London: It looks much like any other cover of the children’s magazine National Geographic Kids. Cuddly animals: check. Free Sea Turtle poster: check. Story about rescued hippos: check. Only the lack of colour and the slight graininess make you suspect it might be something other than the real thing. In fact the reason for these imperfections is that this magazine cover is so small that a single human red blood cell would cover most of it. It measures just 11 by 14 thousandths of a millimetre, and is invisible to the naked eye.
Yesterday, at the US National Science and Engineering Festival in Washington DC, the Guinness Book of Records confirmed that this is the smallest magazine cover in the world. It has been carved out of a lump of plastic using a silicon needle 100,000 times sharper than the sharpest pencil tip. The contrast of the image reflects the topography of the surface: the higher it is, the lighter it appears.
The National Geographic Kids cover was created by physicists after the magazine ran a readers’ poll to discover their favourite image. Although the researchers expect the technique will be used mainly as a research tool for universities, novelty applications like this might prove popular too.
It could be used to add security tags to artworks, passports and personalised Swiss watches that would be virtually impossible to forge. Some companies have already used nanopatterning methods to write the entire Bible on a crucifix for especially devout customers, and even to engrave tiny patterns on the surface of chocolate that scatter light to create different colours.
The technique was developed over the past five years by physicist Armin Knoll and his colleagues at IBM’s research laboratory in the suburb of Ruschlikon in Zurich, Switzerland. The needle, attached to a bendy silicon strip that scans across the sample surface, is electrically heated so that when it is brought close to the specially developed plastic, the material evaporates. In this way the researchers can remove blobs of material just five nanometres (millionths of a millimetre) across, paring away the surface pixel by pixel like a milling machine.
By reducing the heat, the tip can be used to take a snapshot of the carved structure it has produced. Surrounded by plastic in a valley, the tip radiates away more heat than if it hovers above a peak, and so this heat flow traces the surface contours. The IBM team first reported the method in 2010.
IBM has licensed the technology to a start-up company in Zurich called SwissLitho, founded in 2012 by former IBM scientists Philip Paul and Felix Holzner. The company has developed it into a commercial machine called the NanoFrazor, costing around EUR500,000. McGill University in Montreal, Canada, has bought the first one.
“It’s a cool tool,” says McGill physicist Peter Grutter. Aside from the ability to make tiny structures for electronics, he says part of the attraction is that, unlike other nanopatterning methods, it is very easy to find where you are on a surface and take images of large areas or go back and overlay a second pattern.