FABRICATION AND CHARACTERIZATION OF HIGHLY ORDERED POROUS ANODIC OXIDE AND NANOWIRES

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Abstract

Porous anodic films with highly ordered pores were successfully fabricated with multi-steps anodizing. The degree of pore ordering was quantitatively assessed by obtaining the pore distribution regularity based on fast Fourier transform (FFT) of scanning electron micrographs of the resultant porous anodic films. It is revealed that the degree of pore ordering in anodic films increases with increased number of repeated steps of anodizing. Anodizing conditions, i.e. anodizing voltage and the electrolyte concentration, are found to have significant effects on pore ordering. The best regularity was recorded on the porous anodic films formed at 30 V in 0.3 M oxalic acid and 40 V in 0.4 M oxalic acid. Further, anodic oxide films, with pores arranged in hexagonal or square patterns, were obtained by anodizing of aluminium with corresponding pre-patterns induced by optic grating impressions under selected anodizing voltages. Additionally, anodic film templates were successfully fabricated using optimised procedures with selective removal of the aluminium substrate and the barrier oxide layer. Nickel nanowires were produced by electrodeposition using anodic film templates. The current density-time response reveals three growth stages of nickel nanowires during electrodeposition. The electrodeposition current efficiency varied with the variation of electrodeposition parameters, mainly due to side reactions i.e. hydrogen evolution. The process temperature and applied voltage have a significant influence on the growth rate of nickel nanowires. Further, the structure of the resultant nickel nanowires depends on the process temperature. At a process temperature of 3°C, single crystal nanowires grew preferentially along [110] orientation. However, polycrystalline nanowires were obtained at an increased temperature of 37°C due to the increased surface diffusion rate of nickel adatoms. Optical limiting assessment of the nickel nanowires revealed significant non-linear scattering in the wavelength range of 532 to 1064 nm, suggesting potential applications in the fields of ultrahigh-density magnetic recording, ultrafast optical switching and microwave devices. Manganese oxide nanowires were also fabricated via the anodic film template route in a mixed solution of 0.1 M manganese acetate and 0.1 M sodium sulphate. The resultant nanowires exhibit an amorphous structure with short range ordering. A high population of fine crystalline particles, with an average diameter of 3~5 nm, was revealed within the nanowires. The crystalline particles were determined as ε-Manganese dioxide with a hexagonal structure. Further, a high specific capacitance of 220 F g-1 was recorded on the electrode fabricated from the deposited manganese oxide nanowire array in a cyclic voltammetry measurement at a scan rate of 5 mV s-1 from 0 to 1 V (SCE) in 0.1 M sodium sulphate solution at 25°C , indicating excellent capacitive properties.

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