CVD-Assisted Synthesis of 2D Layered MoSe₂ on Mo Foil and Low Frequency Raman Scattering of Its Exfoliated Few-Layer...

Transition-metal dichalcogenides (TMDCs) are unique layered materials with exotic properties. So, examining their structures holds tremendous importance. 2H-MoSe₂ (analogous to MoS₂; Gr. 6 TMDC) is a crucial optoelectronic material studied extensively using Raman spectroscopy. In this regard, low-frequency Raman (LFR) spectroscopy can probe this material's structure as it reveals distinct vibration modes. Here, we focus on understanding the microstructural evolution of different 2H-MoSe₂ morphologies and their layers using LFR scattering. We grew phase-pure 2H-MoSe₂ (with variable microstructures) directly on a Mo foil using a two-furnace ambient-pressure chemical vapor deposition (CVD) system by carefully controlling the process parameters. We analyzed the layers of exfoliated flakes after ultrasonication and drop-cast 2H-MoSe₂ of different layer thicknesses by choosing different concentrations of 2H-MoSe₂ solutions. Further detailed analyses of the respective LFR regions confirm the presence of newly identified Raman signals for the 2H-MoSe₂ nanosheets drop-cast on Raman-grade CaF₂. Our results show that CaF₂ is an appropriate Raman-enhancing substrate compared to Si/SiO₂ as it presents new LFR modes of 2H-MoSe₂. Therefore, CaF₂ substrates are a promising medium to characterize in detail other TMDCs using LFR spectroscopy.