What do you do if you've got the resources of a university nanotechnology group and time on your hands in the run-up to Christmas? Build the world's tiniest Advent Calendar, of course. The 8.4 x 12.4-micron calendar was carved into a layer of acrylic on a gallium-arsenide wafer after normal clean-room business was done for the day. "We just wanted to have a nice picture of Christmas on our home page," claims the team. More info after the jump.

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The nanostructures group at the University of Regensburg used an electron microscope and electron-beam and ion-beam etching to make their festive nano-calendar, of which you would need several hundred million copies just to cover a normal-sized calendar.

The first 6 days' doors are open, showing what must also be the world's smallest Santa and snowman, as well as a candle, bell, star of Bethlehem and a church. The smallest details are the church windows - just 20nm across - and the tiny message at the bottom is a Christmas wish in German. Now, if only they could get the doors to work like the real thing. [Chemistry World via New Scientist]