Hexagonal tin diselenide $\left(6\mathrm{Hb}-{\mathrm{SnSe}}_2\right)$, a two-dimensional (2D) layered metal dichalcogenide from the IVA and VIA groups, has recently drawn numerous attention in 2D nano-optoelectronics. In this paper, we investigate characteristic lattice dynamics of mechanically exfoliated mono- and few-layer $6\mathrm{Hb}-{\mathrm{SnSe}}_2$ samples by Raman spectroscopy. Bulk ${\mathrm{SnSe}}_2$ has all four Raman active modes of low-frequency shear $E_g^2$ and layer-breathing $A_{1g}^2$ modes, and high-frequency intralayer vibrational $E_g^1$ and $A_{1g}^1$ modes observed around 18.9, 33.6, 107.9, and $182.1\mathrm{c}{\mathrm{m}}^{-1}$, respectively. From polarized Raman measurements, we find that $E_g^1$ mode intensity is independent of polarization configuration and increases linearly with layer number, which provides an effective approach to determine sample thickness. From low-temperature Raman measurements, $E_g^1$ and $A_{1g}^1$ mode temperature coefficients of one-layer, three-layer, and bulk ${\mathrm{SnSe}}_2$ are around $-0.018$ and $-0.014\mathrm{c}{\mathrm{m}}^{-1}/\mathrm{K}$, whereas they have almost zero values for low-frequency $E_g^2$ and $A_{1g}^2$ modes of bulk ${\mathrm{SnSe}}_2$ due to different thermal responses of intralayer and interlayer vibrations. Using multiple excitation laser lines of 488, 514.5, 568, 647, and 785 nm, $E_g^1$ and $A_{1g}^1$ mode intensities of bulk ${\mathrm{SnSe}}_2$ have a similar trend with weak maxima around 2.41 eV. Our work provides valuable information about ${\mathrm{SnSe}}_2$ lattice vibrations for further fundamental research and potential applications in 2D devices such as thermoelectric and infrared light detectors.

• Received 21 January 2017

DOI:https://doi.org/10.1103/PhysRevB.96.035401