The dielectric function of 2D materials and heterostacks provides key information about the interaction of these systems with light, and can be exploited as a non-destructive probe of their electronic structure and physical morphology, but also of their interaction with the environment, including other 2D layers. Optical spectroscopies provide the further advantage of being applicable in different environments of both scientific and technological relevance, and to explore the real-time evolution of the optical fingerprint of 2D materials as a function of experimental variables such as temperature, applied voltages, environmental characteristics and so on. Here we present an experimental study on the temperature-dependent evolution of the permittivity of continuous single-layer WS2 on sapphire in the 298-823 K range, performed under high-vacuum (HV) conditions. The main excitonic peaks show a progressive damping, broadening and redshift as a function of increasing temperature. Interestingly, after the HV annealing, the optical response of WS2 is reversible. The experiment was performed within a custom HV cell fitted between the arms of a commercial spectroscopic ellipsometer (J.A. Woollam M-2000). The forthcoming extension to cryogenic temperatures can provide further insights into quantum phenomena in 2D materials and heterostacks.

Marzia Ferrera

Università degli Studi di Genova, Physics Department