Exfoliated and restacked MoS2 and WS2: Ionic or neutral species? Encapsulation and ordering of hard electropositive cations

The relationship between charge and structure in restacked MS2 (M = Mo, W) has been probed by cation encapsulation and chemical oxidation and characte rized by elemental analysis, electron diffraction, X-ray diffraction, and D ifferential Scanning Calorimetry. Alkali cations have been encapsulated in MoS2 and WS2 without the presence of a co-intercalated counterion, suggesti ng a negative charge in the 0.15-0.25 electrons per M atom range. Electron diffraction studies show ordering of these cations between the layers. Chem ical oxidation with I-2 or Br-2 results in a change in the structure of res tacked MoS2, giving rise to a root 3a x root 3a superlattice, whereas no ch ange is observed in the strucrure of restacked WS2. Differential Scanning C alorimetry studies show that the irreversible exothermic transition to 2H-M S2 shifts to lower temperature with oxidation. The observed structural dist ortion and residual negative charge uniquely explain the thermopower measur ements, which indicate that restacked MoS2 and WS2 are p-type metallic cond uctors.