  Controllable doping of two-dimensional materials is highly desired for ideal
device performance in both hetero- and p-n homo-junctions. Herein, we propose
an effective strategy for doping of MoS2 with nitrogen through a remote N2
plasma surface treatment. By monitoring the surface chemistry of MoS2 upon N2
plasma exposure using in-situ X-ray photoelectron spectroscopy, we identified
the presence of covalently bonded nitrogen in MoS2, where substitution of the
chalcogen sulfur by nitrogen is determined as the doping mechanism.
Furthermore, the electrical characterization demonstrates that p-type doping of
MoS2 is achieved by nitrogen doping, in agreement with theoretical predictions.
Notably, we found that the presence of nitrogen can induce compressive strain
in the MoS2 structure, which represents the first evidence of strain induced by
substitutional doping in a transition metal dichalcogenide material. Finally,
our first principle calculations support the experimental demonstration of such
strain, and a correlation between nitrogen doping concentration and compressive
strain in MoS2 is elucidated.
