Ageing of plasma-mediated coatings with embedded silver nanoparticles on stainless steel: An XPS and ToF-SIMS investigation

Nanocomposite thin films (∼170 nm), composed of silver nanoparticles enclosed in an organosilicon matrix, were deposited onto stainless steel, with the aim of preventing biofilm formation. The film deposition was carried out under cold plasma conditions, combining radiofrequency (RF) glow discharge fed with argon and hexamethyldisiloxane and simultaneous silver sputtering. XPS and ToF-SIMS were used to characterize Ag-organosilicon films in native form and after ageing in saline solution (NaCl 0.15 M), in order to further correlate their lifetime with their anti-fouling properties. Two coatings with significantly different silver contents (7.5% and 20.3%) were tested. Surface analysis confirmed the presence of metallic silver in the pristine coating and revealed significant modifications after immersion in the saline solution. Two different ageing mechanisms were observed, depending on the initial silver concentration in the film. For the sample exhibiting the low silver content (7.5%), the metal amount decreased at the surface in contact with the solution, due to the release of silver from the coating. As a result, after a 2-day exposure, silver nanoparticles located at the extreme surface were entirely released, whereas silver is still present in the inner part of the film. The coating thickness was not modified during ageing. In contrast, for the high silver content film (20.3%), the thickness decreased with immersion time, due to significant silver release and matrix erosion, assigned to a percolation-like effect. However, after 18 days of immersion, the delamination process stopped and a thin strongly bounded layer remained on the stainless steel surface.     

凹凸棒石/硅橡胶复合材料的热氧化降解和老化性能研究

本文采用高压均质结合对辊挤压工艺对天然凹凸棒石进行棒晶解离得到了纯度较高和比表面积较大(133.7 m²/g)的纳米解离凹凸棒石. 进一步通过机械共混法分别将天然凹凸棒石和纳米解离凹凸棒石与硅橡胶生胶复合制备了天然凹凸棒石-硅橡胶和纳米解离凹凸棒石-硅橡胶材料,研究了天然凹凸棒石和纳米解离凹凸棒石对凹凸棒石/硅橡胶复合材料热氧化降解和老化性能的影响. 结果表明,天然凹凸棒石-硅橡胶和纳米解离凹凸棒石-硅橡胶在300 oC热氧老化处理0.5 h后,相比于纯硅橡胶,初始5%失重温度从385 oC提高至396∽399 oC. 系列表征结果表明,天然凹凸棒石和纳米解离凹凸棒石增强了纳米粒子与硅橡胶之间的相互作用从而抑制了纳米颗粒聚集,并且可显著提高硅橡胶侧链Si-CH₃的保存率,从而提高了该复合材料的热氧化降解和老化性能. 此外,纳米解离凹凸棒石可大大抑制纳米粒子的长大;因此老化后,纳米解离凹凸棒石-硅橡胶表现出了比硅橡胶(10.6%、7.4%和5.0%)更高的拉伸强度、断裂伸长率和撕裂强度保留率(40.6%、34.9% 和30.1%).     

银纳米粒子自组装复合LB膜的结构与性质

纳米粒子的自组装和有序组装膜的结构与性质近年来受到了人们的广泛关注,纳米粒子的表面结构与性质对由其组装成的有序膜的结构与性质有直接的影响。文章报道了利用自组装技术制备的银纳米粒子与双亲有机分子的单层和多层复合LB膜,通过吸收光谱和表面增强拉曼光谱研究了银纳米粒子与吸附分子间的相互作用,探讨了复合膜的成膜特性及银纳米粒子的拉曼增强特性。十八胺/银粒子复合LB膜的吸收光谱及拉曼光谱显示,十八胺分子与银纳米粒子表面的活位通过NH₂中的氮原子以复合体的形式结合;同时,在激发光的作用下复合体可能存在光催化过程。根据银粒子复合LB膜的实验结果,十八胺和十八酸之间的反应产物在复合膜中起空间位阻作用,与银粒子表面的相互作用较弱。     

Significant modifications in the electrical properties of poly(methyl methacrylate) thin films upon dispersion of silver nanoparticles

Electrical conductivity of thin solid films of PMMA with dispersed silver nanoparticles, synthesized by a novel method, was studied in dark conditions by changing the applied voltage and temperature and also under photoexcitation (by a mercury lamp, 125 W) at room temperature. Anomalous hysteresis in current-temperature characteristics during heating and cooling cycles was observed. The hysteresis-like behaviour was explained on the basis of the movements of molecules associated with different parts of a PMMA matrix and diffusion of silver nanoparticles in the PMMA matrix. Dark current in the PMMA films with dispersed silver nanoparticles has been observed to be higher than the corresponding current in the PMMA films without silver nanoparticles due to the creation of conduction paths by the silver nanoparticles/nanoclusters. The photoresponse in the thin solid films of PMMA with dispersed silver nanoparticles was the reverse of that observed in thin solid films of PMMA without silver nanoparticles. A decrease in photocurrent under illumination of light was observed due to the destruction of conduction paths by the illumination of light.     

Photoinduced formation and aggregation of silver nanoparticles at the surface of carboxymethylcellulose films

Formation and aggregation of photolytic silver nanoparticles at the surface of silver salt of carboxymethylcellulose films (CMCAg films) have been investigated. Detailed X-ray photoelectron spectroscopy (XPS) study and field emission type scanning electron microscopy (FE-SEM) observation have been carried out to characterize silver nanoparticles at the film surface. When the CMCAg films were irradiated with UV light in wet air at room temperature for 30–60 min, silver nanoparticles of ca. 10 nm size were formed at the irradiated surface. According to the FE-SEM observation, the growth of the particle diameter and aggregation of nanoparticles took place after prolonged irradiation, and finally, the irradiated side of the film surface was densely covered with the silver nanoparticles of ca. 35 nm size. Chemical composition analysis by the XPS measurements has confirmed the increase in the atomic concentration of silver with irradiation time. It is suggested that silver atoms and clusters can move in the film and precipitate at the irradiated surface.     

The effect of the deposition parameters on size, distribution and antimicrobial properties of photoinduced silver nanoparticles on titania coatings

Controlled photodeposition of silver nanoparticles (AgNP) on titania coatings using two different sources of UV light is described. Titania (anatase) thin films were prepared by the sol-gel dip-coating method on silicon wafers. AgNPs were grown on the titania surface as a result of UV illumination of titania films immersed in aqueous solutions of silver nitrate. UV xenon lamp or excimer laser, both operating at the wavelength 351 ± 5 nm, was used as illumination sources. The AFM topography of AgNP/TiO₂ nanocomposites revealed that silver nanoparticles could be synthesized by both sources of illumination, however the photocatalysis carried out by UV light from xenon lamp illumination leads to larger AgNP than those synthesized using the laser beam. It was found that the increasing concentration of silver ions in the initial solution increases the number of Ag nanoparticles on the titania surface, while longer time of irradiation results the growth of larger size nanoparticles. Antibacterial tests performed on TiO₂ covered by Ag nanoparticles revealed that increasing density of nanoparticles enhances the inhibition of bacterial growth. It was also found that antibacterial activity drops by only 10-15% after 6 cycles compared to the initial use.     

Self-assembled silver nanoparticle films at an air-liquid interface and their applications in SERS and electrochemistry

In this paper, we present a novel technique to prepare silver nanoparticle films by controlling the self-assembly of nanoparticles at an air-liquid interface. In an ethanol-water phase, silver nanoparticles were prepared by reduction of AgNO₃ aqueous solution with NaBH₄ in the presence of cinnamic acid. It was found that the silver nanoparticles in this process could be trapped at the air-liquid interface to form 2-dimensional nanoparticle films. The morphology of nanoparticle films could be controlled by systematic variation of the experimental parameters. It is worth noting that the nanoparticle films could serve as the active substrates for surface-enhanced Raman scattering (SERS). 4-Aminothiophenol (4-ATP) molecule was used as a test probe to investigate the SERS sensitivity of different nanoparticle films. The results indicated that the nanoparticle films showed excellent Raman enhancement effect. Furthermore, the nanoparticle films prepared by our strategy were found to be efficient electrocatalysts for anodic oxidation of formaldehyde in alkaline medium.     

Spatially controlled dissolution of Ag nanoparticles in irradiated SiO2 sol-gel film

In this paper, we report the spatially controlled dissolution of silver nanoparticles in irradiated SiO₂ sol-gel films. The Ag nanoparticles have been formed in the sol-gel solution before the film deposition by adding Triton and ascorbic acid and also after the film deposition using a heat treatment at 700 °C for few minutes or at 550 °C for 6 h in reducing atmosphere. Using a spectrometer, a new view white light interferometer and a micro-thermal analyzer, we demonstrate that the silver nanoparticles can be dissolved using a continuous black ray UV lamp or with a near-infrared (NIR) femtosecond laser, due to a significantly increase in the local temperature. We confirm that the micro-thermal analyzer can be used as a new tool to study the dissolution of metallic nanoparticles in thin film if located at the surface of the films.     

Preparation of triethylamine stabilized silver nanoparticles for low-temperature sintering

In this article, silver nanoparticles were synthesized by chemical reduction from silver nitrate using triethylamine as the protecting and reducing agents simultaneously. The average size of the silver nanoparticles was about 2.10–4.65 nm, which allowed low-temperature sintering of the metal. X-ray diffraction (XRD), thermogravimetric analysis (TGA), and energy dispersive spectrometric (EDS) analysis results indicate that silver nitrate has been converted to silver nanoparticles completely. Using a 20 wt% silver nanoparticles suspension with thermal treatment at 150 °C, silver films with a resistivity of 8.09 × 10⁻⁵ Ω cm have been produced, which is close to the resistivity of bulk silver.     

Surface-enhanced optical third-harmonic generation in Ag island films

Surface-enhanced optical third-harmonic generation (THG) is observed in silver island films. The THG intensity from Ag nanoparticles is enhanced by more than 2 orders of magnitude with respect to the THG intensity from a smooth and homogeneous silver surface. This enhancement is attributed to a local plasmon excitation and resonance of the local field at the third-harmonic wavelength. The diffuse and depolarized component of the enhanced THG is associated with the third-order hyper-Rayleigh scattering in a two-dimensional random array of silver nanoparticles.     

Time-dependent micro-Raman scattering studies of polyvinyl alcohol and silver nitrate thin films

In-situ monitoring of silver nanoparticle formation was studied in thin films of polyvinyl alcohol and silver nitrate. We proposed the observation of surface-enhanced Raman spectroscopy (SERS) as a novel and simple technique to record the growth of silver nanoparticles in polyvinyl alcohol thin films. Observed enhancement in the Raman bands of polyvinyl alcohol is explained through the localized surface plasmon resonance of silver nanoparticles. Influence of temperature generated by silver nanoparticles on the formation of nanoparticles is also discussed.     

樟脑磺酸掺杂聚苯胺在不同有机溶剂中的UV-Vis光谱

由于不同的有机溶剂与樟脑磺酸的聚苯胺（PANI．HCSA）有不同的作用，故PANI．HCSA在不同的有机溶剂中有不同的紫外－可见光谱。本文研究了PANI．HCSA在有机溶剂间甲酚（m-cresol)、二甲基亚砜（DMSO）、N，N－二甲酰胺（DMF）、N－甲基－2－吡咯烷酮（NMP）中的UV－Vis光谱的不同及其变化，并对其进行了合理的解释。     

Thiol‐immobilized silver nanoparticle aggregate films for surface enhanced Raman scattering

We report a novel method for the fabrication of films of silver nanoparticle aggregates that are strongly attached to Si substrates (Thiol‐immobilized silver nanoparticle aggregates or TISNA). The attachment is achieved by chemically modifying the surface of a Si(100) surface in order to provide SH groups covalently linked to the substrate and then aggregating silver nanoparticles on these thiol covered surfaces. The transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) characterization show a high coverage with single nanoparticles or small clusters and a partial coverage with fractal aggregates that provide potential hot spots for surface enhanced Raman scattering (SERS). We have confirmed the SERS activity of these films by adsorbing rhodamine 6G and recording the Raman spectra at several concentrations. By using the silver‐chloride stretching band as an internal standard, the adsorbate bands can be normalized in order to correct for the effects of focusing and aggregate size, which determine the number of SERS active sites in the focal area. This allows a quantitative use of SERS to be done. The adsorption–desorption of rhodamine 6G on TISNA films is reversible. These features make our TISNA films potential candidates for their use in chemical sensors based on the SERS effect. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of high temperature annealing on strain and band gap of GaN nanoparticles

Black-coloured GaN nanoparticles with an average grain size of 50 nm have been obtained by annealing GaN nanoparticles under flowing nitrogen at 1200 oC for 30 min. XRD measurement result indicates an increase in the lattice parameter of the GaN nanoparticles annealed at 1200 oC, and HRTEM image shows that the increase cannot be ascribed to other ions in the interstitial positions. If the as-synthesised GaN nanoparticles at 950 oC are regarded as standard, the thermal expansion changes nonlinearly with temperature and is anisotropic; the expansion below 1000oC is smaller than that above 1000 oC. This study provides an experimental demonstration for selecting the proper annealing temperature of GaN. In addition, a large blueshift in optical bandgap of the annealed GaN nanoparticles at 1200 oC is observed, which can be ascribed to the dominant transitions from the C(Γ₇) with the peak energy at 3.532 eV.     

Influence of surface properties on the structure of granular silver films and excitation of localized plasmons

Granular silver films deposited on a thin insulating film of amorphous hydrogenated carbon (a-C:H) and transparent conducting electrode (polycrystalline indium tin oxide (ITO) layer) have been investigated by spectroscopy and microscopy methods. The extinction spectra of silver films on the surface of these materials are found to be significantly different. An annealing of silver films causes a blue shift of the peak of plasmon resonance band in the spectrum of silver nanoparticles: by 16 nm on the a-C:H surface and by 94 nm on the ITO surface. Silver films on the surface of a-C:H films are characterized by a narrower band in the extinction spectrum, which is peaked at 446 nm. The changes observed in the optical density of Ag films are related to the change in size and area of nanoparticles. The results of spectral studies of Ag films are in agreement with the data on the nanostructure obtained by scanning electron microscopy and statistical image processing. The spectra of granular silver films are shown to correlate well with the nanoparticle distribution function over the film area.     

Modelling of optical absorption of silver NP’s produced by UV radiation embedded in mesostructured silica films

Hexagonal mesostructured films containing silver ions were obtained by sol–gel method. Brij 58 was used to produce channels into the film, which house these ions. The films were exposure to UV radiation to produced silver metallic nanoparticles. The presence of the metallic nanoparticles was determined by infrared spectroscopy and optical absorption. Besides, these nanoparticles and core–shell structures of silver–silver oxide nanoparticles were identified by high-resolution transmission electronic microscopy. From these measurements, the obtained size range for silver nanoparticles was 6.1 nm. The absorption spectrum located at 440 nm was modelled and well fitted with the Gans theory considering refractive index higher than the one coming from host matrix. This index is explained because the silver oxide shell modifies the local surrounding medium of the metallic nanoparticles.     

Fabrication and optical study of Ag@SnO<Subscript>2</Subscript> core-shell structure nanoparticle thin films

Ag@SnO₂ core-shell nanoparticles dispersed in poly-(vinyl) alcohol films were fabricated on glass substrate by employing a dip-coating technique. Synthesis of Ag@SnO₂ nanoparticles with core-shell morphology is carried out by a soft-chemical technique in aqueous phase at 60°C. Formation of core-shell structure is monitored by the red-shift of the surface plasmon band of Ag nanoparticles (from 390 to 410 nm) in the UV-visible spectrum. These nanoparticles are deposited on the glass substrate. The structure and morphology of these films were investigated by X-ray diffraction technique and field-emission transmission electron microscopy, respectively. Optical properties of these pseudo-solids were studied by UV-visible spectroscopy. Surface plasmon spectrum of the core-shell nanoparticles film remained unaltered with increase in the number of layers. However, silver nanoparticles films have shown peak broadening and development of additional peaks with increase in the number of layers. Our investigations showed that the surface plasmon band of the silver nanoparticles could be preserved by controlled deposition of the tin dioxide shell.     

In Situ Synthesis of Oil-Based Polymer/Silver Nanocomposites by Photoinduced Electron Transfer and Free Radical Polymerization Processes

In this study, in situ synthesis of oil-based polymer–silver nanocomposites was achieved by using photoinduced free radical polymerization processes in which silver nanoparticles were formed by electron transfer reaction. An oil-based macromonomer was prepared and then copolymerized with styrene in the presence of AgNO₃. Copolymerization was started with free radicals formed by photolysis of 2,2-dimethoxy-2-phenyl acetophenone and simultaneously silver nitrate was reduced to metallic silver in nanosize by electron transfer reaction. The amount of photoinitiator influenced the size of silver nanoparticles formed within the polymer films. Nanocomposite films were characterized by TEM and TGA analysis. The obtained polymer nanocomposite film was also examined in respect of surface coating material that would have an antibacterial effect against Gram-positive, Gram-negative and spore-forming bacteria. It was demonstrated that suitably coated nanocomposite samples exhibited an antibacterial effect against these bacteria.     

SERS characterization of metallic silver nanoparticle self‐assembly within thin films

Clusters of silver nanoparticles are generated by the thermally initiated reduction of silver carboxylates (long‐chain fatty acids) in the thin polymer films. The size, shape, and aggregation of these nanoparticles are affected by the reduction reaction in the presence of capping agents. In order to understand the mechanism(s) controlling the silver structure formation, it is essential to understand the surface coordination chemistry occurring during this process. We now report the first application of surface‐enhanced Raman spectroscopy (SERS) to directly characterize adsorbates on the surfaces of silver nanoparticles within a thin film imaging construction containing multiple components. In addition, SERS investigation of model silver substrates was used to confirm the identify of specific adsorbates of silver complexes. This is a powerful tool for revealing the chemistry involved with the control of silver nanoparticle aggregation during thermally induced metallic silver formation within thin films. Both the catechol‐reducing agent and the phthalazinone (PAZ) particle aggregation agent are observed on the metallic silver surface at the initial particle formation and during its crystal growth. However, careful attention to excitation wavelength is required in order to observe all the surface species. PAZ appears to be more effective at stabilizing individual silver particles than other aggregation agents investigated. An understanding of the roles of the aggregation/reducing agents in the growth and aggregation of silver nanoparticles is important for preparing different types of silver particles for specific applications including silver‐based thermal imaging systems. Copyright © 2008 John Wiley & Sons, Ltd.     

Ag/Fe/Ag 纳米颗粒膜磁特性和微结构

"利用对靶磁控溅射法制备了一系列Ag/Fe/Ag纳米薄膜,沉积态样品Fe层厚度固定为35 nm,Ag层厚度为1、2、3、4、5 nm．随后对沉积态样品进行了退火处理,退火温度分别为200、300、400、500、600 ℃ , 退火30 min． 利用VSM测量了样品的磁特性, 利用SPM观察样品表面形貌和磁畴结构,并且利用XRD分析了样品的晶体结构．研究结果表明,沉积态样品随Ag层厚度的变化,垂直和平行膜面矫顽力均先增加后减小．当Ag层厚度为3 nm时,垂直膜面矫顽力最大约为260 Oe,样品颗粒分布均