Identification of individual and few layers of WS2 using Raman Spectroscopy

著者: Ayşe Berkdemir, Humberto R. Gutiérrez, Andrés R. Botello‐Méndez, Néstor Perea‐López, Ana Laura Elías, Chen-Ing Chia, Bei Wang, Vincent H. Crespi, Florentino Lopéz‐Urías, Jean‐Christophe Charlier, Humberto Terrones, Mauricio Terrones - Scientific Reports 2013 被引用: 1,568

The Raman scattering of single- and few-layered WS 2 is studied as a function of the number of S-W-S layers and the excitation wavelength in the visible range (488, 514 and 647 nm). For the three excitation wavelengths used in this study, the frequency of the A 1g (Γ) phonon mode monotonically decreases with the number of layers. For single-layer WS 2 , the 514.5 nm laser excitation generates a second-order Raman resonance involving the longitudinal acoustic mode (LA(M)). This resonance results from a coupling between the electronic band structure and lattice vibrations. First-principles calculations were used to determine the electronic and phonon band structures of single-layer and bulk WS 2. The reduced intensity of the 2LA mode was then computed, as a function of the laser wavelength, from the fourth-order Fermi golden rule. Our observations establish an unambiguous and nondestructive Raman fingerprint for identifying single- and few-layered WS 2 films.