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Nanoworld ‘snow blowers’ carve straight channels in semiconductor surfaces


Nanoworld ‘snow blowers’ carve straight channels in semiconductor surfaces

Researchers report important addition to toolkit of ‘self-assembly’ methods eyed for making useful devices


December 28, 2015


National Institute of Standards and Technology (NIST)


Easy to control, new gold-nanoparticle-catalyzed process for creating patterns of channels with nanoscale dimensions could help to spawn entirely new technologies fashioned from ensembles of ultra-small structures.

In the nanoworld, tiny particles of gold can operate like snow blowers, churning through surface layers of an important class of semiconductors to dig unerringly straight paths. The surprising trenching capability, reported by scientists from the National Institute of Standards and Technology (NIST) and IBM, is an important addition to the toolkit of nature-supplied ‘self-assembly’ methods that researchers aim to harness for making useful devices.

Foreseeable applications include integrating lasers, sensors, wave guides and other optical components into so-called lab-on-a-chip devices now used for disease diagnosis, screening experimental materials and drugs, DNA forensics and more. Easy to control, the new gold-catalyzed process for creating patterns of channels with nanoscale dimensions could help to spawn entirely new technologies fashioned from ensembles of ultra-small structures.

Preliminary research results that began as lemons — a contaminant-caused failure that impeded the expected formation of nanowires — eventually turned into lemonade when scanning electron microscope images revealed long, straight channels.

“We were disappointed, at first,” says NIST research chemist Babak Nikoobakht. “Then we figured out that water was the contaminant in the process — a problem that turned out to be a good thing.”

That’s because, as determined in subsequent experiments, the addition of water vapor served to transform gold nanoparticles into channel diggers, rather than the expected wire makers. Beginning with studies on the semiconductor indium phosphide, the team teased out the chemical mechanisms and necessary conditions underpinning the surface-etching process.

First, they patterned the surface of the semiconductor by selectively coating it with a gold layer only a few nanometers thick. Upon heating, the film breaks up into tiny particles that become droplets. The underlying indium phosphide dissolves into the gold nanoparticles above, creating a gold alloy. Then, heated water vapor is introduced into the system. At temperatures below 300 degrees Celsius (572 degrees Fahrenheit), the tiny gold-alloy particles, now swathed with water molecules, etch nanoscale pits into the indium phosphide.

But at 440 degrees Celsius (824 degrees Fahrenheit) and above, long V-shaped nanochannels formed. The channels followed straight paths dictated by the regularly repeating lattice of atoms in the crystalline semiconductor. During the process, indium and phosphorus atoms interact with oxygen atoms in the water molecules on the surface of the gold alloy droplet. The oxidized indium and phosphorus evaporate, and the droplet advances, picking up more semiconductor atoms to oxidize as it goes.

The result is a series of crystalline groves. The dimensions of the grooves correspond to the size of droplet, which can be controlled.

In effect, the droplet is the chemical equivalent of the auger on a snow blower that, instead of snow, burrows through the top portion of the semiconductor and ejects evaporated bits, Nikoobakht explains.

The team observed the same phenomena in gallium phosphide and indium arsenide, two more examples of semiconductors formed by combining elements from the third and fifth columns of the periodic table. Compound semiconductors in this class are used to make LEDs, and for communications, high-speed electronics and many other applications. Nikoobakht believes that, with adjustments, the etching process might also work for creating patterns of channels on silicon and other materials.

Controllable, fast and flexible, the “bottom up” channel-fabrication process shows promise for use on industrial scales, the researchers suggest. In their article, the teams describe how they used the process to etch patterns of hollow channels like those used to direct the flow of liquids, such as a blood sample, in a microfluidic device, or lab on a chip.


3 thoughts on “Nanoworld ‘snow blowers’ carve straight channels in semiconductor surfaces

  1. Interesting.
    COULD is the opperative word here –
    I’ll find some further reading material & see if everyone agrees or if this story is crap.
    Matt – barrister – he is away a lot – I keep an eye on his house= keys – the carpet sellers brought him a big hand made gold colored (you could hardly tell that it had been gold) carpet from the Middle East TO EXPERIENCE to see if he wanted to buy it – I swim in his pool (this was 15 years ago) “go & have a look at it” he said on the phone – so took by bathers & went – on the floor was an old – faded – thing that used to be a carpet & needed a new home at the tip – I hoped that Mr. Money-bags was not silly enough to spend $9.000 was the asking price – I went for a swim – I thought I had better have another look just in case – the back wall was all glass – the sun was just coming around to the back of the house – as the sun touched the rag on the floor it began to shine a most beautiful mellow GOLD – the Gold Glow rose & filled the whole room till the air in the room was a bright translucent GOLD – the carpet itself looked like a thick & lush bed of gold grass – I have never seen anything so magnificent.
    Recently I remembered the carpet & looked to discover how & what this carpet was – THE CARPET IS A SEMI-CONDUCTOR WHEN THE SUN INTERACTS WITH IT –
    The told us that there were carpets where every character moved independent of the others – where the mood & story line of the carpet would change with the light & shade it had to play with.

  2. With the advent of the internal combustion engine – the oil that had stained to sandscape of the Middle East for thousands of years – became GOLD – all else was trampled
    “we’re rich”
    “we’re rich”
    “we’re filty rich forever” they cried with joy.
    And overlooked everything else – all the while technology that could & would have stood us in good stead into future was discarded as rubbish. These were the brilliant men of yesterday – the mover shake power brokers that we owe modernity to & in their infinite wisdom look were we are today – on the doorstep of WORLD WAR THRE. Today we are left to wonder how they did it – these primative ape like heathens – the vermin that wasted the air that descent & worthy folk breathed.
    La – di – fucking – da to that –
    please note that Gus used the same f word –
    Mankind had choices – and kept is simple.

  3. A nano particle is :- Any particle less that 100nm is a nano-particle. Since particles are three dimensional the ASTM standard defines two or three dimensions must be 1-100nm.
    * ANY PARTICLE – PARTICLE OF ANYTHING THAT MEASURE ACCORDLY ARE NANO PARTICLES – not magic stuff – not blocks of gold but tiny bits of gold ground to minute particles –
    Interseting stuff – and they can watch how these particles interact & react – but I am not yet convinced that they can manipulate and/or control a tiny particle that they can only see under a powerful microscope.
    Nor can the control the environment that they conduct these trials because they cannot exclude or introduce the same particle equation everytime – thin air is actually full of all manner of particles.
    Like Professor Jim Alkhalili’s Double Slit Experiment.

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