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American Chemical Society, ACS Nano, 6(7), p. 5235-5242, 2013

DOI: 10.1021/nn400971k

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Controlled Synthesis and Transfer of Large-Area WS2 Sheets: From Single Layer to Few Layers

This paper is available in a repository.
This paper is available in a repository.

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Abstract

The isolation of few-layered transition metal dichalcogenides has mainly been performed by mechanical and chemical exfoliation with very low yields. In this account, a controlled thermal reduction-sulfurization method is used to synthesize large area (~1cm2) WS2 sheets with thicknesses ranging from monolayers to a few layers. During synthesis, WOx thin films are first deposited on Si/SiO2 substrates, which are then sulfurized (under vacuum) at high temperatures (750-950°C). An efficient route to transfer the synthesized WS2 films onto different substrates such as quartz and transmission electron microscopy (TEM) grids has been satisfactorily developed using concentrated HF. Samples with different thicknesses have been analyzed by Raman spectroscopy, TEM, atomic force microscopy (AFM), and their photoluminescence properties have been evaluated. We demonstrated the presence of single-, bi- and few-layered WS2 on as-grown samples. It is well known that the electronic structure of these materials is very sensitive to the number of layers, ranging from indirect band-gap semiconductor in bulk phase to direct band-gap semiconductor in monolayers. This method has also proved successful in the synthesis of heterogeneous systems of MoS2 and WS2 layers, thus shedding light on the controlled production of hetero-layered devices out of transition metal chalcogenides.