Low-temperature synthesis of 2D anisotropic MoTe₂ using a high-pressure soft sputtering technique

Area of Science:

• Materials Science
• Condensed Matter Physics
• Thin Film Deposition

Background:

• 1T' phase Molybdenum Ditelluride (MoTe₂) is a promising 2D material with unique electronic properties.
• Achieving large-area, stoichiometric synthesis of 1T' MoTe₂ remains a significant challenge.
• Existing synthesis methods often require high temperatures or result in undesirable defects.

Purpose of the Study:

• To develop a scalable synthesis technique for large-area 1T' phase MoTe₂ sheets.
• To investigate the effect of sputtering and annealing parameters on film stoichiometry and phase purity.
• To understand the role of tellurium vacancies in stabilizing the 1T' phase.

Main Methods:

• High-pressure soft sputtering with Mo/Te co-deposition.
• Two-step deposition and annealing process (in situ).
• Ex situ annealing under tellurium pressure.
• Hall effect measurements for carrier concentration and type determination.

Main Results:

• Successful growth of large-area 1T' MoTe₂ sheets on HOPG and Al₂O₃ substrates at 300 °C.
• A two-step sputtering and annealing process significantly improved film stoichiometry compared to single-step deposition.
• Lowest tellurium vacancy concentration (x=0.14) achieved with 300 °C annealing, limited by MoTe₂ decomposition.
• Ex situ annealing further reduced tellurium vacancies, improving composition to MoTe_1.9.
• Films exhibited n-type conductivity with a carrier concentration of 4.6 × 10¹⁴ cm^-2 per layer, attributed to tellurium vacancies.

Conclusions:

• Large-scale synthesis of tellurium-based van der Waals materials like MoTe₂ is feasible using industrial sputtering techniques.
• The developed method allows for controlled synthesis of 1T' MoTe₂ with reduced tellurium vacancies.
• Challenges in achieving perfectly stoichiometric MoTe₂ persist, highlighting the trade-off between phase stability and defect concentration.