  Two-dimensional (2D) materials may exhibit intriguing band structure features
(e.g., Dirac points), that lay far away from the Fermi level. They are, thus,
not usable in applications. The semiconducting 2D material PC6 has two Dirac
cones above and below the Fermi level. Therefore, it is an ideal playground to
demonstrate chemical functionalization methods for shifting the Fermi level in
order to access interesting band structure features. PC6 is based on the
sqrt(7) x sqrt(7)R19.1deg super cell of graphene with two carbon atoms per unit
cell substituted by phosphorous. It is demonstrated how substitution with other
heteroatoms that contain a different number of valence electrons, the Dirac
points can be accessed. Alternatively, hydrogen atoms can be used as adatoms at
the heteroatom sites. This increases electron filling and shifts the Fermi
level upwards.
