Transition metal dichalcogenides (TMDs) are a class of 2D materials which have unique optical and electronic properties. They are semiconductors with the chemical structure MX2 where M is a transition metal and X a chalcogen. After the isolation of graphene layers, research into alternative 2D layered materials which offer the same, or better, properties has surged. Bulk MoS2 has an indirect band gap, while in monolayer form the band gap becomes direct. The direct band gap is formed due to the removal of interlayer interactions meaning electrons are confined to a single plane. Mechanically MoS2 monolayers are highly flexible, they have a higher breaking strength than commonly used flexible plastics, and stiffness comparable to steel.
The applications of MoS2 are numerous and wide-ranging, with interest from fields such as optoelectronics, water treatment, solar energy and biomedicine. For the material to perform at its highest capability it must be defect free. Defects, stress and strain can significantly influence the properties of the material. For example, removing defects responsible for non-radiative recombination allows photoluminescence quantum yields of over 95 % to be realised. Correlative Raman and photoluminescence (PL) imaging can be used to provide highly detailed sample information without any sample preparation or damage.
Using a confocal Raman microscope both Raman and PL maps can be obtained on the same sample area. In this Application Note, CVD-grown MoS2 flakes are analysed using Raman and PL imaging with the RM5 Raman Microscope.