Lubricity, a phenomenon which enables
the ease of motion of objects,
and wear resistance, which minimizes material damage or degradation,
are important fundamental characteristics for sustainable technology
developments. Ultrathin coatings that promote lubricity and wear resistance
are of huge importance for a number of applications, including magnetic
storage and micro-/nanoelectromechanical systems. Conventional ultrathin
coatings have, however, reached their limit. Graphene-based materials
that have shown promise to reduce friction and wear have many intrinsic
limitations such as high temperature and substrate-specific growth.
To address these concerns, a great deal of research is currently ongoing
to optimize graphene-based materials. Here we discover that angstrom-thick
carbon (8 Å) significantly reduces interfacial friction and wear.
This lubricant shows ultrahigh optical transparency and can be directly
deposited on a wide range of surfaces at room temperature. Experiments
combined with molecular dynamics simulations reveal that the lubricating
efficacy of 8 Å carbon is further improved via interfacial nitrogen.
Using a q+ atomic force microscopy
at low temperature, a sexiphenyl
molecule is slid across an atomically flat Ag(111) surface along the
direction parallel to its molecular axis and sideways to the axis.
Despite identical contact area and underlying surface geometry, the
lateral force required to move the molecule in the direction parallel
to its molecular axis is found to be about half of that required to
move it sideways. The origin of the lateral force anisotropy observed
here is traced to the one-dimensional shape of the molecule, which
is further confirmed by molecular dynamics simulations. We also demonstrate
that scanning tunneling microscopy can be used to determine the comparative
lateral force qualitatively. The observed one-dimensional lateral
force anisotropy may have important implications in atomic scale frictional
phenomena on materials surfaces.
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