AgNP Films Research Articles

Influence of natural oxidation on the surface enhancement effect of silver nanoparticle films

Silver nanomaterials are often used as surface enhancement substrates even though silver is easily oxidized in air. In this paper, we investigate the influence of natural oxidation on the surface enhancement effect of silver nanoparticle (AgNP) films. The AgNP films were prepared by the vacuum thermal evaporation method, and the AgNP size range was 10–100 nm. Changes in the AgNP film thickness, surface morphology, particle size, and roughness with oxidation time were continuously measured with atomic force microscopy for 2 weeks. A detailed analysis of these parameters is presented. In addition, we used Rhodamine 6G to examine the surface enhancement effect of the AgNP films with different oxidation times. The results showed that the intensity of both the Raman and fluorescence signals increased and approximately periodically oscillated with increasing oxidation time. Here, we qualitatively discuss the mechanism of the influence of natural oxidation on the surface enhancement effect of silver nanostructures, which could provide a feasible way to improve the surface enhancement performance of silver nanomaterial substrates.

Highly Reflective Liquid Mirrors: Exploring the Effects of Localized Surface Plasmon Resonance and the Arrangement of Nanoparticles on Metal Liquid-like Films

In this paper, we describe a high-reflectance liquid mirror prepared from densely packed silver nanoparticles (AgNPs) of two different sizes. We controlled the particle size during the synthetic process by controlling the temperature. Varying the concentration of the ligand also allowed us to optimize the arrangement of the AgNPs to achieve liquid mirrors exhibiting high specular reflectance. Scanning electron microscopy and atomic force microscopy confirmed that the particles of the liquid mirror were well-packed with an interparticle distance of merely 2 nm; thus, the interstices and surface roughness of the NPs were effectively minimized. As a result of decreased scattering loss, the reflectance in the shorter wavelength regime was increased effectively. The AgNP film was also sufficiently thick to reflect the light in the longer wavelength regime. In addition, we used three-dimensional finite-difference time domain simulations and experimental measurements to investigate the relationship between the localized surface plasmon resonance (LSPR) and the specular reflection of the liquid mirrors. By changing the packing density of the AgNPs, we found that the LSPR effect could yield either a specular reflection peak or dip at the LSPR wavelengths in the reflection spectra of the liquid mirrors. Relative to previously reported liquid mirrors, the reflectance of our system is obviously much greater, especially in the shorter wavelength regime. The average reflectance in the range from 400 to 1000 nm could reach 77%, comparable with that of mercury-based liquid mirrors.

Low temperature plasma sintering of silver nanoparticles

The fabrication of flexible electronics using the deposition of solution-processed nanomaterials generally requires low-temperature post-processing to optimize functionality. We studied sintering of silver nanoparticle (AgNP) films on glass substrates by applying argon (Ar) plasma to achieve improved electrical conductivity. This process meets the low temperature processing requirements for standard low-cost polymeric flexible substrates. The relationship between plasma parameters (such as power and sintering time) versus sintering results (such as electrical sheet resistance, sintered structure depth, materials composition variation, and film nanostructure) is reported for 23 and 77nm diameter AgNPs. In addition, plasma processing typically induces a small surface thermal effect. We monitored the surface temperatures of the AgNP films in-situ during plasma sintering. By sintering control groups at these monitored surface temperatures using a vacuum oven, we confirmed that the resistivity due to plasma sintering is less than that produced by thermal sintering. Our data show that, the measured lowest resistivities for plasma sintered AgNP films are about only 5 and 12 times greater than the bulk Ag resistivity for 23 and 77nm, respectively.

Facile preparation of silver nanoparticle films as an efficient surface-enhanced Raman scattering substrate

Here, we report a new and facile method to prepare silver nanoparticles (Ag NPs) film for surface-enhanced Raman scattering (SERS)-based sensing. The porous Ni foam was used as a template to generate high quality of Ag NPs by seed-mediated growth of metallic nanoparticles. The preparation process is very economic and environment-friendly, can achieve the recovery of the raw materials. We found that the type of silver-plating solution and the growth time are two key factors to determine the magnitude of SERS signal enhancement. Using rhodamine 6G (R6G) and 4-animothiophenol (4-ATP) as probe molecules, the created Ag NP films exhibited relatively high enhancement ability, good stability, and well reproducibility. The synthesized SERS-active substrate was further used to detect melamine molecules, an illegal additive in infant milk powder, and the limitation of detection can reach 1μM.

Fast detection of hydrogen sulfide gas in the ppmv range with silver nanoparticle films at ambient conditions

Based on the chemical reaction of silver nanoparticles (Ag NPs) with hydrogen sulfide (H2S), an optical sensor to detect H2S gas at room temperature was designed. Peak intensity of localized surface plasmon resonance (LSPR) absorption of Ag NPs was monitored as the sensor responded to H2S. The fabricated Ag NP films were very sensitive to the presence of H2S with a gas concentration in the parts per million by volume (ppmv) range. The reaction of H2S on silver nanoparticle surfaces proceeded very quickly, as indicated by a significant and rapid decrease in the peak absorbance of LSPR. From analysis of the reaction kinetics, the initial reaction between Ag NPs and H2S gas was revealed to be a first-order reaction in Ag, and the initial reaction rate was proportional to the gas concentration in the ppmv range. The H2S gas concentration can be determined from either the initial reaction rate or from the H2S dose measured after extended reaction periods. Performance of the Ag NP film as a dosimeter at ambient conditions was evaluated by exposure to H2S in air, to water vapor with different relative humidity, to ammonia, to hydrochloric acid and to some volatile organic compound vapors.

Controlled Preparation of Uniform TiO2-Catalyzed Silver Nanoparticle Films for Surface-Enhanced Raman Scattering

Silver nanoparticle (AgNP) film is a kind of useful material in biochemical and biomedical fields as it can be used as a sensor based on its surface plasmon resonance for surface enhanced Raman scattering (SERS) analysis. In this work, a uniform AgNP film with controlled nanoparticle size, shape, and density have been prepared on TiO2 film in a AgNO3 solution by photocatalysis reduction method. The influences of TiO2 film thickness and morphology on the AgNP’s growth have been systemically studied. It is found that a thicker TiO2 film with nanocrystalline morphology leads to a higher AgNP’s growth rate, while a thinner TiO2 film with membrane morphology leads to a lower AgNP’s growth rate. Experimental SERS results show that the AgNP film prepared with different TiO2 films and ultraviolet light irradiation time exhibit different SERS signals of rhodamine 6G (10–6 M). Atomic force microscope and scanning electron microscope analysis reveal that the size effect is a key factor affecting the SERS of our prepared AgNP films, which has also been evaluated by finite-difference time-domain simulation. It is found that the larger the average AgNP’s size (≤λ/4) and roughness, the higher the Raman enhancement. The SERS mapping images exhibit a good uniform Raman enhanced results in our prepared TiO2-catalyzed AgNP film with a low relative standard deviation of approximately 10%.

Evaluation of biocomposite films containing alginate and sago starch impregnated with silver nano particles

In recent years, the metal nanoparticles/polymer composites have created lot of attraction due to their wide range of applications. In the present study, the composite films of alginate (AL) and sago starch (SG) impregnated with silver nano particles (AgNP) with and without antibiotic gentamicin (G) were prepared by solvent casting method. The films prepared were characterized for thermo gravimetric analysis, SEM, TEM and mechanical properties and the results have shown the composite nature of the films. AL–SG–AgNP and AL–SG–AgNP–G composites were used as wound dressing materials in experimental wounds of rats. The healing pattern of the wounds was evaluated by planimetric studies, macroscopic observations, biochemical studies and histopathological observations. The results have shown faster healing pattern in the wounds treated with AL–SG–AgNP and AL–SG–AgNP–G composites compared to untreated control. This study revealed that AL–SG–AgNP film might be a potential and economical wound dressing material.

SERS imaging for label-free detection of the phospholipids distribution in hybrid lipid membrane

A label-free and low-cost mapping method based on SERS imaging was reported for illustrating the distribution of phospholipids with similar structures in binary lipid membranes on Ag nanoparticles (Ag NPs) films. The Ag NPs films exhibited strong SERS activity and good reproducibility which were investigated with p-aminothiophenol (p-ATP) as probe molecules. Atomic force microscope (AFM) measurement proved that compact lipid membranes formed on the Ag NPs films. Basing on the Ag NPs films, the SERS spectra of phospholipids in the mixed lipid membranes were achieved and the inherent vibration of 1,2-dimyristoyl-sn-lycero-3-phosphoglycerol, sodium salt (DMPG), 1482 cm−1, was used to distinguish between DMPG and dimyristoylphosphatidylcholine (DMPC). The proportions of phospholipids in the mixed lipid membranes were represented by the intensity ratio of peaks at 1482 cm−1 and 1650 cm−1 (R 1482/1650) simultaneously: increasing R 1482/1650 indicated higher proportion of DMPG and lower proportion of DMPC. SERS imaging of the lipid membranes was constructed as a combination of spacial information and the semiquantitative detection of phospholipids according to R 1482/1650, which showed that the charged phospholipids, DMPG, aggregated in the hybrid lipid membranes. The presented mapping strategy based on SERS imaging carried out on Ag NPs films supplied a facile, label-free and inexpensive way for potential applications in the research on the structure of the lipid membrane, such as lipid domains and rafts.

Chitosan/silver nanoparticles composite: Molecular relaxations investigation by dynamic mechanical analysis and impedance spectroscopy

AbstractBy impedance spectroscopy, Gonzalez‐Campos et al. J Polym Sci Part B: Polym Phys 2009, 47, 932–943, reported the first evidence of a glass transition in a polysaccharide. To gain a better understanding on the molecular relaxations in polysaccharides, we study composites of chitosan (CS)/silver nanoparticles (AgnP) films by dynamic mechanical analysis (DMA) and dielectric spectroscopy in the 2–250 °C temperature range. CS/AgnP films conductivity increases in two orders of magnitude in comparison with pristine CS. Three relaxation processes ascribed to the α‐relaxation, σ‐relaxation, and degradation process have been observed for the first time. Molecular dynamics and conductivity strongly depends on moisture content; since a plasticizing effect on the glass transition temperature is observed, similarly the increase in AgnP weight percent leads to a glass transition temperature decrease and also increases CS thermal stability. Infrared spectroscopy analysis reveals the AgnPs interaction with OH, NH2, CO.NH2, and COC groups implying an evident redistribution of the vibration bands for these groups. These new bonds affects the molecular dynamics of the CS chain bearing important changes in relaxations processes when compared CS/AgnP composite with pristine CS. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 739–748, 2010

Surface plasmon absorption study of silver NP thin film containing 2,2′-bipyridine

Abstract The fine tuning of localized surface plasmon resonance (LSPR) of Ag-NP film containing 2,2′-bipyridine (bipy), self-assemble at room temperature when solution cast from dispersions on the glass substrate is described. The suspension of Ag colloid was prepared via polyol reduction stabilization using microwave radiations. SEM, EDS study reveals that NPs are uniform in size and reduced to metallic Ag. The cooperative SPR (approx. at 418 nm) of 2D assembly has been depressed due to 2,2′-bipyridine ligand structured around Ag-NPs showing red shift (456 nm). The cooperative resonance can be controlled by varying impingement time of microwave power on film. As the impingement time increased co-operative resonance begins blue shift due to increase in the cooperative interaction between Ag-NPs via decomposition of bipyridine. The co-operative resonance of 2D assembly that is at 418 nm was regained after complete removal of 2,2′-bipyridine at higher temperatures thus showing tunable LSPR properties of Ag-Bipy nanostructure. Opposite type of behavior that is strong damping were seen in case of Ag-NPs in solution phase. Temperature dependent viscosity characteristics suggest that Plasmon damping can be attributed to decrease in viscosity of Ag-NP solution.

Alloying process at the interface of silver nanoparticles deposited on Au(1 1 1) substrate due to the high-temperature treatments

X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) have been used to study the silver nanoparticles (AgNPs) deposited on Au(1 1 1). It is found out that the AgNPs form a layer which covers most of the Au surface. XPS has been used to observe the changes in the core levels of the AgNPs due to a high-temperature treatment. The XPS investigations clearly show that annealing of the AgNPs films at 620 K results in decreasing of the Ag 3d peaks intensity. At 770 K it is not possible to detect silver signal in the XPS spectra. However, after soft Ar + sputtering of the sample silver is again detectable. Our results show that during annealing of the AgNPs deposited on Au(1 1 1), the hydrocarbon-based ligands decompose and at higher temperatures diffusion of silver cores into gold substrate takes place. In the theoretical part of the work the Ag diffusion has been studied using a mean field theory for minimizing the mixing free energy with respect to the atomic configuration and local spatial relaxation. The present approach searches for energetically the most favorable equilibrium structure of the surface region described in terms of random-alloy within the Valenta model of the inhomogeneous systems. As a result, the layer resolved atomic configuration in the surface region in different temperatures has been obtained. Both results, experimental and theoretical, are consistent.

Silver Nanoparticle Films as Sulfide Gas Sensors in Oddy Tests

AbstractThe preparation and performance of a silver nanoparticle-based sensor for use in Oddy tests are reported. A suspension of spherical silver nanoparticles (Ag NPs) (mean diameter of 30 nm, absorption of surface plasmon resonance (SPR) at 428 nm) in methanol was synthesized and the Ag NPs were self-assembled into monolayer films on glass slides, using polyethylenimine as a linking agent. UV-vis spectrophotometry was employed to measure the SPR intensity of the Ag NP films in order to evaluate the extent of reaction. It was observed that the Ag NP films were quite stable under Oddy test conditions in a blank test, after a brief alteration of the spectrum due to particle dispersal, with no significant decrease in the SPR intensity after 1.5 months at 60°C and 100% RH. The sensitivity of Ag NP films to sulfide gases emitted from a test wool fabric in the Oddy test was investigated. UV-vis spectra taken after the Oddy tests showed the disappearance of the Ag NP SPR peak and the growth of the UV absorption due to Ag2S. Elemental analysis with energy dispersive x-ray spectroscopy confirmed that sulfur had been incorporated into the Ag NP film. Ag NP assemblies of lower NP density were created that indicated the presence of sulfide gases prior to significant tarnishing of a Ag foil. The results demonstrate that the Ag NP films can be used as sensitive, quantitative optical sensors to replace Ag foils in the Oddy test system.