title: New first order Raman-active modes in few layered transition metal dichalcogenides.
abstract: Although the main Raman features of semiconducting transition metal dichalcogenides are well known for the monolayer and bulk, there are important differences exhibited by few layered systems which have not been fully addressed. WSe2 samples were synthesized and ab-initio calculations carried out. We calculated phonon dispersions and Raman-active modes in layered systems: WSe2, MoSe2, WS2 and MoS2 ranging from monolayers to five-layers and the bulk. First, we confirmed that as the number of layers increase, the E', E″ and E2g modes shift to lower frequencies, and the A'1 and A1g modes shift to higher frequencies. Second, new high frequency first order A'1 and A1g modes appear, explaining recently reported experimental data for WSe2, MoSe2 and MoS2. Third, splitting of modes around A'1 and A1g is found which explains those observed in MoSe2. Finally, exterior and interior layers possess different vibrational frequencies. Therefore, it is now possible to precisely identify few-layered STMD.
authors.affiliation: 1] Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, 104 Davey Lab, University Park, PA 16802, USA [2].
authors.forename: H
authors.initials: H
authors.lastname: Terrones
authors.affiliation: Universidade Federal de Minas Gerais, Departamento de Física, Av. Antônio Carlos, 6627 Caixa Postal 702 - cep 30.123-970 Belo Horizonte/MG - Brazil.
authors.forename: E
authors.initials: E
authors.lastname: Del Corro
authors.affiliation: Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, 104 Davey Lab, University Park, PA 16802, USA.
authors.forename: S
authors.initials: S
authors.lastname: Feng
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Poumirol
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA.
authors.forename: D
authors.initials: D
authors.lastname: Rhodes
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA.
authors.forename: D
authors.initials: D
authors.lastname: Smirnov
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA.
authors.forename: N R
authors.initials: NR
authors.lastname: Pradhan
authors.affiliation: Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, 104 Davey Lab, University Park, PA 16802, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Lin
authors.affiliation: Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, United States.
authors.forename: M A T
authors.initials: MA
authors.lastname: Nguyen
authors.affiliation: Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, 104 Davey Lab, University Park, PA 16802, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Elías
authors.affiliation: 1] Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, 104 Davey Lab, University Park, PA 16802, USA [2] Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, United States.
authors.forename: T E
authors.initials: TE
authors.lastname: Mallouk
authors.affiliation: National High Magnetic Field Laboratory, Florida State University, Tallahassee-FL 32310, USA.
authors.forename: L
authors.initials: L
authors.lastname: Balicas
authors.affiliation: Universidade Federal de Minas Gerais, Departamento de Física, Av. Antônio Carlos, 6627 Caixa Postal 702 - cep 30.123-970 Belo Horizonte/MG - Brazil.
authors.forename: M A
authors.initials: MA
authors.lastname: Pimenta
authors.affiliation: 1] Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, 104 Davey Lab, University Park, PA 16802, USA [2] Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, United States [3] Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, USA & Research Center for Exotic Nanocarbons (JST), Shinshu University, Wakasato 4-17-1, Nagano, 380-8553, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Terrones