Diameter-dependent coloration of silver nanowires

Silver nanowires were synthesized with a green method and characterized with microscopic and diffractometric methods. The correlation between the colors of the nanowires deposited on a solid substrate and their diameters was explored. Silver nanowires that appear similar in color in the optical micrographs have very similar diameters as determined by atomic force microscopy. We have summarized the diameter-dependent coloration for these silver nanowires. An optical interference model was applied to explain such correlation. In addition, microreflectance spectra were obtained from individual nanowires and the observed spectra can be explained with the optical interference theory. This work provides a cheap, quick and simple screening method for studying the diameter distribution of silver nanowires, as well as the diameter variations of individual silver nanowires, without complicated sample preparation.     

Solvothermal fabrication of uniform silver nanowires

Conventional polyol synthesis has been widely used for the preparation of silver nanostructures with different morphologies. However, there is a drawback that it is difficult to control the reaction parameters for shape-controlled synthesis of silver nanostructures, such as the rate of the addition of silver ions to the solution. In this paper, we combine polyol process and solvothermal method for easily synthesizing silver nanostructures. Importantly, the introduction of cuprous chloride (CuCl) to the reaction leads to increasing the population of twinned Ag seeds (required for wire growth) at the expense of that of single Ag seeds. Silver nanowires (Ag NWs) with uniform width (~80?nm in width) can be obtained in the presence of poly(vinyl pyrrolidone) (PVP). Some other parameters, such as the reaction temperature and molar ratios of the repeating unit of PVP to AgNO₃ (R), also have been discussed. A possible mechanism is put forward to understand the evolution of silver nanostructures.     

Synthesis of silver nanowires in aqueous solutions

Silver nanowires with a diameter of 30 nm and typical lengths of 5-10 μm have been synthesized in an aqueous medium. To initiate the reaction, citrate ions were used, and during the reaction the aromatic organic molecules polymerize forming “straight” chain surfactants which support the formation of nanowires. Characterization by TEM and HRETM revealed the nanowires to be highly crystalline with a growth along the [110] direction.     

填充银纳米线各向同性导电胶的性能

以Ti (OC₄H₉)₄ 水解形成的溶胶体系为模板, 以AgNO₃ 为银纳米线的前驱体, 低温下合成长径比为50～60 的银纳米线, 采用TEM 和XRD 对所制得的银纳米线进行表征。以银纳米线作为导电胶的导电填料, 成功制备了一种高电导率的各向同性导电胶。导电胶的电学性能和力学性能测试表明: 这种导电胶在导电填料含量为56 wt %时的电导率比填充75 wt %微米银粒子的导电胶高约6 倍(体积电阻率为1. 2 ×10-4Ω·cm) 。由于填料含量的降低, 该导电胶的抗剪切强度(以Al 为基板时的抗剪切强度为17. 6 MPa) 相比于填充75 wt %微米银粒子和75 wt %纳米银粒子导电胶均有不同程度的提高。      

Sonochemical synthesis of amorphous long silver sulfide nanowires

Long silver sulfide nanowires have been prepared via the thioglycolic acid (TGA)-assisted sonochemical method. The transmission electron microscope (TEM) and field emission scanning electron microscope (FESEM) images reveal that the nanowires have uniform width and length. The selected area electron diffraction (SAED) pattern indicates that the Ag₂S nanowires are amorphous. Furthermore, the mechanism for the TGA-assisted sonochemical synthesis of Ag₂S nanowires has been preliminarily presented.     

In situ electrical measurements of polytypic silver nanowires

Novel 4H structure silver nanowires (4H-AgNWs) have been reported to coexist with the usual face-centered cubic (FCC) ones. Here we report the electrical properties of these polytypic AgNWs for the first time. AgNWs with either 4H or FCC structures in the diameter range of 20-80?nm were measured in situ inside a transmission electron microscope (TEM). Both kinds of AgNW in the diameter range show metallic conductance. The average resistivity of the 4H-AgNWs is 19.9?μΩ?cm, comparable to the 11.9?μΩ?cm of the FCC-AgNWs. The failure current density can be up to ～10(8)?A?cm(-2) for both 4H-and FCC-AgNWs. The maximum stable current density (MSCD) is introduced to estimate the AgNWs' current-carrying ability, which shows diameter-dependence with a peak around 34?nm in diameter. It is attributed to fast annihilation of the current-induced vacancies and the enhanced surface scattering. Our investigations also suggest that the magnetic field of the electromagnetic lens may also introduce some influence on the measurements inside the TEM.     

One step synthesis of silver nanowires used in preparation of conductive silver paste

For mass preparation of conductive silver paste, a convenient approach to synthesize silver nanowires (Ag NWs) is presented. Monodisperse Ag NWs with ca. 40 nm in diameter and over 10 μm in length were successfully obtained in high yield only by heating a mixture of AgNO₃, poly(vinyl pyrrolidone), ethylene glycol and HCl prepared previously. This method not only simplifies the conventional polyol process but also extremely improves its repeatability. More important, the patterns fabricated with the Ag NWs naturally have a high conductivity, up to ca. 13 % of bulk silver, due to the cross-linked network structure formed by accumulation of nanowires. The conductivity even can be improved to 41 % of bulk silver conductivity through a chemical sintering at room temperature, which makes us believe that the Ag NWs could be broadly applied in preparation of conductive paste.     

Effect of silver nanowires on electrical conductance of system composed of silver particles

Silver nanowires were prepared by polyol process and doped to the system containing conventional micro-scaled sphere or flake silver particles. It is found that the conductance of doped system is much better than the undoped system with the same quantity silver. A plausible mechanism is described as that these nanowires are favor to act as bridges to establish perfect linkage among particles, and the chance of contact and contact area become more than the cases without wires. This development will be meaningful for the preparation of advanced electrically conductive adhesive (ECA) with high conductivity and good adhesive strength.     

Fabrication of luminescent silver doped PbS nanowires in polymer

We report here fabrication of silver (0 to 1.76 mol%) doped PbS nanowires (radius r approximately 1.75 nm) in polymer by a simple wet chemical process. An X-ray photoelectron spectroscopy study clearly confirms the possibility of silver (Ag) doping in PbS nanowires. Both absorption and photoluminescence spectra reveal very strong quantum confinement effect in PbS nanowires as expected for a r/Bohr radius ratio approximately 0.0972 nm. Visible excitonic emission is observed at room temperature in the photoluminescence spectra of undoped and silver doped PbS nanowires in polymer. The excitonic emission is appreciably blue-shifted when doped by silver (1.76 mol%) indicating strong modification of the electronic states by magnetic silver ions. While Ag2+ centers at the substitutional lattice site show an emission band around 525 nm, Ag0 at the interstitial site act as nonradiative recombination centers. Effect of silver doping on the luminescence intensity is also discussed.     

Size effect on the crystal structure of silver nanowires

A 4H structural silver nanowire (4H-AgNW) is discovered to coexist with a face-centered cubic (FCC) one prepared by electrochemical deposition and to have the highest concentration in the total of 4H- and FCC-AgNWs with diameters around 30 nm. Moreover, the concentration becomes smaller when the diameters deviate from 30 nm. This size effect arises from the fact that 4H-AgNW has a more favorable surface configuration but higher volume internal energy than FCC-AgNW, which is proved by our model.     

Large-scale synthesis of defect-free silver nanowires by electrodeless deposition

We report a new method that generates high-density, long aspect ratio and large-area silver nanowire arrays within the pores of anodic aluminum oxide (AAO) membrane by reducing silver nitrate with ethylene glycol. The freestanding and defect-free silver nanowires can be obtained at high yields. In a typical procedure, the as-prepared silver nanowires have a mean diameter of ∼ 53 nm. It is found out that both temperature and reaction time are important factors in determining the morphology and aspect ratios of nanowires. Lower temperature and longer time are favorable to form polycrystalline silver nanowires with high uniformity and aspect ratios.     

Large-scale synthesis of silver nanowires via a solvothermal method

Silver nanostructures have been synthesized through a simple solvothermal method by reducing silver nitrate (AgNO₃) with ethylene glycol (EG) and using poly(vinylpyrrolidone) (PVP) as an adsorption agent. Different concentrations of ferric chloride (FeCl₃) are added into the solution. It is found that AgCl colloids formed in the initial stage greatly influence the final morphologies of the products. When a low-concentration FeCl₃ solution is used, there is a mixture of silver nanoparticles and nanowires. However, when a high-concentration FeCl₃ solution (100 μM) is used, large amounts of AgCl colloids appear, resulting in decreasing free Ag⁺ during initial formation of silver seeds and slowly releasing of Ag⁺ to the solution in the subsequent reaction. This leads to the formation of silver nanowires. Furthermore, an increase in the concentration of FeCl₃ from 100 to 300 μM results in the synthesis of silver nanowires with larger sizes. In addition, Fe(III) is reduced to Fe(II) form which in turn reacts with and removes adsorbed atomic oxygen from the surface of silver seeds. In this case, uniform silver nanowires can be obtained.     

Highly conductive supercapacitor based on laser-induced graphene and silver nanowires

One of the foremost necessary desires of energy systems has been the existence of efficient, flexible, transportable, and eco-friendly devices. Among all the energy storage systems, supercapacitors have attracted plenty of attention thanks to their distinctive properties. Among all capacitor technologies, laser-induced graphene (LIG)-based capacitors are within the spotlight nowadays due to their high flexibility and simple manufacture. The most downside with LIG-based capacitors is their low conductivity and low charge capacity. During this work, to overcome this problem, the surface of LIG is covered with silver nanowires (AgNWs) and LIG/AgNWs composite is employed to form supercapacitor. In this study, all the electrochemical properties of the prepared composite were investigated, and therefore the results showed that AgNWs could increase the electrical conductivity of LIG by about 2.25 times, improve electrode–electrolyte interaction, and increase areal capacitance by 1.3 times. Additionally, the synthesized supercapacitor shows stable cyclic behavior and retention capacity equal to 78% after 1000 charge–discharge cycles. A singular increase in LIG conductivity and improved in its cyclic performance. Furthermore, galvanostatic charge/discharge curves indicated acceptable charge capacity of the LIG/AgNWs supercapacitor.

     

Electrical properties optimization of silver nanowires supported on polyethylene terephthalate

ABSTRACT

The aim of this study is the enhancement of the electrical properties of thin films obtained from silver nanowires (AgNWs) deposited on a flexible polyethylene terephthalate (PET) support. First, AgNWs were obtained by the “polyol” liquid phase synthesis method in the presence of chloride ions. After purification, the AgNWs were successively deposited on a flexible support of PET by doctor blade method. To improve the adhesion of the AgNWs coating to the substrate, thin films of polymethyl methacrylate (PMMA) were interposed between the layer of AgNWs and PET substrate. The properties of the thin films have been studied depending on the number of AgNWs layers and heat treatment procedure. Characterization of pure AgNWs as well as of AgNWs/PMMA/PET structures has been carried out by x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray analysis, transmission electron microscopy, UV–Vis spectroscopy, and scanning probe microscopy. The sheet resistance of the transparent conducting films was determined by four point probe measurement. Best results in terms of homogenous conductance across the film and optical transmittance have been obtained for samples prepared by deposition of four successive layers of AgNWs. Further heat treatment improved the conductivity of AgNWs on the PMMA/PET substrate. For these films, the sheet resistance decreased from 41.25 to 29.55 Ω/sq after 40 min of heat treatment in air at 150°C.     

Isotropical conductive adhesives with very-long silver nanowires as conductive fillers

Isotropical conductive adhesives (ICAs) have garnered great attention from the researchers in electronic industry as a potential substitute to lead-bearing solders for novel microsystem. In this paper, silver nanowires with a diameter of approximately 390 nm and a length of over 100 μm were synthesized by a polyol process. The ICAs composed of an epoxy-based binder containing silver nanowire were prepared and the curing behaviors, electrical properties, hygroscopicity, and the tensile shear strength of ICAs were investigated. Silver nanowires affect the curing behavior of epoxy resin and reduce the cross-linking density. The resistivity of the ICAs filled with 10, 35 and 45 wt% silver nanowire cured at 150 °C is 8.9 × 10^?3, 1.69 × 10^?5 and 4.9 × 10^?6 Ω cm respectively. The resistivity of the ICAs filled with silver nanowire cured at 150 °C is little change after aged under 85 °C/85 % for 264 h. With the increase of the loading of silver nanowire the tensile shear strength of the ICAs increase. The reasons for the effects of silver nanowires on the curing behavior and the electrical property and hygroscopicity and the tensile shear strength were discussed in terms of the morphology, distribution, and higher activity of silver nanowires.     

Single particle plasmon spectroscopy of silver nanowires and gold nanorods

The excitation of surface plasmons in individual silver nanowires and gold nanorods is investigated by means of high-resolution electron energy loss spectroscopy in a transmission electron microscope. The transverse and longitudinal modes of these nanostructures are resolved, and the size variation of the plasmon peaks is studied. The effect of electromagnetic coupling between closely spaced nanoparticles is also observed. Finally, the relation between energy-loss measurements and optical spectroscopy of nanoparticle plasmon modes is discussed.