A novel nanostructure with hexagonal-prism pores fabricated under vacuum circumstance

• A novel anodizing technology under a vacuum system is presented.
• An unusual nanostructure with hexagonal-prism pores is fabricated.
• Morphologies of the pores are strongly influenced by the system pressure.
• A new method is proposed to enlarge the pore diameter in PAA.
• Anion-contaminated oxide and oxygen bubbles are associated with pore formation.

It is well known that electrochemical anodizations of valve metals are performed under the normal pressure (1 atm = 0.1 MPa), and only columnar pores could be usually obtained in porous anodic alumina (PAA). So far, there have been very few reports involving the atmosphere pressure and its effect on the nanostructure of PAA. Here, a novel PAA nanostructure with hexagonal-prism pores has been successfully fabricated under a vacuum system (0.01 MPa), and its forming process is clarified by the anion-contaminated alumina model and oxygen bubble mold. The present results can provide unique insights into the inherent relations between the structural features and anodizing parameters in all anodizing process.

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