Electronic structure and magnetic behaviors of exfoliated MoS₂ nanosheets

Abstract

The correlation of electronic structure and magnetic behaviors of layered molybdenum disulfide (MoS2) nanosheets, mechanically exfoliated from pristine hexagonal crystal (2H-MoS2) have been studied. Raman spectra show the energy difference (ΔE) between two Raman peaks A1g and 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.

Facile fabrication of defect-induced 2D-stanene/stanene-oxide nano-sheet structure material through etching of SnOx thin film by the process of successive Ar+ ion sputtering

“…As the SnO-layer number decreased, a blue shift of the (E g ) band and a red shift of the (A 1g ) bands would observed in the exfoliated 2D MoS 2 nanosheets [13] and their energy difference between two Raman peaks (Δω = A 1g ~ E g ) are used to identify the number of 2D MoS 2 layers. It can be seen that the Δω (= A 1g ~ E g ) values obtained from our present β-Sn (stanene), SnO (stanene-oxide) and SnO 2 after etching time τ = 4000 s are reduced about 8 cm −1 /16 cm −1 , 4 cm −1 /12 cm −1 and 3 cm −1 , respectively that clearly indicates the existence and/or formation of the few-layered 2D stanene/ stanene-oxide structure materials as also observed in 2D MoS 2 materials [27].…”

Covalent 0D–2D Heterostructuring of Co9S8–MoS2 for Enhanced Hydrogen Evolution in All pH Electrolytes

“…The decreased intensity of S 2p 1/2 indicates the decrease in the number of layers, which is in agreement with our Raman results. [ 19 ]…”

“…The decreased intensity of S 2p 1/2 indicates the decrease in the number of layers, which is in agreement with our Raman results. [19] In order to gain in-depth insight into structural and electronic characteristics of the Co 9 S 8 -MoS 2 heterostructure, X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses were employed. Figure 2b,e reveals Co K-edge and Mo K-edge XANES spectra of Co 9 S 8 -MoS 2 , respectively.…”

Strain-Modulated Magnetism in MoS2

“…Except for graphene, MoS 2 [ 17 , 18 , 19 , 20 , 21 ] has also attracted extensive attention. Interestingly, many experimental studies show that the defective MoS 2 nanostructures [ 18 , 19 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ] also exhibit FM.…”