Anomalous Raman spectra and thickness-dependent electronic properties of WSe2
By H. Sahin, S. Tongay, S. Horzum, W. Fan, Jian Zhou, J. Li, Junqiao Wu, François M. Peeters. 2013
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Typical Raman spectra of transition metal dichalcogenides (TMDs) display two prominent peaks, E2g and A1g, that are well separated from each other. We find that these modes are degenerate in bulk WSe2 yielding one single Raman peak. As the dimensionality is lowered, the observed peak splits in two as a result of broken degeneracy. In contrast to our experimental findings, our phonon dispersion calculations reveal that these modes remain degenerate independent of the number of layers. Interestingly, for minuscule biaxial strain the degeneracy is preserved but once the crystal symmetry is broken by uniaxial strain, the degeneracy is lifted. Our calculated phonon dispersion for uniaxially strained WSe2 shows a perfect match to the measured Raman spectrum which suggests that uniaxial strain exists in WSe2 flakes possibly induced during the sample preparation and/or as a result of interaction between WSe2 and the substrate. Furthermore, we find that WSe2 undergoes an indirect to direct bandgap transition from bulk to monolayers which is ubiquitous for semiconducting TMDs. These results not only allow us to understand the vibrational properties of WSe2 but also provides detailed insight to their physical properties.
Subfields: Materials Chemistry
View Paper: https://www.semanticscholar.org/paper/b850f79f973c512ad29e57903da4987f50726b0a
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In Materials Chemistry
Citations in the corpus
- WSe 2 2D p‐type semiconductor‐based electronic devices for information technology: Design, preparation, and applications (2020, background): “…number of WSe 2 can be distinguished with various characterization tools, such as photo-luminescence spectroscopy, 211-213 Raman spectroscopy, 7,196,214 scanning electron microscopy, 215,216 transmission electron microscopy, 217 electron diffraction, 218-222 scanning tunneling microscopy,…”