Real-time monitoring of plasmonic evolution in thick Ag:SiO(2) films: nanocomposite optical tuning

An in situ optical microspectroscopy study of the surface plasmon resonance (SPR) evolution of Ag nanoparticles (NPs) embedded in thick SiO(2) films deposited on soda-lime glass has been conducted during thermal processing in air. The temperature and time dependences of the SPR were analyzed in the context of Mie extinction and crystal growth theories and were discussed along with consideration of oxidation processes and film/substrate physicochemical interactions. At relatively high temperatures, Ag NPs were indicated to grow first through a diffusion-based process and subsequently via Ostwald ripening. At lower temperatures, an initial decrease in Ag particle size was indicated due to oxidation, followed by NP diffusion-based growth. The growth and oxidation stages appeared temperature and time dependent, allowing for the tuning of material properties. The product of Ag NP oxidation was revealed by photoluminescence spectroscopy performed ex situ as single Ag(+) ions. The oxidative effect of the air atmosphere on Ag NPs was shown to be ultimately circumvented by the thick nanocomposite film. The phenomenon was explained on the basis of the displacement of the Ag/Ag(+) redox equilibrium toward Ag NP stability after ion migration toward the substrate being self-constrained. In addition, the current spectroscopic approach has been proposed for estimating the activation energy for silver diffusion in the SiO(2) matrix.     

Photocatalytic degradation of methyl red dye by silica nanoparticles

Silica nanoparticles (SiO2 NPs) were found to be photocatalytically active for degradation of methyl red dye (MR). The SiO2 NPs and SiO2 NPs doped with silver (and or) gold nanoparticles were prepared. From the transmission electron microscopy (TEM) images the particle size and particle morphology of catalysts were monitored. Moreover, SiO2 NPs doped with silver and gold ions were used as a photocatalyst for degradation of MR. The rate of photocatalytic degradation of MR was found to be increased in the order of SiO2 NPs, SiO2 NPs coated with gold nanoparticles (Au NPs) and silver nanoparticles (Ag NPs), SiO2 NPs coated with Ag NPs, SiO2 NPs coated with Au NPs, Ag+-doped SiO2 NPs, and Au3+-doped SiO2 NPs. The kinetic and mechanism of photocatalytic reaction were studied and accorded well with experimental results.     

In situ optical microspectroscopy of the growth and oxidation of silver nanoparticles in silica thin films on soda-lime glass

An in situ optical microspectroscopy investigation of the growth and oxidation of silver nanoparticles (NPs) embedded in SiO₂ thin films deposited on soda-lime glass has been conducted in real time during thermal processing in air. Variation of Ag NP size is followed by fitting of surface plasmon resonance (SPR) with spectra calculated by Mie theory, and analysed concurrently with the time evolution of SPR peak intensity. The NP transformations appeared to be temperature and time dependent. Silver NPs were indicated to grow at relatively high temperatures (e.g. 600 °C) due to Ostwald ripening, followed by a plateau and a gradual decrease in size resulting in SPR vanishing due to oxidation. The three phases were well separated in time. Oxidation appeared dominant at lower temperatures (e.g. 400 °C) as indicated by a continuous decrease in Ag particle size. The product of Ag NP oxidation was revealed by photoluminescence spectroscopy as single Ag⁺ ions. Furthermore, the data indicated that: (i) Ag⁺ ions are formed during heat treatment under an Ag/Ag⁺ redox equilibrium; (ii) the ions diffuse from the SiO₂ matrix towards the soda-lime substrate where they stabilize; and (iii) the continuous removal of these ions from the matrix is necessary in order for the equilibrium to be displaced towards oxidation.     

Enhanced ferroelectric and dielectric properties of the P(VDF-TrFE)/Ag nanoparticles composite thin films

The scope of the present work was the synthesis of homogeneously dispersed silver (Ag) nanoparticles (NPs) in P(VDF-TrFE) polymer by N,N-dimethylformamide’s reducing reaction on silver nitrate and the study on the surface micromorphology, crystalline phases, electrical and optical properties of the P(VDF-TrFE)/Ag NPs composite thin films. The results demonstrate that incorporating appropriate concentration of Ag NPs improve the ferroelectric and dielectric properties with an increase of 38 % in the remanent polarization and 47 % in dielectric constant respectively compared with the pristine P(VDF-TrFE) films. The reasons for the improved properties are explained by the effective compensation to the bounding charges provided by the appropriate amount of the Ag NPs fillers and Ag NPs’ acting as micro capacitors in P(VDF-TrFE) matrix. Furthermore, the surface plasmon resonance absorption in the composite films thin films is observed at the wavelength of ~415 nm, whose intensity is dependent on the density of the Ag NPs.     

Type I collagen-templated assembly of silver nanoparticles and their application in surface-enhanced Raman scattering

Silver nanoparticles (Ag NPs) are one of the active substrates that are employed extensively in surface-enhanced Raman scattering (SERS), and aggregations of Ag NPs play an important role in enhancing the Raman signals. In this paper, we fabricated two kinds of SERS-active substrates utilizing the electrostatic adsorption and superior assembly properties of type I collagen. These were collagen-Ag NP aggregation films and nanoporous Ag films. Two probe molecules, 4-aminothiophenol (4-ATP) and methylene blue (MB), were studied on these substrates. These substrates showed reproducible SERS intensities with relative standard deviations (RSDs) of 8-10% and 11-14%, respectively, while the RSDs of the traditional thick Ag films were 12-28%. Also, the intensities for the 4-ATP spectrum on the collagen-templated nanoporous Ag film were approximately one order higher than those on the DNA-templated Ag?film.     

Photoelectrochemical performance of Ag nanoparticles on TiO2 films prepared by aerosol pyrolysis

Titanium dioxide (TiO₂) layers were prepared by the pyrolysis of an ethanolic solution of di-iso-propoxy-titanium bis(acetylacetonate) in aerosol form, and then electrodeposited with Ag nanoparticles on their surface. The morphology and photoelectrochemical properties of the resulting Ag nanoparticles (NPs) on TiO₂ films were found to be significantly tuned by varying the electrodeposition time in an aqueous electrolyte containing AgNO₃ and KNO₃. Photocurrent density–voltage curves and electrochemical impedance spectra revealed that the Ag NPs remarkably improved the short-circuit current density and open circuit voltage, and considerably reduced the electrochemical impedance. Therefore, Ag NPs deposition enhanced the photo-absorption of the TiO₂ layer, excited photoelectrons by localised surface plasmon resonance, promoted photo-induced charge separation, and prevented electron–hole recombination.     

退火气氛对镶嵌在SiO2中Ag纳米颗粒热演变影响效应的研究

将70 keV的Ag离子以5×10¹⁶ cm^-2的剂量注入到SiO₂基底中, 随后分别在400~800℃的Ar、N₂、空气气氛中退火, 详细研究了样品的表面形貌、光吸收特性、结构及成分随退火气氛及退火温度的变化规律。原子力显微镜、紫外-可见分光光度计及掠入射X射线衍射仪的测试结果显示: Ar气氛退火样品中形成的Ag纳米粒子(NPs)细小均匀, 其颗粒密度在700℃时达到最大值, 光吸收性能最佳; N₂气氛退火引发Ag纳米颗粒的团聚生长, 在样品近表面形成较大的Ag NPs, 其颗粒密度也在700℃时达到最大值; 而空气中退火后, 由于AgO的形成、分解, 样品的光吸收强度随退火温度升高持续下降。最后, 卢瑟福背散射研究结果表明, 样品的这些变化主要归因于Ag原子在不同退火气氛下随退火温度的扩散行为不同。     

Particle growth mechanisms in Ag-ZrO(2) and Au-ZrO(2) granular films obtained by pulsed laser deposition

Thin films consisting of Ag and Au nanoparticles embedded in amorphous ZrO(2) matrix were grown by pulsed laser deposition in a wide range of metal volume concentrations in the dielectric regime (0.08相似文献   

Few layer graphene/silver nanocomposite based flexible and resistive liquefied petroleum gas sensor

The LPG gas sensing characteristics of hybrid few-layered graphene (FLG)/ silver nanoparticles (Ag NPs) nanoarchitecture have been investigated. FLG and silver nanoparticles (Ag NPs) enhance the LPG gas sensing characteristics by collectively involving in the electronic transportation and diffusion mechanisms. FLG, Ag and FLG/ Silver nanocomposites are developed by ultra-sonication assisted method, and the effect of flexibility on gas sensing performance was thoroughly examined. The sensing materials as thin films are developed via drop-casting technique on photo lithography patterned flexible interdigitated electrodes (IDEs). The gas sensing characteristics of the prepared sensor are studied for LPG and other analytes at room temperature. The maximum response is observed for FLG/Ag nanocomposite to 100 ppm LPG at room temperature. FLG/Ag nanocomposite sensor demonstrates rapid response, high selectivity, reproducibility and good stability over a period of 30 days. Further the durability and flexibility tests conducted for the FLG/Ag hybrid sensor at bending angles reveal 78% stability even after 15 days of sensing studies.

     

The preparation of highly active antimicrobial silver nanoparticles by an organometallic approach

Silver nanoparticles of small size with a high surface to volume ratio have been prepared using an organometallic approach. For this, the complex NBu(4)[Ag(C(6)F(5))(2)] has been treated with AgClO(4) in a 1:1 molar ratio, giving rise to the nanoparticle precursor [Ag(C(6)F(5))] in solution. Addition of one equivalent of hexadecylamine (HDA) and 5?h of reflux in toluene leads to a deep yellow solution containing monodisperse silver nanoparticles (Ag NPs) of ca.?10?nm. This approach leads to nanoparticles with almost uncontaminated surfaces which make them very reactive. Antimicrobial studies show that these nanoparticles are very active as antimicrobial agents. Very low concentrations between 12 and 25?μg?ml(-1) of Ag NPs are enough to produce bacteriostatic and bactericidal effectiveness.     

Efficiency enhancement of polymer solar cells with Ag nanoparticles incorporated into PEDOT:PSS layer

In this study, large-sized silver nanoparticles (Ag NPs) (average size: 80 nm) have been introduced into the anodic buffer poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer (thickness: about 55 nm) of poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester bulk heterojunction polymer solar cells. The results showed that the short-circuit current density can increase from 8.73 to 11.36 mA/cm², and power conversion efficiency increases from 2.28 to 2.65 % when 0.1 wt% Ag NPs was incorporated in PEDOT:PSS layer, corresponding to an efficiency improvement of 16.2 %. Absorption spectrums of the active layers indicate that large-sized Ag NPs have no clear contribution to optical absorption improvement. By measuring the conductivity of PEDOT:PSS films without and with Ag NPs and analyzing device structure of this polymer solar cell, it was founded that the improvements in power conversion efficiency was originated from higher conductivity of PEDOT:PSS layer incorporated with Ag NPs and the shorter routes for holes to travel to the anode.     

Plasmon-enhanced luminescence of YAG: Yb, Er nanopowders by Ag nanoparticles embedded in silicate glass

Solid-state field-assisted diffusion was used to prepare Ag nano-composite silicate glass. After positive diffusion process, small Ag atoms clusters were formed in the slides. The Ag atom clusters could aggregate into Ag nanoparticles (NPs) with bigger size after subsequent reverse diffusion process. YAG: Yb, Er nanopowders were screen-printed on the glass slides after positive and reverse diffusion, respectively, for up-conversion luminescence measurement. Almost no luminescence enhancement was observed for the slide after positive diffusion. Whereas, obvious enhancement was obtained for the slide after reverse diffusion, and the enhancement factor could reach about 26. The strong enhancement was due to the larger size of Ag NPs. The present work suggested a new promising method to enhance the luminescence of YAG: Yb, Er nanopowders.     

A new approach causing the patterns fabricated by silver nanoparticles to be conductive without sintering

Silver nanoparticles (Ag NPs) with a mean size of about 90?nm were synthesized by polyol reduction of silver nitrate with ethylene glycol (EG) in the presence of poly(vinyl pyrrolidone) (PVP). The Ag NPs undergo a spontaneous coalescence in the presence of chloride ions even without a traditional sintering process which occurs at a relatively high temperature. Such behavior can cause a rapid decrease in the resistivity of the patterns fabricated by Ag NPs. Conductive silver lines were successfully fabricated on FR-4 substrate using this method. The resulting conductivity of the silver lines reached about 16% of the bulk silver value, which enables fabrication of conductive patterns on some electronic devices.     

Synthesis and Photoluminescence Enhancement of Silver Nanoparticles Decorated Porous Anodic Alumina

Silver nanoparticles(Ag NPs) were successfully assembled in porous anodic alumina(AAO) templates via a green silver mirror reaction.The Ag NPs/AAO composite templates then were characterized by field emission scanning electron microscopy(FESEM),energy-dispersive X-ray microanalysis(EDX),and X-ray diffraction(XRD).Furthermore,the photoluminescence(PL) properties were also investigated.Compared with the blank AAO,the PL intensity of Ag NPs/AAO templates are enhanced and the maximum enhancement is 2.58 times.Based on the local electric field enhancement effect,the theoretical values were also deduced,which are basically coincident with the experimental.     

Synthesis of Au-Ag alloy nanoparticles with Au/Ag compositional control in SiO2 film matrix

Au-Ag alloy nanoparticles with tunable atomic ratios have been generated in SiO2 film matrix using a new two layer (TL) approach. Two successive overlapping coating layers of similar thickness were deposited on silica glass substrates using Au- and Ag-incorporated inorganic-organic hybrid silica sols, respectively. The Au and Ag concentrations in the individual layers were varied to obtain the desired Au-Ag alloys of different compositions. Four sets of such TL coating assemblies were prepared from the following pair of sols: (i) 4 equivalent mol.% Au-96% SiO2 and 2 equivalent mol.% Ag-98% SiO2, (ii) 3 equivalent mol.% Au-97% SiO2 and 2 equivalent mol.% Ag-98% SiO2, (iii) 3 equivalent mol.% Au-97% SiO2 and 3 equivalent mol.% Ag-97% SiO2, and (iv) 2 equivalent mol.% Au-98% SiO2 and 3 equivalent mol.% Ag-97% SiO2 and subjected to UV (2.75 J/cm2) and heat-treatments (450-550 degrees C) in air and H2-N2 atmospheres for the generation of Au-Ag alloy nanoparticles of approximate compositions Au.66Ag0.33, Au0.6Ag0.4, Au0.5Ag0.5, and Au0.4Ag0.6, respectively. After UV-treatment, individual Au and Ag nanoparticles were formed in the respective layers. The heat-treatment (450-550 degrees C) induces interlayer diffusion of Au and Ag to each other with the generation of Au-Ag alloy nanoparticles, and as a result, Au-Ag alloy surface plasmon resonance (SPR) absorptions were observed in between the Ag- and Au-SPR absorption positions in the visible spectra. The expected alloy compositions are formed through several intermediate alloy nanoparticles, which can also be arrested by controlling the annealing parameters. The alloy formations were monitored by UV-VIS, FTIR, XRD, EDAX, and TEM studies.     

Electrical percolation threshold in Ag–DLC nanocomposite films prepared by RF-sputtering and RF-PECVD in acetylene plasma

Silver–diamond like carbon (Ag–DLC) nanocomposite films were deposited on glass and silicon substrates by co-deposition of RF-sputtering and RF-PECVD method in acetylene plasma. The effects of deposition time on creation of conductive percolation pathway in Ag–DLC nanocomposite films were investigated. The films were characterized by XRD pattern, AFM images, UV–Vis and FTIR spectra. Pressure of chamber’s variation over time was illustrated the rate of carbon and silver deposition changing. The results showed that nanoparticles’ size and surface roughness was increased by increasing deposition time. Surface plasmon resonance peak’s red shift in optical absorption spectra of samples could be depends on silver nanoparticles’ scale up. Based on electrical measurements, electrical percolation threshold was observed only in the film with 35 min deposition time. Pathway was created for electric current by Ag nanoparticles’ moving in carbon matrix due to sp³ bonds and silver content in the films. The aging effect was studied for sample #2 in the threshold of percolation, where obtained Ag nanoparticles memorize its previous pathway. This investigation provides a better understanding for electric properties of Ag–DLC nanocomposite based on the percolation theory.     

A facile method to prepare size-tunable silver nanoparticles and its antibacterial mechanism

The antibacterial effect of silver nanoparticles (denoted as Ag NPs) is closely related to size. This could partly explain why size controllable synthesis of Ag NPs for bactericidal application is drawing much attention. Thus, we establish a facile and mild route to prepare size-tunable Ag NPs with highly uniform morphologies and narrow size distributions. The as-prepared Ag NPs with averaged sizes of 2, 12 and 32?nm were characterized by transmission electron microscopy (TEM), ultraviolet–visible absorption spectroscopy (UV–vis), X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The antimicrobial effect of the as-prepared Ag NPs with different particles size was assessed by broth dilution and disk diffusion as well as measurement of optical density (OD₆₀₀). Moreover, their antibacterial mechanism was discussed in relation to morphology observation of microorganism by scanning electron microscopy (SEM) and to concentration detection of Ag⁺ by stripping voltammetry. It was found that the parameters such as reactant molar ratio, reaction time, dropping speed, and most of all, pH of the reactant solutions, have significant influences on size-regulation of Ag NPs. The as-prepared Ag NPs exhibit excellent antibacterial properties, and their antimicrobial activities increase with decreasing particles size. Besides, two kinds of mechanisms, i.e., contact action and release of Ag⁺, are responsible for the antimicrobial effect of Ag NPs.     

Preparation of nickel–silver core–shell nanoparticles by liquid-phase reduction for use in conductive paste

Nickel–silver (Ni–Ag) core–shell nanoparticles (NPs) were prepared by depositing Ag on Ni nanocores using the liquid-phase reduction technique in aqueous solution, and their properties were characterised using various experimental techniques. The core–shell NPs had good crystallinity, and the thicknesses of the Ag nanoshells could be tuned effectively. The oxidation resistance of the Ag surface and the electroconductive properties of the Ni core allowed these Ni–Ag core–shell NPs to be used in a conductive paste. Thick films composed of Ni–Ag core–shell NPs were screen-printed on a polycrystalline silicon substrate then sintered at temperatures ranging from 500 °C to 800 °C. Stable resistivity was obtained when the sintering temperature was higher than 650 °C, and the electrical properties of the Ni–Ag core–shell paste were close to those of pure Ag paste. Thus, the Ni–Ag NPs can partly replace pure Ag NPs in conductive pastes.     

Photocatalytic and antibacterial properties of a TiO2/nylon-6 electrospun nanocomposite mat containing silver nanoparticles

Silver-impregnated TiO(2)/nylon-6 nanocomposite mats exhibit excellent characteristics as a filter media with good photocatalytic and antibacterial properties and durability for repeated use. Silver nanoparticles (NPs) were successfully embedded in electrospun TiO(2)/nylon-6 composite nanofibers through the photocatalytic reduction of silver nitrate solution under UV-light irradiation. TiO(2) NPs present in nylon-6 solution were able to cause the formation of a high aspect ratio spider-wave-like structure during electrospinning and facilitated the UV photoreduction of AgNO(3) to Ag. TEM images, UV-visible and XRD spectra confirmed that monodisperse Ag NPs (approximately 4 nm in size) were deposited selectively upon the TiO(2) NPs of the prepared nanocomposite mat. The antibacterial property of a TiO(2)/nylon-6 composite mat loaded with Ag NPs was tested against Escherichia coli, and the photoactive property was tested against methylene blue. All of the results showed that TiO(2)/nylon-6 nanocomposite mats loaded with Ag NPs are more effective than composite mats without Ag NPs. The prepared material has potential as an economically friendly photocatalyst and water filter media because it allows the NPs to be reused.     

Hydroxy propyl cellulose capped silver nanoparticles produced by simple dialysis process

Silver (Ag) nanoparticles (∼6 nm) were synthesized using a novel dialysis process. Silver nitrate was used as a starting precursor, ethylene glycol as solvent and hydroxy propyl cellulose (HPC) introduced as a capping agent. Different batches of reaction mixtures were prepared with different concentrations of silver nitrate (AgNO₃). After the reduction and aging, these solutions were subjected to ultra-violet visible spectroscopy (UVS). Optimized solution, containing 250 mg AgNO₃ revealed strong plasmon resonance peak at ∼410 nm in the spectrum indicating good colloidal state of Ag nanoparticles in the diluted solution. The optimized solution was subjected to dialysis process to remove any unreacted solvent. UVS of the optimized solution after dialysis showed the plasmon resonance peak shifting to ∼440 nm indicating the reduction of Ag ions into zero-valent Ag. This solution was dried at 80 °C and the resultant HPC capped Ag (HPC/Ag) nanoparticles were studied using transmission electron microscopy (TEM) for their particle size and morphology. The particle size distribution (PSD) analysis of these nanoparticles showed skewed distribution plot with particle size ranging from 3 to 18 nm. The nanoparticles were characterized for phase composition using X-ray diffractrometry (XRD) and Fourier transform infrared spectroscopy (FT-IR).