Smallest greetings card

In December 2017, the National Physical Laboratory in Teddington, UK, used a beam of ions (positively charged atomic particles) to etch a Christmas card only 15 x 20 micrometres (0.0006 x 0.0009 inches) in size. Using a substrate of platinum-coated silicon nitride, the card is a true folded 3D shape, with the Christmas greetings message etched on the inner side of the card. The greetings card is so small that when an electron microscope was used to "photograph" the card, it pinged off the stand and was lost somewhere within the microscope itself.