Excitonic Dynamics in Janus MoSSe and WSSe Monolayers

Abstract

We report here details of steady-state and time-resolved spectroscopy of excitonic dynamics for Janus transition metal dichalcogenide monolayers, including MoSSe and WSSe, which were synthesized by low-energy implantation of Se into transition metal disulfides. Absorbance and photoluminescence spectroscopic measurements determined the room-temperature exciton resonances for MoSSe and WSSe monolayers. Transient absorption measurements revealed that the excitons in Janus structures form faster than those in pristine transition metal dichalcogenides by about 30% due to their enhanced electron−phonon interaction by the built-in dipole moment. By combining steady-state photoluminescence quantum yield and time-resolved transient absorption measurements, we find that the exciton radiative recombination lifetime in Janus structures is significantly longer than in their pristine samples, supporting the predicted spatial separation of the electron and hole wave functions due to the built-in dipole moment. These results provide fundamental insight in the optical properties of Janus transition metal dichalcogenides.

Reaching the Excitonic Limit in 2D Janus Monolayers by In Situ Deterministic Growth

“…The FWHM values of the PL peaks of exfoliated Janus monolayers presented here are, to the best of our knowledge, the narrowest reported to date in the literature for Janus monolayers both at 4 and 300 K. [ 4,5,10,20,31 ] Furthermore, the FWHM values of the highest energy peak of SWSe and SMoSe are, respectively, comparable to the FWHM of X 0 reported for exfoliated, un‐encapsulated, traditional TMD monolayers at 4 K: 24 meV for SWSe versus ≈10 meV for WSe 2 and ≈15 meV for WS 2 as extracted from Figure 2b in ref. [32] and 23 meV for SMoSe versus ≈15 meV for MoSe 2 and ≈20 meV for MoS 2 , as extracted from Figure 2b in ref.…”

“…Upon cooling down to 4 K, the narrowing of the spectrum and lack of an X B band allow us to distinguish two peaks: one at 1.75 eV with an FWHM of 54 meV (indicated by a pink arrow in Figure 5d) and another one at 1.79 eV (indicated by a purple arrow in Figure 5d) with an FWHM of 23 meV, which can potentially be assigned to the neutral exciton X 0 . [10,20] The FWHM values of the PL peaks of exfoliated Janus monolayers presented here are, to the best of our knowledge, the narrowest reported to date in the literature for Janus mono layers both at 4 and 300 K. [4,5,10,20,31] Furthermore, the FWHM values of the highest energy peak of SWSe and SMoSe are, respectively, comparable to the FWHM of X 0 reported for exfoliated, un-encapsulated, traditional TMD monolayers at 4 K: 24 meV for SWSe versus ≈10 meV for WSe 2 and ≈15 meV for WS 2 as extracted from Figure 2b in ref. [32] and 23 meV for SMoSe versus ≈15 meV for MoSe 2 and ≈20 meV for MoS 2 , as extracted from Figure 2b in ref.…”

Recent advances in low-dimensional Janus materials: theoretical and simulation perspectives

“…[88] These considerations have prompted interest in excitonic effects for low dimensional Janus materials. From the experimental side, Zheng et al [107] used absorbance and photoluminescence spectroscopy to investigate room-temperature exciton resonances for Janus MoSSe and WSSe monolayers. Transient absorption measurements reveal that excitons in Janus structures form about 30% faster than in pristine TMDs as a result of enhanced electronphonon interactions due to the built-in electrostatic dipole moment.…”

Dipole moment and pressure dependent interlayer excitons in MoSSe/WSSe heterostructures

“…Experiments have proved that the intrinsic dipole moments in monolayer MoSSe enhance the exciton-phonon coupling interaction, which makes the recombination rate of excitons 30% faster than in MoS 2 , and a longer exciton radiative recombination time than pristine MoS 2 was obtained. 45 Moreover, if the degree of freedom brought by the intrinsic dipole moment is introduced into the heterostructures, the generation and recombination of the IX can be greatly influenced by the huge polarization field and the interlayer interaction, which can be tailored via the combination of different interfaces, and therefore, the scope of designing optoelectronic devices can be greatly expanded.…”