A study on chemical exfoliation and structural and optical properties of two-dimensional layered titanium diselenide

Titanium diselenide (TiSe₂) is the least studied member of the transition metal dichalcogenide family due to a lack of available synthesis methodology, controlled bandgap engineering, and rapid characterization of layers. In this paper, we report the chemical exfoliation of TiSe₂ platelets synthesized by the chemical vapor transport route in ortho-dichlorobenzene (o-DCB) functionalized with oleylamine (OLA), for the first time to the best of our knowledge. It is found that the addition of OLA supports the formation of a stable dispersion of a large area of the TiSe₂ sheets due to surface capping with the OLA molecules indicating the importance of the ligand in dispersion behavior. The X-ray diffraction pattern confirms the hexagonal structure of the TiSe₂ platelets with the space group P3[combining macron]m1 while Raman spectroscopy reveals that two modes of vibration i.e. A_1g and E_2g exist with layered structures having dimensions in micrometers as confirmed by scanning electron microscopy. Fourier transform infrared spectroscopy confirms the successful functionalization of chemically exfoliated TiSe₂ nanosheets. Field-emission scanning electron microscopy reveals that exfoliated TiSe₂ has a thickness of 15-55 nm whereas high-resolution transmission electron microscopy indicates thicker sheets for ligand-free exfoliated TiSe₂ which are crystalline. Atomic force microscopy confirms the formation of nanosheets. UV-Visible, photoluminescence, and time-resolved PL spectroscopy showed an enhanced effect and better average lifetime of excitation for the exfoliated sheets with OLA than those without OLA. The C-V studies reveal that with increasing scan rate, the corresponding current also increases. The present study offers the possibility of their utilization in optoelectronics, advanced low-power electronics, voltage-controlled oscillators, ultra-fast electronics, and electrochemical devices.