Fig. 4. ToF-SIMS depth profile for: (a) Pb²⁺ in film doping with different amounts of PbS QDs within 5 nm, (b) Pb²⁺, C⁺ and O²⁻ in whole film with 5% PbS QDs. The inset figure is an amplification of local curves of the film with 1%, 3%, 5% PbS QDs doped. The top horizontal axis respect the reference thickness at sputter rate is 0.263 nm s⁻¹ for SiO₂. (c) Structure of devices with doping 5% PbS QDs.