Nanostructured CeO2 ultrathin film deposited by the Langmuir Blodgett technique for highly sensitive and specific detection of sub ppm level NO2 gas at room temperature

Abstract

High quality ultrathin metal oxides are beneficial to improve charge transport and various properties in the field of basic materials science and heterogeneous catalysis. The difference in physical and chemical properties of ultrathin films from their bulk counterparts arises owing to large surface to volume ratio, enhanced charge transfer and greater flexibility in bonding configurations. In this view, ultrathin cerium oxide (CeO₂) nanostructured films were deposited by a self-assembly process using the Langmuir–Blodgett (LB) technique to develop a high-precision, low-cost room temperature operated NO₂ sensor having high sensitivity and selectivity as well as a low limit of detection. The formation of an ordered and crystalline layered structure of as-deposited LB multilayers and subsequent formation of crystalline CeO₂ after decomposition was established by X-ray diffraction (XRD). The nanoparticle size of 3–4 nm as estimated by XRD was confirmed from the Raman peak width. The characteristic emission band of nanostructured CeO₂ observed in the photoluminescence spectra suggested the presence of defects and oxygen vacancies. X-ray photoelectron spectroscopy study revealed the presence of Ce³⁺ (12%) and a large quantity of surface adsorbed oxygen species (33%) in the nanostructured CeO₂ films. These CeO₂ films were used to develop a room temperature operable highly sensitive NO₂ gas sensor (200% for 1 ppm). The developed sensor is stable and distinctly specific towards NO₂ gas and shows a linear response in the range of 10 ppb–2 ppm. This study indicates the potential of the LB method for nanostructured metal oxide ultrathin film deposition and fabrication of room temperature toxic gas sensors with high sensitivity, repeatability and selectivity.