Correlation between optical, structural, and sensor properties of nanostructures of nickel oxide on aluminum oxide substrates

Abstract

We have established a correlation between diffuse reflection of nickel oxide-based composites in the red region of the spectrum and the nanostructural properties of the roughness profile of the composite. We present calculations of the absorption spectra for samples of nanostructured nickel oxide of thickness 0.25-0.35 μm on aluminum oxide substrates from diffuse reflection and transmission of the layers by multiple scattering methods, taking into account the luminescence of the samples in the weak absorption region. Using a special optical system, we have determined the selective sensitivity to carbon monoxide exposure of a nanostructured nickel oxide composite at room temperature. The result is of fundamental importance for development of optical selective gas sensor technology in the visible region of the spectrum.Introduction. Interest in technologies for fabrication and study of the physicochemical properties of nanosized structures made from transition metal oxides has grown significantly over the past decade, in connection with the search for new industrial applications. These structures, having electronic and hole conductivity at room temperature [1-3], sensor properties, photoconductivity, luminescence and absorption [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], are quite attractive for study. Important parameters of oxides include environmental friendliness, thermal stability and resistance to aging, and also low cost. Nickel oxide occupies a significant place in this series, especially with regard to designing high-sensitivity selective optoelectronic gas sensors (determination of CO, CO 2 , CH 4 ). We have proposed an approach involving the use of optical data in the visible region of the spectrum, in contrast to existing gas sensors operating in the IR region of the spectrum (see, for example, [21,22]). It is hypothesized that the sensitivity of optoelectronic gas sensors will be improved as a result of the higher sensitivity of radiation detectors in the visible region of the spectrum and the change in conductivity after identification of the gas. The previously identified broad absorption band of nickel oxide in the 600-800 nm region, due to recombination of charge carriers [2], is utilized in the optical system. Since the sensor, optical, and topographical properties of the nanostructures are interconnected, they are the object of study in this paper.Materials and Methods. In order to obtain the nickel oxide layers, we developed and made substrates of a special configuration based on thin (100 μm) anodic aluminum oxide (γ modification) wafers. Then we developed the technology for making oxide layers of thickness 0.3-0.4 μm by thermal oxidation of a previously deposited metal film. The nickel films deposited on the γ-Al 2 O 3 substrate have a crystalline structure. Calculation of the crystal parameters showed that the nickel is formed into a cubic lattice on the substrate. The process of obtaining the nickel oxide from a previously deposited nickel film was carried out by heating ...