Version 2 2021-01-28, 15:33Version 2 2021-01-28, 15:33
Version 1 2021-01-25, 21:43Version 1 2021-01-25, 21:43
journal contribution
posted on 2021-01-28, 15:33authored byManoj Tripathi, Frank Lee, Antonios Michail, Dimitris Anestopoulos, James G. McHugh, Sean P. Ogilvie, Matthew J. Large, Aline Amorim Graf, Peter J. Lynch, John Parthenios, Konstantinos Papagelis, Soumyabrata Roy, M. A. S. R. Saadi, Muhammad M. Rahman, Nicola Maria Pugno, Alice A. K. King, Pulickel M. Ajayan, Alan B. Dalton
Two-dimensional
materials such as graphene and molybdenum disulfide
are often subject to out-of-plane deformation, but its influence on
electronic and nanomechanical properties remains poorly understood.
These physical distortions modulate important properties which can
be studied by atomic force microscopy and Raman spectroscopic mapping.
Herein, we have identified and investigated different geometries of
line defects in graphene and molybdenum disulfide such as standing
collapsed wrinkles, folded wrinkles, and grain boundaries that exhibit
distinct strain and doping. In addition, we apply nanomechanical atomic
force microscopy to determine the influence of these defects on local
stiffness. For wrinkles of similar height, the stiffness of graphene
was found to be higher than that of molybdenum disulfide by 10–15%
due to stronger in-plane covalent bonding. Interestingly, deflated
graphene nanobubbles exhibited entirely different characteristics
from wrinkles and exhibit the lowest stiffness of all graphene defects.
Density functional theory reveals alteration of the bandstructures
of graphene and MoS2 due to the wrinkled structure; such
modulation is higher in MoS2 compared to graphene. Using
this approach, we can ascertain that wrinkles are subject to significant
strain but minimal doping, while edges show significant doping and
minimal strain. Furthermore, defects in graphene predominantly show
compressive strain and increased carrier density. Defects in molybdenum
disulfide predominantly show tensile strain and reduced carrier density,
with increasing tensile strain minimizing doping across all defects
in both materials. The present work provides critical fundamental
insights into the electronic and nanomechanical influence of intrinsic
structural defects at the nanoscale, which will be valuable in straintronic
device engineering.