Silver Thin Films Research Articles

Development of advanced biopolymer thin films of Carboxymethyl cellulose, Silver, and Zinc Oxide nanoparticles for avocado fruit preservation applications

Nanomaterials in post-harvest preservation offer advantages such as non-toxicity, chemical residue-free protection, and effective inhibition of mold and bacteria. Due to their strong antimicrobial properties and their ability to form a thin nano-coating on fruit surfaces, even small amounts of nanoparticles provide extensive coverage, preventing microbial penetration. This technology significantly improves fruit quality and longevity during storage and transportation. In this work, we introduced an advanced biopolymer film of carboxymethyl cellulose (CMC) incorporating ZnO and Ag nanoparticles (NPs). Ag NPs and ZnO NPs demonstrated an outstanding antimicrobial inhibition property that can be used for fruit preservation. As a proof of concept, the biopolymer thin films enable to extend avocado ripening from up to 35 days. The sugar concentration variation, the hardness, and the weight loss of the avocado with and without the advanced biopolymer thin film integrated ZnO and Ag nanoparticles in 35 days were compared with each other to clarify the ripening reduction ability of the biopolymer thin film.

SU-8-meta-phenylenediamine-conjugated thin film for temperature sensing.

Polymers have distinctive optical properties and facile fabrication methods that have been well-established. Therefore, they have immense potential for nanophotonic devices. Here, we demonstrate the temperature-sensing potential of SU8-meta-phenylenediamine (SU8-mPD), produced by epoxy amination of the SU-8 polymer. Its properties were examined through a series of molecular structural techniques and optical methods. Thin layers have demonstrated optical emission and absorption in the visible range around 420 and 520 nm, respectively, alongside a strong thermal responsivity, characterized by the 18 ppm °C-1 expansion coefficient. A photonic chip, comprising a thin 5-10 μm SU8-mPD layer, encased between parallel silver and/or gold thin film mirrors, has been fabricated. When pumped by an external light source, this assembly generates a pronounced fluorescent signal that is superimposed with the Fabry-Pérot (FP) resonant response. The chip undergoes mechanical deformation in response to temperature changes, thereby shifting the FP resonance and encoding temperature information into the fluorescence output spectrum. The time response of the device was estimated to be below 1 s for heating and a few seconds for cooling, opening a new avenue for optical sensing using SU8-based polymers. Thermoresponsive resonant structures, encompassing strong tunable fluorescent properties, can further enrich the functionalities of nanophotonic polymer-based platforms. This article is part of the theme issue 'Celebrating the 15th anniversary of the Royal Society Newton International Fellowship'.

SERS detection of dopamine in artificial cerebrospinal fluid and in Parkinson’s disease-induced mouse cortex using a hybrid ZnO@Ag nanostructured platform

Rapid, direct, and sensitive detection of metabolites or clinically relevant biomarkers in complex biological samples is still challenging. We report a label-free surface-enhanced Raman scattering (SERS)-based approach for highly sensitive detection of dopamine (DA) in artificial cerebrospinal fluid (aCSF) and mouse brain tissue samples. The hybrid SERS-active sensing platform was designed to maximize the hot spot distribution. It encompasses a network of flexible and polymeric nanotrenches and nanogaps fabricated by nanoimprint lithography (NIL) covered by thin films of zinc oxide (ZnO) and silver (Ag) deposited using pulsed laser deposition (PLD) and direct current magnetron sputtering (DC-MS), respectively. The growth of the ZnO and Ag thin films was assessed by scanning electron microscopy (SEM) technique. The proposed SERS substrate benefits from the interlayered semiconductor–metal contribution in SERS enhancement, leading to a versatile sensing platform with improved detection sensitivity through the increased hot spots distribution. Using this strategy, the proposed assay can achieve an ultralow DA determination at the nM level, a short testing time (<30 min), and high signal reproducibility (RSD 11 %). We also assessed the sensing attributes of our in house developed SERS platform to detect DA in spiked aCSF samples, and a limit of detection (LOD) of 10 μM was achieved. Additionally, after in vivo inducing Parkinson’s disease (PD) in mice, relevant biological samples (striatum and cortical brain tissue) were investigated by SERS and ELISA. Given its good stability and accuracy in complex samples, the SERS-ELISA analysis has great potential to be a powerful tool for the reliable detection of DA in remote conditions.

Angle-insensitive perfect light transmission and absorption in one-dimensional photonic crystal heterostructures

Abstract Prefect light transmission in metamaterials typically suffers a frequency shift as the incident angle of wave increase, limiting their applicability across wide angles. One-dimensional photonic crystal heterostructures, with elliptic-shaped equi-frequency contours, exhibit angle-insensitive properties. However, there remains an inevitable blue shift in the optical response as the incident angle increases. In this work, we present two photonic crystal heterostructures, one of which is composed of the optical phase-change material Sb2S3. By combining two heterostructures with distinct Zak phases, we achieve perfect light transmission. Specifically, as incident angle of wave increases, the transmission peak can be strictly maintained without a frequency shift by tuning the phase (refractive index) of Sb2S3. Moreover, by jointing the heterostructures with a thin silver film, we demonstrate a Tamm plasma polariton mode with angle-insensitive property. This mode can facilitate angle-tolerant light absorption. Our work provides an alternative way to designing high angle-tolerant and tunable devices.&amp;#xD;

Plasmonic Ag Nanoparticles on SiC for Use as SERS Substrate and in Integrated Optical Sensors for Bio-Chemical Applications

Development of optical chemical sensors for the detection of specific toxic chemicals at ultratrace levels and analysis of complex mixtures is crucial for new green and safe technologies [1, 2]. Metallic structures confined at the nanoscale acquire interesting properties such as strongly localizing E fields on their surfaces through Plasmonic Resonance under stimuli of light at certain wavelengths. This nanostructures are called plasmonic structures [3–5]. This effect is exploited to amplify the optical signal obtained by the molecules of interest, located near plasmonic structures [3, 6]. Purpose of the work is the development of innovative, easy to manufacture and cheap optical active layer consisting of Plasmonic Ag Nanoparticles on a Wide Band Gap semiconductor material such as Silicon Carbide to be used as substrate for Surface Enhanced Raman Scattering or for the fabrication of integrated optical sensor for remote chemical and biological applications. In this contest, the phenomenon of Ag thin film thermal dewetting on SiC substrate was implemented to develop a simple nanoparticles synthetic approach. Scanning Electron Microscopy confirmed the formation of Ag nanoparticles by thermal annealing of thin silver film. 4-MBA was used as probe molecule for SERS phenomenon investigation. The formation of a covalent bond between the silver nanostructures, acting as plasmonic "hot spots", and the species of interest enable its detection at very low concentrations, in the range of 10-5 M or less, in both Raman and UV-Vis configurations.

Impact of fractal dimension and lateral correlation length on surface plasmon resonance activity in sputtered silver layers

Fractal and optical characteristics of self-affine surfaces of silver(Ag) thin films deposited through direct current (dc) magnetron sputtering as a function of thickness are investigated and explored here. The surface morphology of Ag thin films is characterized by field emission electron microscopy, and atomic force microscopy technique. The cube counting algorithm is used to extract the fractal dimension of Ag thin film. The surface roughness (interface width) shows monotonic increases with film thickness, while the other parameters, such as lateral correlation length, roughness exponent, and fractal dimension exhibit linear variation with thickness. Our findings reveal distinctive scaling behaviors, with scaling exponents α, β, and 1/z indicating unique growth characteristics. The interface width w increases as a power law of thickness t, w(t)∝tβ, with β=0.39± 0.007, and the lateral correlation length ξ grows as ξt∝t1/z with 1/z=0.14± 0.002. The roughness exponent extracted from height-height correlation analysis is α=0.61–0.41. The self-affine nature of the Ag thin films is further confirmed by the autocorrelation function. X-ray photoelectron spectroscopy (XPS) is used to the confirm the growth of Ag thin film. Additionally, we have studied the role of fractal dimensions and lateral correlation length (ξ) on the surface plasmon resonance (SPR) of Ag thin film. Our results indicate a red-shifting behavior of SPR with increasing interface width (w), lateral correlation length (ξ), and fractal dimensions. This study suggests the significance of not only the roughness exponent and fractal dimension but also the local surface slope in SPR activity in Ag thin films.

Optical fiber sensor based on magneto-optical surface plasmon resonance with ultra-high figure of merit

Compared to surface plasmon resonance (SPR), the sensors based on the magneto-optical SPR (MOSPR) technique have much higher figure-of-merit (FOM). However, there are no reports about applying MOSPR in the optical fiber structure now. In this work, a novel D-shaped optical fiber sensor based on the MOSPR technique is proposed. The D-shaped optical fiber is coated with a thin silver film and a magneto-optical (MO) material film of Cerium-doped Yttrium-Iron garnet (CeYIG). By applying a magnetic field on the sensing region, the magneto-optical Kerr effect (MOKE) of the CeYIG layer and the related MOSPR phenomenon could be excited when appropriate light is transmitted in the proposed optical fiber sensor. The influence of the structural parameters including the residual cladding thickness, silver and MO material film thicknesses are analyzed theoretically by the finite element method (FEM). With the optimal parameters, the sensor achieves the sensitivity of 5304 nm RIU−1. Since the peak width of MOSPR spectra is much narrower than that of the SPR spectra, the FOM of the sensor is largely enhanced to 3864 RIU−1 on average and 13260 RIU−1 in maximum, which surpasses the optical fiber SPR sensors vastly. The miniaturized and simple design of the D-shaped optical fiber MOSPR sensor, coupled with the ultra-high FOM, offers itself great potential in biochemical sensing applications.

Carbon nanotubes induced the enhancement of Raman scattering performance in silver thin films

In this study, Ag/CNTs composite films with excellent properties of surface-enhanced Raman scattering (SERS) were fabricated. The SEM images show that the template effect and stress concentration area of carbon nanotubes (CNTs) can not only induce the growth of Ag nanoparticles, but effectively increase the number and intensity of "hot spots". Due to the introduction of CNTs, the plasma absorption peak of Ag/CNTs composite films was observed to be enhanced in the range of visible light. The as-deposited Ag/CNTs samples showed high sensitivity and good temporal stability in the detection of MB probe molecules, with the detection limit of 10−9 mol/L and the enhancement factor of 6 × 105, respectively. In addition, the enhancement contribution of the substrate was further investigated by Finite difference time domain simulation, and the simulation results were consistent with those of the experimental results, which indicate that the synthesized Ag/CNTs thin films have potential application prospect in SERS technology.

Hydrogen peroxide and glucose detection using surface plasmon resonance imaging biosensor with corrodible silver thin film

A surface plasmon resonance imaging (SPRI)-based biosensor is demonstrated for the detection of both hydrogen peroxide (H2O2) and glucose. The H2O2 to be detected acts as an oxidant and etch the silver film. This process gradually effects on resonance condition and consequently the reflected light intensity at a fixed angle. The etching rate of the silver film shows a clear relation with the H2O2 concentration. Therefore, monitoring the reflected light intensity progressively changing over a few minutes, enables accurate detection of H2O2 concentrations ranging from 0 to 200 μM (within physiological range of 0.25–50 μM), with a remarkable limit of detection (LOD) as low as 40 nM. In this regard, the behavior of the surface plasmon resonance (SPR) dip in response to the reduction of the silver film thickness is predicted by Winspall simulation software. These simulation results are in good agreement with the experimental results. Moreover, the proposed method can be applied to determine glucose concentrations ranging from 0 to 10 mM, encompassing the physiological range of 3–8 mM. This is achieved by observing the generated H2O2 through the enzymatic oxidation reaction between glucose and glucose oxidase (Gox). The sensor demonstrates remarkable sensitivity and selectivity, with a detection limit as low as 175 μM for glucose concentration. Furthermore, accurate measurement of glucose concentration in an actual human serum sample is achievable with the proposed sensor, using the standard addition method. The suggested glucose sensor shows promising prospects for use in routine glucose testing, employing a label-free, real-time, and multiplex detection approach.© 2017 Elsevier Inc. All rights reserved.

Polymeric laser rods based on modified poly(methyl methacrylate) matrix synthesized by FeIII complex catalyzed atom transfer radical polymerization with enhanced optical gain and Photostability

AbstractThe investigation of fabricating ultra‐compact solid‐state dye laser (SSDL) using N'N‐dimethylformamide (DMF) modified poly(methyl methacrylate) (PMMA) as the polymeric matrix was carried out. Atom transfer radical polymerization (ATRP) was introduced to manipulate the polymerization process of PMMA. By adjusting the additive amount of the FeIII complex (mixture of FeCl3 and 2,2’‐Bipyridyl (bPy)), the polymerization degree of PMMA was coordinated to gain better amplified spontaneous emission (ASE) properties of the embedded laser dye, Lumogen Orange 240 (LO). The ASE threshold of the FeIII complex catalyzed sample decreased as high as ~75%, from 225.3 ± 11.2 μJ cm−2 to 57.2 ± 2.9 μJ cm−2, comparing to that measured in common PMMA matrix. Additionally, a secondary dye, Stilbene 420 was added in the system for sharing excess excitation energy and oxidization damage, to overcome the photostability problem caused by the oxygen‐rich solvent, DMF. The operational lifetime of the resulted sample increased 200%, to the similar level of that without DMF component. Finally, by mechanical polishing and coating a thin film of silver at one end of the PMMA rod, an analogous Fabry‐Perot resonator was structured within the rod. Decent laser emission was obtained from the resulted SSDL without complex external cavities.

Early-stage silver growth during sputter deposition on SiO2 and polystyrene – Comparison of biased DC magnetron sputtering, high-power impulse magnetron sputtering (HiPIMS) and bipolar HiPIMS

The integration of silver thin films into optoelectronic devices has gained much interest due to their exceptional properties in terms of conductivity and compatibility with flexible substrates. For this type of application, ultra-thin layers are desirable, because of their optical transparency. Standard direct current magnetron sputtering (DCMS) is known to lead to undesirable formation of islands at low effective film thicknesses on typical substrates like SiO2 or polystyrene (PS). Therefore, in this study, we explore high-power impulse magnetron sputtering (HiPIMS) with optional further acceleration of metal ions by biasing the substrate or an additional positive pulse (bipolar HiPIMS) for the fabrication of ultra-thin silver layers. The morphology and electrical properties of ultra-thin silver layers with selected effective thicknesses are characterized on SiO2 and PS substrates. The growth evolution of characteristic parameters is further investigated by in-situ grazing-incidence small-angle X-ray scattering (GISAXS). The results show that HiPIMS deposition yields films with a higher density of clusters than DCMS leading to a percolation threshold at lower effective film thicknesses. This effect is amplified by further ion acceleration. Thus, we suggest HiPIMS as a promising technique for fabricating ultra-thin, conductive layers on organic and oxide substrates.

Deformed graphene FET biosensor on textured glass coupled with dielectrophoretic trapping for ultrasensitive detection of GFAP

Numerous efforts have been undertaken to mitigate the Debye screening effect of FET biosensors for achieving higher sensitivity. There are few reports that show sub-femtomolar detection of biomolecules by FET mechanisms but they either suffer from significant background noise or lack robust control. In this aspect, deformed/crumpled graphene has been recently deployed by other researchers for various biomolecule detection like DNA, COVID-19 spike proteins and immunity markers like IL-6 at sub-femtomolar levels. However, the chemical vapor deposition (CVD) approach for graphene fabrication suffers from various surface contamination while the transfer process induces structural defects. In this paper, an alternative fabrication methodology has been proposed where glass substrate has been initially texturized by wet chemical etching through the sacrificial layer of synthesized silver nanoparticles, obtained by annealing of thin silver films leading to solid state dewetting. Graphene has been subsequently deposited by thermal reduction technique from graphene oxide solution. The resulting deformed graphene structure exhibits higher sensor response towards glial fibrillary acidic protein (GFAP) detection with respect to flat graphene owing to the combined effect of reduced Debye screening and higher surface area for receptor immobilization. Additionally, another interesting aspect of the reported work lies in the biomolecule capture by dielectrophoretic (DEP) transport on the crests of the convex surfaces of graphene in a coplanar gated topology structure which has resulted in 10 aM and 28 aM detection limits of GFAP in buffer and undiluted plasma respectively, within 15 min of application of analyte. The detection limit in buffer is almost four decades lower than that documented for GFAP using biosensors which is is expected to pave way for advancing graphene FET based sensors towards ultrasensitive point-of-care diagnosis of GFAP, a biomarker for traumatic brain injury.

The investigation of thickness-dependent mono-fractal, optical and optoelectronics properties of sputtered silver thin film for silicon solar cell

Here we report, the room temperature deposition of silver (Ag) thin films on silicon, glass and silicon solar cell substrates by magnetron sputtering. The effect of thickness on the deposited thin films and their morphological, fractal, optical and solar cell parameters have been extensively investigated. AFM results show that the Ag thin films are composed of different-size of nano-grains and the grain size increases with increasing thickness. Mono-fractal parameters, namely fractal dimension (Df) and Hurst exponent (H), were determined from the power spectral density function. X-ray photoelectron spectroscopy studies indicate that the deposited samples exhibit the presence of oxidation state of Ag (0) in thin films, confirming the stable structure. The optical analysis shows that the transmittance of the deposited thin films decreases with increasing thickness, on the other hand, the silver thin film with thickness of 20 nm shows surface Plasmon resonance (SPR) at 436 nm. Current-voltage (I–V) curves were measured in dark and under illumination mode at standard testing conditions, i.e., 300K, 1000 W/m2 and 1.5 AM global using a solar simulator. These measurement studies indicate that thicknesses are effectively impacts on photovoltaic performance. The calculated values of change in solar efficiency (Δη) are 0.26, −0.20, −0.76 and −6.88 % for thin films with nominal thickness 0.5, 1, 2 and 20 nm respectively.

Conformal Coating Testing in Various Test Environments

Conformal coatings have traditionally been tested by determining the mean time to failure of conformally coated hardware exposed to corrosive test environments. This test approach has serious shortcomings: The test temperatures are most often too high. At these high temperatures, the conformal coating properties may be quite different from those at the application temperatures. In addition, the times to failure are unacceptably long extending into many months. Overcoming these shortcomings is an iNEMI championed test that involves exposing conformally coated thin films of copper and silver to sulfur vapors at 40-50 oC in flowers of sulfur (FoS) chamber and using the corrosion rates of the coated metal thin films as a measure of the corrosion protection capabilities of the conformal coatings. The test temperatures are similar to the application temperatures, the test durations are no more than a week and can be conducted under various temperature and humidity conditions. The purpose of this paper was to determine if testing in the industry-standard mixed-flowing gas corrosion chamber would give similar results as those using the FoS chamber. Acrylic, fluorinated acrylate, and atomic layer deposition conformal coatings were tested in three environments: (a) flowers of sulfur (FoS), (b) mixed-flowing gas (MFG), and (c) iodine vapor. The performance of the coatings tested in the FoS and the MFG corrosion chambers were quantitatively similar. The iodine vapor test results were in qualitative agreement with the FoS and MFG test results. In addition, we present early results pointing to the utility of terahertz-frequency imaging as a technique for measuring conformal-coating thickness nondestructively.

High-performance, large-area flexible SERS substrates prepared by reactive ion etching for molecular detection

In the realm of molecular detection, the surface-enhanced Raman scattering (SERS) technique has garnered increasing attention due to its rapid detection, high sensitivity, and non-destructive characteristics. However, conventional rigid SERS substrates are either costly to fabricate and challenging to prepare over a large area, or they exhibit poor uniformity and repeatability, making them unsuitable for inspecting curved object surfaces. In this work, we present a flexible SERS substrate with high sensitivity as well as good uniformity and repeatability. First, the flexible polydimethylsiloxane (PDMS) substrate is manually formulated and cured. SiO2/Ag layer on the substrate can be obtained in a single process by using ion beam sputtering. Then, reactive ion etching is used to etch the upper SiO2 layer of the film, which directly leads to the desired densely packed nanostructure. Finally, a layer of precious metal is deposited on the densely packed nanostructure by thermal evaporation. In our proposed system, the densely packed nanostructure obtained by etching the SiO2 layer directly determines the SERS ability of the substrate. The bottom layer of silver mirror can reflect the penetrative incident light, the spacer layer of SiO2 and the top layer of silver thin film can further localize the light in the system, which can realize the excellent absorption of Raman laser light, thus enhancing SERS ability. In the tests, the prepared substrates show excellent SERS performance in detecting crystalline violet with a detection limit of 10−11 M. The development of this SERS substrate is anticipated to offer a highly effective and convenient method for molecular substance detection.

Surface modification of a commercial bone plate (Ti6Al4V) implant for improved antibacterial and cytocompatibility via thermal dewetting of a silver thin film

The high demand for bone grafts has motivated the development of implants with excellent osteogenic activity, whereas the risk of implant-associated infection, particularly given the rise of antimicrobial resistance, has compelled the development of implants with innovative antimicrobial strategies in which a small amount of bactericidal agent can effectively kill a wide range of bacteria. To induce antibacterial property, the surface of Grade-5 bone plate titanium implants used in clinical applications was modified using direct current (DC) sputter coating followed by thermal annealing. The 15 nm silver film-coated implants were thermally annealed in the furnace for 15 min at 750 °C. The modified implant surface’s antibacterial efficacy against Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), Salmonella typhi, and Methicillin-resistant staphylococcus aureus bacteria has been assessed using a colony-forming assay. On the modified implant surface, the growth of E. coli and S. aureus bacteria is reduced by 99.72%, while highly drug-resistant bacteria are inhibited by 96.59%. The MTT assay was used to assess the cytotoxicity of the modified bone-implant surface against NIH3T3 mouse fibroblast cells. The modified bone-implant surface promoted fibroblast growth and demonstrated good cytocompatibility. Furthermore, the mechanical properties of the implant were not harmed by this novel surface modification method. This method is simple and provides new insight into surface modification of commercial metallic implants to have effective antibacterial properties against various classes of bacteria.

Crystallinity as a factor of SERS stability of silver nanoparticles formed by Ar+ irradiation

The plasmonic sensors based on silver nanoparticles are limited in application due to their relatively fast degradation in the ambient atmosphere. The technology of ion-beam modification for the creation of monocrystalline silver nanoparticles (NPs) with stable plasmonic properties will expand the application of silver nanostructures. In the present study, highly-stable monocrystalline NPs were formed on the basis of a thin silver film by low-energy ion irradiation. Combined with lithography, this technique allows the creation of nanoparticle ensembles in variant forms. The characterization of the nanoparticles formed by ion-beam modification showed long-term outstanding for Ag nanoparticles stability of their plasmonic properties due to their monocrystalline structure. According to optical spectroscopy data, the reliable plasmonic properties in the ambient atmosphere are preserved for up to 39 days. The mapping of crystal violet dye via surface-enhanced Raman spectroscopy (SERS) revealed a strong amplification factor sustaining at least thrice as long as the one of similarly sized polycrystalline silver NPs formed by annealing. The plasmonic properties sustain more than a month of storage in the ambient atmosphere. Thus, ion-beam modification of silver film makes it possible to fabricate NPs with stable plasmonic properties and form clusters of NPs for sensor technology and SERS applications.

Oxygen-induced Ag-based binary structure for efficient heat-regulating windows

Heat-regulating (HR) windows are essential for net-zero-energy building approaches. Silver (Ag) thin films are preferred for developing high-functioning HR windows because of their unique optoelectrical properties. The quality of the HR windows depends on the tradeoff between the transparency and conductivity of the Ag film. Ultrathin Ag (thickness < 10 nm) obtained using the wetting technique has been universally adopted to overcome this trade-off. However, the use of a wetting layer can hinder the optimum transparency of HR windows because of the possible optical loss associated with the wetting layer. Herein, the partial oxidation technique was thoroughly investigated for fabricating one-step grown Ag used for high-functioning HR windows. The incorporation of oxygen (5.7 % volume) during Ag sputtering allowed the direct growth of continuous Ag film on substrates with a percolation threshold below 4 nm. Partial oxidization of Ag resulted in modulated optical coefficients of Ag, thereby facilitating the ease of developing AZO/Ag (6.5 nm)/glass with optimum transparency of 98 % and sheet resistance of 12 Ω sq−1. AZO/Ag/glass possessing a high Haacke figure of merit 68.1 (10−3 Ω−1) was developed for HR windows, with the capability of providing a temperature discrepancy of 2 °C for different simulated weather conditions.

Structure and Microchannel Catalytic Bed Performance of Silver Thin Films Prepared by Electroplating

The morphology of catalysts in microchannels plays a crucial role in the orbital maneuvering and networking applications of micro/nano satellites using hydrogen peroxide as a unit propellant. In this paper, a microfluidic reaction chip was designed and fabricated to detect the reaction rate of the catalytic decomposition of hydrogen peroxide solution by a microchannel catalytic bed. In addition, a silver thin film prepared by constant-current electroplating was used as a substrate for the microchannel catalyst. The results show that the ratio of surface area to area of silver film and the average particle size of silver particles have a significant positive correlation on the reaction rate of catalytic decomposition, while the thickness, silver content, and surface roughness of the silver film have no significant effect on the reaction rate of catalytic decomposition. The catalytic performance of the microchannel catalytic bed of silver thin film is greatly influenced by the conditions of electroplating, namely, the electroplating temperature (T), time (t), and current (I). And when I = 0.3 mA, t = 180 s, and T = 60 °C, the microchannel catalytic bed of the silver film prepared by electroplating reaches the optimal reaction rate for the catalytic decomposition of hydrogen peroxide solution. This study has the best process parameters for the design and optimization of heterogeneous catalysts applied to microfluidic reactors.

Giant Raman radiation from molecules in a spherical metal shell

The work considers an electrodynamic model of radiation from molecules placed in a metal shell. The model qualitatively describes the enhancement of the surface-enhanced Raman scattering (SERS) signal from spherical nanoparticles coated with a thin silver film. The change in the SERS signal is calculated depending on the thickness of the metal nanolayer on top of the spherical particles. The radiating molecular dipole interacts with the metal shell and excites surface plasmons. Plasmonic oscillations reach a maximum when the frequency of the dipole is close to the plasmon resonance of the metal shell, and the dipole itself is close to the plasmonic shell. It has been theoretically shown that the intensity of secondary radiation generated by spherical nanoparticles coated with a silver film several nanometers thick can reach up to six or more orders of magnitude. The effect of a tenfold amplification of the SERS signal was experimentally demonstrated using the example of a large ensemble of single polystyrene microspheres with an average diameter of about 300 nm, coated with a silver nanolayer, which have characteristic Stokes frequencies of 1001 cm-1, 1602 cm-1. We believe that the tenfold enhancement of Raman scattering is due to the electromagnetic amplification mechanism.