Aspect Ratio Of Silver Nanowires Research Articles

Controlling the aspect ratio of silver nanowires in the modified polyol process

Metal nanowire-based conducting networks, primarily based on silver nanowires (Ag NWs), show promise for flexible transparent conducting electrodes. The synthesis of high aspect ratio Ag NWs is the key to accomplishing good optoelectronic performance. Among the various synthesis routes available, the one-pot polyol method is widely used. It is based on the reduction of silver nitrate (AgNO3) by a polyol, typically ethylene glycol, in the presence of polyvinylpyrrolidone (PVP) and ferric chloride. The present work provides a systematic study of the role of PVP to AgNO3 weight ratio on the physical dimensions (length, diameter, and aspect ratio) of the Ag NWs and the role of NW concentration and spin coating speed on the optoelectronic properties (transparency and conductivity) of the NW-based network.

Low‐loss percolative epsilon‐negative composites derived from the ultra‐low percolation threshold

AbstractIn this work, the mechanism of negative permittivity response with low losses in the silver nanowires/polyvinylidene fluoride composites were demonstrated. Due to the large aspect ratios of silver nanowires, ultra‐low percolation threshold () between 0.7 and 0.8 wt% was achieved with the losses effectively decreased by several orders of magnitude down to a low level of about 0.2. The negative permittivity response from Lorentz type and Drude type presented the transition from insulator to conductor. The tunable Drude type negative permittivity was ascribed to the plasma oscillation of free electrons, which leads to an inductive property. The conduction mechanism was switched from hopping to metallic conduction with the observation of skin effect. The epsilon‐negative materials with lower losses have potential applications in communication devices, such as novel capacitors and antennas.

An eco-friendly water-assisted polyol method to enhance the aspect ratio of silver nanowires.

With water as an eco-friendly heterogeneous nucleation accelerator, silver nanowires (Ag NWs) have been successfully prepared with a high aspect ratio (>1600). The Ag NW-based film exhibits a low sheet resistance of 8.1 Ω sq−1 with a transparency of 81.9% at 550 nm, showing the potential application of electrode materials in polymer solar cells.

Recent progress in the synthesis of silver nanowires and their role as conducting materials

Synthesis of silver nanowires got much attention of researchers due to their promising applications in various fields of nanoelectronic devices. Many research articles focusing on silver nanowires synthesis have been reported since past decade. A number of techniques have been applied for successful synthesis of silver nanowires. Solution-based polyol process was proved as a dominant approach to the fabrication of silver nanowires with homogeneity and high aspect ratio. Various inorganic salts have been used in solution-based polyol synthesis of silver nanowires which play a key role in controlling the final morphology of silver nanowires and lead to uniform growth of silver nanowires. The different experimental parameters have been studied, which directly influence the final morphology of silver nanowires. The research on the development of an efficient synthesis approach of silver nanowires is still in progress to accomplish the need of advanced technology for controlled morphology and highest aspect ratio of silver nanowires. Moreover, the unique applications of silver nanowires in conducting polymers composites were discussed.

Controlled Synthesis of Uniform Silver Nanowires via a Simple Polyol Process

Uniform silver nanowires were synthesized via a simple polyol process. Different aspect ratio of silver nanowires was obtained by regulating the concentration of ferric chloride and polyvinyl pyrrolidone, the maximum aspect ratio of synthesized silver nanowires is 570. The silver nanowires film with the aspect ratio of 240 was prepared and its conductivity was measured by four probe method. Controlled synthesis of uniform silver nanowires is crucial, silver nanowires will be the most promising material in the optical, electrical and photonic fields.

A parametric study on synthesis of Ag nanowires with high aspect ratio

In this study, the effect of the experimental parameters of the polyol process on the aspect ratio of silver nanowires (AgNWs) was investigated. The one-factor-at-a-time method was adopted to analyze the effect of various parameters, such as the amount of reducing agent, seeds and the ratio of PVP/Ag, on the growth of AgNWs. The optimal parameters were determined to obtain a high aspect ratio of AgNWs. Synthesized AgNWs were analyzed by SEM, TEM, and XRD, and the four-point probe method was applied to measure the average aspect ratio, morphology, crystal direction, crystalline structure, and the electrically property of its sheet resistance. From the result of the morphology measurement, a high aspect ratio of 74.85 can be fabricated, where the average diameter and length were about ~55 and 4117 nm, respectively. Regarding electrical property, the sheet resistance of AgNWs with a high aspect ratio is about ~16.34 kΩ/sq with the film thickness of 142.1 nm. However, when the film thickness was increased to 1.123 µm, the resistance decreased to 3.012 Ω/sq.

The Effect of FeCl3 in the Shape Control Polyol Synthesis of Silver Nanospheres and Nanowires

Morphologically controlled nanostructures have been increasingly important because of their strongly shape dependent physical and chemical properties. This study discusses the effect of FeCl3 concentration over synthesis of silver nanospheres and nanowires (NWs) by reducing silver nitrate (AgNO3) with ethylene glycol through a simple polyol method and using poly(vinylpyrrolidone) as capping agent. X-ray diffraction (XRD), ultraviolet visible spectroscopy, scanning electron microscopy and transmission electron microscopy were performed in order to find the structural and geometrical features of silver nanostructures. XRD analysis confirmed formation of metallic silver phase and microscopic studies revealed formation of NWs with average diameters ranging from 50 to 100 nm. Different concentrations of ferric chloride (FeCl3) are used to control the morphology and shape changes of primary silver seeds. A mixture of silver nanospheres and NWs are formed at 0.05 mM concentration of FeCl3 while increasing the concentration of FeCl3 to 0.1 mM lead to formation of silver NWs. Moreover, an increase in the concentration of FeCl3 from 0.1 to 0.3 mM results in reduction of aspect ratio of silver NWs. Furthermore, more increase in FeCl3 concentration from 0.3 mM results again in formation of semi spherical shapes silver nanostructures.

Effect of silver nitrate concentration of silver nanowires synthesized using a polyol method and their application as transparent conductive films

Silver nanowires were synthesized using a polyol process by employing ethylene glycol, poly(N-vinylpyrrolidone), and silver nitrate as precursors. The concentration of silver nitrate was varied to study the resulting changes in aspect ratios of silver nanowires. The experimental results indicated that the growth characteristics of silver nanowires were affected by the synthesis temperature, the concentration of silver nitrate, and the rate at which silver nitrate was added. Field-emission scanning electron microscopy, UV–visible spectrophotometry, and X-ray diffractometry were employed to characterize the silver nanowires. As the concentration of silver nitrate was reduced, the diameters of the silver nanowires decreased, increasing the aspect ratio. The optimal diameter and length of the silver nanowires were 100nm and 20μm, respectively. A thin film composed of silver nanowires exhibited average transmittance of 92.15% at visible wavelengths and a sheet resistance of 20Ω/sq; such a film could be used as a transparent conductive film in commercial applications.

Interactive effect of agitation rate and oxidative etching on growth mechanisms of silver nanowires during polyol process

In this work, the interaction between agitation rate and oxidative etching on the growth mechanisms of silver nanowires during polyol process, the most conventional applied method for metallic nanoparticles synthesis, is evaluated. It was found that the main reason for the formation of multidiameter nanowires (MDNWs) is the local accumulation of silver ions in the system, i.e. even at a low concentration of silver ions (94 mM) under the mild agitation conditions, MDNWs were producible. Moreover, it was inferred that the more stress (stemming from the high agitation) applied on the initially formed decahedron Ag particles affects the ‘re-entrant grooves opening’ process which results in the formation and growth of irregular nanostructures. A polynomial equation for tuning aspect ratio of silver nanowires using different concentration of CuCl2 solution was also proposed. Finally, based on the obtained experimental data together with the thermodynamic considerations, a growth mechanism was proposed which can promisingly be employed for describing the one-dimensional growth of silver nanowires in both surfactant-modified and surfactant-free procedures.

The concentration effect of capping agent for synthesis of silver nanowire by using the polyol method

Silver nanowires were synthesized by the polyol method employing ethylene glycol, Poly(N-vinylpyrrolidone) (PVP) and silver nitrate (AgNO3) as the precursors. Most of the studies used metal salts (PtCl2, NaCl) as seed precursor to synthesize the silver nanowires. In the study, the metal salts were not used and the concentration of capping agent was changed to observe the aspect ratio of silver nanowires. The experimental results showed that controlling synthesis temperature, Poly(N-vinylpyrrolidone) (PVP) molecular weight, reactant concentrations, and addition rates of AgNO3 affects the growth characteristics of silver nanowires. Field-emission scanning electron microscopy, UV–vis spectrophotometry, and X-ray diffractometry were employed to characterize the silver nanowires. As increasing the concentration of PVP, the silver nanowire diameter widened and resulted in a smaller aspect ratio. We successfully prepared silver nanowires (diameter: 170nm, length: 20μm). The silver nanowire thin film suspension showed high transmittance, low sheet resistance, and may be used for transparent conductive film applications.

Effect of AgNO3 addition rate on aspect ratio of CuCl2–mediated synthesized silver nanowires using response surface methodology

Nanomaterials have size-dependant properties which are important in their field of application. In this study response surface methodology (RSM) was successfully used to consider the effects of AgNO3 addition rate and Cl− concentration on the aspect ratio of silver nanowires synthesized via polyol method; the most commonly applied method for synthesizing metallic nanoparticles. Moreover, a suitable model for the relationship between the factors (AgNO3 addition rate and Cl− concentration) and the response (aspect ratio) was statistically developed. Based on the statistical analysis, it was shown that the first order of these two factors have the same significance on the aspect ratio of silver nanowires; while, the second order term of AgNO3 addition rate has a much higher effect on the response compared to Cl− concentration. Furthermore, the interaction between these two factors was statistically significant. It was found that when the concentration of Cl− is lower than 1.05mM, the aspect ratio of formed silver nanowires is remarkably low regardless of AgNO3 addition rate in the studied range. Moreover, by the use of proposed second order polynomial model, the optimum values of the factors were estimated for obtaining nanowires with fairly high aspect ratio (∼100).

Controlling the Aspect Ratio of Silver Nanowires by Variation of Polyvinylpyrrolidone/AgNO3 Contents

The effects of different molar ratios between polyvinylpyrrolidone (PVP) and AgNO3 on the length of silver nanowires and of the aspect ratio of the silver nanowires on the electrical percolation threshold were investigated. The electrical percolation thresholds of the silver nanowires were negatively correlated to the aspect ratio due to their ease of contact with other silver nanowires for the silver nanowires with higher aspect ratio. These results demonstrate the need to control the aspect ratio of silver nanowires in order to maximize their efficient use in electrical applications.

High-Yield Synthesis of Uniform Ag Nanowires with High Aspect Ratios by Introducing the Long-Chain PVP in an Improved Polyol Process

Polyvinyl pyrrolidone (PVP) with different molecular weights was used as capping agent to synthesize silver nanowires through a polyol process. The results indicated that the yields and aspect ratios of silver nanowires were controlled by the chain length of PVP and increased with increasing the molecular weight (MW) of PVP. When the long-chain PVP-K90 (MW = 800,000) was used, the product was uniform in size and was dominated by nanowires with high aspect ratios. The growth mechanism of the nanowires was studied. It is proposed that the chemical adsorption of Ag+on the PVP chains at the initial stage promotes the growth of Ag nanowires.

Electrospun Metal Nanofiber Webs as High-Performance Transparent Electrode

Transparent electrodes, indespensible in displays and solar cells, are currently dominated by indium tin oxide (ITO) films although the high price of indium, brittleness of films, and high vacuum deposition are limiting their applications. Recently, solution-processed networks of nanostructures such as carbon nanotubes (CNTs), graphene, and silver nanowires have attracted great attention as replacements. A low junction resistance between nanostructures is important for decreasing the sheet resistance. However, the junction resistances between CNTs and boundry resistances between graphene nanostructures are too high. The aspect ratios of silver nanowires are limited to ∼100, and silver is relatively expensive. Here, we show high-performance transparent electrodes with copper nanofiber networks by a low-cost and scalable electrospinning process. Copper nanofibers have ultrahigh aspect ratios of up to 100000 and fused crossing points with ultralow junction resistances, which result in high transmitance at low sheet resistance, e.g., 90% at 50 Ω/sq. The copper nanofiber networks also show great flexibility and stretchabilty. Organic solar cells using copper nanowire networks as transparent electrodes have a power efficiency of 3.0%, comparable to devices made with ITO electrodes.