Effects of Proton Radiation-Induced Defects on Optoelectronic Properties of MoS 2

We report on photoluminescence (PL) spectroscopy and transmission electron microscope imaging of suspended and substrate-supported flakes of the 2-D semiconductor MoS 2 before and after exposure to 100-keV proton radiation with fluences of $6 \times 10^{13}$ , $6\times 10^{14}$ , and $6 \times 10^{15}$ p/cm 2 , respectively, and subsequent annealing. An indirect-to-direct bandgap transition is observed, which is preserved after annealing. This transition is accompanied by an unexpected increase in PL intensity after radiation exposure of multilayer samples, which is attributed to higher radiative efficiency of the direct-gap transition.