New insights in the lattice dynamics of monolayers, bilayers, and trilayers of WSe2 and unambiguous determination of few-layer-flakes' thickness
De Luca, Marta (University of Basel)
Cartoixà Soler, Xavier (Universitat Autònoma de Barcelona. Departament d'Enginyeria Electrònica)
Martín-Sánchez, Javier (Universidad de Oviedo)
López-Suárez, Miquel (Institut de Ciència de Materials de Barcelona)
Trotta, Rinaldo (Università degli Studi di Roma "La Sapienza")
Rurali, Riccardo (Institut de Ciència de Materials de Barcelona)
Zardo, Ilaria (University of Basel)

Data:	2020
Descripció:	12 pàg.
Resum:	Among the most common few-layers transition metal dichalcogenides (TMDs), WSe2 is the most challenging material from the lattice dynamics point of view. Indeed, for a long time the main two phonon modes (A 1g and) have been wrongly assigned. In the last few years, these two modes have been properly interpreted, and their quasi-degeneracy in the monolayer has been used for its identification. In this work, we show that this approach has a limited validity and we propose an alternative, more general approach, based on multi-phonon bands. Moreover, we show and interpret all the peaks (about 40) appearing in the Raman spectra of monolayers, bilayers, and trilayers of WSe2 by combining experimental wavelength- and polarization-dependent Raman studies with density-functional theory calculations providing the phonon dispersions, the polarization-resolved first-order Raman spectra, and the two-phonon density of states. This complete study not only offers a method to distinguish between monolayers, bilayers, and trilayers with no need of optical images and atomic force microscopy, but it also sheds light on the interpretation of single and multi-phonon bands appearing in the inelastic light scattering experiments of layered WSe2; some of these bands were never observed before, and some were observed and uncertainly assigned. We promote the full understanding of the lattice dynamics of this material that is crucial for the realization of optoelectronics devices and of novel phononic metamaterials, such as TMDs superlattices.
Ajuts:	Agencia Estatal de Investigación MAT2017-90024-P Ministerio de Economía y Competitividad SEV-2015-0496 Agència de Gestió d'Ajuts Universitaris i de Recerca 2017/SGR-1506 Ministerio de Economía y Competitividad TEC2015-67462-C2-1-R Agencia Estatal de Investigación RTI2018-097876-B-C21 European Commission 785219 European Commission 679183
Drets:	Aquest material està protegit per drets d'autor i/o drets afins. Podeu utilitzar aquest material en funció del que permet la legislació de drets d'autor i drets afins d'aplicació al vostre cas. Per a d'altres usos heu d'obtenir permís del(s) titular(s) de drets.
Llengua:	Anglès
Document:	Article ; recerca ; Versió sotmesa a revisió
Matèria:	DFT calculations ; Monolayers ; Raman spectroscopy ; Second-order Raman ; Transition metal dichalcogenides ; Tungsten diselenide
Publicat a:	2D materials, Vol. 7, Núm. 2 (April 2020) , art. 25004, ISSN 2053-1583

DOI: 10.1088/2053-1583/ab5dec

Preprint 21 p, 1.3 MB

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