Electronic structure and magnetic behaviors of exfoliated MoS 2 nanosheets

The correlation of electronic structure and magnetic behaviors of layered molybdenum disulfide (MoS ) nanosheets, mechanically exfoliated from pristine hexagonal crystal (2H-MoS ) have been studied. Raman spectra show the energy difference (ΔE) between two Raman peaks A and [Formula: see text] was about 20.2 cm , indicating the formation of mono-/bi-layered MoS nanosheets as obtained after mechanical exfoliation from pristine 2H-MoS . The absence of the reflection peak (0 0 2) in x-ray diffraction patterns confirms the formation of few-layered and mono-/bi-layered MoS 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 MoS . As the number of layers decreased, valence band maximum position increased from 1.11 eV (pristine MoS ) to 1.57 eV (mono-/bi-layered MoS nanosheets), whereas the surface work function (Ф) reduced from 4.85 eV (pristine MoS ) to 4.47 eV (mono-/bi-layered MoS nanosheets), as observed from UPS (He-I) measurements. UPS (He-II) spectra, as well as VB-PES spectra of mono-/bi-layered MoS nanosheets, exhibits an enhanced valence band density of states (DOS) of S 3p -derived states near Fermi level (E ). Mo L -edge and S K-edge x-ray absorption near edge structure spectra of mono-/bi-layered MoS 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 MoS , due to the existence of defects ('S'-vacancies or defects at the grain boundaries region) and the increase of DOS.