Understanding the interlayer interaction at the nanoscale
in two-dimensional
(2D) transition metal carbides and nitrides (MXenes) is important
to improve their exfoliation/delamination process and application
in (nano)-tribology. The layer–substrate interaction is also
essential in (nano)-tribology as effective solid lubricants should
be resistant against peeling-off during rubbing. Previous computational
studies considered MXenes’ interlayer coupling with oversimplified,
homogeneous terminations while neglecting the interaction with underlying
substrates. In our study, Ti-based MXenes with both homogeneous and
mixed terminations are modeled using density functional theory (DFT).
An ad hoc modified dispersion correction scheme is used, capable of
reproducing the results obtained from a higher level of theory. The
nature of the interlayer interactions, comprising van der Waals, dipole–dipole,
and hydrogen bonding, is discussed along with the effects of MXene
sheet’s thickness and C/N ratio. Our results demonstrate that
terminations play a major role in regulating MXenes’ interlayer
and substrate adhesion to iron and iron oxide and, therefore, lubrication,
which is also affected by an external load. Using graphene and MoS
2
as established references, we verify that MXenes’
tribological performance as solid lubricants can be significantly
improved by avoiding −OH and −F terminations, which
can be done by controlling terminations via post-synthesis processing.