  Silicon and germanium are the well-known materials used to manufacture
electronic devices for the 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 which are more stable than the
extensively studied semimetallic silicene and germanene, respectively. More
importantly, the newly discovered two-dimensional allotropes of Si and Ge have
Fermi velocities superior to the Dirac fermions in graphene, indicating that
the metal wires needed in the silicon-based integrated circuits can be made of
Si atom itself without incompatibility, allowing for all-silicon-based
integrated circuits.
