Helium ion modified luminescence and valley depolarization of atomically thin MoS2

We show a systematic study of the impact of disorder on the optical properties and intervalley scattering of atomically thin MoS2. Using a helium ion microscope (HIM) we induce defects in the crystal lattice. Optical analysis reveals significant shifts of both first order Raman modes E’ and A1 which are well explained by phonon confinement due to increasing disorder linking the ion dose to the inter-defect distance. Low-temperature (T=10K) confocal micro-photoluminescence (µ-PL) exhibits additional pronounced defect-related luminescence that can be precisely tailored with the ion dose used for exposure. We attribute the observed luminescence to originate from chemisorbed atoms/molecules at mono-sulfur vacancies in good agreement with DFT calculations. Quasi-resonant polarization resolved µ-PL measurements reveal a robust degree of circular polarization 𝜂 ~ 85% for doses where ion-induced luminescence is observed. This observation is in good agreement with the occurrence of mono-sulfur vacancies that are not contributing to intervalley scattering due to their C3-symmetry as recently theoretically reported [2]. Our results demonstrate the potential of helium ion microscopy applied to 2D layered materials for modifying intrinsic optical properties and fundamental understanding of disorder and its implication on the valley depolarization [3].     «

We show a systematic study of the impact of disorder on the optical properties and intervalley scattering of atomically thin MoS2. Using a helium ion microscope (HIM) we induce defects in the crystal lattice. Optical analysis reveals significant shifts of both first order Raman modes E’ and A1 which are well explained by phonon confinement due to increasing disorder linking the ion dose to the inter-defect distance. Low-temperature (T=10K) confocal micro-photoluminescence (µ-PL) exhibits additio...     »