Quantum manifestation of elastic constants in nanofilms.

Generally, there are two distinct effects in modifying the properties of low-dimensional nanostructures: surface effect (SE) due to increased surface-volume ratio and quantum size effect (QSE) due to quantum confinement in reduced dimension. The SE has been widely shown to affect the elastic constants and mechanical properties of nanostructures. Here, we demonstrate that QSE can also have a strong effect on the elastic constants of nanofilms from first-principles calculations. We conclude that generally QSE is dominant in affecting the elastic constants of metallic nanofilms while SE is more pronounced in semiconductor or insulator nanofilms. We also demonstrate that QSE affects the elastic constants of armchair graphene nanoribbons. Our findings have broad implications in quantum aspects of nanomechanics.