| AVS 66th International Symposium & Exhibition | |
| 2D Materials | Tuesday Sessions |
| Session 2D+EM+MI+NS-TuA |
| Session: | Properties of 2D Materials including Electronic, Magnetic, Mechanical, Optical, and Thermal Properties II |
| Presenter: | Saujan V. Sivaram, U.S. Naval Research Laboratory |
| Authors: | S.V. Sivaram, U.S. Naval Research Laboratory A.T. Hanbicki, U.S. Naval Research Laboratory M.R. Rosenberger, U.S. Naval Research Laboratory G. Jernigan, U.S. Naval Research Laboratory H.-J. Chuang, U.S. Naval Research Laboratory K.M. McCreary, U.S. Naval Research Laboratory B.T. Jonker, U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
Monolayers of transition metal dichalcogenides (TMDs) are promising components for flexible optoelectronic devices due to their direct band gap and atomically thin nature. The photoluminescence (PL) from these materials is often strongly suppressed by non-radiative recombination mediated by mid-gap defect states. Here, we demonstrate up to a 200-fold increase in PL intensity from monolayer MoS2 synthesized by chemical vapor deposition (CVD) by controlled exposure to laser light in ambient. This spatially resolved passivation treatment is air and vacuum stable. Regions unexposed to laser light remain dark in fluorescence despite continuous impingement of ambient gas molecules. A wavelength dependent study confirms that PL brightening is concomitant with exciton generation in the MoS2; laser light below the optical band gap fails to produce any enhancement in the PL. We highlight the photo-sensitive nature of the process by successfully brightening with a low power broadband white light source (< 10 nW). We decouple changes in absorption from defect passivation by examining the degree of circularly polarized PL. This measurement, which is independent of exciton generation, confirms that laser brightening reduces the rate of non-radiative recombination in the MoS2. A series of gas exposure studies demonstrate a clear correlation between PL brightening and the presence of water. We propose that H2O molecules passivate sulfur vacancies in the CVD-grown MoS2, but require photo-generated excitons to overcome a large adsorption barrier. This work represents an important step in understanding the passivation of CVD-synthesized TMDs and demonstrates the interplay between adsorption and exciton generation.
This research was performed while S.V.S and M.R.R held a National Research Council fellowship and H.-J.C. held an American Society for Engineering Education fellowship at NRL.