Epitaxial multilayered Co/Cu ferromagnetic nanocolumns grown by oblique angle deposition

Slanted Co/Cu multilayer nanocolumns were grown on Si and gold-coated Si substrates by two-source oblique-angle vapour deposition. The respective column lengths and layer thicknesses were varied from similar to 400 to similar to 700 nm and similar to 6 to similar to 16 nm. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show the column diameters to be less than 65 nm. The ferromagnetic nature of the nanocolumns was verified by vibrating sample magnetometry. Compositional analysis using electron energy loss spectroscopic elemental mapping and energy dispersive x-ray spectrometry of a single nanocolumn showed alternating bands of Co and Cu, indicating a multilayer structure. X-ray diffraction (XRD) results showed that the Co and Cu layers are predominantly face-centred cubic (fcc) and a minor hexagonal close packed (hcp) Co phase was also detected. The hcp phase may be due to a high density of stacking faults in the fcc Co. TEM studies have shown an epitaxial relationship between the Co and Cu layers within the individual columns. By comparing the XRD and TEM results, we conclude that the (020) planes are parallel to the column axis, and the column growth is nearly parallel to the [101] direction.