Nanoparticles of CuO thin films for room temperature NO2 gas detection: Annealing time effect

Abstract

In this work, the effect of annealing time on sensing properties of cupric oxide nanoparticles deposited on black silicon (CuO/BSi) as a gas sensor device was studied. CuO nanoparticles were prepared using pulsed laser ablation (PLA) beyond which, the prepared precursor was deposition using the spin coating deposition technique. The deposited CuO thin films were annealed in air for 1, 2, and 3 h at 400 °C. The influence of annealing time on the structural, morphological, and sensing performance at room temperature of prepared CuO/BSi was investigated in details. XRD patterns revealed nanocrystal of CuO with the crystallite size increased from 17 to 25 nm when that annealing time increased from 1 h to 3 h. The FESEM images revealed a nanostructured stone-like structure of different sizes. The average diameter increased with 1 h annealing time. The appearance of the porous surface of the annealed sample for two hours, while the porosity on the surface of the annealed sample for three hours decreased. A strong, sharp emission in the Visible-region was observed in the spectrum of CuO nanostructures, revealed by PL measurements at room temperature. The PL spectrum also showed a shift towards a shorter wavelength in the visible region that refers to the decreasing of energy gap from 1.73 eV to 1.71 eV. The prepared films were exposed to NO2 to detect the sensitivity of the nanostructured CuO/BSi thin films. It was found that the annealing time had a major role in increased sensitivity. The sensitivity of the annealed sample increased from 77% to 90% when the annealing time increased from one to two hours, while the sensitivity of the third model decreased to 4% at a three-hour annealing time. The reason for this behavior has been also discussed.