Spectroscopic and structural dynamics of MoS₂ thin films

A promising two-dimensional material for applications in optoelectronic and photonics, MoS₂ is in focus since last decade. Its optical, structural and electronic properties are of practical importance along with its exciton dynamics. MoS₂ thin films were synthesized with Chemical Vapour Deposition (CVD) technique on Si/SiO₂ substrates. The thickness dependent regularities were controlled and examined to quantitatively control the film quality with thickness variation. Various characterization techniques were employed to investigate structural and morphological changes induced systematically to reveal the van der waal stacked layers of MoS₂ material. The In-plane characteristic mode E¹_2g and out of plane A_1g vibrational modes were detected in different configurations of film's structure. Optical absorption spectra gave us information on photon energy with the absorbance; extrapolation of this curve gave optical bandgap (E_g) in the form of Tauc plot. These energies can be associated to interband electronic transitions in the Brillouin zone. The intrinsic excitonic response as a consequence of layer stacking and velly indexing can be attributed to this change in bandgap from 1.68 to 1.91 eV. Surface morphology of the as-grown films also provides better understanding of MoS₂ material with root mean square (RMS) roughness in the range of 1.32 to 3.85 nm.