@article{d7aaaf829dcf4b09b042e19dbc874a67,
title = "Identification of individual and few layers of WS2 using Raman Spectroscopy",
abstract = "The Raman scattering of single- and few-layered WS2 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 WS2, 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 WS2. 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 WS2 films.",
author = "Ayse Berkdemir and Guti{\'e}rrez, \{Humberto R.\} and Botello-M{\'e}ndez, \{Andr{\'e}s R.\} and N{\'e}stor Perea-L{\'o}pez and El{\'i}as, \{Ana Laura\} and Chia, \{Chen Ing\} and Bei Wang and Crespi, \{Vincent H.\} and Florentino L{\'o}pez-Ur{\'i}as and Charlier, \{Jean Christophe\} and Humberto Terrones and Mauricio Terrones",
note = "Funding Information: M.T., H.R.G., A.L.E. and V.H.C. acknowledge funding from the U. S. Army Research Office MURI grant W911NF-11-1-0362. This research was partially supported by the Materials Simulation Center of the Materials Research Institute, the Research Computing and Cyberinfrastructure unit of Information Technology Services. MT acknowledges JST-Japan for funding the Research Center for Exotic NanoCarbons, under the Japanese regional Innovation Strategy Program by the Excellence. M.T. and V.H.C. also acknowledge support from a Penn State Center for Nanoscale Science Seed grant on 2-D Layered Materials (DMR-0820404). This publication was also supported by the Pennsylvania State University Materials Research Institute Nanofabrication Lab and the National Science Foundation Cooperative Agreement No. ECS-0335765. Electron microscopy characterization facilities within the Materials Research Institute at the Pennsylvania State University were also used for this research. A.R.B.M. and J.-C.C. acknowledge financial support from the F.R.S.-FNRS of Belgium. This research is directly connected to the ARC on « Graphene StressTronics » sponsored by the Communaut{\'e} Fran{\c c}aise de Belgique.",
year = "2013",
doi = "10.1038/srep01755",
language = "English (US)",
volume = "3",
journal = "Scientific reports",
issn = "2045-2322",
publisher = "Nature Research",
}