Nanotube Motion on Layered Materials: A Registry Perspective

At
dry and clean material junctions of rigid materials the corrugation
of the sliding energy landscape is dominated by variations of Pauli
repulsions. These occur when electron clouds centered around atoms
in adjacent layers overlap as they slide across each other. In such
cases there exists a direct relation between interfacial surface (in)­commensurability
and superlubricity, a frictionless and wearless tribological state.
The Registry Index is a purely geometrical parameter that quantifies
the degree of interlayer commensurability, thus providing a simple
and intuitive method for the prediction of sliding energy landscapes
at rigid material interfaces. In the present study, we extend the
applicability of the Registry Index to nonparallel surfaces, using
a model system of nanotube motion on flat hexagonal materials. Our
method successfully reproduces sliding energy landscapes of carbon
nanotubes on graphene calculated using a Lennard-Jones-type and the
Kolmogorov–Crespi interlayer potentials. Furthermore, it captures
the sliding energy corrugation of a boron nitride nanotube on hexagonal
boron nitride calculated using a recently developed interlayer potential
for hexagonal boron nitride (h-BN). Finally, we use
the Registry Index to predict the sliding energy landscapes of the
heterogeneous junctions of a carbon nanotubes on h-BN and of boron nitride nanotubes on graphene that are shown to
exhibit a significantly reduced corrugation. For such rigid interfaces
this is expected to be manifested by superlubric motion.