High selectivity of a CuO modified hollow SnO2 nanofiber gas sensor to H2S at low temperature Jiejie Yang, Chaojun Gao, Hui Yang, Xinchang Wang and Jianfeng Jia Eur. Phys. J. Appl. Phys., 79 3 (2017) 30101 Published online: 02 August 2017 DOI: 10.1051/epjap/2017170123