Figure 7 XPS analysis
of MoS 2  grown at 780 °C: (a) XPS survey.
(b) Peaks for Mo 3d orbitals 3d 5/2  and 3d 3/2  at 229.68 and 232.80 eV, respectively. Sulfur oxidation peak at
226.99 eV. A peak of low intensity observed at 235.98 eV representing
MoO 3 . (c) Orbitals of S 2p, 2p 3/2  and 2p 1/2 , observed at 162.62 and 163.80 eV, respectively. (d) Carbon
calibration peak at 284.28 eV. (e) O 1s peak at 532.78 eV representing
the oxide layer of the Si substrate. (f) Na 1s peak observed at 1071.69
eV representing Na 2 Mo x O x  or Na 2 SO 4 .