The detection of hazardous gases at different concentration levels at low and room temperature is still an actual and challenging task. In this paper, Al-doped ZnO thin films are synthesized by the electrochemical deposition method on the gold electrodes of AT-cut quartz resonators, vibrating at 10 MHz. The average roughness, surface morphology and gas sensing properties are investigated. The average roughness of Al-doped ZnO layers strongly depends on the amount of the doping agent Al₂(SO₄)₃ added to the solution. The structural dependence of these films with varying Al concentrations is evident from the scanning electron microscopy images. The sensing properties to ethanol and ammonia analytes were tested in the range of 0–12,800 ppm. In the analysis of the sensitivity to ammonia, a dependence on the concentration of the added Al₂(SO₄)₃ in the electrochemically deposited layers is also observed, as the most sensitive layer is at 3 × 10⁻⁵ M. The sensitivity and the detection limit in case of ammonia are, respectively, 0.03 Hz/ppm and 100 ppm for the optimal doping concentration. The sensitivity depends on the active surface area of the layers, with those with a more developed surface being more sensitive. Al-doped ZnO layers showed a good long-term stability and reproducibility towards ammonia and ethanol gases. In the case of ethanol, the sensitivity is an order lower than that for ammonia, as those deposited with Al₂(SO₄)₃ do not practically react to ethanol.

This article focuses on the impact of the deposition temperature (in the range from 60 to 80 °C) in ZrO₂ films obtained by the electrochemical deposition process on SnO₂-covered glass substrates. The solution in which the deposition takes place is aqueous, containing ZrOCl₂ with a concentration of 3 × 10⁻⁵ M and KCl with a concentration of 0.1 M. By implementing X-ray diffraction (XRD), optical profilometry, scanning electron microscopy (SEM), and UV-VIS-NIR spectroscopy, the temperature dependence of ZrO₂ films properties was revealed. The X-ray Diffraction XRD spectra showed six different diffraction maxima ((−111)M, (101)T, (111)M, (112)M, (202)M, and (103)M) associated with the electrochemical ZrO₂ layers, and the polycrystalline structure of the films was confirmed at all deposition temperatures. The determination of the average roughness did not indicate significant temperature dependence in the deposited layers. SEM micrographs showed that the layers were composed of grains, most of them of a regular shape, although their size increased slightly with an increased deposition temperature. The coarsest-grained structure was observed for the layers deposited at 80 °C. It was demonstrated that the deposition temperature weakly impacts the reflectance and transmittance spectra of the ZrO₂ layers. Such layers with low values of specular and high values of diffuse transition, and reflection in the spectral range from 380 to 800 nm, can be applied to various optoelectronic devices such as thin-film solar cells.

A study is presented on the sensitivity of electrochemically deposited ZrO₂ and ZnO on a quartz resonator. The nanostructured ZrO₂ and ZnO layers are deposited by electrochemical method on the Au electrodes of the quartz resonators. The deposition of the electrochemical layers of ZrO₂ and ZnO is carried out in aqueous solution of (ZrOCl₂ (5. 10^-3 M) and KCl (0.1 M) for ZrO₂ and (ZnCl₂ (5. 10^-3 M) and KCl (0.1 M) for ZnO) at 70°C and (vs SCE) using a three-electrode electrochemical cell. The structure of the ZrO₂ and ZnO layers deposited on the polished surface of quartz resonator is studied by Scanning Electron Microscopy (SEM) and optical profilometry. The influence of the roughness on the ZrO₂ and ZnO sorption properties is investigated. The sorption ability of the ZrO₂ and ZnO layers is defined by measuring the resonant frequency shift (ΔF) of the quartz structure in the presence of different concentration of methanol, ethanol and ammonia (0 - 25000 ppm).