Thermal expansion behavior of holes in graphene nanomeshes

Abstract

The thermal expansion of a hole, in a planar system, follows the same trend as the thermal expansion of the whole system, i.e., the hole expands (contracts) if the material expands (contracts) under thermal excitation. At nanoscale, this phenomenon has not been studied so far. Here, using tools of classical molecular dynamics simulations, we show that graphene nanomeshes (GNMs) behave oppositely: While the whole structure contracts (expands), the nanoholes expand (contract) under thermal excitation. We propose and test a simple mechanism to describe this unexpected behavior in terms of out-of-plane vibrations of the atoms close to and far from the edges of the holes. This mechanism allows us to see that, contrary to usual planar systems, this behavior comes from nonuniform thermal expansion along the structure. Although the thermal expansion of holes in GNMs is contrary to the classical prediction, we verify that the thermal expansion of the whole GNM structure is the same as that of pristine graphene.