Bottom Layer of Ag Nanoparticles

We investigated the dependency of plasmon-enhanced luminescence on the refractive index of a dielectric substrate of Ag nanoparticles. We used silicon dioxide ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> =1.456) and indium tin oxide ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> =1.8) as bottom layers for Ag nanoparticles. Due to the extinction spectra of Ag nanoparticles on substrates with high refractive indexes, the localized surface plasmon band moved toward a longer wavelength. Asymmetric ratios for probing plasmon effects can increase in proportion to the extinction of Ag nanoparticles. Adjusting the dielectric medium connected to the Ag nanoparticles, the increase of the extinction and the asymmetric ratios, led to the enhancement of the emission intensities from the Eu <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions.

Tuning the Excitonic and Plasmonic Properties of Copper Chalcogenide Nanocrystals

The optical properties of stoichiometric copper chalcogenide nanocrystals (NCs) are characterized by strong interband transitions in the blue part of the spectral range and a weaker absorption onset up to ~1000 nm, with negligible absorption in the near-infrared (NIR). Oxygen exposure leads to a gradual transformation of stoichiometric copper chalcogenide NCs (namely, Cu(2-x)S and Cu(2-x)Se, x = 0) into their nonstoichiometric counterparts (Cu(2-x)S and Cu(2-x)Se, x > 0), entailing the appearance and evolution of an intense localized surface plasmon (LSP) band in the NIR. We also show that well-defined copper telluride NCs (Cu(2-x)Te, x > 0) display a NIR LSP, in analogy to nonstoichiometric copper sulfide and selenide NCs. The LSP band in copper chalcogenide NCs can be tuned by actively controlling their degree of copper deficiency via oxidation and reduction experiments. We show that this controlled LSP tuning affects the excitonic transitions in the NCs, resulting in photoluminescence (PL) quenching upon oxidation and PL recovery upon subsequent reduction. Time-resolved PL spectroscopy reveals a decrease in exciton lifetime correlated to the PL quenching upon LSP evolution. Finally, we report on the dynamics of LSPs in nonstoichiometric copper chalcogenide NCs. Through pump-probe experiments, we determined the time constants for carrier-phonon scattering involved in LSP cooling. Our results demonstrate that copper chalcogenide NCs offer the unique property of holding excitons and highly tunable LSPs on demand, and hence they are envisaged as a unique platform for the evaluation of exciton/LSP interactions.

Control over the surface plasmon band of block copolymer/Ag/Au nanoparticles composites by the addition of single walled carbon nanotubes

In this study, we demonstrate control over the localized surface plasmon band (SPB) of a micellar poly(styrene- block-4vinylpyridine) (PS- b-P4VP) copolymer thin film composite that includes Ag and Au nanoparticles (NPs) in the presence of single walled carbon nanotubes (SWCNTs). Ag and Au NPs are preferentially located in the P4VP core and the PS corona of ordered spherical PS- b-P4VP copolymer micelles, respectively. This structure gave rise to a single SPB due to the coupling of Ag and Au SPBs. The non-covalent addition of SWCNTs in the block copolymer micelles shifts the coupled SPB to a lower wavelength. The maximum shift in the coupled SPB of approximately 30 nm was achieved in the PS- b-P4VP/Ag/Au NPs composite. The carbon nanotube induced modulation of the coupled SPB stems from the charge accumulation effect of the SWCNTs placed between the two types of nanoparticles.

Gold Nanoparticle-Assisted Laser Surface Modification of Borosilicate Glass Substrates

This paper describes the photomodification of borosilicate glass substrates assembled with 40 nm diameter gold nanoparticles (Au NPs) with surface coverages ranging from 17 to 23% on excitation of the localized surface plasmon band of the NPs with a 532 nm nanosecond pulsed-laser beam. The laser irradiation allowed the splitting and fusion of NPs on the substrate surface and, at the same time, the formation of craters of less than 10 nm diameter at various places following one laser shot with a relatively high intensity of 460 or 370 mJ·cm−2·pulse−1 but well below the breakdown threshold of 25−40 J·cm−2·pulse−1. The formation of the craters was more and more distinctly observed by continuous irradiations. The number density, average diameter, and the surface coverage of the craters were not linearly dependent on the laser shot number but exhibited the saturation behavior due to the consumption of Au NPs. The threshold laser energy for the crater formation was dependent on the accumulated number of laser shots: a greater number of laser shots were necessary to form craters as the laser fluence decreases. Most interestingly, the laser-irradiated areas of the substrate exhibited a greater susceptibility to the wet chemical etching with aqueous hydrogen fluoride. The mechanism of the laser modification and a possible application to nanofabrication on glass surfaces by utilizing Au NPs were discussed on the basis of the scanning electron microscopy (SEM) observation as well as the extinction and light scattering spectroscopic measurements.

Sensitivity of metal nanoparticle plasmon resonance band position to the dielectric environment as observed in scattering

Electrodynamic simulations of gold nanoparticle scattering spectra were used to investigate the sensitivity of localized surface plasmon band position to the refractive index, n, of the medium for moderately high aspect ratio nanoparticles of various shapes and hollow nanoshells of various sizes. For the sub-150 nm particles investigated here, the sensitivity of the peak scattering wavelength, λ*, to refractive index, n, is found to increase linearly with peak wavelength. The refractive index sensitivities of scattering peak location, thus, are found to have the same dependence upon peak position as was previously observed to characterize the sensitivities of extinction peak position. Whereas the plasmon bands of solid nanospheres display peak scattering at longer wavelengths than the wavelengths of peak extinction, the scattering and extinction peaks of high aspect ratio particles of comparable sizes have scattering and extinction spectra that are more closely overlapping. Thus, for these particles, band position sensitivities are independent both of the nature of the spectral measurement and the particle shape, except through shape control of the location of the resonance. Using an analytical expression for the sensitivity of peak wavelength to index of refraction of the medium that captures the dependence of the sensitivity upon the slope of the real part, e', of the particle dielectric function as a function of wavelength, the peak wavelength dependences of the sensitivities were characterized in terms of parameters derived from both linear and quadratic fits to e' in the visible wavelength range. Comparison of sensitivities determined by electrodynamic simulation with the predictions based upon these two dielectric function models indicates that sensitivity estimates based upon linear fit parameters provided better estimates of the sensitivities of plasmon bands in the visible than do estimates based upon quadratic fits appropriate to true Drude metals. The bulk refractive index sensitivities presented here serve as upper bounds to sensitivities of nanoparticles on dielectric substrates and sensitivities of nanoparticles to local refractive index changes, such as those associated with biomolecule sensing.

Sensitivity of Metal Nanoparticle Surface Plasmon Resonance to the Dielectric Environment

Electrodynamic simulations of gold nanoparticle spectra were used to investigate the sensitivity of localized surface plasmon band position to the refractive index, n, of the medium for nanoparticles of various shapes and nanoshells of various structures. Among single-component nanoparticles less than 130 nm in size, sensitivities of dipole resonance positions to bulk refractive index are found to depend only upon the wavelength of the resonance and the dielectric properties of the metal and the medium. Among particle plasmons that peak in the frequency range where the real part of the metal dielectric function varies linearly with wavelength and the imaginary part is small and slowly varying, the sensitivity of the peak wavelength, lambda, to refractive index, n, is found to be a linearly increasing function of lambda, regardless of the structural features of the particle that determine lambda. Quasistatic theory is used to derive an analytical expression for the refractive index sensitivity of small particle plasmon peaks. Through this analysis, the dependence of sensitivity on band position is found to be determined by the wavelength dependence of the real part, epsilon', of the particle dielectric function, and the sensitivity results are found to extend to all particles with resonance conditions of the form, epsilon' = -2chin(2), where chi is a function of geometric parameters and other constants. The sensitivity results observed using accurate computational methods for dipolar plasmon bands of gold nanodisks, nanorods, and hollow nanoshells extend, therefore, to particles of other shapes (such as hexagonal and chopped tetrahedral), composed of other metals, and to higher-order modes. The bulk refractive index sensitivity yielded by the theory serves as an upper bound to sensitivities of nanoparticles on dielectric substrates and sensitivities of nanoparticles to local refractive index changes, such as those associated with biomolecule sensing.