Zinc Oxide Thin Film Surface Controlled Invasive Studies

It is well know that the wettability of solid surfaces is a very importantproperty. A significant attention focuses on super-hydrophobic surface (CAis larger than 150ｏ) and super-hydrophilic surface (CA close to 0ｏ).Recently, the controllable wettability by light illumination has arousedgreat interests, and has been considered to be an important technology inmany fields. ZnO is a n-type semiconductor with wide band gap of 3.2 eV.ZnO smooth surface indicates hydrophobicity with a contact angle of 109o,which can convert to hydropholicity by UV illumination. It is veryimportant and significative to study wettability of ZnO, since ZnO indicatespecial wettability on the smooth surface. In the present dissertation, a series of ZnO thin films were obtained by asimple electro-depositional method at different condition. It was discussedin detail that the effect of depositional temperature, depositional voltageand concentration of electrolyte. It is show that all of the depositionalparameter can affect surface morphologies and roughness of ZnO surface.Depositional voltage and concentration of electrolyte affect greatlymorphologies, resulting in the greatly change of contact angle. Whereas,effect of depositional temperature is not enough to greatly change ofcontact angle. Controllable wettability and mechanism of wettability conversion wasdiscussed in detail. High hydropholicity was observed on new preparedZnO thin films with contact angle of several degrees. Whereas, contactangle will gradual increase both put in air and heated treatment, resultingin super-hydrophobic surface. It is considered that adsorbent water on thesurface can be replaced by oxygen spontaneous, which heating treatmentcan promote the process of oxygen replace. After UV illumination, thecontact angle will decrease to 0? on the ZnO thin films that were heated. Itis reported that UV illumination generates electron-hole pairs in ZnO.Some of the holes can also react with lattice oxygen, leading to the II东北师范大学硕士学位论文formation of surface oxygen vacancies. In the ambient conditions, watermolecules may coordinate into the oxygen vacancy sites, which lead todissociative adsorption of the water molecules on the surface, resulting inthe hydrophilic sites. A mass of hydrophilic sites formed on surfaceresult in super-hydrophilicity of ZnO surfaces. Cycles of heating-UVillumination were achieved and good reversibility of surface wettabilitywas observed.