  Glasses have a wide range of technological applications. The recent discovery
of ultrastable glasses that are obtained by depositing the vapor of a
glass-forming liquid onto the surface of a cold substrate has sparked renewed
interest in the effects of confinements on physicochemical properties of
liquids and glasses. Here we use molecular dynamics simulations to study the
effect of substrate on thin films of a model glass-forming liquid, the
Kob-Andersen binary Lennard-Jones system, and compute profiles of several
thermodynamic and kinetic properties across the film. We observe that the
substrate can induce large oscillations in profiles of thermodynamic properties
such as density, composition and stress, and we establish a correlation between
the oscillations in total density and the oscillations in normal stress. We
also demonstrate that the kinetic properties of an atomic film can be readily
tuned by changing the strength of interactions between the substrate and the
liquid. Most notably, we show that a weakly attractive substrate can induce the
emergence of a highly mobile region in its vicinity. In this highly mobile
region, structural relaxation is several times faster than in the bulk, and the
exploration of the potential energy landscape is also more efficient. In the
subsurface region near a strongly attractive substrate, however, the dynamics
is decelerated and the sampling of the potential energy landscape becomes less
efficient than the bulk. We explain these two distinct behaviors by
establishing a correlation between the oscillations in kinetic properties and
the oscillations in lateral stress. Our findings offer interesting
opportunities for designing better substrates for the vapor deposition process
or developing alternative procedures for situations where vapor deposition is
not feasible.
