Silver Nanoparticle Arrays Research Articles

Differentiation of water samples based on sensor array of silver nanoparticles

Differentiation of water samples based on sensor array of silver nanoparticles

Controlling Plasmon Resonance of Gold and Silver Nanoparticle Arrays with Help of Liquid Crystal

The tunability of plasmonic resonances in gold and silver nanosphere arrays on a glass substrate, embedded in a liquid crystal matrix, was explored. The calculations involving the finite element method revealed that the optical properties of these arrays can be modulated by reorienting the liquid crystal. When the liquid crystal director was reoriented between planar and homeotropic configurations in the plane containing the incident wave polarization vector, the plasmonic resonance wavelength shifted within an approximately 100 nm range. A reduced shift of about 40 nm was observed when the reorientation occurred in the plane perpendicular to the polarization. Both metal nanosphere arrays showed notable near-field amplification. Gold achieved up to 18 times the amplification of the incident wave electric field, while silver reached 16 times but showed a remarkable 40 times amplification at the inter-band transition resonance wavelength. This research underscores the potential of using liquid crystal reorientation for controlling the plasmonic lattice resonance in metal nanosphere arrays, opening up new possibilities for adaptable plasmonic devices.

Rapid detection of nicotine and benzoic acid in e-liquids with surface-enhanced Raman scattering and artificial intelligence-assisted spectrum interpretation

Electronic cigarettes have rapidly gained acceptance recently. Nicotine-containing electronic cigarette liquids (e-liquids) are prohibited in some countries, but are permitted and simply available online in others. A rapid detection method is therefore required for on-site inspection or screening of a large amount of samples. Our previous study demonstrated a surface-enhanced Raman scattering (SERS)-based approach to identify nicotine-containing e-liquids; without any pre-treatment, e-liquid can be directly tested on our solid-phase SERS substrates, made of silver nanoparticle arrays embedded in anodic aluminium oxide nanochannels (Ag/AAO). However, this approach required manual determination of spectral signatures and negative samples should be validated in the second round detection. Here, after examining 406 commercial e-liquids, we refined this approach by developing artificial intelligence (AI)-assisted spectrum interpretations. We also found that nicotine and benzoic acid can be simultaneously detected in our platform. This increased test sensitivity because benzoic acid is usually used in nicotine salts. Around 64% of nicotine-positive samples in this study showed both signatures. Using either cutoffs of nicotine and benzoic acid peak intensities or a machine learning model based on the CatBoost algorithm, over 90% of tested samples can be correctly discriminated with only one round of SERS measurement. False negative and false positive rates were 2.5–4.4% and 4.4–8.9%, respectively, depending on the interpretation method and thresholds applied. The new approach takes only 1 microliter of sample and can be performed in 1–2 min, suitable for on-site inspection with portable Raman detectors. It could also be a complementary platform to reduce samples that need to be analyzed in the central labs and has the potential to identify other prohibited additives.

Plasmonic volcano-like fiber-optic probe for Raman enhancement.

Light-matter interaction is a fascinating topic extensively studied from classical theory, based on Maxwell's equations, to quantum optics. In this study, we introduce a novel, to the best of our knowledge, silver volcano-like fiber-optic probe (sensor 1) for surface-enhanced Raman scattering (SERS). We employ the emerging quasi-normal mode (QNM) method to rigorously calculate the Purcell factor for lossy open system responses, characterized by complex frequencies. This calculation quantifies the modification of the radiation rate from the excited state e to ground state g. Furthermore, we use and extend a quantum mechanical description of the Raman process, based on the Lindblad master equation, to calculate the SERS spectrum for the plasmonic structure. A common and well-established SERS probe, modified by a monolayer silver nanoparticle array, serves as a reference sensor (sensor 2) for quantitatively predicting the SERS performance of sensor 1 using quantum formalism. The predictions show excellent consistency with experimental results. In addition, we employ the FDTD (finite-difference time-domain) solver for a rough estimate of the all-fiber Raman response of both sensors, revealing a reasonable range of SERS performance differences compared to experimental results. This research suggests potential applications in real-time, remote detection of biological species and in vivo diagnostics. Simultaneously, the developed FDTD and quantum optics models pave the way for analyzing the response of emitters near arbitrarily shaped plasmonic structures.

Sol-Gel Synthesis of Uniform Arrays of Ag and Au Nanoparticles

The obtaining of uniform arrays of silver and gold nanoparticles with a surface density up to 3.3∙109 cm–2 on the zinc oxide buffer layers by sol-gel method is described. The variations of the solution composition and synthesis mode, layers coating and subsequent heat treatment were carried out. The absorption spectra of the obtained samples had a peak near 400–570 nm corresponding to the plasmon resonance in the Ag and Au nanoparticles. Wavelength and shape of Ag and Au nanoparticles plasmon peak varied depending on the synthesis mode: the use of ZnO buffer layers leads to an increase in the intensity of the nanoparticles plasmon peak, the annealing leads to a gradual decrease and broadening of the absorption peak of Ag and mixed Ag and Au nanoparticles arrays, but does not affect the peak of Au nanoparticles.

Strong light-matter coupling in pentacene thin films on plasmonic arrays.

Utilizing strong light-matter coupling is an elegant and powerful way to modify the energy landscapes of excited states of organic semiconductors. Consequently, the chemical and photophysical properties of these organic semiconductors can be influenced without the need of chemical modification but simply by implementing them in optical microcavities. This has so far mostly been shown in Fabry-Pérot cavities and with organic single crystals or diluted molecules in a host matrix. Here, we demonstrate strong, simultaneous coupling of the two Davydov transitions in polycrystalline pentacene thin films to surface lattice resonances supported by open cavities made of silver nanoparticle arrays. Such thin films are more easily fabricated and, together with the open architecture, more suitable for device applications.

Broadband and large-depth terahertz modulation by self-assembly monolayer silver nanoparticle arrays

Broadband and large-depth THz modulation are crucially important for building next-generation THz devices in THz communication systems. Here, we present a broadband and large-depth THz modulator based on silicon/self-assembled silver nanoparticle (SAM AgNP) arrays, which exhibits a broadband modulation within the frequency range of 0.2–2.0 THz and a large modulation depth of ∼91.2% under a moderate near-infrared (NIR) light intensity of 1.77 W cm−2. For a modulation mechanism, the plasmon-enhanced NIR light absorption of SAM AgNP arrays shows a key role in increasing the photoconductivity of the device under NIR light irradiation. The experimental results are verified well by the numerical simulation. The proposed device can significantly improve the overall performance of THz systems, and opens the opportunity for designing novel nanoparticle-based THz devices.

Optimization of Colloidal Gold Nanoparticles on Porous Anodic Aluminum Oxide Substrates for Refractometric Sensing.

A new composite metal-insulator-metal (MIM) system consisting of exceptionally dense non-close-packed (NCP) arrays of gold or silver nanoparticles, porous anodic aluminum oxide (PAAO), and bulk aluminum substrate interacts strongly with visible light and may become a very useful component for optical applications. The proposed MIM structure can be synthesized using accessible lithography-free chemical and physical processes (anodization and capillary force assisted colloidal particle deposition) that are suitable for the low-cost production of specialized devices. Here, we present a systematic study to determine the essential MIM structure parameters (nanoparticle size and PAAO layer thickness) for localized surface plasmon resonance (LSPR) refractometric sensing. A performance comparison was done by recording the spectra of scattered light upon angled illumination in media with different refractive indices. A clear advantage for maximizing the signal to background ratio was observed in the case of 60 and 80 nm Au nanoparticles with a PAAO thickness in a narrow range between 300 and 375 nm. Sensitivity exceeding a 200 nm peak wavelength shift per refractive index unit was found for 60 nm Au nanoparticles on approximately 500-nm-thick PAAO. The experimental observations were supported by finite-difference time-domain (FDTD) simulations.

Plasmon resonance of gold and silver nanoparticle arrays in the Kretschmann (attenuated total reflectance) vs. direct incidence configuration

While the behaviour of plasmonic solid thin films in the Kretschmann (also known as Attenuated Total Reflection, ATR) configuration is well-understood, the use of discrete nanoparticle arrays in this optical configuration is not thoroughly explored. It is important to do so, since close packed plasmonic nanoparticle arrays exhibit exceptionally strong light-matter interactions by plasmonic coupling. The present work elucidates the optical properties of plasmonic Au and Ag nanoparticle arrays in both the direct normal incidence and Kretschmann configuration by numerical models, that are validated experimentally. First, hexagonal close packed Au and Ag nanoparticle films/arrays are obtained by air–liquid interfacial assembly. The numerical models for the rigorous solution of the Maxwell’s equations are validated using experimental optical spectra of these films before systematically investigating various parameters. The individual far-field/near-field optical properties, as well as the plasmon relaxation mechanism of the nanoparticles, vary strongly as the packing density of the array increases. In the Kretschmann configuration, the evanescent fields arising from p- and s-polarized (or TM and TE polarized) incidence have different directional components. The local evanescent field intensity and direction depends on the polarization, angle of incidence and the wavelength of incidence. These factors in the Kretschmann configuration give rise to interesting far-field as well as near-field optical properties. Overall, it is shown that plasmonic nanoparticle arrays in the Kretschmann configuration facilitate strong broadband absorptance without transmission losses, and strong near-field enhancement. The results reported herein elucidate the optical properties of self-assembled nanoparticle films, pinpointing the ideal conditions under which the normal and the Kretschmann configuration can be exploited in multiple light-driven applications.

Annealing Temperature-Dependent Surface-Enhanced Raman spectroscopy on MoS2-Covered silver nanoparticle array

Surface-enhanced Raman spectroscopy (SERS) is an ultra-sensitive analytical tool that can effectively detect and identify molecules by their unique vibrational fingerprints. Development of SERS substrates with good stability, high sensitivity and reproducibility is still a big challenge in practical applications. Recently, 2D materials/metallic hybrid SERS substrates provide a new prospect to improve the SERS performance. Here, we obtain a monolayer MoS2 covered silver nanoparticle (AgNP) array as a high-performance SERS substrate. Annealing temperature-dependent SERS signals on the hybrid substrate have been explored. The optimum SERS performance was obtained at 290 ℃ (the detection limit of 10−13 M for Rhodamine 6G and the corresponding SERS enhancement factor of 8.3 × 109), which is attributed to the better contact between AgNPs and MoS2 and the uniform AgNPs with appropriate particle sizes. The prepared MoS2/AgNPs hybrid substrates also have been utilized to detect various molecules, which demonstrates a great potential for applications in food safety and biochemical environmental detection.

Silver Nanoparticle Arrays onto Glass Substrates Obtained by Solid-State Thermal Dewetting: A Morphological, Structural and Surface Chemical Study.

Silver nanoparticles (NPs) on glass substrates were obtained by a solid-state thermal dewetting (SSD) process using vacuum-evaporated-silver precursor layers. An exhaustive investigation of the morphological, structural, and surface chemistry properties by systematically controlling the precursor film thickness, annealing temperature, and time was conducted. Thin silver films with thicknesses of 40 and 80 nm were deposited and annealed in air by applying a combined heat-up+constant temperature–time program. Temperatures from 300 to 500 °C and times from 0 to 50 min were assayed. SSD promoted the morphological modification of the films, leading to the Ag NPs having a discrete structure. The size, shape, surface density, and inter-nanoparticle distance of the nanoparticles depended on the initial film thickness, annealing temperature, and time, exhibiting a cubic silver structure with a (111) preferred crystallographic orientation. The prepared NPs were found to be highly enriched in the Ag{111}/Ag{110}/Ag{100} equilibrium facets. SSD not only promotes NP formation but also promotes the partial oxidation from Ag to AgO at the surface level. AgO was detected on the surface around the nanoparticles synthesized at 500 °C. Overall, a broad framework has been established that connects process factors to distinguish resultant Ag NP features in order to develop unique silver nanoparticles for specific applications.

Quadrupolar lattice plasmon modes induced by diffraction of high-quality factors in silver nanoparticle arrays

Periodic nanoparticle arrays with lower loss or high-quality (<i>Q</i>) factor resonances have made great advances in numerous applications. Such arrays can support narrow resonance modes by the hybridization of plasmonic-photonic modes, known as lattice plasmon modes (LPMs). The LPMs arise from the diffraction-induced coupling between localized surface plasmon resonances (LSPRs) of nanoparticles in symmetric or quasi-symmetric refractive index environment. To date, the great majority of researches have focused on the coupling of dipolar modes to in-plane orthogonal diffraction waves in nanoparticle arrays, resulting in dipolar lattice plasmon modes (DLPMs). However, there are few studies about quadrupolar lattice plasmon modes (QLPMs) for parallel coupling in symmetric environment, especially for high <i>Q</i>-factor QLPMs. In this work, we explore the sharp QLPMs of the silver nanodisk arrays by <i>x</i>-polarized light at normal incidence. In the first place, the scattering cross-section and near-field electric field distribution of single silver nanodisk indicate the existence of dipolar and quadrupolar LSPRs, thus, the optical responses of silver nanodisk arrays exhibit the peak-and-dip profiles of DLPMs and QLPMs at different wavelengths. Also, the electromagnetic field distributions confirm that the parallel propagating electric field introduces QLPM and results in electric field delocalization, while DLPM is existent in another way in periodic silver nanodisk arrays. Moreover, the position, linewidth and lineshape of the QLPM strongly depend on the role of lattice period. We enable these resonance modes to be selectively accessed and individually optimized by tuning lattice periods in the <i>x</i>- or <i>y</i>-direction. By changing the lattice period in the <i>x</i>-direction from 300 to 550 nm in steps of 50 nm, the dip of transmission intensity increases gradually, and when periods in the two directions are equal, the transmission dip exhibits a narrow-band QLPM resonance with a linewidth of 0.4 nm, corresponding quality factor is as high as <i>Q</i> = 1815 under the <i>x</i>-polarized light. In particular, by varying periods in the <i>y</i>-direction, the QLPM can also be manipulated in a range from an asymmetric Fano-like lineshape peak to a dip. The acquisition of these results may provide a design strategy for high-<i>Q</i> factor resonance in nanolaser, sensing, and nonlinear optics.

Laser nanoprinting of floating three-dimensional plasmonic color in pH-responsive hydrogel

Recent demonstrations of metasurfaces present their great potential to implement flat and multifunctional optical elements, which are accomplished with the designs of planar optics and micro-/nano- fabrications. Integrating metasurfaces in three dimensions has manifested drastically increasing advantages in manipulating light fields by extending design freedom. However, fabricating three-dimensional metasurfaces remain a tough challenge due to the lack of stereo printing protocols. Herein, we demonstrate laser nanoprinting of floated silver nanoparticle array in transparent hydrogel films for 3D metasurface to achieve color patterning. It is found that spatially resolved nanoparticles can be produced through laser induced photoreduction of silver ions and robustly anchored to the gel backbones by a focused femtosecond laser beam within a pH-responsive smart hydrogel matrix. With the aid of expansion properties of the pH-responsive hydrogel, repetitive coloration of the patterned plasmonic nanoparticle array over a wide spectrum range is achieved via reversible regulation of nanoparticle spacing from 550 to 350 nm and vice versa. This approach allows broadband 3D color-regulation in nanoscale for applications in active spectral filtering, information encryption, security tagging and biological colorimetric sensing, etc.

Silver nanoparticle array on weakly interacting epitaxial graphene substrate as catalyst for hydrogen evolution reaction under neutral conditions

The paucity of research on hydrogen evolution reaction (HER) under neutral conditions, which is a more sustainable way to produce H2 compared to acidic and alkaline HER, encourages the development of efficient catalytic materials and devices and deeper investigation of the mechanisms behind neutral HER. We present an electrode concept for facilitating HER under neutral conditions. The concept entails the use of annealing-reshaped silver (Ag) nanoparticle array on monolayer epitaxial graphene (MEG) on 4H-SiC. Measurements of HER performance show more positive onset potential of the cathodic HER for Ag-decorated MEG compared to that for pristine MEG, indicating improved water dissociation at Ag/MEG electrodes. Complementary morphological characterization, absorption measurements, and Raman mapping analysis enable us to ascribe the enhanced catalytic performance of electrodes decorated with 2 nm thick annealed Ag on the synergetic effect originating from simultaneous water reduction on circular Ag nanoparticles of 31 nm in diameter and on compressively strained Ag-free graphene regions. The overall results pave the way toward development of stable van der Waals heterostructure electrodes with a tunable metal–carbon interaction for fast HER under neutral conditions.

Magnetic and Plasmonic Composite Nanostructures for Creating Optical Filters at Substance and Material Diagnostics Systems

Introduction. Porous silicon (PS) and materials on its basis are of interest for application in nanoelectronics, targeted drug delivery and advanced gas sensors. In addition, PS-based nanostructures are promising as filters in fibre-optic communication systems, since conventional thin-film deposition filters possess sidebands in their operating range thus requiring high vacuum for nanometer-thick coatings.Aim. To develop optical band-stop filter prototypes based on composite magnetic nanoparticles and the effect of localized surface plasmon resonance (LSPR) in an array of silver nanoparticles located on the PS surface. Materials and methods. The development and synthesis of nanostructures for the creation of filter prototypes. The double differentiation method in conjunction with Mie absorption theory was used for processing and analyzing the prototypes attenuation characteristics.Results. Two prototypes were developed. An analysis of the attenuation characteristics of a prototype based on SiO2 matrix functionalized by FemOn indicated that the parameters of the detected absorption bands depend on the size of FemOn nanoparticles. The attenuation characteristics of the LSPR-based prototype contain two absorption bands. The center wavelength value in the band caused by LSPR in the array of silver nanoparticles, close to spherical, is 367.5 nm. Excitation of LSPR in silver quantum clusters, manifested by the appearance of the corresponding band, occurs at a wavelength of 265.5 nm. The suppression in each of the bands can be controlled by changing the parameters of the PS matrix synthesis.Conclusion. Despite the disadvantages, e.g. a relatively low accuracy in setting the center wavelength, as well as certain difficulties concerned with reducing the unevenness in the absorption band, the obtained prototypes surpass existing analogues and are prospective for the development of compact analysis and diagnostics systems in a wide energy range.

Influence of plasmonic resonant wavelength on energy transfer from an InGaN quantum well to quantum dots

We demonstrated the enhanced nonradiative resonant energy transfer (NRET) process by localized surface plasmon (LSP) in the hybrid InGaN quantum well (QW) and CdSe/ZnS quantum dot (QD) structures. The LSP resonant wavelengths could be adjusted by silver (Ag) nanoparticle (NP) arrays annealed from different thicknesses of Ag films. The LSP resonant wavelengths that are close to the peak QD emission helped to enhance the NRET between the QW and QDs. Compared to the original NRET in the absence of Ag NPs, the LSP-enhanced NRET rate was improved by 6.9 times at the resonant wavelength of 600 nm. The calculated efficiency of the LSP-enhanced NRET was 73.1%, which was almost twice that of the original efficiency. Although Ag NPs exhibited a quenching effect, the LSP-enhanced NRET at the resonant wavelength of 465 nm enhanced QD luminescence, which demonstrated their potential use in energy conversion devices.

Diffraction-induced quadrupolar lattice plasmon modes of high-quality factors for silver nanoparticle arrays

金属纳米颗粒阵列中形成的四偶极晶格共振模式具有低辐射损耗、高品质因子的特性，因此广泛应用于纳米激光、传感、固态照明等领域。基于时域有限差分法在均匀环境下研究了银纳米圆柱阵列的光谱与近场特性。研究结果表明，在x偏振光直入射下，通过调节阵列x方向的周期，共振强度先增加后降低，当两个方向上的周期相等时，提出的阵列结构能够产生一个线宽约0.4 nm、品质因子高达1815的四偶极晶格共振模式，这种共振模式呈现出Fano线型的透射谷；调控y方向的周期能够实现从Fano线型的透射峰到透射谷的转变；此外，银纳米圆柱直径、高度的增加将更有利于四偶极晶格共振模式的产生。本文说明了粒子大小、晶格周期对四偶极晶格共振模式的重要性，同时为银纳米颗粒在可见光波段设计高品质因子共振提供了优化策略。

Thermal Stabilization of the Geometric Parameters of an Array of Silver Nanoparticles Obtained by Vacuum-Thermal Evaporation on an Unheated Substrate

The nanoscale state for many substances differs significantly from the massive state. During the formation of arrays of silver nanoparticles by condensation on a cold substrate, the initial condensate is unstable. For the formation of stable arrays with a shape close to spherical, subsequent weak heat treatment is required. In this work the behavior of an array of silver nanoparticles during low-temperature annealing is shown. Using atomic force microscopy, the evolution of an array of silver nanoparticles formed on the SiO2 surface by vacuum-thermal evaporation onto an unheated substrate during in-situ heating to a temperature of 200°C is studied. A qualitative assessment of the effect of temperature on the geometry of nanoparticle arrays is obtained. It is experimentally shown that a sharp coarsening of silver nanoparticles and a decrease in their number on the surface take place in the narrow temperature range of 75 to 100°C, while in the temperature range of 100 to 200°C, there are no noticeable changes in the array of silver nanoparticles. After the statistical processing of the obtained data, the average size of the formed particles and their density per unit area at each stage of the experiment are determined. The corresponding dependences are obtained.

The study of radiation attenuation in disordered silver nanoparticles arrays formed by dry aerosol printing

The interaction processes of continuous laser radiation with wavelengths 527 and 980 nm with disordered arrays of spherical silver nanoparticles formed by dry aerosol printing are studied. The arrays were deposited on a glass substrates in the form of lines of various thickness and differed in the mean sizes of nanoparticles. It is shown that the radiation attenuation by arrays with disordered nanoparticle structure depends on the optical effects both on isolated spherical nanoparticles and on nanoparticle agglomerates.

Plasmonic and Dielectric Metasurfaces for Solid State Lighting

The coupling of layers of light emitting materials to nanostructured surfaces and metasurfaces provides an unique opportunity to tailor the emission, and opens new venues for the design of phosphors in solid-state-lighting. A significant enhancement of the photoluminescence, both spectrally and spatially, have been demonstrated in recent year using metallic metasurfaces.[1] In contrast, the effect of optical absorption by metals on the conversion efficiency is less studied. Here, we investigate the conversion efficiencies for emitter layers deposited on metasurfaces consisting of the periodic arrays of plasmonic and dielectric nanoparticles using an integrating sphere. [2]Total photoluminescence intensity measured in the integrating sphere (see Figure (a)) is larger for the emitting layer on the silver (Ag) nanoparticle array than the same layer on the titanium dioxide (TiO2) array and on unpatterned flat substrate, manifesting a larger pump or absorption enhancement for the Ag nanoparticle array. The conversion efficiencies are 0.95 and 0.38 for the TiO2 and Ag arrays, respectively (Figure (b)). The excitation wavelength of λ = 532 nm is well below the bandgap of TiO2 and the nanoparticles are virtually transparent, which leads to a conversion efficiency of almost one. For the Ag array, the conversion efficiency is lower due to the intrinsic losses of Ag. The results show that absorption at the excitation wavelengths by the emitter has a critical impact on the conversion efficiency.The evaluation technique used in this work to quantify the optical absorption by the array, leads to a working recipe to design resonant systems that can be exploited in solid-state-lighting applications.[1] G. Lozano et al., Light: Sci. Appl. 2 (2013) e66[2] S. Murai et al., ECS J. Solid State Sci. Technol. 9 (2020) 011614 Figure 1