Investigation of the selective growth of ZnO and Zn(OH)₂ films deposited by chemical bath near room temperature

Zinc oxide (ZnO) and zinc hydroxide (Zn(OH)₂) thin films were deposited by the chemical bath deposition onto glass substrates at temperatures of 25°C, 35°C and 45°C. The experimental conditions for the selective deposition of the films such as the concentration of the reagents, temperature, and pH of the chemical bath were determined from the predictions of the species distribution diagrams (SDDs) and solubility curves (SCs). SDDs and SCs were elaborated by considering the chemical reagents, temperature, and pH, and give information about the probability of formation of specific compounds. The reagents used were ZnSO₄, KOH, and NH₄NO₃. The physicochemical of the synthesis of both ZnO and Zn(OH)₂ films are proposed. X-ray photoelectron spectroscopy and X-ray diffraction indicate the presence of ZnO and/or Zn(OH)₂ compounds, where the selective deposition of each material (or coexistence) is dependent on the bath temperature and pH. The crystalline structure was hexagonal (zincite) for ZnO and orthorhombic (wulfingite) for Zn(OH)₂. The bandgap energy of the deposited films ranged from 3.32 to 3.51 eV. A better understanding of the selective deposition of specific compounds by controlling the experimental parameters represents an important step toward the fabrication of nanomaterials with tailored properties for a wide range of applications.