Oxygen Passivation Mediated Tunability of Trion and Excitons in MoS2

Abstract

Using wide spectral range in situ spectroscopic ellipsometry with systematic ultra high vacuum annealing and in situ exposure to oxygen, we report the complex dielectric function of MoS2 isolating the environmental effects and revealing the crucial role of unpassivated and passivated sulphur vacancies. The spectral weights of the A (1.92 eV) and B (2.02 eV) exciton peaks in the dielectric function reduce significantly upon annealing, accompanied by spectral weight transfer in a broad energy range. Interestingly, the original spectral weights are recovered upon controlled oxygen exposure. This tunability of the excitonic effects is likely due to passivation and reemergence of the gap states in the bandstructure during oxygen adsorption and desorption, respectively, as indicated by ab initio density functional theory calculation results. This work unravels and emphasizes the important role of adsorbed oxygen in the optical spectra and many-body interactions of MoS2.

Temperature dependence of the double‐resonance Raman bands in monolayer MoS2

“…Figure a shows the fitting of the PL spectra at T = 173 K using four Voigt components. The most intense feature, named T A , is associated with the A trion . The strong intensity of T A is due to the excess of charge (possible optical doping) induced by the relatively high laser power used in our experiments .…”

“…The strong intensity of T A is due to the excess of charge (possible optical doping) induced by the relatively high laser power used in our experiments . The two smaller bands, better observed in Figure a, are named X A and X B and associated with the A and B excitons, respectively. The positions of T A , X A , and X B as a function of temperature are shown in Figure b and were fitted according to the equation: where E X ( T = 0) is the extrapolated band gap at 0 K, a is a fitting parameter, and Θ is an average phonon energy .…”

Modulation of New Excitons in Transition Metal Dichalcogenide‐Perovskite Oxide System

“…[17] The monolayer-MoS 2 was then transferred to TiO 2 -terminated (001)-STO substrate and Cu foil using polymethylmethacrylate. [26,34] The O-K edge spectra from the XAS data showed the presence of the MoO bond in the MoS 2 /STO heterostructure. In this study, the TiO 2 -terminated STO substrate was chosen because the 3d electrons of the transition metal Ti-atoms play an important role in generating new and exotic properties in both the STO bulk materials and in the formation of other heterostructure systems.…”

“…In Figure 5e, while the Ti3dt 2g -O2p (≈530.4 eV) and Ti3de g -O2p (≈532.8 eV) peaks are nearly polarization independent, the new O2p-Mo4d peak (≈531.9 eV) is polarization dependent. [33] Therefore, we postulate that some of the sulfur vacancies in CVD-fabricated monolayer-MoS 2 are partially occupied by the O-atoms (Figures 1e and 2a) during its transfer process, [26] thereby forming MoO covalent bonds. [32] Thus, there is strong anisotropy in the electronic properties.…”

“…Due to the formation of MoO bonds (to be demonstrated later), the oxygen atoms from atmosphere are introduced at the sulfur-vacancy sites during their growth and transfer processes [26] as displayed in Figure 2a, which further affects the interfacial strain and the many-body interactions in MoS 2 . Due to the formation of MoO bonds (to be demonstrated later), the oxygen atoms from atmosphere are introduced at the sulfur-vacancy sites during their growth and transfer processes [26] as displayed in Figure 2a, which further affects the interfacial strain and the many-body interactions in MoS 2 .…”