Review
Silver nanowires: Synthesis technologies, growth mechanism and multifunctional applications

https://doi.org/10.1016/j.mseb.2017.05.002Get rights and content

Highlights

  • The latest study progress on the synthesis of silver nanowires was reviewed in this article.

  • The latest application of silver nanowires in multifunctional areas was also concluded.

  • The typical synthetic technologies and the representative studies were also summarized and discussed.

  • The challenges that remain with silver nanowires were proposed.

Abstract

Silver nanowires have attracted a lot of attention in both academia and industry because of their potential applications in many electronic devices. In the past decade, there have been many research articles relating to silver nanowires, but there have been relatively few review articles focusing on these unique nanomaterials. In this review, the definition and the characterization of silver nanowires will be introduced. The synthetic methods employed to prepare silver nanowires and the factors that influence their final morphology will also be discussed in detail. Examples of typical synthetic technologies and the representative studies will also be summarized and discussed. In addition, the applications of silver nanowires as conductive materials and components of electronic devices will be reviewed. Lastly, the challenges that remain with silver nanowires will be proposed.

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Introduction

Silver nanowires (AgNWs) are 1-dimensional silver nanostructures with diameters that are typically in a range of 10–200 nm, and lengths in a range of 5–100 μm. Strategies for the synthesis of AgNWs are derived from those employed for the fabrication of quantum wires of semiconductors and metallic alloys, which were found to exhibit interesting electrical and magnetic properties [1]. Consequently, the traditional fabrication methods employed to synthesize quantum dots and wires were also used to fabricate metallic wires, such as gold wires, silicon wires, selenium wires, gallium wires, aluminum wires and silver wires. However, the nanoscale silver wires fabricated by these methods were not uniform, and these nanowires required complex separation processes, which limited their production to small scales.

During the first decade of the 21st century, many researchers dedicated their efforts toward the synthesis of AgNWs with uniform size and high yields [2]. These efforts have led to the development of numerous methods to prepare AgNWs, and these materials have a wide range of potential applications. The rapid growth of this field is demonstrated by the fact that if you type “silver nanowires” in the Google Scholar search engine, you will find more than 124,000 results [3]. This massive range of information can be overwhelming, particularly for researchers who are beginning to investigate this field. There are a few review articles describe some related aspects of AgNWs including synthesis, optical properties, and application of AgNWs. For example, Xia and coworkers have published various reviews on silver nanostructures [2], [4], [5], [6] and 1-D metallic materials [7], [8], these reviews have highlighted the progress that has been achieved with a diverse range of silver nanostructures and other 1-D metallic nanostructures and also discussed their physical properties. Most recently, a few reviews [9], [10], [11], [12], [13], [14], [15] highlighting transparent conductive films (TCFs) from AgNWs have also been published. Since reviews only cover various aspects of AgNWs [11], [16], [17], [18], [19], [20], [21], [22], [23], [24], we believe that there is still a requirement for a detailed review that is aimed toward scientists and engineers who are relatively new to the field of AgNWs and are beginning to work or study in this area. The aim of this review is to summarize some of the recent developments that have been achieved with AgNWs, and provide not an overview of the synthetic methods, the growth mechanism and the applications of these materials, but a comparison of the results reported by different research groups which seems to be conflict sometime. This review is focused on the practical use of AgNWs, many details and specific discussions relating to the synthesis technique of AgNWs will be provided.

This review is organized in the following manner: Following the general overview that has been provided in Section 1, a brief description of the range of morphologies observed among silver nanostructures will be provided in Section 2. Subsequently, Section 3 will provide a brief description of the methods of characterizing AgNWs and a description of their optical properties. Section 4 will highlight the various synthetic strategies that are employed to synthesize AgNWs, while the effects of various parameters on the synthesis of AgNWs (primarily via polyol strategies) will be the focus of Section 5. The growth mechanism of AgNWs will be the emphasis of Section 6, while the various applications of AgNWs and their composites will be highlighted in Section 7. Lastly, the future outlook of AgNWs will be discussed in Section 8. It is our hope that this review will provide an useful overview of AgNWs and inspire interest in these versatile and unique materials.

Section snippets

Silver nanoparticles with diverse morphologies

Silver nanoparticles are derived from ultrathin silver powder, which has applications in the electronics field on account of silver’s high conductivity. The diameters of the silver powder particles are on the scale of several hundred nanometres, but the morphologies of these particles are irregular. As is the case with electronic materials, morphology plays an important role in the effectiveness of silver nanoparticles used as antibacterial agents, since an essential factor influencing the

Definition and characterization of AgNWs

Specific definitions of AgNWs have not been proposed by researchers, but there are several common properties of AgNWs that can be summarized. In this section we will first provide a common definition of AgNWs and then introduce some methods that are commonly used to characterize these materials.

Synthesis of AgNWs

Researchers have proposed many synthetic methods to prepare nanowires during the past thirty years that were mainly derived from the strategy employed to prepare quantum wires. AgNWs were mainly prepared via electrochemical methods during the early stages, but the AgNWs synthesized by this method were not uniform and they were obtained in low yield. Based on this method, the hard-template and soft-template methods have been developed in the past twenty years. The polyol method is a prominent

Factors influencing the polyol synthesis of AgNWs

Over the last decade, the polyol approach has begun to replace template methods as the most widely used strategy to produce AgNWs. In this section, we will discuss the factors that influence the sizes of AgNWs synthesized by the polyol method.

There are numerous different synthetic strategies for producing AgNWs by the polyol method, but all of these methods are similar in terms of the types of reagents that are exploited. Ethylene fulfils a dual role as both a solvent and reducing agent, AgNO3

The mechanism of AgNW growth

The typical growth mechanism of AgNW formed via the polyol method can be summarized as follows: elemental silver atoms are obtained from the reduction of AgNO3, once the concentration of silver atoms has reached a supersaturation value, they will begin to undergo nucleation and grow into nanoparticles. Both twinned and single-crystal seeds of silver are formed through homogeneous nucleation. The twinned particles are the most abundant morphology because of their relatively low surface energies

Applications of AgNWs

Silver nanowires have been exploited for their desirable properties, which include high conductivity, unique structures with high aspect ratios, excellent optical properties, as well as antibacterial behavior. These nanomaterials provide ideal replacements for traditional conductive materials on account of their nanoscale size and the high aspect ratio. In addition, the optical properties of AgNWs provide them with great potential for applications in transparent devices. In this section, we

Outlook

The polyol method and its various modifications have become widely accepted by researchers as an effective strategy for the synthesis of AgNWs. Depending on the reaction parameters, AgNWs can be obtained with diameters ranging from 40 to 150 nm and lengths in a range from 5 to 20 μm. Although AgNWs with diameters below 30 nm and lengths up to 100 μm have been synthesized under certain conditions by various researchers, the preparation of both the thinner and longer AgNWs requires elaborate

Acknowledgements

The authors wish to thank the National Natural Science Foundation of China (No. 51173204, 51503124, 21404121, and 21404122), the Pearl River Novel Science and Technology Project of Guangzhou, the Development Fund for Special Strategic Emerging Industry in Guangdong Province, the Production Education Research Project in Guangdong Province, the Guangdong Natural Science Foundation (2015A030313799, 2014A030310412, and 2015A030313822,2016A030313163), the Science and Technology Program of Guangzhou

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