Zhitao Zhou

Effect of ethylene glycol monomethyl ether ratio in mixed solvent on surface morphology, wettability and photocatalytic properties of ZnO thin films

AbstractZinc oxide (ZnO) thin films with different ethylene glycol monomethyl ether (EGME) ratio were prepared on Si substrates using a two-step process. The results show that they possess a polycrystalline hexagonal wurtzite crystal structure. The topography of the ZnO thin films evolves from nanoparticles to hexagonal nanorods with the decrease of EGME content. The photoluminescence spectra consist of a near-band-edge emission and two visible emissions. The optical band gap energy decreases first and then increases with the increase of EGME ratio in mixed solvent, the broadening of the optical band gap can be explained by Moss–Burstein effect. The wetting behavior of all the samples can switch from hydrophobicity to hydrophilicity through UV illumination. The degradation efficiency of the thin films increases with decreasing EGME content, photocatalytic reaction mechanism of the ZnO thin films is discussed in detail.

The improved photo-induced hydrophilicity of ZnO by adjusting the solution concentration

The microstructure, surface topography and wetting properties of zinc oxide (ZnO) thin films, which were grown at different concentrations of zinc nitrate hexahydrate, were measured by x-ray diffractometry, scanning electron microscopy and water contact angle apparatus. It is revealed that at concentrations larger than 0.01 mol l−1, one peak corresponds to the (111) direction of the cubic phase of ZnO, except for six peaks of the hexagonal phase of ZnO, was observed. As the concentration increases, the average diameter and density of the ZnO nanorods increase but the area proportion of the nonpolar planes in the outermost surface increase first, then decrease. All the ZnO thin films exhibit hydrophobic behavior. After 120 min of ultraviolet irradiation, the wettability of the ZnO surfaces change from hydrophobicity to hydrophilicity. The photo-induced change of the water contact angle increases first then decreases with the increase of concentration. The differences of photo-induced hydrophilicity may be determined by the transition of the wetting model, the area proportion of the nonpolar planes and the surface roughness.

Influence of Solution Concentrations on Surface Morphology and Wettability of ZnO Thin Films

ZnO thin films were grown on silicon substrates using a hydrothermal method. The XRD patterns show that all of the peaks can be attributed to the wurtzite structures of ZnO. The TC value of (002) plane and average crystal size increase first and then decrease with the increase of solution concentration. SEM and AFM results show that many dense hexagonal cylinder particles have been observed on the surface of the thin films, which grown at 0.08 and 0.10 mol/L. The surface roughness of the thin films deposited at 0.06, 0.08, 0.10, and 0.12 mol/L are 24.5, 38.3, 32.0, and 39.4 nm, respectively. Surface wettability results show that the preferential orientation along c-axis and surface roughness contribute significantly to the hydrophobicity. The reversible switching between hydrophobicity and hydrophilicity is related to the synergy of the transition of wetting model, surface crystal structure, and surface roughness.