Silicon and germanium are well-known materials used to manufacture electronic devices for integrated circuits, but they themselves are not considered as promising options for interconnecting the devices due to their semiconducting nature. We have discovered that both Si and Ge atoms can form unexpected metallic monolayer structures with a square lattice which are more stable than the semimetallic silicene and germanene, respectively, in line with the energetically more favored dumbbell and wavy-bilayer structures. More importantly, these two-dimensional allotropes of Si and Ge host Dirac fermions with Fermi velocities superior to those in graphene, indicating that the metal wires needed in the silicon-based integrated circuits can be made of the Si atom itself without incompatibility, allowing for all-silicon-based integrated circuits.
