The correlation of electronic structure and magnetic behaviors of layered molybdenum
disulfide (MoS2) nanosheets, mechanically exfoliated from pristine hexagonal crystal (2HMoS2) have been studied. Raman spectra show the energy difference (ΔE) between two
Raman peaks A1g and E1
2g was about 20.2 cm−1
, indicating the formation of mono-/bi-layered
MoS2 nanosheets as obtained after mechanical exfoliation from pristine 2H-MoS2. The
absence of the reflection peak (0 0 2) in x-ray diffraction patterns confirms the formation of
few-layered and mono-/bi-layered MoS2 nanosheets with reduced thickness. Mo 3d and S
2p XPS core level peaks shifted to higher energy with the reduction of the number of layers
in exfoliated MoS2. As the number of layers decreased, valence band maximum position
increased from 1.11 eV (pristine MoS2) to 1.57 eV (mono-/bi-layered MoS2 nanosheets),
whereas the surface work function (Ф) reduced from 4.85 eV (pristine MoS2) to 4.47 eV
(mono-/bi-layered MoS2 nanosheets), as observed from UPS (He-I) measurements. UPS
(He-II) spectra, as well as VB-PES spectra of mono-/bi-layered MoS2 nanosheets, exhibits an
enhanced valence band density of states (DOS) of S 3p—derived states near Fermi level (Ef).
Mo LII-edge and S K-edge x-ray absorption near edge structure spectra of mono-/bi-layered
MoS2 nanosheets show the splitting of different peaks that cause a noticeable change in their
band structure. Magnetic M–H hysteresis loops measurement clearly demonstrates the increase
of room temperature ferromagnetism from pristine to mono-/bi-layer MoS2, due to the
existence of defects (‘S’-vacancies or defects at the grain boundaries region) and the increase
of DOS.
關聯:
Journal of Physics: Condensed Matter 31(13), p.135501
