Ag Nanofilms Research Articles

All-water-based solution processed Ag nanofilms for highly efficient electrocatalytic reduction of CO2 to CO

Electrochemical reduction for conversion of CO2 to value-added chemicals is considered a promising method to relieve global warming. To develop a highly active and selective electrocatalyst for efficient CO2 conversion, it is essential to overcome the large overpotential and to suppress the competitive hydrogen evolution reaction (HER). Herein, we report a simple and controllable fabrication method for Ag electrocatalytic films using all-water-based solution processes via a seed-meditated metal growth technique. Varying the deposition conditions allows the N/S doping ratio in Ag films with high coverage and good adhesion to be easily controlled in the range of 1.14–8.23. The doping ratio has a significant effect on the CO Faradaic efficiency (FE), as the S content modulates the binding energy of reaction intermediates, whereas the N content is effective for suppressing the HER on the Ag film surface.

Preparation of a Novel SERS Platform Based on Mantis Wing with High-Density and Multi-Level "Hot Spots".

The recent development of SERS substrates based on irregular nanostructures for directly molecule recognition has aroused increasing attention. By combining the irregular flake-like nanostructures of mantis wings, high SERS performance of Ag nanofilms, and the chemical stability of Au nanoparticles (NPs), an ultra-sensitive and flexible SERS substrate based on Au NPs functionalized Ag nanofilms-mantis wings (Au-Ag-M.w.) hybrid system is successfully fabricated. When 4-aminothiophenol is selected as the probe molecule, the limit of detection (LOD) is as low as 10−13 M and the relative standard deviation (RSD) is lower than 7.15%. This novel SERS platform exhibits high SERS performance in terms of sensitivity, reproducibility and practicability mainly because there are high-density and multi-level “hot spots” in the appropriate nanogaps. Meanwhile, it also systematically compares the differences of the SERS performance of Cu and Ag decorated M.w. hybrids and how these differences can alter their response. Moreover, the proposed substrate is employed to rapidly detect the pesticide residues on apple peels and the LOD for cypermethrin is estimated at 10−10 mg/mL. Therefore, this novel SERS substrate has great potential in rapid sampling of pesticide residues on real samples and expands the investigation to other natural materials for fabricating various SERS platforms.

Biomimetic synthesis of Ag-coated glasswing butterfly arrays as ultra-sensitive SERS substrates for efficient trace detection of pesticides.

In this work, we report a biomimetic synthesis route of 3D Ag nanofilm/glasswing butterfly wing hybrids (Ag-G.b.) by magnetron sputtering technology. The 3D surface-enhanced Raman scattering (SERS) substrate is fabricated from an original chitin-based nanostructure, which serves as a bio-scaffold for Ag nanofilms to be coated on. The novel crisscrossing plate-like nanostructures of 3D Ag-G.b. nanohybrids with thick Ag nanofilms provide a substantial contribution to SERS enhancement. Measuring the SERS performance with crystal violet (CV), the Ag-G.b. nanohybrids with the sputtering time of 20 min (Ag-G.b.-20) shows the highest enhancement performance with an enhancement factor (EF) of up to 2.96 × 107. The limit of detection (LOD) for CV was as low as 10−11 M, demonstrating the ultrahigh sensitivity of the Ag-G.b.-20 substrate. In addition, the Ag-G.b.-20 substrate has an outstanding reproducibility across the entire area with the maximum value of relative standard deviation (RSD) of less than 10.78%. The nanohybrids also exhibit a long-term stability regarding Raman enhancement, as suggested by a duration stability test over a period of 60 days. Importantly, the high-performance Ag-G.b.-20 substrate is further applied as an ultra-sensitive SERS platform for the trace detection of acephate, showing its great potential application in biochemical sensing and food security.

Interaction of Te and Se interlayers with Ag or Au nanofilms in sandwich structures.

Noble metal nanolayers on flat substrates are often deposited with the use of semiconductor interlayers, which may strongly interact with the noble metal overlayer. We investigated the crystallinity, atomic concentration profile and optical parameters of ≈35 nm-thick silver and gold layers deposited on glass substrates with 2 nm-thick tellurium or selenium interlayers. Our study, based on X-ray reflectometry (XRR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and ellipsometric measurements, showed that using either of these interlayers introduces strain in nanocrystals of both plasmonic films. This, in turn, influences the migration of Se and Te into the metal layers. Selenium atoms migrate both in the silver and gold nanolayers, while tellurium atoms migrate only in silver. The Te concentration curve clearly suggests that this migration is an effect of the segregation of Te atoms in the silver structure. The differences in crystallinity, as well as the migration process, strongly influence the optical parameters of Ag and Au. In the permittivity of Ag deposited on either Te or Se, additional plasmonic bands originating from grain boundary segregation or diffusion occur, while for the Au layer, such resonances were not pronounced. In the permittivity of both materials, the intensity of the interband transition peaks is strongly altered, possibly due to the nano-alloy formation, but more likely due to the microstrain on metal grains.

Plasmonic Conglobation of Ultrathin Ag Nanofilms Far below Their Melting Points by Infrared Illumination

Plasmon heating has been employed as a low-temperature annealing method for the conglobation of ultrathin Ag nanofilms into nanoparticles both on silicon and carbon spheres, with complex surface structures, simply under illumination with infrared light. Finite-difference time-domain results provide evidence that the plasmonic light enhancements in the films’ gaps and voids, rather than random surface fluctuations, are the main reason for the conglobation of Ag nanofilms far below the melting point of Ag. This technology can be applied in modern organic optoelectronic devices and photothermal pharma projects to reduce the thermal damage to materials or biological tissues.

Fluorescence Modulation of Graphene Quantum Dots Near Structured Silver Nanofilms.

Here, we study the plasmonic metal-enhanced fluorescence properties of blue-emitting graphene quantum dots (GQDs) and green-emitting graphene oxide quantum dots (GOQDs) using fluorescence lifetime imaging microscopy. Reactive ion sputtered silver (Ag) on zinc oxide (ZnO) thin films deposited on silicon (Si) wafers are used as the substrates. The morphology of the sputtered Ag gradually changes from nanoislands, via and elongated network and a continuous film with nanoholes, to a continuous film with increasing sputtering time. The fluorescence properties of GQD and GOQD on the Ag are modulated in terms of the intensities and lifetimes as the morphology of the Ag layers changes. Although both GQD and GOQD show similar fluorescence modulation on the Ag nanofilms, the fluorescence of GQD is enhanced, whereas that of GOQD is quenched due to the charge transfer process from GOQD to ZnO. Moreover, the GQD and GOQD exhibit different fluorescence lifetimes due to the effect of their electronic configurations. The theoretical calculation explains that the fluorescence amplification on the Ag nanofilms can largely be attributed to the enhanced absorption mechanism arising from accumulated optical fields around nanogaps and nanovoids in the Ag nanofilms.

Raman probe based on hollow-core microstructured fiber

Surface-enhanced Raman scattering (SERS) technology can effectively enhance the Raman signal of sample molecules. It has a higher sensitivity to detect biomolecule and thus has many potential applications in biochemistry. The combination of hollow-core microstructured fiber and SERS technology not only enables remote real-time and distributed detection, but also can increase the effective action area between the light field and the object to be measured, and further reduce silica glass background signal that is unavoidable in traditional fiber probes. In this paper, the hollow-core microstructure fiber Raman probes with excellent performance are investigated from the aspects of fiber preparation and SERS experi-mental testing. First, we design and manufacture a kind of hollow-core microstructured fiber with multi-bands in the visible and near-infrared wavelength. The fibers show good light guide performance and thus can fully meet the requirements for surface-enhanced Raman excitation and signal transmission. At the same time, the large core size facilitates the coupling of excitation light, and provides enough room for the test object and the light field. Then, this hollow-core microstructured fiber is used in surface-enhanced Raman experiment. A layer of nano-Ag film is modified on the inner surface of the hollow-core microstructure fiber to prepare the SERS probe by the vacuum physical sputtering method, and Rhodamine 6G (R6G) alcohol solutions with different concentrations are prepared by the dilution method. The hollow-core microstructured fiber deposited with the Ag nano-film is immersed in R6G alcohol solution for 2 min. The alcohol solution of R6G is sucked into the air hole of the hollow-core microstructured fiber by the capillary effect. Then this fiber with R6G alcohol solution is placed in a drying oven at 40 ℃ for 3 h until the alcohol solvent in the air hole is completely volatilized. After that, this fiber is taken out and tested under a detection environment full with air. The fiber SERS probes are tested by microscopic confocal Raman spectroscopy, then the Raman spectra of R6G alcohol solvents with different concentrations are obtained. An R6G Raman signal with a concentration as low as 10-9 mol/L is successfully detected on the front side of the probe. In the far-end back-side detection mode, the detected concentration of SERS probe can be less than 10-6 mol/L. The designed hollow-core microstructured fiber probe has a simple structure and is easy to prepare and test. Compared with the traditional optical fiber, it has advantages of large effective area for the test object and the light field, small interference from the silica glass background signal. This hollow-core microstructured fiber probe has wide application prospects in biochemical detection and other fields.

Design of Electrochemically Modified fMWCNT‐pencil Graphite Electrode Decorated with Cu and Ag Nanofilm and its Electrocatalytic Behavior Towards Imazethapyr

AbstractHerein, a facile procedure was developed for designing an electrochemical sensor based on pencil graphite electrode modified with electrochemically synthesized silver and copper nanoparticles (AgNP and CuNP) supported on functionalized multiwalled carbon nanotubes (fMWCNTs). The electrochemical and morphological characterization was carried out by cyclic voltammetry, Electrochemical Impedance Spectroscopy, Powder X‐ray diffraction, Field Emission Scanning Electron Microscopy, Transmission electron microscopy and Atomic Force Microscopy. The designed sensor exhibited electrocatalytic behavior towards the reduction of Imazethapyr. Results indicates the combination of AgNPs, CuNPs and fMWCNTs on PGE produced remarkable enhancement in electrocatalytic and sensing properties. Various electro‐kinetic parameters like Rct, kapp, n, α, E0, k0, Γ, D and k have been evaluated by CV, impedance and Chronoamperometric studies. The electrochemical performance was improved by optimizing the effect of pH, scan rate, amount of fMWCNTs and deposition parameters of AgNP and CuNP. The sensor was efficaciously applied for determination of Imazethapyr and exhibited a linear correlation in the concentration range of 0.01–5.0 μg mL−1 with low detection limits, 0.159 ng mL−1 using AdSWV. The fabricated sensor exhibited good accuracy, acceptable stability and high efficacy for quantitative determination of Imazethapyr in real samples with notable recoveries ranging from 98 % to 100.2 %.

Large-area uniform electron doping of graphene by Ag nanofilm

Graphene has attracted much attention at various research fields due to its unique optical, electronic and mechanical properties. Up to now, graphene has not been widely used in optoelectronic fields due to the lack of large-area uniform doped graphene (n-doped and p-doped) with smooth surface. Therefore, it is rather desired to develop some effective doping methods to extend graphene to optoelectronics. Here we developed a novel doping method to prepare large-area (> centimeter scale) uniform doped graphene film with a nanoscale roughness(RMS roughness ∼1.4 nm), the method (nano-metal film doping method) is simple but effective. Using this method electron doping (electron-injection) may be easily realized by the simple thermal deposition of Ag nano-film on a transferred CVD graphene. The doping effectiveness has been proved by Raman spectroscopy and spectroscopic ellipsometry. Importantly, our method sheds light on some potential applications of graphene in optoelectronic devices such as photodetectors, LEDs, phototransistors, solar cells, lasers etc.

Harnessing Ag nanofilm as an electrons transfer mediator for enhanced visible light photocatalytic performance of Ag@AgCl/Ag nanofilm/ZIF-8 photocatalyst

An Ag@AgCl/Ag nanofilm/ZIF-8 composite photocatalyst was successfully constructed for the first time by loading Ag@AgCl and Ag nanofilm on the surface of ZIF-8 simultaneously via a simple deposition-photoreduction method. The formed Ag nanofilm was harnessed as a mediator to transfer photo-induced electrons from the plasmonic Ag@AgCl nanostructure to ZIF-8 for enhancing the photocatalytic reaction rate with visible light. The photocatalytic activity was evaluated by photocatalytic degradation of methylene blue (MB) under visible light irradiation. The first-order kinetic constant of MB degradation over Ag@AgCl/Ag nanofilm/ZIF-8 (14.762h−1) was nearly 2 times of Ag@AgCl/ZIF-8 (7.932h−1). The electrochemical impedance spectra, photoelectric conversion spectra and ESR DMPO-O2− species spectra revealed that AFZ had a lower resistance, higher photocurrent density and more generation of superoxide radical than those of AZ, meaning that the extended interface between Ag nanofilm and ZIF-8 could promote the quick electrons transfer and electron-hole pairs separation. This work provides a new type electrons transfer mediator in fabrication of efficient plasmonic photocatalysts.

Fast diffusion of silver in TiO2 nanotube arrays.

Using magnetron sputtering and heat treatment, Ag@TiO2 nanotubes are prepared. The effects of heat-treatment temperature and heating time on the evolution of Ag nanofilms on the surface of TiO2 nanotubes and microstructure of Ag nanofilms are investigated by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Ag atoms migrate mainly on the outmost surface of the TiO2 nanotubes, and fast diffusion of Ag atoms is observed. The diffusivity for the diffusion of Ag atoms on the outmost surface of the TiO2 nanotubes at 400 °C is 6.87 × 10−18 m2/s, which is three orders of magnitude larger than the diffusivities for the diffusion of Ag through amorphous TiO2 films. The activation energy for the diffusion of Ag atoms on the outmost surface of the TiO2 nanotubes in the temperature range of 300 to 500 °C is 157 kJ/mol, which is less than that for the lattice diffusion of Ag and larger than that for the grain boundary diffusion. The diffusion of Ag atoms leads to the formation of Ag nanocrystals on the outmost surface of TiO2 nanotubes. Probably there are hardly any Ag nanocrystals formed inside the TiO2 nanotubes through the migration of Ag.

Effects and mechanisms of water matrix on surface-enhanced Raman scattering analysis of arsenite on silver nanofilm

Abstract Ag nanofilm was synthesized using a modified mirror reaction and used as surface-enhanced Raman scattering (SERS) substrate for analysis of arsenite (As(III)). The SERS substrate can detect 20 and 50 μg L −1 As(III) spiked in aged tap water and groundwater respectively. The effect of nine common ions (Na + , K + , Ca 2+ , Mg 2+ , NO 3 − , CO 3 2− , HPO 4 2− , SO 4 2− and Cl − ) in natural water on SERS of 0.5 mg L −1 As(III) was investigated. Na + and K + (100 mg L −1 ) had no obvious negative effects on the SERS intensity of 0.5 mg L −1 As(III), but Ca 2+ and Mg 2+ significantly decreased that of 0.5 mg L −1 As(III) as their concentrations increased to 1 and 10 mg L −1 respectively. NO 3 − , SO 4 2− and CO 3 2− (HPO 4 2− ) had negligible, medium and significant inhibition on the SERS of As(III) respectively. The inhibition effect of Ca 2+ might be through the formation of surface complexes with As(III) on SERS substrate. The inhibition effect of CO 3 2− , HPO 4 2− and SO 4 2− could be explained by the competitive adsorption of anions with As(III) for adsorption sites of Ag nanofilm. It was confirmed that Cl − can activate the SERS of As(III) alone and in the presence of Ca 2+ , CO 3 2− , HPO 4 2− and SO 4 2− . The activation effect of Cl − on SERS of As(III) could be attributed to charge transfer (CE) mechanism.

Thickness and Annealing Effects on the Particle Size of PLD Grown Ag Nanofilms

This work reports the effects of film thickness and annealing temperature on pulsed laser deposited silver nanofilms. Structural and optical properties of nanostructures are studied with scanning electron microscopy, energy dispersive analysis of x-ray, x-ray diffraction, and UV-visible spectroscopy. A direct relation is observed between the film thickness and dimensional range of silver nanoparticles that can be produced by annealing. With the increase in annealing temperature, formation of well-separated nanoparticles is promoted. Optical characterization of different samples shows the effective coupling of silver nanoparticles, and surface plasmon resonance is observed over a wide spectrum. Finite-difference time-domain (FDTD)-simulated results illustrate shifts in the plasmon resonance wavelengths due to the combination of different nanoparticle sizes and support experimental findings. This generic study produces a wide range of plasmonic nanostructures and may be extremely useful for various applications.

Fluorescence emission of BDMO-PPV enhanced by different plasmon modes

Herein we report a symmetric study of metal surface plasmon-enhanced emission of conjugated polymer (poly[2,5-bis(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene], BDMO-PPV) in the process that silver metal substrates changed from isolated nano-particles to continuous metal film. It was found that photoluminescence (PL) enhancement was mainly raised from coupling of BDMO-PPV excitons with localized surface plasmon (LSP) of Ag nano-particles when the thickness of deposited Ag film was smaller than 15nm. However, surface plasmon polaritons (SPPs) dominated the PL enhancement when the thickness of deposited Ag film reached 20nm or thicker. Temperature dependent PL of BDMO-PPV on the silver substrates were also investigated in the range of 10–300K. Bose–Einstein statistical factors were calculated to reveal the mechanistic aspects of the observed temperature dependent fluorescence enhancement on Ag nano-films with variable thickness.

Co-catalytic mechanism of Au and Ag in silicon etching to fabricate novel nanostructures

The co-catalytic mechanism of silicon etching with a bilayer Au and Ag nanofilm is revealed, resulting in two very different structures.

Preparation and Properties of Ag Nanofilms for Organic Solar Cells

nanoAg island thin films with different thickness have been prepared by vacuum vapor deposition method on ITO substrates for organic solar cells. UV-Vis absorption spectrum and surface morphology have been studied by UV-Vis scanning spectrophotometer and SEM. The influence of different thickness nanoAg has also been discussed. The results show that, when the nanoAg thickness is 3.0 nm, the surface plasmon response is most obvious, the resonance absorption peak appears red-shift, the surface plasmon response could enhance optical absorption, photocurrent, fill factor and power conversion efficiency obviously. The research results provide theoretical guidance to optimize the design and increase the performance of solar cells.

Anisotropic electronic conduction in metal nanofilms grown on a one-dimensional surface superstructure

We performed in situ conductivity measurements by multiple microscopic probes of Ag nanofilms grown on a periodic array of indium atomic wires on Si(111). Within the investigated thickness range the transport properties differ markedly from the bulk case. The ratio between the in-plane conductivity along and perpendicular to the In wires is 1.4 for the 3 monolayer (0.7 nm) thick Ag film and approaches unity with increasing film thickness. The observed anisotropy at the initial stage of the film growth is far larger than expected from the quasi-one-dimensional quantum well electronic structure of the films and ascribed to the carrier scattering at the film/vacuum and film/substrate interfaces. Our findings show that an ordered monolayer inserted at the interface enables drastic changes of the transport behavior of the whole metal nanofilm.

A facile route of microwave to fabricate PVA-coating Ag nanofilm used as NIR-SERS active substrate

Surface-enhanced Raman spectroscopy (SERS) is a very sensitive and selective technique for detecting surface species. Recently, SERS has been increasingly employed in the study of biological macromolecules, from DNA and peptides to whole proteins, and cells. However, visible laser sources usually employed in SERS detections always lead to photochemical reactions as well as intensive fluorescence emission from the biological samples. A way to avoid these questions is the employment of near infrared (NIR) laser excitation; thus, it demands the appropriate designs of NIR-SERS substrates in order to obtain the maximum enhancement of the Raman signals from biological analytes. In this work, we demonstrate the fabrication of a new NIR-SERS substrate of polyvinyl alcohol (PVA) coating Ag nanofilms (PVA-coating Ag nanofilm) using a simple and low-cost microwave strategy. The experimental data show that, the plasmon resonance band of the PVA-coating Ag nanofilm is in the region of 400–900nm, and the maximum center is at ∼780nm, which matches well with the 785nm laser excitation employed in this work. With the NIR-SERS detections of hematin and hemoglobin molecules adsorbed on this PVA-coating Ag nanofilm, one can see that the NIR-SERS activity and spectroscopy reproducibility of this NIR-SERS substrate are all perfect. By using of the tested molecule of hematin, the PVA-coating Ag nanofilm shows a high enhancement factor (EF) of ∼107. As the fabrication process of this NIR-SERS substrate is very simple and inexpensive, this method may be used in large-scale preparation of SERS substrates that have been widely applied in Raman analysis. Especially, this PVA-coating Ag nanofilm can also be served as a novel NIR-SERS substrate in biochemical analysis due to its good NIR characteristics.

SEM/EDX and XRD characterization of silver nanocrystalline thin film prepared from organometallic solution precursor

The Ag nano-structured thin films prepared on flat glass substrates have been studied. The ball-like silver nanoparticles have been synthesized in large quantity by using a modified method of hydrolytic decomposition of silver complexes with amino types ligands formed in ethanol aqueous solution. SEM analysis revealed that Ag nanoparticles are all sphere shaped with bimodal size (40 and 70 nm) distribution. The results of XRD powder pattern examination show that Ag nanoparticles are pure phase, well crystallized. The unit cell dimensions measured on synthesized Ag nano films show small but frequent contraction in comparison to Ag metal standard.

Band edge emission enhancement by quadrupole surface plasmon–exciton coupling using direct-contact Ag/ZnO nanospheres

Periodic Ag nanoball (NB) arrays on ZnO hollow nanosphere (HNS) supporting structures were fabricated in a large area by a laser irradiation method. The optimized laser power and spherical supporting structure of ZnO with a certain size and separation were employed to aggregate a sputtering-deposited Ag nano-film into an ordered, large-area, and two dimensional Ag NB array. A significant band edge (BE) emission enhancement of ZnO HNSs was achieved on this Ag NB/ZnO HNS hybrid structure and the mechanism was revealed by further experimental and theoretical analyses. With successfully fabricating the direct-contact structure of a Ag NB on the top of each ZnO HNS, the highly localized quadrupole mode surface plasmon resonance (SPR), realized on the metal NBs in the ultraviolet region, can effectively improve the BE emission of ZnO through strong coupling with the excitons of ZnO. Compared with the dipole mode SPR, the quadrupole mode SPR is insensitive to the metal nanoparticle's size and has a resonance frequency in the BE region of the wide band gap materials, hence, it can be potentially applied in related optoelectronic devices.