Transition metal dichalcogenides : strain engineering and exfoliation of large-area monolayers

Transition metal dichalcogenides (TMDs) like MoS2 and WSe2 are a class of layered materials with applications for electronic and optoelectronic devices. They can be scaled down to a uniform atomically thin monolayer (~ 0.65 nm) with naturally passivated surfaces. This property along with the presence of large bandgaps and a low dielectric constant make them strong candidates for the channel material in sub-5 nm gate length transistors.

Strain engineering of the electronic bandstructure is used in modern Si MOSFETs to improve device mobility and performance. In this talk, we will discuss the strain engineering of TMDs using the example of multilayer WSe2, which undergoes an indirect to direct bandgap transition on the application of uniaxial tensile strain. We will also discuss the large area exfoliation of monolayer TMDs using a gold-mediated exfoliation technique. The strong affinity of gold to chalcogens is used to exfoliate monolayers upto ~10000X larger in area as compared to the tape exfoliation method originally used for graphene. The large-area monolayers thus obtained, enable large-area electronics using TMDs and further research using characterization techniques earlier not available due to the small size of tape-exfoliated monolayers.

Bio:
Sujay Desai is a PhD candidate in the Electrical Engineering and Computer Sciences department at the University of California Berkeley and a recipient of the Lam Research Graduate Fellowship and EECS Departmental Fellowship. He graduated from IIT Bombay in 2013 with a B.Tech (Honors) in Electrical Engineering, M.Tech in Microelectronics and a Minor in Computer Science and Engineering, and was awarded the Institute Silver medal and Bharat Fritz Werner Scholarship at the 51st IIT Bombay convocation. His current research focuses on the devicephysics and materials properties of transition metal dichalcogenides and their applications in transistors at the ultimate scaling limit.