Enhanced localized plasmonic detections using partially-embedded gold nanoparticles and ellipsometric measurements (original) (raw)
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Plasmonics and Its Applications
Plasmonics is a quickly developing subject that combines fundamental research and applications ranging from areas such as physics to engineering, chemistry, biology, medicine, food sciences, and the environmental sciences. Plasmonics appeared in the 1950s with the discovery of surface plasmon polaritons. Then, plasmonics went through a novel impulsion in mid-1970s when the surface-enhanced Raman scattering was discovered. Nevertheless, it is in this last decade that a very significant explosion of plasmonics and its applications has occurred. Thus, this special issue reports a snapshot of current advances in these various areas of plasmonics and its applications presented in the format of several articles and reviews written by worldwide researchers of this topic.
Near-Field and Far-Field Sensitivities of LSPR Sensors
The Journal of Physical Chemistry C, 2015
The present study compares the near-field and far-field sensitivities of localized surface plasmon resonance (LSPR) sensors. To put into evidence the difference between far-field and near-field sensors, optical extinction measurements have been performed on gold nanoparticle gratings coated with dielectric superstrates of varying thicknesses. The potential of LSPR sensors is usually considered to lie in the near-field regime. Therefore, a comparison of the near-field sensitivities for gold nanoparticle gratings and continuous gold films of 50 nm in thickness is provided. The difference in refractive index sensitivities of both sensors is discussed in relation with the decay length of the evanescent near-field. SPRs sensors are usually considered more sensitive than LSPRs in terms of the m factor, refractive index sensitivity. We argue that the m factor sensitivity can only be defined for thick (15−100 nm) superstrates; for thin superstrates (d < 15 nm), the decay length of the evanescent field must be taken into account to properly compare both sensors.
Metal island film-based structures for sensing using spectrophotometry and ellipsometry
Applied Physics A, 2014
Metal island films (MIF) are good candidates for sensors due to the strong sensitivity of the localised surface plasmon resonance to the environment refractive index. The strong near field enhancement in the vicinity of the island surface can be even higher if a metal layer (ML) is placed close to a MIF. Structures containing MIF with and without ML are prepared and sensitivities of spectrophotometric and ellipsometric features of the measurements are compared. It is shown that simple MIF is preferable for ellipsometry-based sensing and the one including ML in the case of spectrophotometric measurements.
Sensors and Actuators B: Chemical, 2013
Colloidal solutions of Au and TiO 2 nanoparticles are prepared and deposited as nanocrystal inks for the fabrication of porous thin films to be used as optical gas sensor. The introduction of Au nanoparticles within the anatase matrix affects the reactions mechanism improving the sensing process; moreover the Au surface plasmon resonance peak can be used for the realization of a gas sensor with tunable sensitivity. Different thermal treatments, Au dimensions and concentrations are investigated and optimized in order to tailor films microstructure and their sensing properties. The nanocomposites show reversible change in optical absorption/reflection when exposed to reducing gasses (H 2 , CO) at 300 • C operative temperature or when exposed to volatile organic compounds (alcohols) at room temperature.
Quaternized chitosan mediated assembly of gold nanoparticles multilayers
Electrochimica Acta, 2014
A c c e p t e d M a n u s c r i p t Multilayer films containing gold nanoparticles and quaternized chitosan were built on quartz gold substrates. The surface coverage and the interlayer coupling of AuNps depend on the particles adsorption time. The obtained values of thickness per bilayer show a progressive enhance as the AuNps surface coverage increases. The gold nanoparticles increase the heterogeneous charge transfer rate constant of redox probes being the values independent of the number of bilayers in the structure Research Highlights Abstract Self-assembled multilayers of quaternized chitosan (QCHI) and gold nanoparticles (AuNPs) were built up on quartz and gold substrates. To evaluate the effect of the surface coverage of AuNP on the structural, optical and electrochemical properties of multilayers prepared with different AuNPs adsorption time were compared. UV-Vis and AFM characterization indicated that AuNPs in each bilayer are spatially separated, and interparticle interactions are mainly produced between bilayers. The complex refractive index and thickness of the QCHI-AuNPs multilayers were properly determined using an anisotropic single layer model. The optical constants obtained were quite different from those of bulk gold, and their values depend on the coverage of AuNPs. The thickness per bilayer of the structures present a progressive increase as AuNP's coverage augments, reaching a value close to the nominal AuNPs diameter after 60 min of adsorption. These results indicate that the interpenetration of bilayers in the structure depends on the surface concentration of AuNPs. The charge transport through the QCHI-AuNPs film was studied using different redox probes. The effects of the adsorption time of AuNPs and the number of bilayers (n) of the structure on the charge transfer rate constants, k ct , were analyzed.
We report a detailed correlation analysis of the size, shape, and distribution of Au nanoparticles (NPs) on fine-tuning of localized surface plasmon resonance and optical absorption cross-section. Experimental analysis of annealing temperature and initial Au layer thickness on NP parameters such as size, interparticle distance, surface coverage, and circularity factor has been studied. The effect of annealing on the morphological, structural, dielectric, and elemental behavior of Au NPs has been reported. Theoretically, we have analyzed the tuning of LSPR and absorption cross-section peaks by varying NP parameters, surrounding medium, and substrate. This report is critical in terms of predicting performance enhancement of ultrathin photovoltaics with varied cell architectures.
Optical response of supported gold nanodisks
Optics Express, 2011
It is shown that the ellipsometric spectra of short range ordered planar arrays of gold nanodisks supported on glass substrates can be described by modeling the nanostructured arrays as uniaxial homogeneous layers with dielectric functions of the Lorentz type. However, appreciable deviations from experimental data are observed in calculated spectra of irradiance measurements. A qualitative and quantitative description of all measured spectra is obtained with a uniaxial effective medium dielectric function in which the nanodisks are modeled as oblate spheroids. Dynamic depolarization factors in the long-wavelength approximation and interaction with the substrate are considered. Similar results are obtained calculating the optical spectra using the island-film theory. Nevertheless, a small in-plane anisotropy and quadrupolar coupling effects reveal a very complex optical response of the nanostructured arrays.
ACS nano, 2014
We present a plasmon-active hybrid nanomaterial design with electrochemical tunability of the localized surface plasmon resonances. The plasmonic-active nanostructures are composed of silver nanocube aggregates embedded into an electrochromic polymer coating on an indium tin oxide electrode with the nanocube aggregation controlled by the surface pressure. Such polymer-nanocube hybrid nanomaterials demonstrated unique tunable plasmonic behavior under an applied electrochemical potential. A significant reversible experimental peak shift of 22 nm at an electrical potential of 200 mV has been achieved in these measurements. Finite-difference time-domain (FDTD) simulations show that, under full oxidation potential, a maximal spectral shift of ca. 80 nm can be potentially achieved, which corresponds to a high sensitivity of 178 nm per refractive index unit. Furthermore, FDTD modeling suggests that the electrochemically controlled tunability of plasmonic peaks is caused by reversible chang...
Enhanced gold film-coupled graphene-based plasmonic nanosensor
A particular interesting plasmonic system is that of metallic nanostructures interacting with metal films. As the localized surface plasmon resonance (LSPR) behavior of gold nanostructures (Au NPs) on the top of a gold thin film is exquisitely sensitive to the spacer distance of the film-Au NPs, we investigate in the present work the influence of a few-layered graphene spacer on the LSPR behavior of the NPs. The idea is to evidence the role of few-layered graphene as one of the thinnest possible spacer. We first show that the coupling to the Au film induces a strong lowering at around 507 nm and sharpening of the main LSPR of the Au NPs.