Towards large scale integration of MoS/graphene heterostructure with ALD-grown MoS.

In the pursuit of ultrathin and highly sensitive photodetectors, a promising approach involves leveraging the combination of light-sensitive two-dimensional (2D) semiconducting transition-metal dichalcogenides, such as MoSand the high electrical conductivity of graphene. Over the past decade, exfoliated 2D materials and electron-beam lithography have been used extensively to demonstrate feasibility on single devices. But for these devices to be used in the real-world systems, it is necessary to demonstrate good device performance similar to lab-based devices with repeatability of the results from device to device and a path to large scale manufacturing.

Stabilizing an ultrathin MoS layer during electrocatalytic hydrogen evolution with a crystalline SnO underlayer.

Amorphous MoS has been investigated abundantly as a catalyst for hydrogen evolution. Not only its performance but also its chemical stability in acidic conditions have been reported widely. However, its adhesion has not been studied systematically in the electrochemical context.

Electrocatalytic Performance of Titania Nanotube Arrays Coated with MoS by ALD toward the Hydrogen Evolution Reaction.

The electrochemical splitting of water provides an elegant way to store renewable energy, but it is limited by the cost of the noble metals used as catalysts. Among the catalysts used for the reduction of water to hydrogen, MoS has been identified as one of the most promising materials as it can be engineered to provide not only a large surface area but also an abundance of unsaturated and reactive coordination sites. Using Mo[NMe] and HS as precursors, a desired thickness of amorphous MoS can be deposited on TiO nanotubes by atomic layer deposition.

A novel 2-step ALD route to ultra-thin MoS films on SiO through a surface organometallic intermediate.

The lack of scalable-methods for the growth of 2D MoS crystals, an identified emerging material with applications ranging from electronics to energy storage, is a current bottleneck against its large-scale deployment. We report here a two-step ALD route with new organometallic precursors, Mo(NMe) and 1,2-ethanedithiol (HS(CH)SH) which consists in the layer-by-layer deposition of an amorphous surface Mo(iv) thiolate at 50 °C, followed by a subsequent annealing at higher temperature leading to ultra-thin MoS nanocrystals (∼20 nm-large) in the 1-2 monolayer range. In contrast to the usual high-temperature growth of 2D dichalcogenides, where nucleation is the key parameter to control both thickness and uniformity, our novel two-step ALD approach enables chemical control over these two parameters, the growth of 2D MoS crystals upon annealing being ensured by spatial confinement and facilitated by the formation of a buffer oxysulfide interlayer.