Characterisation of electrodeposited nickel nanowires using NCA template

Abstract

This paper reports on the growth of nanowires of nickel by electrodeposition in nano channel alumina (NCA) membranes. To make ohmic contact, one side of the NCA was sputtered with aluminium and nickel was electrodeposited from the other side. Nickel ions in solution migrate into the pores by the action of electrical potential, filling them approximately to 80% of solid-metal density. These ions form wires imbedded in the NCA matrix. Scanning electron microscopy (SEM) images were used to examine the growth mechanism of the nanowires. The images revealed that the wires started to grow from the aluminium backing plate, although a small number of wires grew from the middle of the pores. One possible reason of this partial pore fill-up could be the trapped air pocket inside the pores when the NCA was placed into the electrolyte. The mechanism of growth of the wires was studied by varying the electrochemical cell parameters temperature, pH and time. Purer nickel wire growth was observed with less nickel hydroxide species contamination at higher temperatures and at lower pH. X-ray diffraction spectra of FCC nickel nanowires were found to be polycrystalline and had a preferred orientation of (200) plane at higher bath temperature (60°C). Bulk magnetic properties of nickel filled nanoporous arrays were investigated by the vibrating sample magnetometer (VSM). The magnetization hysteresis at room temperature showed enhancement of coercivity for magnetic field applied parallel to the nanowires compared to that for perpendicular applied field. Magneto-impedance was measured as a function of applied magnetic field and wire diameter.