Scientists at the National Physical Laboratory (NPL) in London have broken the record for the smallest Christmas card every created. At 15 by 20 microns, the card is not visible to the naked eye, and it would take 200 million of them to cover the surface of a postage stamp, according to the researchers. For comparison, a human hair is about 50 to 80 microns across. One micrometer is a millionth of a meter.

One of the researchers who created the card, Dr. David Cox, explained that the technology used to create the tiny Christmas greeting offers important practical uses as well.

According to Cox:

“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.”

The card demonstrates the ability of scientists to work with materials at a micron scale, and to improve miniaturization and find new applications in electronics, computers, and medicine, according to the statement from the NPL. For the inscription on the card, the scientists utilized a focused ion beam, which uses charged particles. The technology is often employed to produce smaller versions of electronic products, or to create battery materials.

While it is only visible through a microscope, the front of the card features the text “season’s greetings” alongside an image of a snowman. The inside includes the text a second time, along with “From NPL.”

It was created from a 200-nanometer thick membrane of silicon nitride, and then coated with a layer of platinum 10 nanometers thick. Silicon nitride is frequently used in electronics production.

In 2009, the NPL created the world’s smallest snowman, using platinum. It measured just 0.01 micrometers across. Two tiny beads made up the snowman’s head and body, welded together with platinum. A focused ion beam was used to inscribe eyes and a smiling mouth.

“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,” said Cox.

Cox, and his colleague Kin Mingard, led the effort to produce the record-breaking holiday card. The NPL scientists said their card was 100 times smaller than the previous record holder, which they said measured 200 by 209 micrometers.

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