Magnetic field strength controlled liquid phase syntheses of ferromagnetic metal nanowire
Nanomaterials such as nanostructures and nanoparticles exhibit unique properties, making them attractive for numerous applications. With the rapid advancement in nanotechnology, numerous studies have been conducted to enhance nanomaterials’ fabrication, improve their properties and extend their applications to different niches. In particular, ferromagnetic nanowires are of critical importance owing to their potential practical applications. They are easily synthesized by applying eternal magnetic fields during the formation of the nanoparticles. The resulting nanowires further entangle themselves in solution to produce flexible nanowire nonwoven sheets (NNS) having a combination of features of both metal nanowires and flexible sheets.
To improve the NNS properties further, developing effective synthesis techniques for controlling the nanowires’ morphology is key. Considering the nanowire formation process, two critical parameters: reducing power of the solution and external magnetic field strength, have been identified for good morphology control. A formation speed of nanowire is strongly influenced by a reducing power, and the appropriate reducing power can allow for the formation of smooth nanowires. Similarly, the strength of the magnetic field influences different reaction conditions such as pH and temperature, and a strong magnetic field is generally good for smooth nanowire formation. Nevertheless, despite the extensive research work, controversies still emerge regarding the fabrication of nickel nanowires. For instance, there is little consensus regarding the relationship between the shape of the synthesized nickel nanowires and that of the magnetic flux. Furthermore, the effects of the magnetic field on the growth directions of nickel nanowires remain underexplored.
Recently, Dr. Shohei Shiomi from Kyoto Municipal Institute of Industrial Technology and Culture collaborated with Dr. Siti Rahmah Shamsuri and Professor Eiichiro Matsubara from Kyoto University investigated the effects of external magnetic field strength on the morphology of ferromagnetic metal nickel nanowires. Their main aim was to synthesis different types of nickel nanowire nonwovens by leveraging the effects of the magnetic field on the morphology of nickel nanowires. The work is currently published in the research journal, Nanotechnology.
In their approach, the nickel nanowires were synthesized via the electroless deposition method. The reducing power and the deposition behavior of Ni were evaluated using quartz crystal microbalance (QCM) and mixed potential measurements. Furthermore, based on these electrochemical evaluations, the formation mechanisms and the influence of the stirring in the solution were investigated under strong and weak magnetic fields. Using the same process, the authors also synthesized a composite of nickel nanowires grown on non-magnetic copper metal sheets. The formation mechanism of the composite was investigated and compared to that of the nickel nanowires for validation.
The authors observed that the formation behavior of nickel nanowires was influenced by the magnetic field conditions. This was attributed to the effects of the magnetic field on the attractive forces of nickel particles, the nanowire precursors. In a strong magnetic field (> 20.5 mT), nickel nanoparticles aligned along the magnetic fields to produce smooth and straight nanowire surfaces. In contrast, branched nickel nanowires with rough surfaces were formed under weak magnetic fields (< 9.3 mT). Taking the advantages of the magnetic effects on the morphology of nickel nanowires such as altering the external magnetic field, the authors synthesized different types of nickel nanowire nonwovens. Similarly, different nickel nanowires were grown on non-magnetic copper metal sheets, and the morphology of the resulting composite closely correlated with the microstructures of the nickel nanowires.
In summary, the effects of the magnetic field on the morphology of ferromagnetic nickel nanowires were established. Like the formation of nickel nanowires, the morphology of the composite of nickel nanowires grown on non-magnetic copper sheets was significantly affected by the magnetic field. These results confirmed that the overall microscopic properties of the composite depended on the microstructure of the nickel nanowires as well as the morphology control on the nanoscale level. Altogether, the study clarified some of important research issues that were never addressed before and will potentially advance future research and design of high-performance ferromagnetic nanowires.
Shiomi, S., Shamsuri, S., & Matsubara, E. (2020). Magnetic field strength controlled liquid phase syntheses of ferromagnetic metal nanowire. Nanotechnology, 31(36), 365602.