11 research outputs found
Simulated Nanoscale Peeling Process of Monolayer Graphene Sheet - Effect of Edge Structure and Lifting Position
The nanoscale peeling of the graphene sheet on the graphite surface is numerically studied by molecular mechanics simulation. For center-lifting case, the successive partial peelings of the graphene around the lifting center appear as discrete jumps in the force curve, which induce the arched deformation of the graphene sheet. For edge-lifting case, marked atomic-scale friction of the graphene sheet during the nanoscale peeling process is found. During the surface contact, the graphene sheet takes the atomic-scale sliding motion. The period of the peeling force curve during the surface contact decreases to the lattice period of the graphite. During the line contact, the graphene sheet also takes the stick-slip sliding motion. These findings indicate the possibility of not only the direct observation of the atomic-scale friction of the graphene sheet at the tip/surface interface but also the identification of the lattice orientation and the edge structure of the graphene sheet
Time-Lapse Nanoscopy of Friction in the Non-Amontons and Non-Coulomb Regime
Originally discovered by Leonard
da Vinci in the 15th century,
the force of friction is directly proportional to the applied load
(known as Amontons’ first law of friction). Furthermore, kinetic
friction is independent of the sliding speed (known as Coulomb’s
law of friction). These empirical laws break down at high normal pressure
(due to plastic deformation) and low sliding speed (in the transition
regime between static friction and kinetic friction). An important
example of this phenomenon is friction between the asperities of tectonic
plates on the Earth. Despite its significance, little is known about
the detailed mechanism of friction in this regime due to the lack
of experimental methods. Here we demonstrate in situ time-lapse nanoscopy
of friction between asperities sliding at ultralow speed (∼0.01
nm/s) under high normal pressure (∼GPa). This is made possible
by compressing and rubbing a pair of nanometer-scale crystalline silicon
anvils with electrostatic microactuators and monitoring its dynamical
evolution with a transmission electron microscope. Our analysis of
the time-lapse movie indicates that superplastic behavior is induced
by decrystallization, plastic deformation, and atomic diffusion at
the asperity-asperity interface. The results hold great promise for
a better understanding of quasi-static friction under high pressure
for geoscience, materials science, and nanotechnology