Lattice dynamics in monolayer and few-layer SnSe2
AbstractHexagonal tin diselenide (6Hb−SnSe2), 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 6Hb−SnSe2 samples by Raman spectroscopy. Bulk SnSe2 has all four Raman active modes of low-frequency shear Eg2 and layer-breathing A1g2 modes, and high-frequency intralayer vibrational Eg1 and A1g1 modes observed around 18.9, 33.6, 107.9, and 182.1cm−1, respectively. From polarized Raman measurements, we find that Eg1 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, Eg1 and A1g1 mode temperature coefficients of one-layer, three-layer, and bulk SnSe2 are around −0.018 and −0.014cm−1/K, whereas they have almost zero values for low-frequency Eg2 and A1g2 modes of bulk SnSe2 due to different thermal responses of intralayer and interlayer vibrations. Using multiple excitation laser lines of 488, 514.5, 568, 647, and 785 nm, Eg1 and A1g1 mode intensities of bulk SnSe2 have a similar trend with weak maxima around 2.41 eV. Our work provides valuable information about SnSe2 lattice vibrations for further fundamental research and potential applications in 2D devices such as thermoelectric and infrared light detectors.