Abstract:
Ni-Fe magnetic nanowire array thin films that may be used to realize a magnetic portal
imaging device were electrodeposited in the pores of anodic aluminium oxide (AAO)
membranes. The membranes were first fabricated by a two-step process by anodizing
0.47 mm thick commercial aluminium foil in 0.50M sulphuric acid under constant dc
potentials between 11V and 29V. The evolution current during the anodizing and
electrodeposition processes were recorded using a data logger. The surfaces of the AAO
films were studied at different stages of evolution of the nanopores and after
electrodeposition of the Fe-Ni nanowires, using optical and electron microscopy. Results
indicate that a barrier aluminium oxide thin film first formed on the aluminium surface
prior to the formation of AAO membranes. The time for the formation of the barrier
oxide decreased with increasing anodizing voltage, but was less than 40 seconds for
AAO films synthesized at 15 V dc. It was also observed that 0.5 M sulphuric acid
produced an organized nanopore pattern only after the second step anodizing process. It
was noted that the amount of grey colour and pore diameter of AAO films increased
with anodizing voltage, and low anodizing voltage and high temperature produced more
surface defects. Current curves indicated that anodizing current, and hence rate of pore
formation, decreased with temperature but increased with voltage. It was observed that
electrodeposition of nanowires in AAO membranes took place in three stages,
corresponding to deposition at the pore bottom, pore length and deposition outside the
pores. In our study, the first nanopore was filled in approximately 710 s.
