  We demonstrated doping in 2D monolayer graphene via local electrical
stressing. The doping, confirmed by the resistance-voltage transfer
characteristics of the graphene system, is observed to continuously tunable
from N-type to P-type as the electrical stressing level (voltage) increases.
Two major physical mechanisms are proposed to interpret the observed phenomena:
modifications of surface chemistry for N-type doping (at low-level stressing)
and thermally-activated charge transfer from graphene to SiO2 substrate for
P-type doping (at high-level stressing). The formation of P-N junction on 2D
graphene monolayer is demonstrated with complementary doping based on locally
applied electrical stressing.
