Issue 20, 2013

Lattice dynamics in mono- and few-layer sheets of WS2 and WSe2

Abstract

Thickness is one of the fundamental parameters that define the electronic, optical, and thermal properties of two-dimensional (2D) crystals. Phonons in molybdenum disulfide (MoS2) were recently found to exhibit unique thickness dependence due to the interplay between short and long range interactions. Here we report Raman spectra of atomically thin sheets of WS2 and WSe2, isoelectronic compounds of MoS2, in the mono- to few-layer thickness regime. We show that, similar to the case of MoS2, the characteristic A1g and E2g1 modes exhibit stiffening and softening with increasing number of layers, respectively, with a small shift of less than 3 cm−1 due to large mass of the atoms. Thickness dependence is also observed in a series of multiphonon bands arising from overtone, combination, and zone edge phonons, whose intensity exhibit significant enhancement in excitonic resonance conditions. Some of these multiphonon peaks are found to be absent only in monolayers. These features provide a unique fingerprint and rapid identification for monolayer flakes.

Graphical abstract: Lattice dynamics in mono- and few-layer sheets of WS2 and WSe2

Supplementary files

Article information

Article type
Paper
Submitted
13 jun 2013
Accepted
05 ago 2013
First published
08 ago 2013

Nanoscale, 2013,5, 9677-9683

Lattice dynamics in mono- and few-layer sheets of WS2 and WSe2

W. Zhao, Z. Ghorannevis, K. K. Amara, J. R. Pang, M. Toh, X. Zhang, C. Kloc, P. H. Tan and G. Eda, Nanoscale, 2013, 5, 9677 DOI: 10.1039/C3NR03052K

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