The role of pH on the synthesis of a passivation layer comprising MgO-ZnO alloys

Abstract

The aim of this work is to prepare thin films of MgO and alloys MgO-ZnO by the spray pyrolysis technique. and to study the effect of different experimental parameters on the fundamental properties of thin films, The parameters investigated are (substrate temperature, molarity, and pH). Firstly, we prepared the MgO thin films on a glass substrate at 450°C at different MgO concentrations (0.05, 0.10, 0.15, and 0.2 mol.l-1). the MgO thin films show a cubic structure with a strong (002) preferred orientation and a maximum crystallite size of 21.4 nm attained of sprayed film at 0.2 mol.l-1.Good transmission was found in MgO thin film with the lowest molarity. The transmission of MgO thin films decreases rapidly as the wavelength increases in the range of (300-400) nm and then increases slowly at higher wavelengths. The band gap of MgO thin films decreases as the molarity increases and the band gap values range between 4.8-4.3 eV. The electrical resistance of our films is in the order of 2.107Ω. Secondly, the MgO Thin Films have been grown on glass substrates at 450°C by various pH solution values (2.5; 5;6.8; 8.3, and 10 pH). The MgO thin films have a strong preferential crystallinity with a cubic structure with a high (200) phase, the minimum value of crystallite size 9.9 nm is attained of deposit MgO thin film at 450 °C with 10 of pH. The optical transmission spectra showed all the sprayed MgO thin films are transparent within the visible wavelength region. The band gap of MgO thin films decreases from 3.91 to 3.7 eV as the pH increases from 2.5 to 6.8, and the Urbach energy was increased. The surface morphology by SEM indicated that in the MgO prepared with pH = 5 and 6.80 the grains become nearly spherical and bigger, and for the pH increased to pH =10, showing spherical particles and smaller, this may be when coalescence occurs. The thin film obtained with 2.5 pH has a lower electrical resistance. Thirdly, Zn 0.5Mg 0.5O thin films have been grown on glass substrates at 450°C by various pH solution values (2.5; 7.10, and 8.30 pH). The Zn 0.5Mg 0.5O thin films were observed in high crystallinity with a cubic structure with a strong orientation preferential at (200) , corresponding to the maximum value of crystallite size 72.28 nm attained of deposit Zn0.5Mg0.5O thin film at 450 °C with 8.30 of pH. The optical transmission spectra showed all the sprayed Zn 0.5Mg 0.5O thin films are transparent within the visible wavelength region. The band gap of Zn 0.5Mg 0.5O thin films increases from 3.77 to 4.09 eV as the pH increases, The surface morphology of the Zn 0.5Mg 0.5O appears at pH=2.5 big grains sphere and rod-like, whereas at pH=7.10 and 8.30 the grains become nearly spherical. The thin film obtained with 2.5 and 7.10 pH has a lower electrical resistance.