Modeling the Formation of Self-Ordered Nanoporous Anodic Oxides

Iowa State University, Ames IA

Investigators

Abstract

The research objective of this award is to develop new methods for the rational design of highly ordered porous anodic oxide (PAO) films. These films are formed electrochemically by applying voltages to metals such as aluminum and titanium, in electrochemical cells. The films contain self-ordered hexagonal arrays of nanoscale pores, covering macroscopic areas. While much attention has focused on the use of PAO as templates for functional devices, these structures have been developed empirically, in the absence of robust understanding of processes controlling film growth. The goal of this research is to develop a fully predictive model of pore formation and self-ordering. The work will be guided by the concept that oxide material is transported by the combined influence of the electric field and mechanical stress. Experimental stress measurements will determine the operative balances of viscous, electrostatic and oxidation-induced stress governing interface motion in PAO films. Using this knowledge, descriptions of transport processes and driving forces will be formulated as a predictive simulation PAO growth, revealing the relations between electrochemical polarization, bath chemistry, and the dynamics of the self-ordering. If successful, the chemical-mechanical model of PAO formation will provide a fundamental basis for model-based design of self-organized porous anodic films. Thus, the model may permit rational manipulation of process conditions for high-rate fabrication of defect-free films, thus enhancing the commercial potential of PAO-based functional devices for solar energy conversion, catalysis, and biomedical applications. Student training will benefit from the unique aspects of this project: close integration of chemistry and mechanics; rigorous combination of a variety of experimental and modeling approaches; and on-site collaboration with a materials characterization group in England. Student training at Iowa State will take advantage of the strong presence of graduate and undergraduate programs promoting underrepresented groups, both at the Department and University levels.