Curling behavior of free-standing nanofilms driven by surface stress: core–shell modelJiangang Li, Xiao Lei, Jianhua Ding, Zhixiang Gao and Hua WangEur. Phys. J. Appl. Phys., 97 (2022) 85DOI: https://doi.org/10.1051/epjap/2022220185