  We report first principles theoretical investigations of possible metal
contacts to monolayer black phosphorus (BP). By analyzing lattice geometry,
five metal surfaces are found to have minimal lattice mismatch with BP:
Cu(111), Zn(0001), In(110), Ta(110) and Nb(110). Further studies indicate Ta
and Nb bond strongly with monolayer BP causing substantial bond distortions,
but the combined Ta-BP and Nb-BP form good metal surfaces to contact a second
layer BP. By analyzing the geometry, bonding, electronic structure, charge
transfer, potential and band bending, it is concluded that Cu(111) is the best
candidate to form excellent Ohmic contact to monolayer BP. Other four metal
surfaces or combined surfaces also provide viable structures to form metal/BP
contacts, but they have Schottky character.
