Atmospheric-pressure CVD growth of two-dimensional 2H- and 1T'-MoTe2 films with high-performance SERS activity.

Two-dimensional (2D) molybdenum ditelluride (MoTe2) is a member of the transition-metal dichalcogenides family, which is an especially promising platform for surface-enhanced Raman scattering (SERS) applications, due to its excellent electronic properties. However, the synthesis of large-area highly crystalline 2D MoTe2 with controllable polymorphism is a huge challenge due to the small free energy difference (~40 meV per unit cell)) between semiconducting 2H-MoTe2 and semimetallic 1T'-MoTe2. Herein, we report an optimized route for the synthesis of 2H- and 1T'-MoTe2 films by atmospheric-pressure chemical vapor deposition. The SERS study of the as-grown MoTe2 films was carried out using methylene blue (MB) as a probe molecule. The Raman enhancement factor on 1T'-MoTe2 was found to be three times higher than that on 2H-MoTe2, and 1T'-MoTe2 film is an efficient Raman-enhancing substrate that can be used to detect MB at nanomolar concentrations. Our study also imparts knowledge on the significance of a suitable combination of laser excitation wavelength and molecule-material platform for achieving ultrasensitive SERS-based chemical detection.