Electromagnetic Enhancement Effect Research Articles

(1 1 1)-facet dominant ultrafine nanoporous silver as SERS substrates with high sensitivities and ultrahigh detection limits

(111)-facet dominant nanoporous Ag (ONP-Ag@-0.5 V) has been fabricated by electrochemical dealloying of Ag20Zn80 precursor alloys composed of ε-AgZn3 single phase in 0.5 M KOH solution at the applied potential of −0.5 V. The ONP-Ag@-0.5 V has a finer nanoporous structure with an average pore size of 16 nm and the specific surface area of 13.0 m2 g−1. The Surface-enhanced Raman scattering (SERS) activity of the ONP-Ag@-0.5 V for Rhodamine 6G (R6G) Raman probe is evaluated to be with a SERS enhancement factor of 2.53 × 1010 and limit of SERS detection of 4.8 × 10−14 M. The superior SERS activities mainly arise from the local electromagnetic enhancement effects of ultrafine (111)-facet dominant nanoporous structure and the narrow ligaments, the edge effects from co-distribution of Ag bumps, the plasmonic effect of the embedded ZnO, as well as the chemical enhancement of (111)-facet adsorption of more R6G molecules.

Effect of TiO2 arrays on surface enhanced Raman scattering (SERS) performance for Ag/TiO2 substrates

Ag/TiO2 nanostructure arrays were constructed on fluorine-doped tin oxide (FTO) via a controllable hydrothermal route and a magnetron sputtering method with a variety of TiO2 arrays decorated by Ag nanoparticles. Effects of different TiO2 arrays on the microstructure, composition, and optical properties of the samples were revealed. As surface enhanced Raman scattering (SERS) active substrates, we discussed the sensitivity and reproducibility of Ag/TiO2 nanostructure arrays for Rhodamine 6G (R6G) molecule detection. It was found that TiO2 nanosheet (TiO2(S)) array as a supporting made Ag nanoparticles have a uniform and continuous distribution, which achieved much higher SERS signals. The obtained Ag/TiO2(S) substrate had an improved enhancement factor of 4.31 × 105 compared with the other Ag/TiO2 nanostructure arrays of nanorods, nanotubes, and nanotrees. Furthermore, Ag/TiO2(S) active substrate showed good reproducibility with low relative standard deviation values. Such a remarkable SERS activity could be due to the synergistic effect of electromagnetic enhancement and charge transfer enhancement. Moreover, the TiO2(S) array with high-exposed {101} facets provided a large adhesion area and generated a strong interaction with external atoms, which would produce high-density ‘hot spots’ of SERS.

Surface enhanced Raman scattering of defective TiO2 thin film decorated with silver nanoparticles by laser ablation

The defective titanium dioxide (TiO2) thin films decorated with silver (Ag) nanoparticles (NPs) were fabricated by pulsed laser ablating the Ag/TiO2 composite films deposited with ion beam assisted deposition (IBAD). The morphology, crystal structure, element status and optical property of the films were investigated. We found the pulsed laser had a marked impact on the size and distribution of Ag NPs and on the oxidation state of titanium. The localized surface plasmon resonance (LSPR) and defect state were efficiently tuned as well. With the laser power increasing, a blue shift in the LSPR peak, and a reduction in the defect content occurred coincided. Additionally, the SERS intensity of the as-ablated Ag/TiO2 thin film is about triple that of as-deposited Ag/TiO2 thin film. Furthermore, the synergistic effect of electromagnetic enhancement and charge transfer was demonstrated to be the main reason for the improvement of SERS performance.

Gold-Nanoparticles/Boron-Doped-Diamond Composites as Surface-Enhanced Raman Scattering Substrates**Supported by the National Natural Science Foundation of China (Grant Nos. 51672102 and 51972135).

By vacuum sputtering and annealing processes of gold (Au) films on boron-doped diamond (BDD) surfaces, Au-nanoparticles/BDD (AuNP/BDD) composite substrates were prepared as surface-enhanced Raman scattering (SERS) substrates. The SERS performances of the substrate were investigated using methylene blue molecule as a probe. With the AuNPs having an average diameter of 20 nm, high performance of SERS was achieved at an enhancement factor of 9 × 105, arising from the synergistic effect of electromagnetic enhancement from AuNPs and chemical enhancement from diamond. The AuNP/BDD substrate is demonstrated to be highly sensitive, reproducible, stable, and reusable for the SERS examination. Due to the facile preparation process and controllable surface morphology, the AuNP/BDD substrates are favorable as a high performance SERS platform performed in practical applications.

Hierarchical growth of Au nanograss with intense built-in hotspots for plasmonic applications

“Au nanograsses” displaying intertwined nanowires produced by hierarchical growth indicate superior electromagnetic enhancement effect in both simulations and single-particle SERS.

Numerical investigations on the electromagnetic enhancement effect to tip-enhanced Raman scattering and fluorescence processes

In the present work, we theoretically study the electromagnetic (EM) enhancement of the Raman and fluorescence signals for a molecule placed in a nanocavity formed by a metallic tip and substrate that mimics a tip-enhanced Raman scattering (TERS) setup using three-dimensional finite element method calculations. The influence of tip size and tip-molecule distance on the EM enhancements of the incident field as well as the radiative and non-radiative decay rates of the molecule are systematically investigated. Simulation results show that the maximum EM enhancement to the incident light as provided by the localized surface plasmon resonance in the nanocavity can reach ∼285 for the configuration considered in the present work. Meanwhile, it was found that, at the classical limit, decreasing the apex radius or the tip-molecule distance can both reduce the spatial distribution (as characterized by the full width at half maximum) of the Raman enhancement in a linear fashion. Moreover, simulation results show that the nonlocal dielectric response of the tip and the substrate plays a key role to the fluorescence quantum yield of the molecule. However, it was found that the strong EM excitation enhancement is the dominating factor for the tip enhanced fluorescence (TEF) effect and stronger fluorescence enhancement has been found when increasing the apex radius or reducing the tip-molecule distance with an incident wavelength of 532 nm. The best TERS and TEF enhancements were found to be ∼ and ∼, respectively, with the tip-molecule distance around 1 nm.

Fast and green synthesis of silver nanoparticles/reduced graphene oxide composite as efficient surface-enhanced Raman scattering substrate for bacteria detection

Developing facile and environmentally friendly synthesis method to fabricate effective platforms for surface-enhanced Raman scattering (SERS) draws much attention in recent years. Herein, a fast and green method is developed to prepare silver nanoparticles/reduced graphene oxide (Ag NPs/rGO) composite, which exhibits favorable SERS activity in detecting bacteria such as Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). With high-loading and well-dispersed Ag NPs (average size of ~63 nm), the Ag NPs/rGO composite fabricated at a mass ratio of 3:1 between AgNO3 and GO presents the best SERS performance, which may be due to the optimal synergistic effect of electromagnetic enhancement originated from Ag NPs and chemical enhancement originated from rGO sheets. Furthermore, the detection sensitivity of the Ag NPs/rGO composite lowers to 1 × 105 CFU/cm3.

Au@PVP Core-Shell Nanoparticles Used as Surface-Enhanced Raman Spectroscopic Substrate to Detect Malachite Green

Abstract The core-shell nanopaticles of Au@ polyvinyl pyrrolidone (PVP) with uniform size and controllable shell-thickness were prepared by hydrothermal method. The core-shell nanoparticles were assembled on Si substrate as monolayer array relying on the dispersion of core-shell nanoparticles arising from PVP shell. The Malachite green (MG) could be adsorbed on the surface of Au@PVP by H-bond between MG and PVP shell, and could be sensitively detected by surface enhanced Raman spectroscopy (SERS) taking advantages of the electromagnetic enhancement effect of inner-core Au nanoparticles. After adsorption of MG molecules onto the surface Au@PVP with 1.5 nm shell-thickness for 18 h, the detection of MG could be realized in the linear range from 1 × 10−10 M to 1 × 10−5 M with the linear correlation coefficient (R2) of 0.98 and detection limit of 1 × 10−12 M (S/N = 3). This method was applied to the determination of MG in tilapia fish fillets, and no MG was detectable. The recoveries of spiked MG in the sample ranged from 70.8% to 126.0% and the relative standard deviations were 2.9–7.6%. This method is simple and accurate, and can be used for detection of MG in the fish.

Strong competition between electromagnetic enhancement and surface-energy-transfer induced quenching in plasmonic dye-sensitized solar cells: A generic yet controllable effect

Light harvesting strategy using plasmonic metal nanostructures as subwavelength light concentrators provides a highly attractive solution to enhancing the performance of dye-sensitized solar cells (DSSCs). Through comprehensive optical spectroscopy and electrical characterizations together with a theoretical analysis, we demonstrate a strong competition between the surface energy transfer induced non-radiative quenching and the plasmonic electromagnetic enhancement effect in metal-dielectric-semiconductor core-shell-shell nanoparticle doped DSSCs, a generic yet unavoidable phenomenon in all types of plasmonic solar cells. The competition of the two effects results in a non-monotonic relationship between the device efficiency and the thickness of the dielectric shell covering the metal nanoparticles, and leads to an optimal thickness for the highest power conversion efficiency. This observation is further corroborated by photoluminescence spectroscopic measurements. Our experimental results are in good agreement with the Persson model that predicts a strong energy quenching effect when the distance between the photogenerated charge carrier and the metal core is short enough. Both experiment and theory show that the localized surface plasmon resonance enhanced light harvesting efficiency is suppressed by the surface energy transfer to the metal cores for the dielectric shell thickness shorter than a characteristic value (~7nm in our study). Our work sheds new insights into the fundamental understanding of the photophysics mechanisms of plasmonic DSSCs and could push forward the study of plasmonic solar cells in terms of device design and fabrication.

Effect of the Molecule–Metal Interface on the Surface-Enhanced Raman Scattering of 1,4-Benzenedithiol

The influence of the number of molecule–metal interactions on the surface-enhanced Raman scattering (SERS) spectroscopy of 1,4-benzenedithiol (BDT) was investigated. For this purpose, a series of SERS-active samples were prepared featuring one or two molecule–metal interfaces. Molecules were adsorbed on the surface of a rough Au substrate, or sandwiched between Au nanoparticles (NPs) and a flat Au(111) substrate in a “sphere–plane” disposition. In the presence of the Au surface(s), vibrational energy and intensity of the SERS spectra differs significantly from the bulk. Molecule–metal charge transfer upon chemisorption weakens intramolecular bonds, resulting in the observed red shift of the breathing and C═C stretching modes. This effect was found to be more pronounced for samples with multiple molecule–metal interfaces. In addition, the SERS spectra of BDT featured additional b2 signals not present in the bulk spectra. Chemical enhancement of the b2 modes takes place by means of photoinduced charge transfer from an occupied molecular orbital to an unoccupied metal orbital. Analysis of the normalized SERS intensity revealed a larger scattering enhancement for the samples with a sphere–plane disposition arising from the stronger electromagnetic enhancement effect via plasmonic localization of optical fields. Complementary studies on 4-aminobenzenethiol support these findings.

Bioinspired multifunctional Au nanostructures with switchable adhesion.

Inspired by the self-cleaning of cicada wings, well-aligned Au-coated Ni nanocone arrays (Au@Ni NAs) have been fabricated by a simple and cheap electrodeposition method. After surface modification of n-hexadecanethiol, self-cleaning can be realized on this long-lived superhydrophobic surface with extremely low adhesive force. Switchable adhesion is obtained on its complementary porous surface. The porous Au structure is fabricated by a geometric replica of the nanocone arrays. After the same surface modification, it shows superhydrophobicity with high adhesion. The different adhesive behaviors on the two lock-and-key Au structures are ascribed to their different contact modes with a water droplet. Combining the superhydrophobic properties of the two complementary structures, they can be used to transport precious microdroplets without any loss. The bioinspired periodic Au@Ni NAs can also be potentially employed as surface-enhanced Raman scattering (SERS) substrates due to its electromagnetic enhancement effect, especially at the tips of the nanocones. Thus, superhydrophobic, SERS, long-lived, self-cleaning, microtransportation functions are realized on the basis of the two surfaces.

Surface-enhanced Raman scattering effects of gold and InSb nanoparticles at THz frequencies

We present here a theoretical analysis of the possibility to combine SERS with THz by investigating the electromagnetic enhancement effects of gold and InSb nanoparticles under THz excitation. By means of the FDTD simulations, the electrical field enhancement, and thus the SERS enhancement factor of the gold and InSb nanoparticles with different sizes and interparticle separations are demonstrated, which indicate that the SERS effect exists in THz range as well and the SERS enhancement factor could reach 109 under the condition of certain size and interparticle distance. Therefore the SERS effect could be extended from ultraviolet, visible and near-infrared to THz regime.

Multiscale electromagnetic SERS enhancement on self‐assembled micropatterned gold nanoparticle films

In this work, we demonstrate a cascaded, multiplicative electromagnetic enhancement effect in surface‐enhanced Raman scattering (SERS) on periodically micropatterned films made of colloidal gold nanoparticles, prepared by a self‐assembly approach, without implying lithography procedures. The multiplicative enhancement effect is obtained by combining surface plasmon near‐field enhancement due to nanoscale features with far‐field photonic coupling by periodic microscale features. The effect is observed for both internal Raman reporters (molecules attached to the Au colloids before their assembly) and external Raman probes (molecules adsorbed on the samples after film assembly). The ability of the patterned films for far‐field light coupling is supported by reflectivity spectra, which present minima/maxima in the visible spectral range. Finite‐difference time‐domain computer simulations of the electric field distribution also support this interpretation. The fabricated dual‐scale SERS substrates exhibit a good spot‐to‐spot reproducibility and time stability, as proved by the SERS response over a time scale longer than 1 month. The experimental demonstration of this cascaded electromagnetic enhancement effect contributes to a better understanding of SERS and can affect future design of SERS substrates. Moreover, such dual‐scale colloidal films prepared by convective self‐assembly can be of general interest for the broader field of nanoparticle‐based devices. Copyright © 2014 John Wiley & Sons, Ltd.

Solution-based direct readout surface enhanced Raman spectroscopic (SERS) detection of ultra-low levels of thiram with dogbone shaped gold nanoparticles

We report the use of two different sizes of dogbone shaped gold nanoparticles as colloidal substrates for surface enhanced Raman spectroscopy (SERS) based detection of ultra-low levels of thiram, a dithiocarbamate fungicide. We demonstrate the ability to use a solution based, direct readout SERS method as a quantitative tool for the detection of ultra-low levels of thiram. The two different sizes of dogbone shaped gold nanoparticles are synthesized by using the seed-mediated growth method and characterized by using UV-visible spectroscopy and transmission electron microscopy (TEM). The smaller dogbone shaped nanoparticles have an average size of 43 ± 13 nm. The larger dogbone shaped gold nanoparticles have an average size of 65 ± 15 nm. The nanoparticle concentration is 1.25 × 10(11) nanoparticles per mL for the smaller dogbone shaped gold nanoparticles and is 1.13 × 10(11) nanoparticles per mL for the larger dogbone shaped gold nanoparticles. Different concentrations of thiram are allowed to bind to the two different sizes of dogbone shaped gold nanoparticles and the SERS spectra are obtained. From the calibration curve, the limit of detection for thiram is 43.9 ± 6.2 nM when the smaller dogbone shaped gold nanoparticles are used as colloidal SERS substrates In the case of the larger dogbone shaped gold nanoparticles, the limit of detection for thiram is 11.8 ± 3.2 nM. The lower limit of detection obtained by using the larger dogbone shaped gold nanoparticles as colloidal substrates is due to the lightning rod effect, higher contributions from the electromagnetic enhancement effect, and larger number of surface sites for thiram to bind.

TDDFT Investigation of Surface-Enhanced Raman Scattering of HCN and CN−on Ag20†

Density functional calculations at the BP86/TZP level of theory are employed to examine the structures, binding energies, and vibrational frequencies of HCN-Ag(20) and CN(-)-Ag(20) complexes. Excited states are calculated using time-dependent density functional theory. A short time approximation for the perturbed density matrix and an empirical damping factor are employed to calculate surface-enhanced Raman scattering (SERS) intensities that account for both chemical and electromagnetic enhancement effects. Chemical effects provide 1-2 orders of magnitude enhancement, whereas electromagnetic effects yield up to 6 orders of magnitude enhancement for CN(-) or 5 for HCN. The structures and SERS enhancement factors suggest that multiple bonding configurations may be observed in experiment.

A High-Efficiency Surface-Enhanced Raman Scattering Substrate Based on Silicon Nanowires Array Decorated with Silver Nanoparticles

We introduce a unique surface-enhanced Raman scattering (SERS) substrate, which is made of hierarchical nanoarrays comprising silicon nanowires (SiNWs) decorated with silver nanoparticles (AgNPs). SiNWs arrays were produced through chemical etching of n-Si(100) wafer, while AgNPs were directly grown on SiNWs through galvanic redox reaction without any organic contamination. Solid surface extinction spectrum revealed strong surface plasmon absorption in a broad range (from 200 to 1000 nm) indicating that surface plasmon induced by the incident laser could resonate with incident and scattering photons in a broad wavelength region. The 3D arrangement of the AgNPs@SiNWs array offered significant advantages over conventional planar geometry, where the long interaction distance favored multiple plasmon resonances and strong electromagnetic enhancement effect. The substrate exhibited strong surface-enhanced effect in Raman scattering with a few percent reproducibility in Raman signals. The observed enhancement f...

Surface‐ and Resonance‐Enhanced Micro‐Raman Spectroscopy of Xanthene Dyes: From the Ensemble to Single Molecules

Surface-enhanced resonance Raman scattering (SERRS) spectra of various rhodamine dyes, of pyronine G and thiopyronine adsorbed on isolated silver clusters were recorded at the ensemble level and at the single-molecule level with a high-resolution confocal laser microscope equipped with a spectrograph and a CCD-detector. Comparing single-molecule spectra with ensemble spectra, various inhomogeneous spectral features, such as line splitting, spectral wandering, spectral diffusion and abrupt spectral jumps between different metastable spectral states, are revealed positions and the relative intensities of the vibronic bands. Resonance enhancement is investigated with respect to single-molecule surface-enhanced Raman scattering (SERS) spectroscopy and is found to be responsible for approximately three orders of magnitude in sensitivity. A significant influence of the substituents on the single-molecule SERRS sensitivity is found, showing that various chemical effects are responsible for surface enhancement in addition to the electromagnetic enhancement effect.

Electromagnetic enhancement effect in scanning tunneling microscope light emission from GaAs

The electromagnetic enhancement effect in scanning tunneling microscope (STM) light emission from GaAs has been investigated by the finite difference time domain method. We have calculated the intensity of light emitted by the recombination of minority carriers injected from the tip and majority carriers in the sample. The results depend not only on the material and the shape of the tip but also on light polarization. When the tip is tungsten whose dielectric function has a positive real part at 1.5 eV, the p-polarized light intensity depends strongly on the size of the tip and the location of recombination. However, the s-polarized light emission depends only weakly on these parameters. If the tip is a perfect metal, the p-polarized light intensity becomes a few times stronger than that for the W tip of the same shape. On the other hand, the s-polarized light intensity becomes weaker than that for the W tip due to the electromagnetic screening effect of a perfect metal. We conclude that the combination of the W tip and s-polarized light detection is suitable for precise measurement of the tip-position dependence of STM light emission properties. A tip with a negative value of the real part of dielectric function is preferable to the W tip, if one does not analyze the tip-position dependence of STM light emission, because STM light emission is enhanced relative to the case of the W tip.