Most of the micron scale device obvious in the SEM image are just electrodes. The active field emitting element apparently measures 80x80x50 nm. The article doesn't appear to be out yet, but they most likely defined this structure with e-beam lithography. As even relatively bad ebeam lithography systems can do 15 nm line widths, they have plent of room to shrink the active element and explore new nanoscale field emission behavior. Not really MNT though.