This is an experimental demonstration of the technology that makes Neal Stephenson's "Diamond Age" possible. They place an individual carbon atom pair(dimer) on silicon. Silicon has the same crystal structure as diamond, so adding carbon in this manner is similar to building diamond. There is potential for eventually making 3D atomically precise structures of diamond with this tech although that is far off.

This is a very, very basic demonstration, but it's showing for the first time that atoms can be controllably and programmably covalently bonded in something that can probably be extended to 3D. There was a lot of skepticism that this process was possible at all, so an experimental demonstration is important