Temperature-dependent optical constants of monolayer , , , and : spectroscopic ellipsometry and...

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optoelectronics

Background:

• Monolayer transition metal dichalcogenides (TMDs) are crucial for next-generation photonic devices.
• Understanding their temperature-dependent optical properties is essential for device optimization.

Purpose of the Study:

• To investigate the temperature-dependent optical constants of monolayer TMDs.
• To determine the thermo-optic coefficients and optical band gap variations with temperature.
• To provide foundational data for designing TMD-based photonic devices.

Main Methods:

• Spectroscopic ellipsometry was used to measure optical constants from 0.73-6.42 eV.
• First-principles calculations were employed to assign optical excitations.
• Temperature variations were analyzed from room temperature down to 4.5 K.

Main Results:

• Refractive indices showed anomalous dispersion below 800 nm and plateaued in the near-infrared.
• Refractive indices decreased with decreasing temperature due to a temperature-dependent optical band gap.
• Thermo-optic coefficients ranged from -50 to -100 meV/K at 1200 nm.
• Optical band gap increased with decreasing temperature, linked to suppressed electron-phonon interactions.

Conclusions:

• The study provides comprehensive temperature-dependent optical data for monolayer TMDs.
• Findings are critical for the development of temperature-resilient TMD photonic devices.
• The results offer insights into electron-phonon interactions influencing optical properties.