Novel materials have been obtained by restacking single-layer molybdenum disulfide (MoS(2)) with organic molecules included between the layers. A large variety of organic molecules can be included between layers of MoS(2) and other transition-metal dichalcogenides. The films with the included organics are formed at the interface between an aqueous suspension of the MoS(2) and a water-immiscible organic liquid. The organic molecules are not necessarily electron donors. A highly oriented, conducting film of restacked MoS(2) containing ferrocene is presented as an example.
Restacked single-layer MoS2 films have been studied by polarized X-ray absorption spectroscopy at the S K and Mo Lm edges. These restacked single-layer MoS2 films were obtained by exfoliation of MoS2 powder and subsequent collection of the single molecular layer of MoS2 onto a glass substrate. Films with and without tetrachloroethylene (TCE) included between the layers were obtained. The interlayer spacing of the film without tetrachloroethylene is 6.2 Á, and there is a 4.0-Á interlayer expansion on introducing TCE molecules between layers of MoS¡¡. The S K-edge X-ray absorption spectra of restacked single-layer MoS2 films with and without TCE included between the layers have been compared with that of MoS2 powder. A few percent of sulfate anion was found in the restacked single-layer MoS2 films; it may originate from the partial decomposition of the molybdenum disulfide. Apart from that, the S K-edge absorption spectra of restacked single-layer MoS2 films with and without TCE are similar to that of MoS2 powder. This suggests that the chemical bonding of the S atom in the restacked MoS2 films is identical with that found in crystalline MoS2. In particular, we found no evidence for the presence of a new axial ligand on the S atom that should have manifest itself by introducing a new absorption band below the ionization threshold. Also, no difference was observed at the Mo Lm edge between the restacked single-layer MoS2 films and the MoS2 powder. Recently, novel materials have been obtained by restacking single-layer molybdenum disulfide with organic molecules included between the layers.3-4 Molybdenum disulfide is a compound semiconductor, consisting of * To whom correspondence should be addressed.
Highly orientated films of the transition metal dichalcogenides 2H-MoS2, 2H-WS2, 2H-TaS2 and 3R-NbS2 have been prepared using a suspension of the powders in water. The layered material is collected at the water/organic interface by shaking the suspension with a water-immiscible organic liquid. The films are spread spontaneously over a wet substrate using the Marangoni effect. The electrical resistance of spread films of NbS2 increased on exposure to humidity, contrary to conventional behaviour. Rapid, reversible incorporation of water into the spacing between the basal planes of the layered platelets and at platelet edges is believed to be the cause of this curious effect. The response of the other dichalcogenide films to humidity was not significant.
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