Second-order resonant Raman scattering in single-layer tungsten disulfideWS2

Abstract

Resonant Raman spectra of single layer WS2 flakes are presented. A second order Raman peak (2LA) appears under resonant excitation with a separation from the E 1 2g mode of only 4cm −1 . Depending on the intensity ratio and the respective line widths of these two peaks, any analysis which neglects the presence of the 2LA mode can lead to an inaccurate estimation of the position of the E 1 2g mode, leading to a potentially incorrect assignment for the number of layers. Our results show that the intensity of the 2LA mode strongly depends on the angle between the linear polarization of the excitation and detection, a parameter which is neglected in many Raman studies.

Controlled synthesis and mechanism of large-area WS2 flakes by low-pressure chemical vapor deposition

“…Here, the E 1 2g mode exhibited slight blueshifts, while the A 1g modes exhibited opposite shifts when the temperature of substrate was decreased. A secondorder mode of longitudinal acoustic phonon 2LA(M) is also observed in each spectra at 351 cm -1 approximately [32,35]. Furthermore, the frequency difference (D ¼ A 1g À E 1 2g ) between E 1 2g and A 1g peak increases from *63 to *68 cm -1 with the decrease in substrate temperature, indicating the layer number of WS 2 flakes gradually increased [36], which is in good agreement with the AFM measurements.…”

“…4j [32,33]. Two first-order modes characteristic Raman peaks E 1 2g and A 1g represent the in-plane vibrations of W and S atoms, and also the out-of plane vibrations of S atoms, respectively [33][34][35]. Here, the E 1 2g mode exhibited slight blueshifts, while the A 1g modes exhibited opposite shifts when the temperature of substrate was decreased.…”

Controlled engineering of WS2 nanosheets–CdS nanoparticle heterojunction with enhanced photoelectrochemical activity

“…The E 2g 2 mode is observable only at very low frequencies and not accessible for conventional Raman apparatuses [37]. Therefore, the Raman spectra of WS 2 are dominated by the out-of-plane A 1g and the inplane E 2g 1 modes.…”

Temporal and spatial valley dynamics in two-dimensional semiconductors probed via Kerr rotation

“…However, the slow decay component of 70 ps for monolayer WSe 2 has a different origin than for monolayer MoS 2 . One possible explanation could be related to the existence of an intervalley dark exciton state [33][34][35], where a hole in the valence band of the +K valley is radiatively recombined with an electron in the conduction band of the -K valley upon optical excitation. However, as has been observed in previous PL measurements [33], an important indication of the existence of dark excitons is that the PL intensity increases as the temperature increases, which is the opposite trend to our previous observation [29].…”