Structural Determination and Nonlinear Optical Properties of New 1T‴-Type MoS₂ Compound

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid-State Chemistry

Background:

• Noncentrosymmetric molybdenum disulfide (MoS₂) materials exhibit unique electronic properties like spin-orbit coupling and valley polarization.
• Theoretically predicted 1T‴-MoS₂, built from [MoS₆] octahedral motifs, remained experimentally uncharacterized.
• Previous MoS₂ polymorphs (1H, 3R) showed interesting nonlinear optical effects, motivating the search for new structures.

Purpose of the Study:

• To synthesize and characterize the elusive 1T‴-MoS₂ single crystal structure.
• To investigate the electronic and optical properties of the newly synthesized 1T‴-MoS₂.
• To explore its potential for nonlinear optical applications.

Main Methods:

• Topochemical synthesis method for obtaining 1T‴-MoS₂ single crystals.
• Single-crystal X-ray diffraction for precise crystal structure determination.
• Scanning transmission electron microscopy (STEM) to observe structural motifs.
• Optical and electronic measurements to determine band gap and nonlinear optical properties.

Main Results:

• Successful synthesis of 1T‴-MoS₂ single crystals.
• Crystal structure determined in space group P3₁m, revealing a √3 a × √3 a superstructure of 1T MoS₂ with corner-sharing Mo₃ triangular trimers.
• 1T‴-MoS₂ exhibits semiconducting behavior with a band gap of 0.65 eV, contrasting with metallic 1T/1T' phases.
• Strong optical second-harmonic generation signals were observed.

Conclusions:

• The first layered noncentrosymmetric semiconductor based on edge-sharing MoS₆ octahedra, 1T‴-MoS₂, has been successfully synthesized and characterized.
• This new material possesses distinct semiconducting properties and exhibits significant nonlinear optical activity.
• 1T‴-MoS₂ offers a promising platform for fundamental research in nonlinear optics and advanced electronic devices.