Large scale, highly conductive and patterned transparent films of silver nanowires on arbitrary substrates and their application in touch screens

The application of silver nanowire films as transparent conductive electrodes has shown promising results recently. In this paper, we demonstrate the application of a simple spray coating technique to obtain large scale, highly uniform and conductive silver nanowire films on arbitrary substrates. We also integrated a polydimethylsiloxane (PDMS)-assisted contact transfer technique with spray coating, which allowed us to obtain large scale high quality patterned films of silver nanowires. The transparency and conductivity of the films was controlled by the volume of the dispersion used in spraying and the substrate area. We note that the optoelectrical property, σ(DC)/σ(Op), for various films fabricated was in the range 75-350, which is extremely high for transparent thin film compared to other candidate alternatives to doped metal oxide film. Using this method, we obtain silver nanowire films on a flexible polyethylene terephthalate (PET) substrate with a transparency of 85% and sheet resistance of 33 Ω/sq, which is comparable to that of tin-doped indium oxide (ITO) on flexible substrates. In-depth analysis of the film shows a high performance using another commonly used figure-of-merit, Φ(TE). Also, Ag nanowire film/PET shows good mechanical flexibility and the application of such a conductive silver nanowire film as an electrode in a touch panel has been demonstrated.     

The research of manufacture of flexible conductive tracks at room temperature

Nano silver is widely used in conductive lines for its advantages, nano size, low melt temperature and excellent conductivity. In general, nano silver of less than 50 nm need be sintered at 200 centigrade in order to acquire conductivity, but it limits the choice of the substrates, only high temperature resistant substrate can be used, for example, PI film and glass. In order to acquire flexible tracks with excellent conductivity at room temperature on paper and PET, nano silver emulsion of 2 percent silver content was prepared through liquid phase chemical reduction, and then the concentration of silver was improved to 17 percent by centrifuging at high speed. And the emulsion was adjusted to meet the demand of inkjet printing, such as surface tension, and viscosity, pH value, then was jetted onto photo paper and PET film. High conductivity was acquired after treated by 830 nm infrared laser, and the sheet resistance is less than 2 omega/(see symbol). After aging test, the conductivity was stable. The method can be used in solar cells, flexible LED, intelligent packaging and can replace the traditional screen printing method at low cost.     

A novel process to form a silica-like thin layer on polyethylene terephthalate film and its application for gas barrier

A novel process for polyethylene terephthalate (PET) surface modification with a silica-like thin layer is proposed. 3-Aminopropyltrimethoxysilane was employed to react with acetone to form dimethyliminopropyltrimethoxysilane (DIPTMS) after aging for 10 days at room temperature. After hydrolysis of alkoxy groups in DIPTMS, dimethylimine-modified silica clusters occurred resulting in an increase of the solution viscosity. Consequently, a dense and homogeneous thin layer was easily dip-coated onto a PET film. After heat treatment at 150 °C, a smooth, flexible and transparent silica-like film (about 70 nm thick) was formed via dehydration and condensation. The surface of the PET dramatically changed from hydrophobic (water contact angle: 70±2°) to hydrophilic (45±3°). As an attempt for application, a dense film of lithium metasilicate (Li₂O·2SiO₂·nH₂O) was successfully prepared by dip coating on the modified PET film, which appeared very low oxygen permeability of about 0.17 cm³/m² day atm at 23 °C and 85% humidity.     

PET基纳米Ag薄膜形貌与导电及电磁屏蔽性能的分形表征

采用磁控溅射法在PET非织造布上制备了不同厚度的纳米结构Ag薄膜,用高度相关函数法对薄膜的原子力显微镜(AFM)图像进行分形维计算,用AFM分析不同厚度纳米结构Ag薄膜形貌及粒径的变化;用网络测试仪测试了不同厚度样品的电磁屏蔽效能。结果表明,随着薄膜厚度的增加,薄膜表面质量提高,分形维增大;电磁屏蔽效能也随分形维的增大而增加。可以认为,分形维能有效地表征薄膜的表面形貌,分形维与导电及屏蔽效能存在明显的对应关系,并可以用分形维优化磁控溅射的工艺条件。     

A novel thermal electrochemical synthesis method for production of stable colloids of “naked” metal (Ag) nanocrystals

This paper describes a novel thermal electrochemical synthesis (TECS) method for producing aqueous solutions (or sols) that contain metal silver nanocrystals as small as a few nanometers. The TECS method requires mild conditions (25 to 100 °C), low voltage (1 to 50 V DC) on silver electrodes, and water or simple aqueous solutions as the reaction medium. Furthermore, a tubular dialysis membrane that surrounds the electrodes provides favorable conditions for producing nanosized (less than 10 nm) silver nanocrystals. Unlike nanocrystals reported in the literature, our nanocrystals have several unique features: (1) small nanometer-scale size, (2) “nakedness” (i.e., surfaces of metal nanocrystals are free of organic ligands or capping molecules and need no dispersant in synthesis solutions), and (3) colloidal stability in water solutions. It was discovered that silver nanoparticles with initially large size distribution can be homogenized into near-monodispersed colloidal sol by a low-power (less than 15 mW) He–Ne laser exposure treatment. The combination of the TECS technique and the laser treatment could lead to a new technology that produces metal nanoparticles that are naked, colloidally stable, and uniformly sized. In the presence of a stabilizing agent (also a supporting electrolyte) such as polyvinyl alcohol, high yields of silver nanoparticles (less than 100 nm) in the form of thick milky sols are produced.     

双氧水浸泡对覆膜铁薄膜特性黏度及结晶度的影响

采用自动黏度测定仪和红外光谱分析研究了覆膜、双氧水浸泡及蒸煮过程对覆膜铁薄膜黏度和结晶度的影响。结果表明:覆膜及蒸煮过程会使PET薄膜的特性黏度和结晶度下降,双氧水浸泡可使PET薄膜的特性黏度和结晶度升高;高温及水分子存在会使PET降解,从而使其特性黏度降低,同时结晶度下降;双氧水会使PET薄膜聚合度增加,从而使其特性黏度和结晶度升高。     

银纳米线-聚对苯二甲酸乙二醇酯透明导电胶膜

以银纳米线作为导电填料,以聚对苯二甲酸乙二醇酯(PET)为柔性衬底,采用平板热压机通过热压方式制备了银纳米线-PET透明导电胶膜。研究了银纳米线-PET导电胶膜的耐弯曲性能、电学性能以及透光性。结果表明,所制备的银纳米线-PET导电胶膜透光率达到80%以上,表面电阻率达到1×10^-3Ω·cm。银纳米线-PET导电胶膜经过500次的弯曲循环后电阻率未下降。随着银纳米线溶液浓度的增加,银纳米线-PET导电胶膜透光性下降,表面电阻率增加。     

Silver-doped sol-gel film as a surface-enhanced Raman scattering substrate for detection of uranyl and neptunyl ions

A surface-enhanced Raman scattering (SERS) substrate containing silver particles was prepared by an acid-catalyzed sol-gel method. Silver nitrate was first doped into the sol-gel film followed by chemical reduction of the silver ions with sodium borohydride to produce silver particles. This silver-doped sol-gel substrate exhibits strong enhancement of Raman scattering from adsorbed uranyl ions with a detection limit of 8.5 x 10(-8) M, which is comparable to existing methods of uranyl detection such as spectrophotometry, fluorometry, and a SERS method based on ligand-modified solution silver colloids. However, in the present method, no preconcentration steps, chromogens, or complexing ligands are needed. Compared with the SERS method using Ag colloidal sols, the silver-doped sol-gel film has the advantage that the silver particles trapped in the sol-gel matrix are much more stable than Ag colloids in liquid media. Furthermore, porous silica sol-gel materials are known to have affinities toward many inorganic and organic molecules. The enhanced adsorption affinities could also lead to the increased SERS sensitivity. The performance of the new silver-doped sol-gel substrate was evaluated with uranyl ions and compared to that of a SERS substrate based on silver-coated silica beads prepared by vacuum deposition. The detection limit for the silver-doped sol-gel film was 104 times lower than that for the silver-coated silica beads. The sol-gel substrate was further used to obtain, for the first time, the surface-enhanced Raman spectrum of neptunyl ions in dilute aqueous solutions.     

Synthesis of organic-inorganic hybrid sols with nano silica particles and organoalkoxysilanes for transparent and high-thermal-resistance coating films using sol-gel reaction

Organic-inorganic hybrid sols were synthesized from nano silica particles dispersed in water and from organoalkoxysilanes, using the sol-gel reaction. This work focuses on the effects of the three multifunctional organoalkoxysilanes dimethyldimethoxysilane (DMDMS), methyltrimethoxysilane (MTMS), and tetramethoxysilane (TMOS) to form a transparent and high-thermal-resistance coating film. The stability of the hybrid sol was evaluated as a function of the reaction time for 10 d through the variation of the viscosity. The viscosity of the silica/DMDMS and silica/MTMS sol was slightly increased for 10 d. The multifunctional organoalkoxysilanes formed dense silica networks through hydrolysis and condensation reaction, which enhanced the thermal resistance of the coating films. No thermal degradation of the silica/DMDMS sample occurred up to 600 degrees C, and none of the silica/MTMS and silica/TMOS samples occurred either up to 700 degrees C. The organic-inorganic hybrid sols were coated on the glass substrate using a spin-coating procedure. The organic-inorganic hybrid sols formed flat coating films without cracks. The transmittance of the hybrid sol coating films using MTMS and DMDMS was shown to be over 90%. The transmittance of the silica/TMOS sol coating film reacted for 10 d abruptly decreased due to faster gelation. The silica/DMDMS and silica/MTMS hybrid sols formed smooth coating films while the surface roughness of the silica/TMOS coating film markedly increased when the hybrid sol reacted for 10 d. The increase of the surface roughness of the silica/TMOS coating film can be attributed to the degradation of the stability of the hybrid sol and to the loss of transmittance of the coating film. It was confirmed in this study that the use of organic-inorganic hybrid sol can yield transparent and high-thermal-resistance coating films.     

Crack formation in TiO2 films prepared by sol-gel processing: Quantification and characterization

TiO₂ thin films were prepared by dip-coating from soluble precursor powders using different solvent mixtures. Under certain conditions cracking occurs during drying and thermal treatment. Both extent of damage and time of formation were evaluated from micrographs using image processing software. Different approaches for data evaluation are applied and compared. It is shown that reproducible measurements of defect densities are a useful tool for the optimization of process parameters.Data indicate that the presence of 1,5-pentanediol retards the formation of a rigid xerogel network that is responsible for crack formation during film drying. The air moisture during dip-coating also turns out to have a systematic effect on the microstructure of the densifying film as demonstrated by quantitative defect analysis. This method has to be used carefully, though, that a qualitative change of the damage pattern does not lead to a misinterpretation of the data.     

White light-emitting diode coated with ZnSe:Mn/ZnSe nanocrystal films enveloped by SiO2

Mn-doped nanocrystals (NCs) have attracted much attention for their excellent properties. In our work, colloidal Mn-doped NCs with high quantum yield are synthesized and enveloped with silica hydrosol. The blend of NCs and silica hydrosol is coated on a blue light-emitting diode (LED), and the appropriate thickness of the NC film is found. White light is gained through the mix of the blue emission of the LED and the orange emission from Mn-doped NC films. The chromaticity coordinates and the image of the white LED indicate that Mn-doped NCs can be a good substitute for YAG:Ce phosphor, and the reliability of the white LED can be improved by enveloping NCs with SiO(2).     

基于分子动力学的丝网印刷柔性传感器电极导电性机理研究

目的 研究提高丝网印刷柔性传感器电极的导电性,为提升柔性传感器的电学性能提供参考依据。方法 首先采用分子动力学（Molecular Dynamic,MD）模拟方法,建立在Wenzel模型下导电银浆团簇在不同粗糙因子下的对苯二甲酸乙二醇酯（Polyethylene Terephthalate,PET）表面铺展的分子动力学模型,其次分别计算各体系下的结合能,用以表征不同体系下PET表面对导电银浆团簇结合能力,接下来通过丝网印刷实验的方法探究银浆与不同粗糙因子PET的结合能力对传感器电极的导电性的影响。结果 仿真结果表明,导电银浆团簇在不同粗糙因子的PET表面的铺展过程中会陷入粗糙表面的凹陷处,且导电银浆与基材的结合能随着PET粗糙因子的增加而增加。实验结果表明,使用不同粗糙因子的PET作为承印物能显著提升电极的导电性。相比于未处理的PET,随着粗糙因子的增加,导电线条的电导率逐渐升高,电阻率逐渐降低,方块电阻逐渐降低。电导率最大提升了77%,电阻率最大下降了43%,方块电阻最大下降了38%。结论 导电银浆在粗糙表面铺展的过程中会渗入基材的凹陷处,增加了吸附点位,使得银浆与基材的结合更加紧密...     

Separation of Silver Nanocrystals for Surface-enhanced Raman Scattering Using Density Gradient Centrifugation

One-dimensional silver nanocrystals(AgNCs) have been prepared by a polyol process using sodium hydroxide and nitric acid at a constant silver source concentration.Results indicate that the aciditybasicity plays an important role in silver-nanocrystal formation.Different morphologies of AgNCs were synthesized by changing the NaOH or HNO_3 amount.We demonstrate that nearly monodisperse silver nanocrystals can be separated from polydisperse samples using density gradient centrifugation separation(DGCS).We also demonstrate that the separated AgNCs can be used as substrates for surfaceenhanced Raman scattering(SERS) spectroscopy.The separation approach provides a method of improving the nanocrystal quality produced by large-scale synthetic methods.     

A simple route to synthesize size-controlled Ag(2)S core-shell nanocrystals, and their self-assembly

Silver sulfide (Ag(2)S) nanocrystals were successfully synthesized by the thermal treatment of the single source precursors, silver dialkyldithiophosphates (Ag[S(2)P(OC(n)H(2n+1))(2)]), under mild reaction conditions. The size of Ag(2)S nanocrystals with regular shape can be controlled in the range of tens of nanometers by adjusting critical parameters, such as the carbon number of the substitute alkyl, the solvent and the reaction temperature. Electron diffraction and x-ray powder diffraction confirmed the orthorhombic phase of the Ag(2)S nanocrystals. The as-prepared Ag(2)S nanocrystals have an inorganic-organic core-shell structure, in which Ag(2)S nanocrystals are the inorganic core and the organic modifiers, consisting of oleylamine and dialkyldithiophosphate, are the shell. The organic modifiers were anchored to the surface of Ag(2)S nanocores by their active groups of?-NH(2) and?-SPS-?, respectively, and their direct-alkyl chains spread to the outside. So, these as-prepared Ag(2)S nanocrystals can self-assemble to form orderly two-dimensional arrays easily, and they disperse in some non-polar solvents stably.     

Directly ultraviolet photochemical deposition of silver nanoparticles on silica spheres: Preparation and characterization

A simple method was developed to directly deposit silver nanoparticles on the surface of silica spheres. The photochemical reduction was carried out by ultraviolet irradiation in air atmosphere at room temperature. The [Ag(NH₃)₂]⁺was reduced to silver atoms upon ultraviolet irradiation. Silver atoms subsequently deposited on the surface of silica spheres and agglomerated into silver nanoparticles. Silica spheres with silver nanoparticles of different size and density can be simply controlled by adjusting the UV-light irradiation time. The silver nanoparticles deposited on silica spheres were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and field emission scanning electron microscopy.     

Enhanced photoelectrochemical water-splitting effect with a bent ZnO nanorod photo anode decorated with Ag nanoparticles

Zinc oxide (ZnO) nanorods coated with silver (Ag) film on a polyethylene terephthalate (PET)flexible substrate were used as the photo anode for water splitting. The hybrid nanostructures were prepared via low-temperature hydrothermal growth and electron beam evaporation. The effects of plasmonic enhanced absorption, surface recombination inhibition and improved charge transport are investigated by varying the Ag thickness. Light trapping and absorption enhancement are further studied by optimizing the curvature of the PET substrates. The maximum short circuit current density (JSC, 0.616 mA cm -2) and the photoelectron conversion efficiency (PCE, 0.81%) are achieved with an optimized Ag film thickness of 10 nm and substrate bending radius of 6.0 mm. The maximum JSC and PCE are seven times and ten times, respectively, higher than those of the bare ZnO nanorods on flexible substrates without bending. The overall PEC performance improvement is attributed to the plasmonic effects induced by Ag film and improved charge transport due to inhibition of ZnO surface charge recombination. Enhanced light trapping (harvesting) induced by bending the PET substrates further improved the overall efficiency.     

Polymer dispersion preparation by flow induced phase inversion emulsification. Part 1 The effect of silica on emulsification and dispersion characteristics

Low density polyethylene (LDPE) melt was emulsified in the presence of a hydrophobically modified water soluble polymer (HMWSP) and colloidal hydrophilic silica using the Flow Induced Phase Inversion (FIPI) emulsification technique. HMWSP was used as the surface active material. After the emulsification, LDPE melt was solidified to obtain a polymeric dispersion. Silica was used to aid the emulsification and improve the emulsion/dispersion characteristics. It was shown that the presence of silica increases the amount of aqueous phase necessary for phase inversion from water-in-LDPE melt to LDPE melt-in-water emulsion. The mean particle size and particle size span increased in the presence of silica. However, due to broader particle size distribution, the viscosity was lowered. The dispersions with silica appeared to form a more uniform film compared with the dispersion without silica. When the silica concentration is less than 1% in aqueous phase, an emulsion is obtained. At 2% silica level, a wet powdery material is obtained. This material can be diluted to obtain a dispersion or it could be used in powder coating.     

Formation of silicon nanocrystals in SiN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> film on PET substrates using femtosecond laser pulses

The formation of Si nanoclusters under the action of femtosecond laser pulses in a SiN _x film containing excess silicon has been studied. The initial film was grown by plasmachemical deposition at 100°C on a PET substrate. The pulsed crystallization was effected by a Ti-sapphire laser operating at a wavelength of 800 nm and a pulse duration of about 50 fs. According to the Raman spectroscopy data, the pulsed laser annealing stimulated the accumulation of excess silicon in nanoclusters and their crystallization. The proposed approach can be used for the formation of semiconductor nanocrystals in dielectric films on various plastic (polymer) substrates.     

The sol-gel preparation of ZnO/silica core-shell composites and hollow silica structure

Three kinds of different ZnO colloid particles (flowerlike particles, nanoribbons and microspheres) and one kind of ZnO film have been coated with silica via a simple sol-gel method in the Stöber system and ZnO/silica core-shell microparticles or films have been obtained. The thickness of silica shell can be controlled by adjusting the concentration of TEOS added into the system. If the ZnO core is etched off by HCl, corresponding, hollow silica particles or film will be generated.     

Formation of flower-like Ag colloids using pulsed proton beam

A new solution phase method is presented for the synthesis of "flower-like" silver nanomaterials using a pulsed proton beam irradiation process at room temperature. It was observed that the morphology of the prepared silver crystals was easily controlled by varying the number of exposures to the pulsed proton beam. The synthesized flower-like silver nanocrystals exhibited excellent surface enhanced Raman scattering (SERS) signals, which were attributed to the rough microstructures on the surface of the synthesized Ag crystals.