| Abstract
| - Layered metal disulfides-MS2 (M = Mo, W) in the form of fullerene-like nanoparticles and in theform of platelets (crystallites of the 2H polytype) have been intercalated by exposure to alkali metal(potassium and sodium) vapor using a two-zone transport method. The composition of the intercalatedsystems was established using X-ray energy dispersive spectrometer and X-ray photoelectron spectroscopy(XPS). The alkali metal concentration in the host lattice was found to depend on the kind of sample andthe experimental conditions. Furthermore, an inhomogeneity of the intercalated samples was observed.The product consisted of both nonintercalated and intercalated phases. X-ray diffraction analysis andtransmission electron microscopy of the samples, which were not exposed to the ambient atmosphere,showed that they suffered little change in their lattice parameters. On the other hand, after exposure toambient atmosphere, substantial increase in the interplanar spacing (3−5 Å) was observed for theintercalated phases. Insertion of one to two water molecules per intercalated metal atom was suggestedas a possible explanation for this large expansion along the c-axis. Deintercalation of the hydrated alkaliatoms and restacking of the MS2 layers was observed in all the samples after prolonged exposure to theatmosphere. Electric field induced deintercalation of the alkali metal atoms from the host lattice was alsoobserved by means of the XPS technique. Magnetic moment measurements for all the samples indicatea diamagnetic to paramagnetic transition after intercalation. Measurements of the transport properties reveala semiconductor to metal transition for the heavily K intercalated 2H-MoS2. Other samples show severalorders of magnitude decrease in resistivity and two- to five-fold decrease in activation energies uponintercalation. These modifications are believed to occur via charge transfer from the alkali metal to theconduction band of the host lattice. Recovery of the pristine compound properties (diamagnetism andsemiconductivity) was observed as a result of deintercalation.
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