Back Cover: Low-temperature photoluminescence of oxide-covered single-layer MoS2 (Phys. Status Solidi RRL 3/2012)

The dichalcogenide MoS2, which is an indirect‐gap semiconductor in its bulk form, was recently shown to become a direct‐gap material when it is thinned to a single monolayer. Due to its layered crystal structure, few‐layer flakes of MoS2 can be prepared, just like graphene flakes, by mechanical exfoliation. Scanning Raman spectroscopy is a powerful tool to identify such flakes and to determine the number of layers. In their Letter on pp. 126–128, Plechinger et al. prepare MoS2 flakes and use scanning Raman spectroscopy to identify single‐layer flakes. Some of these flakes are covered by dielectric layers using atomic layer deposition. The authors further analyze the flakes by performing low‐temperature photoluminescence (PL) measurements. In bare MoS2 flakes, they observe a high‐energy PL peak, associated with free excitons, and a low‐energy PL peak, associated with excitons bound to surface adsorbates. This low‐energy peak is suppressed in flakes that are covered with dielectric layers. From the temperature‐induced shift of the PL peaks, they infer that the dielectric‐covered flakes are strained.