Growth and Characterization of NiO Thin Films for Selective Detection of Formaldehyde Vapor

Abstract

The formation of nickel oxide (NiO) nanostructures using controlled thermal oxidation of thin nickel (Ni) films and their successive use as gas‐sensing materials for selective detection of low‐concentration formaldehyde vapor are discussed here. High‐purity Ni were deposited on glass/quartz substrates using a vacuum assisted electron beam (E‐beam) evaporation technique. Afterwards, thermal oxidation of these Ni thin films was conducted at various temperatures in air ambient condition. Different surface characterization techniques are employed to investigate the structure, chemistry, and electronic properties of these as‐grown oxide nanostructures. X‐ray diffraction analysis revealed that the thermal oxidation starts above 400 °C. Presence of metallic nickel peak even after oxidation at 500 °C for 5 h confirms its oxidation resistance. Increase in oxidation temperature improves the crystalline quality. Scanning electron microscopy imaging depicts an increase in particle size with oxidation temperature and a highly porous surface morphology above 800 °C. Raman spectroscopy identified the characteristic modes of NiO. UV‐Visible data exhibits a redshift in optical bandgap whereas X‐ray photoemission spectroscopy analysis reveals a gradual increase in oxygen content within the oxide layer. Finally, these NiO films show a high sensitivity and selectivity toward formaldehyde vapor sensing against a few other volatile organic compounds.