Rolling structure from bilayer nanofilm by mismatch

Abstract

A continuum theoretical scheme for self rolled-up nanotubes from bilayers by mismatch was obtained by considering surface elasticity, surface stress and symmetry lowering effects. For an ultrathin nanofilm with only several nanometers, isotropic mismatch and isotropic surface stress usually induce anisotropic rolling behavior. The isotropic Timoshenko formula should be modified anisotropically to interpret the mechanical behavior of anisotropic rolling structure of nanotubes accurately. The nanofilm rolled up in tangential direction while remain straight in cylindrical direction theoretically. Therefore, this paper considered the anisotropic shape of nanotubes. Along cylindrical direction, although it maintains straight and its residual strain is uniform, the stress varies through radial direction due to the Poisson’s effect of tangential strain. The applications of current theory to Si-Si nanotube, InAs-GaAs nanotube and InGaAs-Cr nanotube systems showed good agreement with experimental data. Besides surface elasticity and surface stress effects, the symmetry breaking and the anisotropic rolling structure are also of great importance in theoretical description of mechanical behavior of rolled-up nanotubes.