Nonlinear Optical Imaging, Precise Layer Thinning, and Phase Engineering in MoTe₂ with Femtosecond Laser

Area of Science:

• Materials Science
• Nanotechnology
• Optics and Photonics

Background:

• Controlling layer thickness and phase structure in 2D transition metal dichalcogenides (2D TMDCs) like MoTe2 is crucial for nanoelectronic and nanophotonic applications.
• Existing continuous-wave laser methods for MoTe2 modification are slow and substrate-dependent.
• The potential of ultrafast lasers for MoTe2 manipulation remains largely unexplored.

Purpose of the Study:

• To investigate the nonlinear optical interactions between MoTe2 and femtosecond (fs) lasers.
• To demonstrate a single fs laser platform for characterizing and modifying MoTe2.
• To achieve precise layer thinning, phase transition, and nanostructure formation in MoTe2.

Main Methods:

• Utilized nonlinear optical phenomena: second-harmonic generation (SHG) and four-wave mixing (FWM) with fs laser excitation.
• Employed varying fs laser fluences to induce layer-by-layer ablation and phase transitions (2H-to-1T').
• Investigated fs laser-induced nanoripple formation on MoTe2 surfaces.

Main Results:

• Observed strong SHG and FWM signals for identifying odd-even layers and layer numbers in MoTe2.
• Achieved controlled layer thinning by ablation at the ablation threshold (Fth).
• Induced 2H-to-1T' phase transition at higher fluences (2Fth to 3Fth) and formed ordered nanoripples.

Conclusions:

• A single fs laser platform provides an efficient method for nonlinear optical characterization of MoTe2.
• Femtosecond laser processing enables precise control over MoTe2 layer thickness and phase.
• This ultrafast approach offers a versatile tool for modifying 2D TMDC properties for diverse applications.