Detection of ethanol vapours with Al-incorporated ZnO thin films

Al2O3 has been incorporated in the nanosize ZnO (Al/ZnO) thin film to enhance its sensitivity to C2H5OH vapour. It is found that the Al/ZnO thin film has a high sensitivity (>20), which is much greater than the plain ZnO by at least 50%. The speciation of zinc in the Al/ZnO thin films during detection of C2H5OH (200 ppm) has also been studied by in situ X-ray absorption near edge structure (XANES) spectroscopy. The least-square fitted XANES spectra indicate that the main zinc species in the thin film are bulky ZnO (>100 nm) (5%) and nanosize ZnO (95%). At the temperature of 300 K, during sensing of C2H5OH, a small amount of Zn(OH)2 (7%) is formed in the thin film. The chemical interaction between C2H5OH and ZnO has also been found by in situ extended X-ray absorption fine structure (EXAFS) spectroscopy. The bond distance of Zn–O is decreased to 1.93 Å during sensing of C2H5OH, which may be caused by the electron donating to ZnO during adsorption of C2H5OH (C2H5HO → Zn–O). In the absence of C2H5OH, the Zn–O bond distance is restored to 1.92 Å.