Detectors based on Pd-doped and PdO-functionalized ZnO nanostructures

In this work, zinc oxide (ZnO) nanostructured films were grown using a simple synthesis from chemical solutions (SCS) approach from aqueous baths at relatively low temperatures (< 95 °C). The samples were doped with Pd (0.17 at% Pd) and functionalized with PdO nanoparticles (NPs) using the PdCl₂ aqueous solution and subsequent thermal annealing at 650 °C for 30 min. The morphological, micro-Raman and optical properties of Pd modified samples were investigated in detail and were demonstrated to have high crystallinity. Gas sensing studies unveiled that compared to pure ZnO films, the Pd-doped ZnO (ZnO:Pd) nanostructured films showed a decrease in ethanol vapor response and slight increase in H₂ response with low selectivity. However, the PdO-functionalized samples showed excellent H₂ gas sensing properties with possibility to detect H₂ gas even at room temperature (gas response of ~ 2). Up to 200 °C operating temperature the samples are highly selective to H₂ gas, with highest response of ~ 12 at 150 °C. This study demonstrates that surface functionalization of n-ZnO nanostructured films with p-type oxides is very important for improvement of gas sensing properties.