Mechanosynthesis

This seems like a pretty big breakthrough:

Working on a single atomic layer of tin atoms grown on a single-crystal silicon surface, the Japanese-European collaboration maneuvered an atomic force microscope (AFM) tip precisely (plus or minus 0.01 nm) over a single silicon atom defect in the tin surface, and were able to reversibly exchange a tin atom on the apex of the tip and the silicon atom on the surface. These experiments were done at room temperature and, unlike earlier demonstrations in which a scanning tunneling microscope (STM) tip was used to interchange atoms weakly bound to a metallic surface through use of an electrical bias, this demonstration used mechanical force to interchange strongly bound atoms.

Plenty of room at the bottom.