National Physical Laboratory

The world's smallest Christmas card

The world's smallest Christmas card

NPL has created the world's smallest Christmas card.

  • Each page of the card is 15 micrometres wide, and 20 micrometres tall (one micrometre is a millionth of a metre)
  • You could fit over 200 million cards in a single postage stamp by volume
  • In a cubic metre, similar to the size of a post box, you could fit 7 quadrillion (7,000,000,000,000,000) of these cards - roughly 900,000 for every person on Earth
  • NPL's card is 10 times smaller than the previous record-holder


The science behind the card

When we want to investigate the 3D structure of materials we can do this by cutting it away in slices with a focused ion beam. The slices may be 20 times thinner than the card shown on the front but it is very difficult to measure precisely how thin. Variation and errors in how thin the slices are can lead to false impressions of the true 3D structure.

To determine each slice thickness, a disposable 'ruler' can be put down on top of the sample so that it is cut away at the same time as the material below. The amount of ruler milled away can be measured accurately and thus the thickness of the slices determined. The disposable rulers are made on the same material and with the same technology used for the card, and it was during making of the rulers that we realised we could make a card which folded itself very quickly and easily.

The card was made on a silicon nitride membrane 200 nm thick, with a coating on each side of 40 nm of platinum. This might make it the world's thinnest 'platinum card' too, but the amount of platinum on it is worth only 0.000002 pence.

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