On the Morphology and Optical Properties of Molybdenum Disulfide Nanostructures from a Monomolecular Layer to a Fractal-Like Substructure

The impact of layer thickness on the morphology and optical properties of MoS 2 nanostructures, including monomolecular layers, formed by the carrier-gas-assisted transport of sulfur vapor to the hot zone of a reactor containing metallic molybdenum and subsequent deposition on mica (muscovite) substrates is investigated. Molybdenum disulfide nanostructures of different thicknesses grown at different temperatures of gas-transport synthesis are studied by atomic-force microscopy, optical absorption spectroscopy, and Raman spectroscopy. It is found that synthesis at temperatures of 525–600°C makes it possible to obtain monomolecular MoS 2 layers containing trigonal domains and featuring direct-gap optical transitions at 1.84 eV with the formation of excitons at room temperature. Fractal-type MoS 2 substructures are obtained for the first time. The frequencies of intralayer and interlayer vibrational modes and A 1 g , respectively, in their Raman spectra (377.5 and 403.8 cm –1 , respectively) differ both from the corresponding values for a monomolecular layer and the known frequencies for bulk samples. The frequency of the intralayer mode in these samples (377.5 cm –1 ) is the lowest of all previously reported.