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Event Details

SEMINAR: "Ripples and Warping of Graphene: A Theoretical Study," by Umesh Waghmare, Theoretical Scie

May 11 @ 1:30 PM - 2:30 PM - BRK 2001

We use first-principles density functional theory based analysis to
understand formation of ripples in graphene and related 2-D materials.
For an infinite graphene, we show that ripples are linked with a low
energy branch of phonons that exhibits quadratic dispersion at long
wave-lengths. Many modes in this branch become unstable as a function of
compressive strain and rippling occurs in a way similar to a structural
phase transition. We use a simple model to develop understanding of this

At the nanoscale, we find that Stone-Wales (SW) defects play an
interesting role. Such defects lead to stresses in a graphene
nano-ribbon (GNR) that are relieved through its deformation or
reconstruction at the edges. Due to a markedly anisotropic interaction
among the SW defects, the resulting localized deformation depends
sensitively on the orientation of an SW defect with respective to the
edge of the GNR.

Work is done in collaboration with K. P. S. S. Hembram, Sandeep Kumar,
Somnath Bhowmick and Professor C. N. R. Rao.
Umesh Waghmare received his B. Tech. degree in Engineering Physics in
1990 from the Indian Institute of Technology, Bombay. He received his
M.S. and M. Phil. degrees in Applied Physics in 1994 and his Ph. D. in
1996, all from Yale University. Umesh’s career started as a
post-doctoral fellow in the Department of Physics at Harvard University
from June 1996 to May 1999. From June 1999 to May 2000, he was a
visiting scholar in the Department of Chemistry and Chemical Biology and
from June 1999 to June 2000, was a research associate in the Department
of Physics, both at Harvard University. In May 2000, he was a faculty
fellow; in 2005, an Associate Professor; and in 2009 became a Professor
within the Jawaharial Nehru Centre for Advance Scientific Research
(JNCASR). He has received several academic and professional honors. His
research interests within his group has three-fold goals: (1) understand
aspects of chemical bonding and microscopic couplings that are essential
to the specific properties of a material; (2) obtain information about
the atomistic structure and electronic states that may be hard to access
experimentally; and (3) design new materials or modify existing
materials to yield desired properties, or narrow down the choices of new
materials for design by experiments.

Host: Tim Fisher (, 45627)

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