Surface eigenstress and size-dependent ultimate tensile strength of thin films

A general continuum framework based on the surface eigenstress model is developed to predict the size-dependent ultimate tensile strength of thin films, which gives analytic equations in terms of intrinsic surface and bulk material properties. First-principles calculations and molecular dynamics (MD) simulations were conducted on Au and Si (100) thin films, showing that the ultimate tensile strengths of the Au and Si (100) thin films increase and decrease with the reduction of the film thickness, respectively, indicating correspondingly the smaller the stronger and the smaller the weaker behaviors. Both behaviors were perfectly predicted by a nonlinear scaling law developed from the surface eigenstress model.