Graphene Blisters with Switchable Shapes Controlled
by Pressure and Adhesion
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Abstract
We created graphene blisters that
cover and seal an annular cylinder-shaped
microcavity in a SiO<sub>2</sub> substrate filled with a gas. By controlling
the pressure difference between the gas inside and outside of the
microcavity, we switch the graphene membrane between multiple stable
equilibrium configurations. We carried out experiments starting from
the situation where the pressure of the gas inside and outside of
the microcavity is set equal to a prescribed charging pressure, <i>p</i><sub>0</sub> and the graphene membrane covers the cavity
like an annular drum, adhered to the central post and the surrounding
substrate due to van der Waals forces. We decrease the outside pressure
to a value, <i>p</i><sub>e</sub> which causes it to bulge
into an annular blister. We systematically increase the charging pressure
by repeating this procedure causing the annular blister to continue
to bulge until a critical charging pressure <i>p</i><sub>c</sub><sup>i</sup> is reached. At
this point the graphene membrane delaminates from the post in an unstable
manner, resulting in a switch of graphene membrane shape from an annular
to a spherical blister. Continued increase of the charging pressure
results in the spherical blister growing with its height increasing,
but maintaining a constant radius until a second critical charging
pressure <i>p</i><sub>c</sub><sup>o</sup> is reached at which point the blister begins
to delaminate from the periphery of the cavity in a stable manner.
Here, we report a series of experiments as well as a mechanics and
thermodynamic model that demonstrate how the interplay among system
parameters (geometry, graphene stiffness (number of layers), pressure,
and adhesion energy) results in the ability to controllably switch
graphene blisters among different shapes. Arrays of these blisters
can be envisioned to create pressure-switchable surface properties
where the difference between patterns of annular versus spherical
blisters will impact functionalities such as wettability, friction,
adhesion, and surface wave characteristics