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Questions and answers

How small is the world's smallest Christmas card?

The card requires a powerful microscope just to see it

Measuring in at 15 x 20  µm (micrometres*) in size, you could fit over 200 million cards in a single postage stamp. The folded card is 200 nm thick, with the stamp thickness about 50 µm thick. The card requires a powerful microscope just to see it, let alone read the festive message inside.

* (1000  micrometres = 1 millimetre)

The previous record-holder was 200 x 290 µm, whereas NPL's version over 10 times smaller. To make the card 10 cm in height, you would have to magnify it 5000 times; equivalent to blowing up a postage stamp to the size of a football field. Approximately seven quadrillion could fit into a letterbox, which would be the equivalent of every person on Earth receiving 900,000 cards each.

What is the card made from?

The card is made from platinum-coated silicon nitride, usually used in electronics, and both the design on the front and the message inside were carved out by a focused ion beam – a jet of charged particles.

This is all very well but how does this help the real world?

The tools used to make the card are cutting-edge techniques being developed to understand materials on a tiny scale, helping to further the miniaturisation of electronics and the development of new battery materials. NPL has world-leading materials characterisation capabilities, spanning everything from micrometre-scale analysis, all the way up to the monitoring of large-scale infrastructure from space. NPL helps industry to understand the most exciting materials, from graphene to high-performance composites, and apply them to new applications.

Dr David Cox, Research Fellow at NPL, who created the card with his colleague Dr Ken Mingard, said: "While the card is a fun way to mark the festive season, it also showcases the progress being made in materials research on this scale. We are using the tools that created the card to accurately measure the thickness of extremely small features in materials, helping to unlock new battery and semiconductor technologies. It's a genuinely exciting development that could help to make new technologies and techniques a reality."

Watch a video of the world's smallest Christmas card:


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