Paper 2D+TF-WeM10
Atomic Layered Large Area Growth of 2D Monolayers Over Different Substrates

Wednesday, November 9, 2016, 11:00 am, Room 103B

Atomically-thin transition metal dichalcogenides (TMDCs) such as molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂) are of great interest because of their unique semiconducting and optical properties. For example, unlike graphene, MoS₂ is a semiconductor whose band gap changes from indirect (~1.2 eV) to direct (~1.85 eV) as the material thickness reduces from bulk to a monolayer state. This makes MoS₂ promising for numerous optoelectronic and biosensing applications. TMDC monolayers have originally been realized through exfoliation. However, the ability to synthesize monolayers over larger areas than those achievable with exfoliation requires scalable techniques such as chemical vapor deposition.

Here, we report the large area growth of monolayer thin films of TMDCs, such as MoS₂ and WS₂, by low-pressure chemical vapor deposition in an oxygen-free inert argon atmosphere. The growth of these materials has been compared on various substrates, such as basal plane sapphire, (001) SiO₂/Si, and GaN/sapphire substrates. The effects of growth conditions, including growth temperature, on the characteristics of the resulting material have been studied. The physical properties of the monolayers have been characterized using electron microscopy and atomic force microscopy to study their topology over the various substrates, in conjunction with confocal micro-Raman and micro-photoluminescence spectroscopy to correlatively assess their optical characteristics. The terahertz time domain spectroscopy of MoS₂ and WS₂ monolayer thin films will also be presented. We will further discuss the impact of these monolayer materials for robust optoelectronic device applications.