Low-Frequency Raman Spectroscopy of Few-Layer 2H-SnS2

Abstract

We investigated interlayer phonon modes of mechanically exfoliated few-layer 2H-SnS2 samples by using room temperature low-frequency micro-Raman spectroscopy. Raman measurements were performed using laser wavelengths of 441.6, 514.4, 532 and 632.8 nm with power below 100 μW and inside a vacuum chamber to avoid photo-oxidation. The intralayer Eg and A1g modes are observed at ~206 cm−1 and 314 cm−1, respectively, but the Eg mode is much weaker for all excitation energies. The A1g mode exhibits strong resonant enhancement for the 532 nm (2.33 eV) laser. In the low-frequency region, interlayer vibrational modes of shear and breathing modes are observed. These modes show characteristic dependence on the number of layers. The strengths of the interlayer interactions are estimated by fitting the interlayer mode frequencies using the linear chain model and are found to be 1.64 × 1019 N · m−3 and 5.03 × 1019 N · m−3 for the shear and breathing modes, respectively.

Optical phonons of SnSe(1−x)Sx layered semiconductor alloys

“…The B 1g and B 2g modes are forbidden in the backscattering geometry 32 , 33 with the incident laser beam in the x -direction. Therefore, six Raman modes should be observed in the Raman spectra of pure compounds SnSe or SnS.…”

“…The same measurements were repeated on samples exfoliated on SiO 2 /Si substrates of thickness in the range of ~ 50 to ~ 300 nm as determined by using a commercial atomic force microscope (AFM) system (NT-MDT NTEGRA Spectra) and the results were identical in terms of Raman peak positions. For polarized Raman measurements, a low-frequency polarized Raman setup was used in the backscattering geometry 32 , 33 with six different excitation wavelengths: the 784.8-nm (1.58 eV) line of a diode laser, the 632.8-nm (1.96 eV) line of a He–Ne laser, the 532-nm (2.33 eV) line of a diode-pumped solid-state (DPSS) laser, the 514.5-nm (2.41 eV) and 488-nm (2.54 eV) lines of an Ar ion laser and the 441.6-nm (2.81 eV) line of a He-Cd laser. The laser beam is linearly polarized and focused onto the sample by a 50 microscope objective lens (N.A.…”

“…It was found that the Ag 2 mode, for example, at 70 cm -1 for SnSe or at 95 cm -1 for SnS, or the corresponding mode in the alloys, is the most reliable mode for determination of the crystallographic direction regardless of the excitation wavelength. The B1g and B2g modes are forbidden in the backscattering geometry [32][33] with the incident laser beam in the x-direction. Therefore, six Raman modes should be observed in the Raman spectra of pure compounds SnSe or SnS.…”

Structural Transformation of SnS2 to SnS by Mo Doping Produces Electro/Photocatalyst for Hydrogen Production

“…In accordance, large, crystalline structures of SnS 2 were also absent from the doped samples, although small fragments comprising of a few layers may still exist in the sample. The Raman spectra of the pristine SnS 2 (Figure b) showed the characteristic A 1g phonon mode at 312 cm −1 of 2D SnS 2 hexagonal crystal, and a low intensity E g phonon mode at 210 cm −1 , indicating thin structures, in nanometer scale . The intensity of the SnS 2 A 1g mode decreased significantly for the 5 and 10 % Mo doped samples, indicating that only a small SnS 2 fraction remained in the 5 % Mo sample, asserting that the doping results in elimination of the SnS 2 phase, in accordance with the XRD data.…”

2D Materials Based on Main Group Element Compounds: Phases, Synthesis, Characterization, and Applications

“…comprehensively investigated the Raman spectrum in an intralayer (A1 and E) and interlayer modes. [ 129 ] The peak position of ≈314 cm −1 (A1 mode) did not change when the thickness of SnS 2 was tuned. However, the peak intensity decreased with as the thickness decreased, particularly from 1L to 3L.…”