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Gold nanoparticles found to have channel-digging capability

05 Jan 2016  | Dylan McGrath

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A team of researchers from the National Institute of Standards and Technology (NIST) and IBM has found that nanoparticles of gold have a trenching capability that could be harnessed for building devices through self-directed assembly. Operating like 'snow blowers,' the particles plow through layers of indium phosphide and other semiconductor materials, forming nanochannels, the scientists stated.

The capability could potentially be used to integrate lasers, sensors, wave guides and other optical components into so called 'lab-on-a-chip' devices now being used for disease diagnosis, screening experimental materials and drugs, DNA forensics and others, according to the researchers.

The channel-digging capability of the gold particles was discovered by accident. An experiment in the formation of nanowires failed due to a contaminant.

"We were very disappointed, at first," said NIST research chemist Babak Nikoobakht. But, Nikoobakht added, then the team serendipitously discovered that the contaminant was water.

A scanning electron microscope image of the experiment revealed that the gold nanoparticles combined with the water vapour resulted in long, straight nanochannels.

Surface-directed nanochannels

Electron micrograph of surface-directed nanochannels formed on the surface of the semiconductor indium phosphide. Nanochannels are formed using a gold-catalysed vapour-liquid-solid etch process and their locations are defined by the deposited gold pattern. (Source: NIST)

The research team next teased out the chemical mechanism and necessary conditions that made possible the etching process. They selectively coated the surface of the semiconductor with gold and heated it. Once heated, the underlying indium phosphide dissolved into the gold nanoparticles, creating a gold alloy.

They next introduced heated water vapour into the system. They discovered that heating the water vapour to 440°C and above created long V-shaped nanochannels.

These channels following straight paths dictated by the regularly repeating lattice of atoms in the crystalline semiconductor.

The researchers were also able to use the technique with gallium phosphide and indium arsenide, two more semiconductor materials formed by combining elements from the third and fifth columns of the periodic table. Compound semiconductors such as these are used to make LEDs, and for communications, high-speed electronics and other applications.

Nikoobakht said he believes that this etching process, with adjustments, could also be used to create patterns of channels on silicon and other materials.

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