Studies And Synthesis Of ZnO Films By Aqueous Solution Method

In this paper, well-aligned and orienting hexagonal wurtzite ZnO nano/micro-rod arrays were prepared in large quantities via aqueous solution growth two-step approach by using zinc nitrate and ammonia as precursors. The growth process was based upon epitaxial growth routine. Supersaturating degree of solutions is the main drive force for rod growth. The growth mechanism of rod crystal films was investigated and it's achieved to transform morphologies of ZnO films. The factors'effectives on morphology and structure were systematically analyzed.XRD, SEM, TEM, SAED, HRTEM were utilized to characterize phase composition, crystallize morphology and structures of ZnO films. It's found that the complex reaction of ammonia with Zn²⁺ behaves a buffer action for Zn²⁺ releasing in ammonia systems and sustains rod growth steady. So, ZnO rod crystals can grow in a broad scope of pH. Via in-situ secondary pH adjustment way, ZnO tubes, sheets and rods with blanket-like shaped surfaces were fabricated. Thereinto, because solutions became unsaturated and into non-nucleation area by elevating pH value and (0001) polar planes of ZnO crystals attracted OH- and were eroded, ZnO nanotubes and nanosheets were formed. As solutions became supersaturating and into nucleation area again by reducing pH value and ZnO crystal nuclei on rod surfaces with lower energy barrier, ZnO rods with blanket-like shaped surfaces were caused.The paper researched all parameters effectives of aqueous solution method, including ZnO seed layer, concentration of the seed solution, primary zinc concentration and primary pH value of growth solution, growth temperature and time on quality, morphology and structure of rod crystals. The results showed ZnO seed layer is crucial for well-aligned ZnO nanorod array. The concentration of seed solution has little influence on film morphology. Primary zinc concentration mainly affect growth rate in c axis direction and ZnO rod density and orderliness got higher with rising temperature. The aspect ratio of ZnO rod obviously rose along with increasing primary pH value in nucleation part and nanorod array became more compact and regular. It is favored for well-aligned ZnO rod crystal array to adding CTAB which also resulted in rod conjunction. Growth rate of rod was quickened with raising temperature. The film density and rod size were larger by prolong growth time. Growth rate in c axis direction is mostly controlled by primary zinc concentration, primary pH value, growth temperature and time. And diameter basically lies on the seed layer, primary pH value and growth time. Different size of ZnO film with average diameter from 50 to 300nm and length from 2 to 8μm can be synthesized by adjusting parameters.