Fig. 2: SEM characterization of all the samples.

a Pristine highly ordered SnO₂ nanobowls (i.e., S@Z0); b highly ordered SnO₂ nanobowls coated with 20nm ZnO film (i.e., S@Z20); c highly ordered SnO₂ nanobowls branched ZnO NWs (i.e., S@Z20-Z5); d S@Z20-Z1; e S@Z20-Z3; f S@Z20-Z8; g S@Z0-Z5; h S@Z10-Z5; i S@Z30-Z5