https://en.wikipedia.org/wiki/Monocrystalline_silicon has 0.5nm for the lattice spacing, distance between Si atoms ranges somewhere between 0.3nm and 0.5nm, I guess. Even if you go to graphene instead of Si wafers, I don’t think you’ll get more than three atoms within 1.5nm, as graphene is not a cubical lattice.

Unit cell of Silicon is about 5 angstroms (0.5 nm), so we'd be at about 7 atoms wide for a diamond cubic structure (I think).

I don't think we can actually make chips out of carbon...

It was an number for the length of a chemical bond that I had easily to hand, other bonds aren't significantly different, definitely not 5 Angstrom.

Also, people working on graphene and related materials are trying damn hard to make chips out of carbon ;)

Unit cell is 5.43 Angstroms, according to this site: http://hyperphysics.phy-astr.gsu.edu/hbase/solids/sili2.html. Of course the bonds by which the cell is constructed are smaller.