Atmospheric-pressure CVD growth of two-dimensional 2H- and 1 T′-MoTe₂ films with high-performance SERS activity

Abstract

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 semi-metallic 1 T′-MoTe2. Herein, we report an optimized route for the synthesis of 2H- and 1 T′-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 1 T′-MoTe2 was found to be three times higher than that on 2H-MoTe2 and the 1 T′-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.

Material design, development, and trend for surface-enhanced Raman scattering substrates

“…53,116,117 After decades of development, more and more semiconductor materials have been reported to exhibit SERS enhancement, including a variety of inorganic semiconductors ( e.g. , metal oxides, 47,118–122 metal sulfides, 123–128 metal selenides, 129–131 metal tellurides, 132–134 metal halides, 135–138 and Si, 139,140 ) and a small number of organic semiconductors ( e.g. , α,ω-diperfluorohexylquaterthiophene 141 ).…”

“…The surface research of SERS-active semiconductor nanomaterials can be traced back to the 1980s. 53,116,117 After decades of development, more and more semiconductor materials have been reported to exhibit SERS enhancement, including a variety of inorganic semiconductors (e.g., metal oxides, 47,[118][119][120][121][122] metal sulfides, [123][124][125][126][127][128] metal selenides, [129][130][131] metal tellurides, [132][133][134] metal halides, [135][136][137][138] and Si, 139,140 ) and a small number of organic semiconductors (e.g., α,ω-diperfluorohexylquaterthiophene 141 ). In the meantime, the EFs of these semiconductors have improved from less than 10 3 to the EF value (10 5 -10 7 ) equivalent to gold and silver nanostructures.…”

Recognition of dipole-induced electric field in 2D materials for surface-enhanced Raman scattering

“…The former is a non-resonant chemical enhancement process that describes the change in molecular electron density distribution by interactions between adsorbed molecules and the substrate under non-excitation conditions (Ling et al, 2012a). In contrast, PICT is a wavelengthdependent mechanism and provides the strongest chemical enhancement when the excitation light and arrangement of energy levels in the SERS system satisfy the energy matching relationship, that is, when resonance occurs (Adhikari et al, 2021;Wang et al, 2021;Zhao et al, 2021). According to Lombardi and Birke's theory (Lombardi and Birke, 2009), the polarizability of molecules consists of three terms that are responsible for molecular resonance, substrate-to-molecule charge transfer, and molecule-to-substrate charge transfer.…”

Application of two-dimensional layered materials in surface-enhanced Raman spectroscopy (SERS)

“…These studies have proved the feasibility of phase engineering in improving the SERS properties. At present, the main strategies in phase engineering include charge doping, 61 controlling the synthesis process, 62 applying strain, 63 heat treatment 64 and interlayer coupling. 65…”