Identifying the number of WS2 layers via Raman and photoluminescence spectrum

Abstract

Abstract:Recently, two-dimensional atomic layers of transition metal dichalcogenides (TMDs) have drawn more attention because of their remarkable electronic and optical properties. How to effectively identify the number of TMDs layers becomes an important issue. Here, we report the determination of the number of tungsten disulfide (WS 2 ) layers using Raman scattering and photoluminescence (PL) spectrum. Under the excitation of 532 nm laser, the Raman scattering of WS 2 shows rich spectrum information. With the number of layers increase, the peak of E 1 2g (Γ) phonon mode of WS 2 redshifts while the peak of A 1g (Γ) blue shifts. For PL measurements, monolayer WS 2 exhibits a performance of direct-bandgap. As the number of layers change from three to single, the PL peak intensity of WS 2 increases, and the peak shifts to the short wavelength. Raman and PL mapping show coincident results. Our study establishes a systematical, noninvasive fingerprint path to identify different layers WS 2 using Raman and PL spectrum simultaneously.Introduction.

Investigating the phonon line shapes of TMDs: An analytical approach

“…The effect of the number of layers ( n ) on the Raman spectra of TMDs, especially WS 2 and MoS 2 , is extensively documented and is attributed to interlayer interactions and the rise in restoring force with the number of layers, and the dielectric screening of long‐range coulombic interactions 15 . These manifest as shifts in the peak position of the phonon line shape: a red shift in the A 1 g mode and a blue shift in the mode with decreasing number of layers 6,15,23–32 . In most of the reported Raman spectra of TMDs, 25,29,30,32 there is an asymmetric broadening of the line shape with decreasing n in addition to the shift.…”

“…Thus, understanding the phonon behavior in these low‐dimensional systems could lead to phonon engineering to optimize electronic and optical properties. There are extensive reports on phonon behavior in TMDs 6,23–35 . Most of them have focused on the effect of the number of layers on the phonon line shape 6,23–32 .…”

“…There are extensive reports on phonon behavior in TMDs 6,23–35 . Most of them have focused on the effect of the number of layers on the phonon line shape 6,23–32 . However, depending on the nature of the TMD material and the Raman measurement parameters, other processes such as the phonon confinement effect, the disorder‐induced effect, the inhomogeneous laser heating effect, and the Breit – Wigner – Fano (BWF) effect can drastically modify the phonon line shape.…”

Optimisation of processing conditions during CVD growth of 2D WS2 films from a chloride precursor

“…It is reported in the literature that these three Raman peaks will shift as the layer thickness is reduced [23,[46][47][48]. The A 1g peak redshifts, whereas the 2LA and E 1 2g peaks slightly blue shift, and Berkdemir et al demonstrate that a separation between the A 1g and E 1 2g of 62 cm -1 is indicative of a WS 2 monolayer [46,[48][49][50]. For the spectrum of Fig.…”

Atomically Thin Semiconducting Transition-Metal Dichalcogenides: From Synthesis to Electro-Optical Properties

“…Moreover, the first order in-plane mode E 1 2g shows redshifts and the out-of-plane A 1g shows blueshifts while increasing the number of layers. The difference in peak position between them in the largest triangle is 61.1 cm −1 , for the middle triangle is 63.2 cm −1 , and for the smallest triangle, it is 64 cm −1 which is the confirmation of monolayer, bilayer and trilayer regions [45,186]. photoluminescence from the three layers.…”