Thickness influences on nanostructured MnO thin films, physical properties and sensing performance

Abstract

This work employed the chemical bath deposition (CBD) technique to fabricate a thin layer of nanostructured MnO. According to XRD measurements, the films have a cubic crystal structure and are polycrystalline, with orientations of (111, 200, 311, and 222), with (200) being the preferred orientation. Although the dislocation density parameters (100.46 to 80.36) and strain decreased from 34.75 to 31.08 and 34.75 to 100.36, respectively, the grain size was largest at (200) nm film thickness and lowest at (300) nm thickness. The deposited films exhibited a smooth surface topography as evidenced by the average surface roughness dropping from 8.70 nm to 4.27 nm, the average particle size observed to be 82.8 nm to 39.2 nm, and a reduction in root mean square (rms) values from 6.82 nm to 3.09 nm in the AFM images. Nanostructured MnO films exhibit a variety of grain morphologies, polycrystalline structure, and uniformity in SEM images. Their optical properties were measured in the 300–900 nm wavelength range. The extinction coefficient ranged from 0.368 to 0.276, whereas the computed refractive indices of the films with varying thicknesses fell between 3.6 and 2.95. The transmittance ranged between 86 and 81% in the VIS-NIR region with a band gap between 3.24 and 3.13 eV, and it was found that the absorption and absorption coefficient increased with film thickness. The thickness of MnO reduces its sensitivity to H2S gas.