Investigation of 2H/1T/1T' phase MoS₂ optical nonlinearity

Area of Science:

• Materials Science
• Optics
• Condensed Matter Physics

Background:

• Molybdenum disulfide (MoS2) exists in distinct crystalline phases, including 2H and 1T/1T'.
• These phases possess unique electronic and optical properties that are crucial for various applications.

Purpose of the Study:

• To synthesize and separately grow 2H and 1T/1T' phase MoS2 thin films.
• To investigate and differentiate the phase-dependent optical nonlinearity of MoS2.
• To characterize the nonlinear optical properties, such as nonlinear refractive index, for each phase.

Main Methods:

• Controlled atmosphere chemical vapor deposition (CVD) for phase-selective MoS2 thin film growth.
• Z-scan technique for measuring optical nonlinearity and nonlinear refractive index.
• Analysis of nonlinear absorption mechanisms (e.g., reversed saturable absorption, single photon absorption).

Main Results:

• Successful separate growth of 2H and 1T/1T' phase MoS2 thin films.
• 2H-MoS2 demonstrated reversed saturable absorption with a peak intensity of 3.78 GW/cm², indicating higher-order nonlinear absorption.
• 1T/1T'-MoS2 exhibited dominant single photon absorption.
• Nonlinear refractive indices were measured as 1.82 × 10⁻¹⁰ cm²/W for 1T/1T'-MoS2 and -4.82 × 10⁻¹⁰ cm²/W for 2H-MoS2.

Conclusions:

• This work is the first to distinguish the phase-dependent optical nonlinearity in MoS2.
• The findings highlight significant differences in nonlinear optical behavior between 2H and 1T/1T' MoS2 phases.
• The methodology provides insights for selecting appropriate MoS2 phases for specific optoelectronic and nonlinear optical applications.