Editorial Feature

Manipulating Nanowires with Atomic Force Microscopy

Nanowires are often utilized in the development of nanoscale detectors and electronics. However, placing individual nanowires quickly and precisely remains a significant challenge.

Manipulating Nanowires with Atomic Force Microscopy

Image Credit: Roberto Lo Savio/Shutterstock.com

Nanowires can be manipulated using an atomic force microscope (AFM) to generate intricate and extremely conductive nanostructures that operate as nano-electrodes, allowing connection and electronic characterization of other nanoobjects.

AFM and Nanotechnology

Atomic force microscopy is a surface probing method with a sub-nanometer magnification and belongs to a group of non-destructive surface analysis methods used at the nanoscale. AFM has a 103 times greater resolution than the optical microscope resolution limit. 

AFM does not need a contact lens or beam illumination, unlike optical and scanning electron microscopy. Its spatial resolution is not limited by scattering or diffraction, and it does not need to establish a reference region by producing a vacuum.

Atomic force microscopy is one of the essential tools in nanotechnology. This instrument has influenced several additional scanning probe technologies by becoming the most frequently used tool for detecting, characterizing, and manipulating materials at the nanoscale. The AFM was originally designed to scan the topographical characteristics of surfaces, but it may now be used to measure other properties, such as electromagnetic and friction.

The constant search for miniaturization has culminated in tools like the AFM, which is why nanotechnologies have taken off with such incredible force over the last 20 years. When coupled with improved technologies like photolithography, scientists were able to manipulate and construct nanostructures in previously impossible ways.

AFM is now particularly prominent as a nano-manipulation technology, in addition to its imaging capabilities. AFM is the only technique that allows for single-molecule investigation in nanomaterials and has recently been used to manipulate nanowires to produce highly conductive nanostructures.

What are Nanowires?

Nanowires are rigid rod-like materials or structures having nanometer-scale diameters. Because of their small size, they have superior thermal, physiological, electrical, photonic, and mechanical characteristics that are not present in bulk materials and have uses in their own capacity.

Nanowires do not exist in nature and must be manufactured under precise settings. Vapor phase deposition, dispersion, and Vapor-Liquid-Solid (VLS) manufacturing processes are all used in the fabrication of nanowires.

Nanowires can be manufactured utilizing multiple ways by employing metals or semiconductors. Nanowires feature an excellent aspect ratio, a diameter of ten nm or less, and a monocrystalline configuration. Nanowires are widely employed in nanodevices as connectors for electron transfer. Silver, gold, silicon, and cobalt have been exploited to produce nanowires.

The Necessity of Manipulation of Nanowires

Precise and accurate manipulation of nanowires is a prerequisite to fully utilizing the capabilities of nanodevices in numerous applications. The chemical and physical characteristics of nanowires with anisotropic nanostructures are greatly reliant on their direction and placement. Such nanowires must be manipulated, to attain the best physicochemical properties,

Manipulating nanowires to improve their properties is common in a range of applications. This includes electrical, photonic, and microelectromechanical devices, nanocomposites, metallurgical couplers in nanoscale quantum equipment, field-emitters, and biologically relevant nanosensor leads.

The atomic force microscope is the most widely used equipment for manipulating nanowires. Nanowire manipulation has recently been developed using AFM-based approaches that use thermomechanical and electromagnetic fields characteristics.

Current Challenges Associated with Manipulation of Nanowires Using AFM

Because the AFM probe cannot be used in both scanning and manipulation operations at the same time, the manipulation procedure is almost imperceptible. After each manipulation process, the image must be adjusted to establish the coordinates and arrange the probe's next motion. Standard AFMs often take minutes to acquire an image, so multi-step modification is exceedingly complex and time-consuming and thus unsuitable for commercial use.

AFM approaches are limited to a small number of applications and do not produce the electrically resistant nanocircuits that EBL supplies. Furthermore, because these procedures need more complex equipment and higher operating abilities, they have not been widely applied.

Strategies to Enhance the Manipulation of Nanowires Using AFM

Many researchers have proposed several strategies to improve the manipulation of nanowires utilizing AFM.

For generic AFM systems, Zhang et al. (2013) developed an autonomous nano-manipulation method. The assumption was that the manipulation effects of each altering phase could be anticipated using theoretical modeling rather than real-time scanning; all manipulation stages could be carried out in parallel without the need for intervening imaging.

The overall time spent on the difficult manipulation was greatly reduced. This method was utilized to modify multi-walled carbon nanotubes with a low aspect ratio by researchers.

With a standard AFM, Liu et al. (2017) explored novel manipulation methodologies for Ag NWs. Because the simplest and most optimal geometric form for constructing electrical connections is a linear configuration, the researchers concentrated on manipulating linear Ag NWs. Translation and rotation, which are the two primary manipulation techniques for moving 1D material, were the strategies utilized by them. The researchers limited the modification to the asymmetric horizontal plane for simplicity. Their findings revealed that the position and layout of Ag NWs on the flat substrate could be better controlled. It also showed that automated nanofabrication with conventional AFMs is possible.

Moreno et al. (2019) established a new method for producing electrodes for measuring electrical transport parameters at the nanoscale.  

Scientists used an atomic force microscope to manipulate gold nanowires to construct complicated and highly conductive nanostructures to connect and analyze other nanoobjects. Mechanically connecting gold nanowires created the pathways, which resulted in a nine ohm/junction contact resistance.  The researchers predicted that this unique approach could supplement or even substitute well-established nanocircuit production techniques such as electron beam lithography (EBL).

Continue reading: Could Copper Nanowires Improve Semiconductor Thermal Conductivity?

References and Further Reading 

Conache, G., Gray, S., Bordag, M., Ribayrol, A., Fröberg, L. E., Samuelson, L & Montelius, L. (2008,). AFM-based manipulation of InAs nanowires. In Journal of Physics: Conference Series (Vol. 100, No. 5, p. 052051). https://doi.org/10.1088/1742-6596/100/5/052051

Zhang, C., Wu, S., & Fu, X. (2013). Automated manipulation of carbon nanotubes using atomic force microscopy. Journal of Nanoscience and Nanotechnology13(1), 598-602. https://doi.org/10.1166/jnn.2013.6862

Liu, H. Z., Wu, S., Zhang, J. M., Bai, H. T., Jin, F., Pang, H., & Hu, X. D. (2017). Strategies for the AFM-based manipulation of silver nanowires on a flat surface. Nanotechnology28(36), 36530. https://doi.org/10.1088/1361-6528/aa7e35

Moreno, M., Ares, P., Moreno, C., Zamora, F., Gomez-Navarro, C., & Gomez-Herrero, J. (2019). AFM manipulation of gold nanowires to build electrical circuits. Nano Letters, 19(8), 5459-5468. https://doi.org/10.1021/acs.nanolett.9b01972

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Usman Ahmed

Written by

Usman Ahmed

Usman holds a master's degree in Material Science and Engineering from Xian Jiaotong University, China. He worked on various research projects involving Aerospace Materials, Nanocomposite coatings, Solar Cells, and Nano-technology during his studies. He has been working as a freelance Material Engineering consultant since graduating. He has also published high-quality research papers in international journals with a high impact factor. He enjoys reading books, watching movies, and playing football in his spare time.

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