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

Transition-metal dichalcogenides (TMDCs) are unique layered materials with exotic properties. So, examining their structures holds tremendous importance. 2H-MoSe 2 (analogous to MoS 2 ; 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-MoSe 2 morphologies and their layers using LFR scattering. We grew phase-pure 2H-MoSe 2 (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-MoSe 2 of different layer thicknesses by choosing different concentrations of 2H-MoSe 2 solutions. Further detailed analyses of the respective LFR regions confirm the presence of newly identified Raman signals for the 2H-MoSe 2 nanosheets drop-cast on Raman-grade CaF 2 . Our results show that CaF 2 is an appropriate Raman-enhancing substrate compared to Si/SiO 2 as it presents new LFR modes of 2H-MoSe 2 . Therefore, CaF 2 substrates are a promising medium to characterize in detail other TMDCs using LFR spectroscopy.