New First Order Raman-active Modes in Few Layered Transition Metal Dichalcogenides

• Published in: Scientific reports Vol. 4; no. 1; p. 4215
• Main Authors: Terrones, H., Corro, E. Del, Feng, S., Poumirol, J. M., Rhodes, D., Smirnov, D., Pradhan, N. R., Lin, Z., Nguyen, M. A. T., Elías, A. L., Mallouk, T. E., Balicas, L., Pimenta, M. A., Terrones, M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 27.02.2014; Nature Publishing Group
• Subjects: 140/133; 639/301/1034/1038; 639/766/119/1000/1018; Humanities and Social Sciences; multidisciplinary; Physics; Science; Splitting; Symmetry
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep04215

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. WSe 2 samples were synthesized and ab-initio calculations carried out. We calculated phonon dispersions and Raman-active modes in layered systems: WSe 2 , MoSe 2 , WS 2 and MoS 2 ranging from monolayers to five-layers and the bulk. First, we confirmed that as the number of layers increase, the E′, E″ and E 2g modes shift to lower frequencies and the A′ 1 and A 1g modes shift to higher frequencies. Second, new high frequency first order A′ 1 and A 1g modes appear, explaining recently reported experimental data for WSe 2 , MoSe 2 and MoS 2 . Third, splitting of modes around A′ 1 and A 1g is found which explains those observed in MoSe 2 . Finally, exterior and interior layers possess different vibrational frequencies. Therefore, it is now possible to precisely identify few-layered STMD.