Iron Oxides Nanoparticles Langmuir-Schaeffer Multilayers for Chemoresistive Gas Sensing

Gas sensors based on mixtures of iron oxides nanoparticles (NPs) modified with Pd NPs at the different NPs Pd: Fe₃O₄/γ-Fe₂O₃ proportions were prepared and characterized. Nanoparticles diameter was 6–7 nm. NPs films were deposited from the mixtures of Fe₃O₄/γ-Fe₂O₃ and Pd NPs colloidal solutions by modified Langmuir-Schaeffer technique onto alumina substrates. Samples were composed from 4 Fe₃O₄/γ-Fe₂O₃ NP monolayers (MLs). Sensors were tested toward acetone vapors and NO₂ at concentration range of 5–200 and 0.5–12 ppm respectively in dry air, and at different working temperatures. Pd-doped Fe₃O₄/γ-Fe₂O₃ sensors showed p-type gas response, higher conductance and higher conduction activation energies compared to pure Fe₃O₄/γ-Fe₂O₃ sensor that gives n-type gas response. Results were tentatively explained in terms of surface interactions with oxidizing and reducing species, and Nearest Neighbor Hopping conduction model (NNH).