Comparison between the optical properties of Ni/AAO and Co/AAO nano-array composite

Ordered Ni/AAO and Co/AAO nano-array composite structure are prepared via electrodeposition of the metal within the process of anodically-grown porous anodic aluminum oxide (AAO) membranes. The optical properties of the two composite are studied. The results show that the difference between the Ni/AAO and Co/AAO are very large. Although the micrograph of the Ni nano-particles and the Co nano-particles are nearly the same, as the metal composition increased, the absorption band-edge of the Ni/AAO composite is small red-shifted (13 nm). However, the absorption band-edge of the Co/AAO composite is strongly red-shifted (80 nm). Meanwhile, the Ni/AAO and Co/AAO composite exhibit the optical features of the semiconductor with indirect and direct band gap respectively.