Promoter-free synthesis of monolayer MoS2 by chemical vapour deposition

Abstract

Molybdenum disulphide (MoS₂), a graphene analogue, is emerging as an exciting material for future nanoelectronics due to its unique electronic transport properties. Here we report the large-scale and homogeneous synthesis of a high quality MoS₂ monolayer directly onto SiO₂ substrate by a facile seed promoter-free chemical vapour deposition (CVD) process. A piranha treatment process favourably reduces the surface free energy of the substrate for the incoming growth species to nucleate, thus paving a way for controlled layered growth via a Frank–van der Merve growth mode. A classical nucleation theory is explored to understand the layered and particle growth of MoS₂ with and without piranha treatment, respectively. By carefully tracking the piranha treatment and sulphurization time, the coverage of the MoS₂ monolayer can be extended to a centimeter scale with highly reproducible features. The electrocatalytic hydrogen evolution reaction (HER) using large-scale MoS₂ demonstrates excellent properties, with a turn-on potential of 0.15 V vs. RHE and a Tafel slope of 46 mV dec⁻¹. Our results confirm that piranha treatment provides an ideal platform for the controlled growth of large-scale monolayer MoS₂ on dielectric and semiconductor substrates, such as SiO₂ and Si, for device applications.