MSE Colloquium - Dr. Manish Chhowalla
Date: May 02, 2014 from 11:00 am to 12:00 pm EDT
Location: Room 214, S.W. Mudd
Contact: For further information regarding this event, please contact Wesley Hattan by sending email to or by calling 2128547860.
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Phase Engineering in 2D Transition Metal Dichalcogenides

Manish Chhowalla

Rutgers University

Two-dimensional transition metal dichalcogenides (2D TMDs) - whose generalized formula is MX2, where M is a transition metal of groups 4-7 and X is a chalcogen - exhibit versatile chemistry and consist of a family of over 40 compounds that range from complex metals to semiconductors to insulator. Complex metal TMDs assume the 1T phase where the transition metal atom coordination is octahedral. The 2H phase is stable in semiconducting TMDs where the coordination of metal atoms is trigonal prismatic. Unlike mechanical exfoliation and chemical vapor deposition, chemical exfoliation of semiconducting layered TMDs yields monolayered nanosheets with heterogeneous atomic structure consisting of metallic (1T) and semiconducting (2H)phases (Figure 1). Metal (1T phase) to semiconductor (2H phase) transition canbe achieved via mild annealing of exfoliated materials. Semiconductor to metal transitions can be achieved via chemistry. The 1T phase in semiconducting TMDs has scarcely been studied but it deserves urgent attention as it exhibits promise as a hydrogen evolution catalyst and as contact electrode in electronic devices. We will describe these phase transitions in semiconducting TMDs and provide examples of how we have learned to exploit them for enhanced catalytic and electronic performance.