Direct Bandgap Transition in Many‐Layer MoS2 by Plasma‐Induced Layer Decoupling. (14th January 2015)

• Record Type: Journal Article
• Authors: Dhall, Rohan; Neupane, Mahesh R.; Wickramaratne, Darshana; Mecklenburg, Matthew; Li, Zhen; Moore, Cameron; Lake, Roger K.; Cronin, Stephen
• Is Part Of: Advanced materials. Volume 27:Number 9(2015)
• Page Start: 1573
• Page End: 1578
• Publication Date: 2015-01-14
• Subjects: Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adma.201405259
• Languages: English
• ISSNs: 0935-9648

Abstract

<abstract abstract-type="main" xml:lang="en"> <title> <x xml:space="preserve">Abstract</x> </title> <p>We report a robust method for engineering the optoelectronic properties of many‐layer MoS<sub>2</sub> using low‐energy oxygen plasma treatment. Gas phase treatment of MoS<sub>2</sub> with oxygen radicals generated in an upstream N<sub>2</sub>–O<sub>2</sub> plasma is shown to enhance the photoluminescence (PL) of many‐layer, mechanically exfoliated MoS<sub>2</sub> flakes by up to 20 times, without reducing the layer thickness of the material. A blueshift in the PL spectra and narrowing of linewidth are consistent with a transition of MoS<sub>2</sub> from indirect to direct bandgap material. Atomic force microscopy and Raman spectra reveal that the flake thickness actually increases as a result of the plasma treatment, indicating an increase in the interlayer separation in MoS<sub>2</sub>. Ab initio calculations reveal that the increased interlayer separation is sufficient to decouple the electronic states in individual layers, leading to a transition from an indirect to direct gap semiconductor. With optimized plasma treatment parameters, we observed enhanced PL signals for 32 out of 35 many‐layer MoS<sub>2</sub> flakes (2–15 layers) tested, indicating that this method is robust and scalable. Monolayer MoS<sub>2</sub>, while direct bandgap, has a small optical density, which limits its potential use in practical devices. The results presented here provide a material with the direct bandgap of monolayer MoS<sub>2</sub>, without reducing sample thickness, and hence optical density.</p> </abstract>