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Distinct photoluminescence and Raman spectroscopy signatures for identifying highly crystalline WS2 monolayers produced by different growth methods

Published online by Cambridge University Press:  08 March 2016

Amber McCreary
Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
Ayse Berkdemir
Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA; and Nanotechnology Research Center and Kayseri Vocational College, Erciyes University, Kayseri 38039, Turkey
Junjie Wang
Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
Minh An Nguyen
Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
Ana Laura Elías
Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
Néstor Perea-López
Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
Kazunori Fujisawa
Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
Bernd Kabius
Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
Victor Carozo
Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
David A. Cullen
Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
Thomas E. Mallouk
Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
J. Zhu
Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
Mauricio Terrones*
Department of Physics and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, Pennsylvania 16802, USA; Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA; Department of Materials Science & Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA; and Research Center for Exotic Nanocarbons, Shinshu University, Nagano 380-8553, Japan
a) Address all correspondence to this author. e-mail:
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Transition metal dichalcogenides such as WS2 show exciting promise in electronic and optoelectronic applications. Significant variations in the transport, Raman, and photoluminescence (PL) can be found in the literature, yet it is rarely addressed why this is. In this report, Raman and PL of monolayered WS2 produced via different methods are studied and distinct features that indicate the degree of crystallinity of the material are observed. While the intensity of the LA(M) Raman mode is found to be a useful indicator to assess the crystallinity, PL is drastically more sensitive to the quality of the material than Raman spectroscopy. We also show that even exfoliated crystals, which are usually regarded as the most pristine material, can contain large amounts of defects that would not be apparent without Raman and PL measurements. These findings can be applied to the understanding of other two-dimensional heterostructured systems.

Invited Articles
Copyright © Materials Research Society 2016 

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