Nature engineered metasurfaces: spin-to-orbital angular momentum conversion in diatom frustules Edoardo De Tommasi, Maria Antonietta Ferrara, Giuseppe Coppola and Gianluigi Zito EPJ Web Conf., 266 (2022) 09011 Published online: 13 October 2022 DOI: 10.1051/epjconf/202226609011