Low‐temperature photoluminescence of oxide‐covered single‐layer MoS2

Abstract We present a photoluminescence study of single‐layer MoS 2 flakes on SiO 2 surfaces. We demonstrate that the luminescence peak position of flakes prepared from natural MoS 2 , which varies by up to 25 meV between individual flakes, can be homogenized by annealing in vacuum. We use HfO 2 and Al 2 O 3 layers prepared by atomic layer deposition to cover some of our flakes. In these flakes, we observe a suppression of the low‐energy luminescence peak which appears in asprepared flakes at low temperatures. We infer that this peak originates from excitons bound to surface adsorbates. We also observe different temperature‐induced shifts of the luminescence peaks for the oxide‐covered flakes. This effect stems from the different thermal expansion coefficients of the oxide layers and the MoS 2 flakes. It indicates that the single‐layer MoS 2 flakes strongly adhere to the oxide layers and are therefore strained. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)