High-Quality Perovskite Thin Films for NO2 Detection: Optimizing Pulsed Laser Deposition of Pure and Sr-Doped LaMO3 (M = Co, Fe)

This study investigates the structural and catalytic properties of pure and Sr-doped LaCoO3 and LaFeO3 thin films for potential use as resistive gas sensors. Thin films were deposited via pulsed laser deposition (PLD) and characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation, and scratch tests. XRD analysis confirmed the formation of the desired perovskite phases without secondary phases. XPS revealed the presence of La3+, Co3+/Co4+, Fe3+/Fe4+, and Sr2+ oxidation states. SEM and AFM imaging showed compact, nanostructured surfaces with varying morphologies (shape and size of surface irregularities) depending on the composition. Sr doping led to surface refinement and increased nanohardness and adhesion. Transmission electron microscopy (TEM) analysis confirmed the columnar growth of nanocrystalline films. Sr-doped LaCoO3 demonstrated enhanced sensitivity and stability in the presence of NO2 gas compared to pure LaCoO3, as evidenced by electrical resistivity measurements within 230 ÷ 440 °C. At the same time, it was found that Sr doping stabilizes the catalytic activity of LaFeO3 (in the range of 300 ÷ 350 °C), although its behavior in the presence of NO2 differs from that of LaCo(Sr)O3—especially in terms of response and recovery times. These findings highlight the potential of Sr-doped LaCoO3 and LaFeO3 thin films for NO2 sensing applications.