NANOSCALE FRICTION ANISOTROPY IN GRAPHENE
Clara M. Almeida1, Rodrigo Prioli2, Benjamin Fragneaud3, Luiz Gustavo
Cançado4, Ricardo Paupitz5, Douglas S. Galvão6, Marcelo De Cicco1, Rodrigo B.
Capaz1,7 and Carlos A. Achete1
1
Divisão de Metrologia de Materiais, Instituto Nacional de Metrologia, Normalização e
Qualidade Industrial (INMETRO) Brazil.
2
Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, Brazil.
3
Departamento de Física, ICE, Universidade Federal de Juiz de Fora, Minas Gerais, Brazil
4
Departamento de Física, Universidade Federal de Minas Gerais, Brazil.
5
Departamento de Física, Universidade Estadual Paulista, Rio Claro, Brazil
6
Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, Brazil
7
Instituto de Física, Universidade Federal do Rio de Janeiro
Presenting author: Rodrigo Prioli; [email protected]
In this presentation, a study on the nanoscale friction process between an atomic
force microscope tip and monolayer graphene is presented. We analyze the differences on
the dissipation mechanisms along distinct crystallographic directions. A lattice resolution
atomic force microscopy technique was used to determine the main crystallographic
directions in graphene (Fig.1). The graphene flakes were prepared in ambient conditions
by micromechanical cleavage of bulk graphite onto a 300 nm SiO2 layer on top of a Si
substrate. All nanoscale friction measurements were performed in a friction force
microscopy mode (FFM) at ambient air with 50% of relative humidity and at 20°C. The
FFM images showing atomic-scale lattice resolution were acquired using silicon nitride Vshape cantilevers, with tip radii of 20 nm and calibrated normal and lateral spring
constants of 0.40 ± 0.01 N/m and 85.4 ± 4.2 N/m respectively. During quantitative FFM
measurements, the scanning direction was kept perpendicular to the cantilever main axis
in such a way that the friction force experienced by the tip was measured by the lateral
torsion of the cantilever. The microscope was calibrated for each tip used, and the lateral
force was obtained from the product between the cantilever’s lateral spring constant and
the lateral tangential displacement of the tip measured in the position sensitivity
photodetector.
Figure 1. Tapping mode AFM topography in (a) and FFM
image in (b). (c) FFT for the zigzag ; 15° misaligned with
the zigzag; and the armchair direction. (d) the periodicity
measured from FFT .
Figure 2. AFM tip scanning over graphene
(top). Energy dissipated along the zigzag
and armchair crystallographic directions.
Our results show that the motion of the tip over the graphene lattice strongly
depends on the crystallographic direction as the microscope tip moves in a discontinuous
stick and slip way. During tip movement friction forces responsible for tip sticking were
observed to increase. The effective lateral contact stiffness between the graphene and the
tip was found to be higher along the armchair direction than along the zigzag direction.
More specifically, we find that energy dissipation along the armchair direction is ~ 80%
higher than along the zigzag direction (Fig.2). This result is different from that found on
highly oriented pyrolytic graphite (HOPG), where energy dissipation along the armchair
direction is ~ 15% higher than along the zigzag direction. Fully atomistic molecular
dynamics and Tomlinson model simulations were also used to gain further insights on
these phenomena. These results contribute to understanding the mechanisms of energy
dissipation due to friction in graphene, which depends on the graphene crystallographic
direction, opening new possibilities for the design of novel nanomechanical systems
involving single layer materials.