Materials Science and Engineering Colloquium
Date: March 13, 2015 from 11:00 am to 12:00 pm EDT
Location: Columbia University
Morningside Campus
S.W. Mudd, Room 214
Contact: For further information regarding this event, please contact Chris A Marianetti by sending email to chris.marianetti@columbia.edu or by calling 212-854-9478.
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Evan Reed

Stanford University

"Emergent Phase Change and Electromechanical Properties of Two-Dimensional and Few-Layer Materials"

Numerous engineering feats are being performed with the increasing array of single-layer and few-layer materials.  Some of the most dramatic accomplishments are enabled by properties that emerge only at the single or few-layer limit and are not found in bulk forms. I will discuss our efforts to elucidate several new and useful emergent properties of monolayer and few-layer materials.  Using and developing a variety of atomistic modeling methods, we have predicted that many of the commonly studied single-layer and few-layer transition metal dichalcogenide (TMD) materials (e.g. MoS2) exhibit substantive electromechanical coupling in the form of piezoelectric and flexoelectric-like effects, unlike their bulk parent crystals.1  I will describe the first recent observations of some of these effects in the laboratory by researchers at Columbia and elsewhere.
Single-layers of two-dimensional Mo- and W-dichalcogenide compounds differ from graphene in an important respect: they can potentially exist in more than one crystal structure.  Some of these monolayers exhibit hints of a poorly understood structural metal-to-semiconductor transition with the possibility of long metastable lifetimes.  If controllable, such a transition could bring an exciting new application space to monolayer materials. We have discovered that mechanical deformations provide a route to switching thermodynamic stability between a semiconducting and a metallic crystal structure in some of these monolayer materials.2  Our DFT-based calculations reveal that single-layer MoTe2 exhibits a phase boundary at a few percent tensile strain, accessible with standard experimental approaches.  The potential application space for this work ranges from information and energy storage to electronic and optical electronic devices.

Biography: Evan Reed is Assistant Professor of Materials Science and Engineering at Stanford University.  He received a B.S. in applied physics from Caltech (1998) and PhD. in physics from MIT (2003).  In 2004, he was an E. O. Lawrence Fellow and staff scientist at Lawrence Livermore National Laboratory before moving to Stanford in 2010.  Evan Reed's group focuses on theory and modeling of nanoscale materials for electronics and energy applications, and materials at conditions of extreme temperatures, pressures, and fields.  He is recipient of the DARPA Young Faculty Award and NSF CAREER award.

Joint work with:

Karel-Alexander N. Duerloo, Yao Li, Mitchell Ong,  Evan J. Reed
Department of Materials Science and Engineering, Stanford University
Web: http://www.stanford.edu/group/evanreed/index.html


References

1    Karel-Alexander N. Duerloo, Mitchell T. Ong, and Evan J. Reed,  Journal of Physical Chemistry Letters 3 (19), 2871 (2012);     Karel-Alexander N. Duerloo and Evan J. Reed,  Nano Letters 13 (4), 1681 (2013).
2    K.-A. Duerloo, Y. Li, and E. J. Reed,  Nature Communications 5, 4214 (2014).


Host: Chris Marianetti