2DMT: Photoluminescence spectroscopy. Part I.

In this article, we will discuss the use of room-temperature photoluminescence spectroscopy for the characterisation of material properties of the four most commonly studied semiconducting group-VI transition metal dichalcogenides (TMDs): WS2, MoS2, WSe2, and MoSe2.

We will show how photoluminescence spectroscopy can be used to identify material composition, number of layers, strain, carrier concentration, and disorder level in atomically thin TMD samples. While the accuracy of information extracted from photoluminescence spectra acquired at room temperature is limited by phonon-induced broadening of emission peaks, it can be used for qualitative assessment, providing convenient and accessible way of characterising various material parameters.

2DMT: Optical contrast measurements

  • Optical contrast is a normalised difference between the intensities of light reflected by sample and surrounding substrate
  • Optical contrast of layered materials changes in a step-like manner with increasing number of layers, allowing accurate thickness estimate for flakes up to 15 layers thick
  • Optical contrast measurements work best for materials with strong absorption in the visible range, such as graphene, transition metal mono- and dichalcogenides, deposited onto silicon substrates with 90 or 290 nm dioxide layer, but can be extended to other types of substrates