Pointillist Xmas Tree

Each dot is an atom from a FeCu alloy. It is an “extreme macro zoom” image taken by Imago’s 3D Atom Probe Microscope, the subject of Puzzle 15.

Atoms are popped off the sample individually and where they hit a screen determines where the atom came from, and the time of flight determines the species of atom (each atom having a different weight). The computer reconstructs the 3D image of the atoms in the sample, which can then be rotated around.