When Andrew Greer, the creator of possibly the world’s smallest diamond coin, wants to show off his work, there is a problem. “It can take a couple of minutes to find,” he says. This is not time spent rooting through pockets — it’s spent scanning an area measuring 8mm sq with an electron microscope.
Somewhere, on a piece of silicon smaller than a Sim card, is a minuscule commemorative coin, 200 times smaller than the width of a human hair.
Made from a shard of diamond, roughly circular and with the profile of the queen’s face etched on to it, this is probably the smallest coin ever made, although that title is not official.
“I can’t imagine anyone making a coin smaller than this,” said Mr Greer, a PhD student at the University of Glasgow.
If you are wondering what sort of person would spend their time crafting a coin that cannot be seen, let alone used or sold, then think competitive postgraduates. Earlier this year, the University of Nottingham announced it had made a miniature diamond engraving of the Queen’s profile for the Jubilee that measured 46 x 32 microns.
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“It was huge,” said Mr Greer: “It was the size of a human hair. I thought, ‘let’s make something better.’”
Glasgow’s engraving is 0.58 by 0.3 microns.
The engraving was done by coating the coin in polymer, imputing a profile of the Queen into a computer, and then using a technique known as electron beam lithography to fire electrons into the polymer, hardening it. The non-hardened polymer is then cleared away. Eventually, the coin is left with a recognisable 3-D profile of the Queen.
“My concern was that her nose would come out a different shape or size,” said Mr Greer. “But it looks okay.” In fact, the profile is astonishingly accurate.
The coin has even been commended by the Royal Mint, although it has not been assigned a value. “Collectors wouldn’t have an eye glass strong enough for this,” a Royal Mint worker said in a letter to Mr Greer.
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But the technique is not just about competing Jubilee memorabilia. Nano technology involving diamonds is an increasingly important area of scientific research.
As well as being hard, diamond can be etched with good resolution, is chemically inert (so can be easily cleaned) and does not easily stick to things. This means diamonds can be crafted into small circular “pillars”, similar to Mr Greer’s coin, and used as stamps. When titanium is used in hip-replacement operations, for example, the minuscule stamps can put a pattern into the implant, making it settle better into the patient and last longer.
Tiny diamond pillars can also be mixed with boron atoms and turned into electrodes. This material can then be used as an interface between prosthetics and the body. Scientists are currently using the technology to experiment with artificial vision.