LI-INTERCALATION AND EXFOLIATION OF WS2

Single-molecular layers of WS2 have been prepared by Li-intercalation using n-butyllithium and exfoliation in water. The preparation of sing le-molecular layers of WS2 was found to be more difficult than that fo r MoS2. The saturated Li content is x = 0.4 in LixWS2 for intercalatio n at room temperature. In order to obtain complete exfoliation, it is necessary that x greater than or equal to 1, which we have shown can b e obtained with elevated-temperature intercalation. X-ray diffraction patterns of single layer WS2 suspensions in water clearly show the two -dimensional features of the material, i.e. only (hkO) peaks are prese nt in the pattern and strong asymmetric line shapes of Bragg peaks due to the Warren effect. The line shapes of X-ray diffraction patterns f rom single layer WS2 are quite different from those of single layer Mo S2 due to structure factor effects. We have determined that single lay er WS2 has an expanded a-spacing and strongly distorted octahedral coo rdination with a 2a(0) superlattice. The 1.8 eV optical band gap absor ption of bulk WS2 is not observed in single layer WS2.