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What Advancements Have Been Made With Nanowires?

Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.

Nanowires sound simple in principle, but like most things in life, we are underestimating them. Sure, you could call a nanowire a small, threadlike material that is scaled down to the nanoscale, but that language is just broad paint strokes. Let’s dig a little deeper by examining some advancements in material sciences via nanowires.

Electrodeposition Method

Germanium nanowires, which offer better electrical properties than silicon courtesy of superconducting principle, can be grown from indium tin oxide substrates via a process known as electrodeposition. In this system, the indium tin oxide surface develops indium nanoparticles via an electrochemical reduction process. These nanoparticles encourage “the crystallization of germanium nanowires” that can have a desired diameter based off the temperature of the solution.

At room temperature, the average diameter of the nanowires was 35 nanometers, while at 95 Celsius it would be 100 nanometers. Interestingly, impurities form in the nanowires because of the indium nanoparticles, giving the nanowires a nice conductivity. This is great news for batteries because the nanowires would be a better anode than the traditional silicon currently found in lithium batteries (Manke, Mahenderkar).

Our germanium nanowires.

Our germanium nanowires.

Anelastic Properties

What the heck does anelastic mean? It’s a property in which a material slowly returns to its original shape after being displaced. Rubber bands, for example, do not exhibit this property, for when you stretch them they return to their original shape quickly.

Scientists from Brown University and North Carolina State University have found that zinc oxide nanowires are highly anelastic after bending them and looking at them via a scanning electron microscope. Upon release from the strain, they would quickly snap back to about 80% their original configuration but then take 20-30 minutes to fully restore themselves. That is unprecedented anelasticity. In fact, these nanowires are nearly 4 times the anelasticity of larger materials, a surprising result. That is shocking because larger materials should be able to retain their shape better than nanoscopic objects, which we would expect to lose integrity easily. This could be due to the crystal lattice of the nanowire having either vacancies that allow condensing or other places with too many atoms allowing larger stress loads.

This theory seems to be confirmed after silicon nanowires filled with boron impurities displayed similar anelastic properties as well as germanium arsenic nanowires. Materials like these are excellent at absorbing kinetic energy, making them a potential source for impact materials (Stacey, Chen).

The anelastic wire in action.

The anelastic wire in action.

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Sensor Capabilities

One aspect of nanowires that isn’t usually discussed is their unusual surface area to volume ratio which is courtesy of their small size. This combined with their crystal structure makes them ideal as a sensor, for their ability to penetrate a medium and gather data via the changes to that crystal structure are easy. One such scope has been demonstrated by researchers from the Swiss Nanoscience Institute as well as the Department of Physics at the University of Basel. Their nanowires were used to measure changes in the forces around atoms courtesy of frequency changes along two perpendicular segments. Normally, these two oscillate at roughly the same rate (because of that crystal structure) and so any deviations on that caused by forces can easily be measured (Poisson).

Transistor Tech

A core component of modern electronics, transistors allow amplifications of electric signals but are usually limited in their size. A nanowire version would offer a smaller scale and therefore make the amplification even faster. Scientists from the National Institute for Material Sciences and Georgia Institute of Technology together created “a double-layered (core shell) nanowire” with the interior being made of germanium and the exterior being made of silicon with trace impurities.

The reason why this new method works is the differing layers, for impurities before would cause our current to flow irregular. The different layers allow the channels to flow much more efficiently and “reducing surface scattering.” An added bonus is the cost of this, with both germanium and silicon being relatively common elements (Tanifuji, Fukata).

The transistor nanowire.

The transistor nanowire.

Nuclear Fusion

One of the frontiers of energy harvesting is nuclear fusion, aka the mechanism which powers the Sun. Achieving it requires high temperatures and extreme pressure, but we can replicate this on Earth with large lasers. Or so we thought.

Scientists from Colorado State University found that a simple laser you could fit onto a tabletop was capable of generating fusion when the laser was fired at nanowires made of deuterated polyethylene. With the small scale sufficient conditions were present to convert the nanowires into plasma, with helium and neutrons flying away. This set-up generated about 500 times the neutron/unit of laser energy than comparable large scale set-ups (Manning).

Nuclear fusion with nanowires.

Nuclear fusion with nanowires.

More advancements are out there (and are being developed as we speak) so be sure to continue your explorations of the nanowire frontier!

Works Cited

  • Chen, Bin et al. “Anelastic Behavior in GaAs Semiconductor Nanowires.”
  • Fukata, Naoki et al. “Clear Experimental Demonstration of Hole Gas Accumulation in GeSi Core-Shell Nanowires.” ACS Nano, 2015; 9 (12): 12182 DOI: 10.1021/acsnano.5b05394
  • Mahenderkar, Naveen K. et al. “Electrodeposited Germanium Nanowires.”
  • Manke, Kristin. “Highly Conductive Germanium Nanowires Made by a Simple, One-Step Process.” innovations report, 27 Apr. 2015. Web. 09 Apr. 2019.
  • Manning, Anne. “Laser-heated nanowires produce micro-scale nuclear fusion. innovations report, 15 Mar. 2018. Web. 10 Apr. 2019.
  • Poisson, Olivia. “Nanowires as sensors in new type of atomic force microscope.” innovations report, 18 Oct. 2016. Web. 10 Apr. 2019.
  • Stacey, Kevin. “Nanowires highly ‘anelastic,’ research shows.” innovations report, 10 Apr. 2019.
  • Tanifuji, Mikiko. “High-Speed Transistor Channel Developed Using a Core-Shell Nanowire Structure.” innovations report, 18 Jan. 2016. Web. 10 Apr. 2019.

© 2020 Leonard Kelley

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