  The differences in the behavior of Re (n-type) and Au (p-type) dopant atoms
in single-layered MoS2 were investigated by in situ scanning transmission
electron microscopy. Re atoms tend to occupy Mo sites, while Au atoms exist as
adatoms and show larger mobility under the electron beam. Re substituted to Mo
site showed enhanced chemical affinity, evidenced by agglomeration of Re
adatoms around these sites. This may explain the difficulties in achieving a
high compositional rate of homogeneous Re doping in MoS2. In addition, an in
situ coverage experiment together with density functional theory calculations
discovered a high surface reactivity and agglomeration of other impurity atoms
such as carbon at the Re doped sites.
