Nature and origin of unusual properties in chemically exfoliated 2D MoS2

MoS2 in its two-dimensional (2D) form is known to exhibit many fundamentally interesting and technologically important properties. One of the most popular routes to form an extensive amount of such 2D samples is the chemical exfoliation route. However, the nature and origin of the specific polymorph of MoS2 primarily responsible for such spectacular properties have remained controversial with claims of both T and T′ phases and metallic and semiconducting natures. We show that a comprehensive scrutiny of the available literature data of Raman spectra from such samples allows little scope for such ambiguities, providing overwhelming evidence for the formation of the T′ phase as the dominant metastable state in all such samples. We also explain that this small bandgap T′ phase may attain substantial conductivity due to thermal and chemical doping of charge-carriers, explaining the contradictory claims of the metallic and semiconducting nature of such samples, thereby attaining a consistent view of all reports available so far.