Enhancement of piezoelectric properties of the PVDF film by interfacial layer Cu-network Lei Peng, Jian Hao, Ping Liu, Qingguo Gao and Jianjun Yang Eur. Phys. J. Plus, 140 8 (2025) 747 Published online: 09 August 2025 DOI: 10.1140/epjp/s13360-025-06674-6