Physics Dept - MtSE Joint Seminar

December 18, Monday

Synthesis of 2D Transition Metal Dichalcogenides beyond Graphene

Prof. Eui-Hyeok Yang

Dept. of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ

(Device Physics/Materials Science, Host: Federici)

*TALK*: Tiernan 409, 11:30am - 12:30pm

(* SPECIAL TIME/ROOM and NO TEA TIME *)

*LUNCH*: Tiernan 406, 12:30pm - 4pm

There has been a growing interest in two dimensional (2D) crystals beyond graphene, exhibiting novel properties and potential applications in next generation electronic and photonic devices. For example, 2D materials exhibit strong in-plane bonding along with weak out-of-plane bonding, enabling the exfoliation of the materials into single crystal, 2D flakes with atomic level thickness. Graphene has superior properties, including high carrier mobility, ultrahigh surface area and excellent thermal conductivity. Whereas the lack of a band gap is a critical limitation for the use of graphene in electronic devices, monolayer semiconducting transition metal dichalcogenides (TMDs) have shown highly promising prospects in electronics and optoelectronics. Therefore, non-graphene 2D atomic layers, such as hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMDs), have been integrated into research scale devices, thereby probing mechanical, chemical, electrical and optoelectrical functions. I will present our investigation of chemical vapour deposition (CVD)-growth, achieving localized, patterned, single crystalline or polycrystalline monolayers of TMDs, including MoS2, WS2, WSe2 and MoSe2, as well as their heterostructures. We particularly focus on enabling the fabrication of epitaxially grown TMDs on other van der Waals materials towards synthesizing TMDs with an ultralow-defect density. We perform microscopic and macroscopic material characterization to provide predictive strategies for TMD growth and in turn, illuminate the role of dissimilar 2D substrates in the prevention of interior defects in TMDs. This research thus provides a detailed observation of the substrate dependent oxidation and anti-oxidation behaviours of TMDs, which corroborate the role of underlying 2D layers in reducing interior defects in TMDs during the growth. We furthermore demonstrate the growth of TMD homobilayers with well-ordered stacking angles by controlling edge structures of the underlying TMD layer. Other related projects include modelling to prevent the anomalies encountered in topographic images of TMD monolayers in dynamic atomic force microscopy, and elucidating the effect of TMD surfaces and their geometric arrangements on cellular morphology and adhesion. We also investigate other nanomaterials, including vertically aligned carbon nanotubes for stretchable supercapacitors. Building on these results, our next step is to combine 2D materials with flexible substrates toward next generation wearable devices. Currently my group is collaborating with many top research groups in the US and around the world.