World's smallest Christmas card
Nanotechnology experts have unveiled a Christmas card so small that more than 8,000 of them could fit on a first-class stamp.
The card produced by the University of Glasgow, said to be the smallest in the world, is invisible to the naked eye.
The university's school of engineering drew up the design to highlight its "world-leading" nanotechnology expertise.
A total of 8,276 of the cards could be placed on an area the size of a stamp.
Professor David Cumming and Dr Qin Chen etched the Christmas tree image on to a minute piece of glass.
Prof Cumming said: "Our nanotechnology is among the best in the world but sometimes explaining to the public what the technology is capable of can be a bit tricky. We decided that producing this Christmas card was a simple way to show just how accurate our technology is.
"The process to manufacture the card only took 30 minutes. It was very straightforward to produce as the process is highly repeatable - the design of the card took far longer than the production.
"The card is 200 micro-metres wide by 290 micro-metres tall. To put that into some sort of perspective, a micro-metre is a millionth of a metre; the width of a human hair is about 100 micro-metres. You could fit over half a million of them on to a standard A5 Christmas card - but signing them would prove to be a bit of a challenge."
The colours were produced by a process known as plasmon resonance in a patterned aluminium film made in the university's James Watt Nanofabrication Centre.
Although the Christmas card example is a simple demonstration, the university said the underlying technology has important real-world applications.