The spectacular progress in controlling the electronic properties of graphene has triggered research in alternative atomically thin two-dimensional crystals. Monolayers (ML) of transition-metal dichalcogenides such as MoS2 have emerged as very promising nanostructures for optical and electronic applications for mainly two reasons.
First, the indirect bulk semiconductor MoS2 becomes direct when thinned to 1ML, resulting in efficient optical absorption and emission. Second, inversion symmetry breaking (usually absent in graphene) together with the large spin-orbit interaction leads to a coupling of carrier spin and k-space valley physics, i.e., the circular polarization (σ+ or σ−) of the absorbed or emitted photon can be directly associated with selective carrier excitation in one of the two nonequivalent k valleys (K+ or K−, respectively).
In this talk we will present cw and time-resolved photoluminescence experiments performed on MoS2 MLs. The inherent chiral optical selectivity allows exciting one of these valleys, and close to 90% polarized emission at 4 K is observed with 40% polarization remaining at 300 K. The high polarization degree of the emission remains unchanged in transverse magnetic fields up to 9 T [1,2].
We will also present micro-Raman and photoluminescence results measured at 300 K to investigate the influence of uniaxial tensile strain on the vibrational and optoelectronic properties of monolayer and bilayer MoS2 on a flexible substrate .
 Sallen et al, PRB 86, 081301(R) (2012)
 Lagarde et al, ArXiv 1308.0696 (2013)
 Wang et al, PRB 88, 121301(R) (2013)