Physical vapour deposition of Zn2+ doped NiO nanostructured thin films for enhanced selective and sensitive ammonia sensing

Abstract

Highly sensitive and selective ammonia sensors based on Zn2+ doped NiO thin films with well-controlled morphology through a substrate temperature variation developed with the electron beam evaporation method. The obtained films were systematically studied using various characterization techniques involving X-ray Diffraction, FESEM, EDS, XPS, AFM, RBS, UV–visible spectrophotometer and Hall effect measurements. The successful preparation of Zn2+ doped NiO thin films has been confirmed by structural, elemental and chemical analysis. The fabricated Zn: NiO sensors have shown excellent selectivity towards ammonia at 100 ppm concentration at room temperature. Sensors deposited with high temperatures ((≥300°C) were more sensitive towards ammonia with a fast response and recovery time (10/15 s) and a low detection limit of 10 ppm. The enhanced ammonia sensing performance could be attributed to the high surface-to-volume ratio and high porosity of films deposited at substrate temperature (≥300°C), and electronic sensitization through Zn2+ incorporation into NiO lattice. The addition of Zn into NiO caused rapid adsorption of oxygen adsorbates on the surface of doped NiO, which increased the sensor's response. The sensing mechanism for the detection of ammonia is formulated. The outcome of this work opens a pathway for the efficient detection of ammonia at ambient temperature for numerous medical and industrial applications.