电沉积法制备金属纳米线阵列膜的偏光特性

Metal nanowire array films were prepared by electrodepositing Cu, Ag, Ni, Co and Cu-Ag on porous anodic alumina film. Optical transmittance of both the porous anodic alumina film and metal nanowire array film was measured in the wavelength range of 400---2600 nm under an obliquely incident light. The experimental results show that metal nanowire array films exhibit a prominent polarization function. It was found that optical polarization properties can be improved by choosing suitable kinds of electrodepositing metal, controlling the shape and length of nanowire, and changing the incident angle.     

Metal ion modulated organization and function of the Langmuir-Blodgett films of amphiphilic diacetylene: photopolymerization, thermochromism, and supramolecular chirality

Some novel properties of organized molecular films of 10,12-tricosadiynoic acid (TDA), which were modulated by transition metal ions, were investigated. It was found that metal ions such as Cu(2+), Zn(2+), Ni(2+), Cd(2+), and Ag(+) in the subphase can greatly affect the monolayer formation of TDA and the properties of the subsequently deposited Langmuir-Blodgett (LB) films, particularly in the case of Ag(+), Zn(2+), and Cu(2+) ions. TDA LB film from the subphase containing Ag(+) ion could not be photopolymerized. It was suggested that both the strong chelating property to the carboxylate and the easy reduction of Ag(+) in the film disrupted the topochemical sequence of TDA and resulted in no polymerization in the film. Zinc ion coordinated TDA film could be photopolymerized into a blue polydiacetylene (PDA) film, which showed a reversible thermochromism between blue and purple color upon thermal stimulation. Fourier transform infrared spectra revealed the difference of the Zn(2+)-PDA film from those of the other ions, and the mechanism of the thermochromism was discussed. Copper ion coordinated TDA film could only be photopolymerized to a red PDA film, which showed supramolecular chirality although TDA itself was achiral. Atomic force microscopic measurements revealed the nanofiber structure in the Cu(2+)-PDA film. The supramolecular chirality of the Cu(2+)-PDA film was suggested to be due to the arrangement of the polymer backbone in a helical sense. Furthermore, it was found that the chiral assemblies from the achiral TDA molecules were very stable and the chirality could be kept even upon heating or treating with alkaline solution. While many synthetic efforts have been devoted to the functionalization of PDA films, we provided a simple method of modulating the organization and function of PDA films through metal ions.     

Surface-enhanced Raman scattering characteristics of 4-nitrobenzenethiol adsorbed on palladium and silver thin films

Palladium is an important catalytic metal, and it is desirable to develop a surface-enhanced Raman scattering (SERS) technique to investigate the reagent and product species adsorbed on its surface. Unfortunately, Pt-group metals, e.g., Pt and Pd, have been commonly considered as non- or weak-SERS-active substrates. In this work, Ag and Pd thin films were deposited very efficiently and evenly onto the surface of glass substrates by using only corresponding metal nitrate salts (AgNO₃ and Pd(NO₃)₂) with butylamine in ethanolic solutions. In this process, pure ethanol was used for Ag deposition, while an ethanol–water (8:2) mixture was used for Pd deposition. The as-prepared Ag and Pd films exhibited SERS activity over a large area. The surface-induced photoconversion capabilities of these Ag and Pd films were then tested on 4-nitrobenzenethiol by means of SERS. It was found that at least under visible laser irradiation, the surface-catalyzed photoreaction occurs more readily on a Ag film than on a Pd film for the conversion of 4-nitrobenzenethiol to 4-aminobenzenethiol, even though Pd is known to be an important transition metal with high catalytic activity.     

Influence of local structure on local electric field in Island‐like silver films

The infrared absorption enhancement phenomenon in the normal configuration of vacuum‐evaporated metal films on a transparent substrate is known to depend not only on the metal film morphology but also on the local structures of metal particles. To date, however, few studies have examined the effect of local structure on the phenomenon. Size distributions of islands and gaps, along with the volume fractions of Ag in thin films, were measured using scanning electron microscopy as a function of film thickness. The local structure of Ag nano clusters deposited on silicon substrates was investigated using a total conversion electron yield X‐ray absorption fine structure (XAFS) method at the Ag K‐edge. We observed a correlation between the electromagnetic field intensity at the surface as evaluated by IR measurement and the coordination numbers evaluated by XAFS. We found that the film morphology had a greater effect on resonant and nonresonant contributions than did the local structure of a particle. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of Metal Nanoparticles on the Electrocatalytic Oxidation of Glucose by Poly(NiIIteta) Modified Electrodes

Conductive polymeric [Ni^II(teta)]²⁺ (teta=C‐meso‐5,5,7,12,12,14‐hexamethyl‐1,4,8,11‐tetra‐azacyclotetradecane) films (poly(Ni)) have been deposited on the surface of glassy carbon (GC), Nafion (Nf) modified GC (GC/Nf) and Nf stabilized Ag and Au nanoparticles (NPs) modified GC (GC/Ag‐Nf and GC/Au‐Nf) electrodes. The cyclic voltammogram of the resulting electrodes, show a well defined redox peak due to oxidation and reduction of poly(Ni) system in 0.1 M NaOH. They show electrocatalytic activity towards the oxidation of glucose. AFM studies reveal the formation of poly(Ni) film on the modified electrodes. Presence of metal NPs increases electron transfer rate and electrocatalytic oxidation current by improving the communication within the Nf and poly(Ni) films. In the presence of metal NPs, 4 fold increase in current for glucose oxidation was observed.     

Charge transfers at metal/oxide interfaces: a DFT study of formation of K delta+ and Au delta- species on MgO/Ag(100) ultra-thin films from deposition of neutral atoms

Ultra-thin oxide films grown on a metal substrate and of thickness smaller than 1 nm may exhibit unusual properties with respect to thicker films or single crystal oxide surfaces. In a previous study [G. Pacchioni, L. Giordano and M. Baistrocchi, Phys. Rev. Lett., 2005, 94, 226104] we have suggested that a Au atom adsorbed on a MgO/Mo(100) thin film becomes negatively charged by direct electron tunneling from the Mo metal and that this is related to the low MgO/Mo(100) work function. Here we show, based on periodic DFT supercell calculations, that charge transfer can occur also in the opposite direction by adsorption of electropositive K atoms on MgO/Ag(100) films. We predict the occurrence of a charge transfer also for Au on MgO/Ag(100) films despite the fact that here the work function is 1 eV larger than in MgO/Mo(100). The formation of a layer of adsorbed negative (Au delta-/MgO/Ag) or positive (K delta+/MgO/Ag) adsorbates results in an increase or decrease, respectively, of the MgO/Ag(100) work function as predicted by the classical Gurney model for ionic adsorbates on metal surfaces.     

Electrochemical Surface Plasmon Resonance Spectroscopy at Bilayered Silver/Gold Films

Bilayered silver/gold films (gold deposited on top of the silver film) were used as substrates for electrochemical surface plasmon resonance spectroscopy (EC-SPR). EC-SPR responses of electrochemical deposition/stripping of copper and redox-induced conformation changes of cytochrome c immobilized onto self-assembled monolayers preformed at these substrates were measured. Influence of the Ag layer thickness and the double-layer capacitance on the EC-SPR behavior was investigated. The results demonstrated that the bilayered Ag/Au metal films produce a sharper SPR dip profile than pure Au films and retain the high chemical stability of Au films. Contrary to the result by the Fresnel calculation that predicts a greater fraction of Ag in the bilayered film should result in a greater signal-to-noise ratio, the EC-SPR sensitivity is dependent on both the Ag/Au thickness ratio and the chemical modification of the surface. Factors affecting the overall SPR sensitivity at the bilayered films, such as the film morphology, potential-induced excess surface charges, and the adsorbate layer were investigated. Forming a compact adsorbate layer at the bilayered film diminishes the effect of potential-induce excess surface charges on the SPR signal and improves the overall EC-SPR sensitivity. For the case of redox-induced conformation changes of cytochrome c, the SPR signal obtained at the bilayered silver/gold film is 2.7 times as high as that at a pure gold film.     

Electrochemistry of conductive polymers 39. Contacts between conducting polymers and noble metal nanoparticles studied by current-sensing atomic force microscopy

Electrical properties of contacts formed between conducting polymers and noble metal nanoparticles have been examined using current-sensing atomic force microscopy (CS-AFM). Contacts formed between electrochemically prepared pi-conjugated polymer films such as polypyrrole (PPy), poly(3-methylthiophene) (P3MeT), as well as poly(3,4-ethylenedioxythiophene) (PEDOT) and noble metal nanoparticles including platinum (Pt), gold (Au), and silver (Ag) have been examined. The Pt nanoparticles were electrochemically deposited on a pre-coated PPy film surface by reducing a platinum precursor (PtCl62-) at a constant potential. Both current and scanning electron microscopic images of the film showed the presence of Pt islands. The Au and Ag nanoparticles were dispersed on the P3MeT and PEDOT film surfaces simply by dipping the polymer films into colloid solutions containing Au or Ag particles for specified periods (5 to approximately 10 min). The deposition of Au or Ag particles resulted from either their physical adsorption or chemical bonding between particles and the polymer surface depending on the polymer. When compared with PPy, P3MeT and PEDOT showed a stronger binding to Au or Ag nanoparticles when dipped in their colloidal solutions for the same period. This indicates that Au and Ag particles are predominantly linked with the sulfur atoms via chemical bonding. Of the two, PEDOT was more conductive at the sites where the particles are connected to the polymer. It appears that PEDOT has better aligned sulfur atoms on the surface and is strongly bonded to Au and Ag nanoparticles due to their strong affinity to gold and silver. The current-voltage curves obtained at the metal islands demonstrate that the contacts between these metal islands and polymers are ohmic.     

Designed fabrication of ordered porous au/ag nanostructured films for surface-enhanced Raman scattering substrates

This article reports the designed preparation of two different kinds of novel porous metal nanostructured films, namely, an ordered macroporous Au/Ag nanostructured film and an ordered hollow Au/Ag nanostructured film. Different from previous reports, the presently proposed method can be conveniently used to control film structures by simply varying the experimental conditions. The morphology of these films has been characterized by scanning electron microscopy (SEM), and their performance as surface-enhanced Raman scattering (SERS) substrates has been evaluated by using rhodamine 6G (R6G) as a probe molecule. We show that such porous nanostructured films consisting of larger interconnected aggregates are highly desirable as SERS substrates in terms of high Raman intensity enhancement, excellent stability, and reproducibility. The interconnected nanostructured aggregate, long-range ordering porosity, and nanoscale roughness are important factors responsible for this large SERS enhancement ability.     

Sol-Gel Preparation of Coating Films Containing Noble Metal Colloids

Coating films containing Au, Ag, Pt and Pd metal colloids have been prepared by sol-gel processing. It is shown that for oxide films the temperature where the metal particles are precipitated by heating in air depends on metal species: 200°C for Au, 600°C for Ag, 800°C for Pt and 1000°C for Pd. The use of reducing atmosphere lowers the temperature for formation of noble metal colloids. This procedure can be used for direct formation of metal colloids from metal ions in the film as well as reduction of oxide particles to metal particles in the film. For an organic-inorganic matrix, noble metal colloids are precipitated by thermal reduction or photo-reduction. Thermal reduction occurs as a result of reduction by decomposing organic matter. Photo-reduction occurs as a result of UV irradiation.     

Adsorption of transition metal atoms on the NiO(100) surface and on NiO/Ag(100) thin films

We have studied the adsorption of Au, Pd, and Pt atoms on the NiO(100) surface and on NiO/Ag(100) thin films using plane wave DFT+U calculations. The scope of this work is to compare the adsorption properties of NiO, a reducible transition metal oxide, with those of MgO, a simple binary oxide with the same crystal structure and similar lattice parameter. At the same time, we are interested in the adsorption characteristics of NiO ultra-thin films (three atomic layers) deposited on Ag(100) single crystals. Also in this case the scope is to compare NiO/Ag(100) with the corresponding MgO/Ag(100) films which show unusual properties for the case of Au adsorption. The results show that the transition metal atoms bind in a similar way on NiO(100) and NiO/Ag(100) films, with Pt, Pd, and Au forming bonds of decreasing strength in this order. No charging effects occur for Au adsorbed on NiO/Ag(100) films, at variance with MgO/Ag(100). The reasons are analyzed in terms of work function of the metal/oxide interface. Possible ways to modify this property by growing alternate layers of MgO and NiO are discussed.     

A green approach to prepare Ag NPs loaded IC/PVA polymeric film for antimicrobial applications

In this study, glyoxal-cross-linked Iota carrageenan (IC) /poly(vinyl alcohol) PVA films were prepared and loaded with silver nanoparticles via a green approach, consisting of sweet lime juice induced in-situ reduction of Ag(I) ions to nano silver within the film matrix. The formation of silver nanoparticles was confirmed using UV–visible spectrophotometry. The Ag NPs-loaded films were also characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR). The dynamic water uptake data were interpreted by the ‘Power functional model’. The films showed fair antimicrobial action against bacteria E. Coli.     

Surface patterns induced by Cu2+ ions on BPEI/PAA layer-by-layer assembly

The multilayer films of branched polyethyleneimine (BPEI) and poly(acrylic acid) (PAA) have been fabricated with the layer-by-layer (LbL) method. Two characteristic courses of the film thickness growth are observed, which are the initial exponential-like growth and the following linear growth. The variation of the COOH/COO- ratio indicates that the ionization degree of the polyelectrolyte molecules decreases at the initial stage of the multilayer buildup and then levels off after about eight bilayers. The as-prepared (BPEI/PAA)n films show a relatively smooth surface. However, great morphology changes occur after immersing these films in Cu2+ or Zn2+ solution. In the case of n > or =7, wavelike surface patterns are induced to form on the films. Both wavelength and fluctuation of these surface patterns show a systematical variation with an increase of the bilayer number. Moreover, thermal treatment can stabilize these patterns and enable the preservation of them after releasing the Cu2+ ions from the LbL films by acidic treatment. Interestingly, only Cu2+ and Zn2+ can induce the formation of such surface patterns, whereas Fe2+, Ca2+, Ag+, and Na+ cannot. This phenomenon may closely relate to the different natures of the metal ions.     

Silver porous nanotube built three-dimensional films with structural tunability based on the nanofiber template-plasma etching strategy

A facile and high-throughput strategy is presented to fabricate three-dimensional (3D) hierarchically porous Ag films, with clean surfaces, via plasma etching Ag-coated electrospun nanofiber template. The films are built of Ag porous nanotubes and are homogeneous in macro-size but rough and porous in nanoscale. Each nanotube-block is micro/nanostructured with evenly distributed nanopores on the tube walls. The film architecture (or the shape, arrangement, and distribution density of porous nanotubes; the number and size of nanopores) can be easily controlled by the nanofiber-template configuration, Ag coating, and plasma etching conditions. Such hierarchically porous films could be very useful, such as in catalysis, sensors, and nanodevices. They have exhibited significantly structurally enhanced surface-enhanced Raman scattering performance with good stability and reproduction, and shown the possibility of molecule-level detection. Also, the strategy is universal for fabricating other hierarchically structured 3D metal porous films, such as porous Ag hollow sphere arrays.     

Electrically anisotropic thin films consisting of polymeric and metallic nanolayers from self-assembled lamellae of diblock copolymers

We demonstrated the fabrication of electrically anisotropic thin films of alternating polymeric layers and metallic layers in nanometer thickness by utilizing self-assembled nanodomains of symmetric diblock copolymers. Nanometer-thick metal layers macroscopically parallel to the film plane were synthesized by electroless Ag deposition on Au nanoparticles selectively in one of the blocks. Every Ag/Au layer was completely separated by nanometer-thick polymer layers in the direction perpendicular to the film plane. Therefore, the conductivity of the film was highly anisotropic, differing by at least 8 orders of magnitude in directions parallel and perpendicular to the film plane, even though the in-plane conductivity (2.8 x10(-6) S/cm) was in the range of semiconductors. If self-assembled nanodomains of diblock copolymers were not employed, a serial layer-by-layer process for each layer would be required to fabricate such an electrically anisotropic thin film.     

AgBF4-impregnated poly(vinyl phenyl ketone): an ethylene sensing film

Incorporation of silver tetrafluoroborate (AgBF4) into poly(vinyl phenyl ketone) (PVPK) renders the photoluminescent polymer responsive to ethylene. Polymer films prepared with a 2:1 ratio of Ag+ ions to polymer acetophenone groups responded with a quench of photoluminescence. Conditioned films showed a luminescence quench that was proportional to ethylene concentration before saturation occurred. Stern-Volmer analysis of the photoluminescence response suggested the presence of sites that were accessible and sites that were inaccessible to ethylene. Perturbations in polymer-metal interactions were monitored with infrared spectroscopy, revealing changes upon Ag+ incorporation, polymer film conditioning, and exposure to ethylene.     

Activation of ultrathin oxide films for chemical reaction by interface defects

Periodic density functional theory calculations revealed strong enhancement of chemical reactivity by defects located at the oxide-metal interface for water dissociation on ultrathin MgO films deposited on Ag(100) substrate. Accumulation of charge density at the oxide-metal interface due to irregular interface defects influences the chemical reactivity of MgO films by changing the charge distribution at the oxide surface. Our results reveal the importance of buried interface defects in controlling chemical reactions on an ultrathin oxide film supported by a metal substrate.     

Porous GaN as a template to produce surface-enhanced Raman scattering-active surfaces

Surface-enhanced Raman spectroscopy (SERS) substrates have been prepared by depositing Au or Ag on porous GaN (PGaN). The PGaN used as the template for the metal deposition in these studies was generated by a Pt-assisted electroless etching technique. PGaN was chosen as a potential SERS template due to its nanostructured surface and high surface area, two characteristics that are important for SERS substrates. Metal films were deposited either by solution-based electroless deposition or by thermal vacuum evaporation. SERS spectra were recorded at lambda = 752.5 nm for Au films and at lambda = 514.5 nm for Ag films deposited on PGaN. The SERS signal strength across the metal coated PGaN substrates was uniform and was not plagued by "hot" or "cold" spots on the surface, a common problem with other SERS surfaces. The Ag film deposited by electroless deposition had the highest overall SERS response, with an enhancement factor (EF) relative to normal Raman spectroscopy of 10(8). A portion of the increase in EF relative to typical SERS-active substrates can be assigned to the large surface area characteristic of the PGaN-Ag structures, but some of the enhancement is intrinsic and is likely related to the specific morphology of the metal-nanopore composite structure.     

ZnO/Ag复合膜的制备及其润湿性转换研究

利用溶胶-凝胶技术制备了ZnO/Ag复合膜. 采用X射线粉末衍射和扫描电子显微镜对其物相组成、 晶型结构以及表面形貌进行了表征, 采用接触角测试仪对其润湿性进行了表征, 并研究了紫外光照射下Ag的掺杂量对ZnO薄膜润湿性的影响. 结果表明, 当Ag掺杂量(摩尔分数)为5%时, 所得膜的润湿性转换速率最快, 紫外光照3 h后, 其润湿性由超疏水性转换为亲水性, 黑暗中放置5 d后, 亲水性再次转换为超疏水, 实现了润湿性的可逆转换.     

Effect of Incorporation of Silver on the Electrical Properties of Sol-Gel-Derived Titania Film

Metallic Ag nanoparticles-incorporating titania films were prepared using the sol-gel method. X-ray diffraction (XRD) patterns, UV/Vis optical spectra and transmission electron microscopy (TEM) images were recorded to characterize the Ag/titania composite films. Electrometer was used to estimate the resistance of Ag/titania composite film to understand the effect of the incorporation of metallic Ag nanoparticles on the electrical properties of titania film. The results showed that metallic Ag nanoparticles distributed randomly in titania film and most metallic Ag particles size was in the range of 5–15 nm. The agglomeration of a small quantity of metallic Ag particles occurred and when the amount of Ag species was increased the agglomeration was enhanced. The resistance of Ag/titania composite films decreased greatly compared with pure titania film.