In this article we review the WS2 Raman spectrum. Its Raman spectrum is quite similar to it’s dichalcogenide neighbour material, molybdenum.

The Raman spectrum of bulk WS2 has two prominent peaks: an in-plane (E2g) mode located around 350cm-1 and an out-of-plane (A1g) mode which is located at 420cm-1. The in-plane mode corresponds to the sulphur atoms vibrating in one direction and the tungsten atom in the other, while the out-of-plane mode is a mode of just the sulphur atoms vibrating out-of-plane.

As WSbecomes single-layer these two modes evolve with thickness. The in-plane Raman mode upshifts, although very slowly (less than 1 cm-1), and the out-of-plane mode downshifts to 417cm-1. This means that monolayer WS2 can be reliably identified by the shift of the A1g mode.

Perhaps a more direct way of monitoring the transition to monolayer, in the case of WS2, is the observation of its photoluminescence. While bulk does not show any photoluminescence, as a result of its indirect band gap nature, monolayer shows strong and sharp photoluminesence which is a signature of a transition to monolayer state.

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[/fusion_builder_column][fusion_builder_column type=”1_1″ background_position=”left top” background_color=”” border_size=”” border_color=”” border_style=”solid” spacing=”yes” background_image=”” background_repeat=”no-repeat” padding=”” margin_top=”0px” margin_bottom=”0px” class=”” id=”” animation_type=”” animation_speed=”0.3″ animation_direction=”left” hide_on_mobile=”no” center_content=”no” min_height=”none”][1] Lattice dynamics in mono- and few-layer sheets of WS2 and WSe2 Zhao et al. Nanoscale, 2013

[2]  Identification of individual and few layers of WS2 using Raman Spectroscopy Berkdemir et al. Scientific Reports, 2013

[3] Electrical and optical characterization of atomically thin WS2 Georgiou et al. Dalton Transaction, 2014


Categories: Research


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