Excitonic Dynamics in Janus MoSSe and WSSe Monolayers

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Transition metal dichalcogenides (TMDs) are crucial 2D materials with unique electronic and optical properties.
• Janus TMD monolayers, featuring asymmetric S-M-Se or S-M-Te structures, offer tunable properties compared to their pristine counterparts.
• Understanding excitonic dynamics in Janus TMDs is key to their application in optoelectronics.

Purpose of the Study:

• To investigate the steady-state and time-resolved spectroscopy of excitonic dynamics in Janus molybdenum (Mo) and tungsten (W) selenide (Se) monolayers (MoSSe, WSSe).
• To elucidate the influence of the built-in dipole moment in Janus structures on exciton formation and recombination.
• To provide fundamental insights into the optical properties of Janus TMDs.

Main Methods:

• Synthesis of Janus MoSSe and WSSe monolayers via low-energy selenium implantation into transition metal disulfides.
• Steady-state absorbance and photoluminescence spectroscopy to determine room-temperature exciton resonances.
• Time-resolved transient absorption spectroscopy and photoluminescence quantum yield measurements to analyze exciton dynamics and recombination lifetimes.

Main Results:

• Room-temperature exciton resonances were identified in MoSSe and WSSe monolayers.
• Exciton formation time in Janus structures was found to be approximately 30% faster than in pristine TMDs, attributed to enhanced electron-phonon interaction.
• Janus structures exhibited significantly longer exciton radiative recombination lifetimes compared to pristine samples, supporting spatial electron-hole wave function separation.

Conclusions:

• Janus TMD monolayers possess distinct excitonic dynamics compared to their pristine counterparts.
• The built-in dipole moment in Janus structures plays a critical role in accelerating exciton formation and prolonging radiative recombination.
• These findings advance the fundamental understanding of optical properties in Janus TMDs, paving the way for novel device applications.