In pursuit of improved nanowires, NIST chemists develop 'nano LEDs'

While refining their approach to crafting nanowires, NIST chemists stumbled across a way to make them produce light just like an LED bulb.

While chemists at the National Institute of Standards and Technology worked to refine the way they make nanowires, they stumbled across a way to make them produce light just like an LED bulb.

Nicknamed "nano LEDs," the nanowires could be used one day in nanogenerators, lab-on-a-chip systems or any number of miniature devices.

Nanowires are made by "growing" them through the controlled deposition of molecules (such as zinc oxide) from a gas onto a base material.

The process is called chemical vapor deposition, or CVD, and it results in nanowires that rise vertically from the substrate like the bristles of a hairbrush. Unfortunately, the technique tends to produce a dense field of nanowires whose exact composition is difficult to determine -- so chemists Babak Nikoobakht and Andrew Herzing developed a "surface-directed" method for growing nanowires horizontally.

Like the old method, the new method uses gold as a catalyst. But the new method heats the gold to 900 degrees Celsius (or 1,652 degrees Fahrenheit), turning it into a nanoparticle that facilitates the crystallization of zinc oxide molecules. As the nanocrystal grows, it pushes the gold nanoparticle along the surface of the substrate to form a horizontal nanowire whose composition is easier to determine.

But it was in further work that the researchers stumbled across LED-like properties. Succinctly, the chemists increased the thickness of the gold catalyst nanoparticle from less than 8 nanometers to about 20 nanometers, which allowed the nanowires to grow a "nanowall" -- a fin-like appendage -- where the zinc oxide portion is rich in electrons and the substrate is electron-poor.

That imbalance allows electrons to flow across the two portions when researchers charged the structure with electricity. As the electrons flowed, they emitted light.

For now, the scientists are working to improve their happy accident through the use of better material designs and with the knowledge that the "nano LEDs" could be applied as part of light sources and detectors in photonic devices.

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