The spatially patterned ion beam implantation of 190 keV Co+ ions into a SiO2 thin film on a silicon substrate has been achieved using nanoporous anodic aluminium oxide (AAO) with a pore diameter of 125 nm as a mask. Implanted cobalt regions are found at the correct relative lateral periodicity given by the mask and at the depth of about 120 nm.

Taking on the challenge

Despite the difficulties of using AAO templates exposed to ion beams for pattern transfer, the team took up the challenge and embedded periodic magnetic nanoparticles in silica. AAO templates are insulators, which can cause severe charging during implantation. In addition, tilted pore walls and/or a tilted beam (the beam must be parallel to the pore wall) can result in sputtering, redeposition and ultimately pore blockage with almost zero transmission of the implanted species into the substrate through AAO.

Characterization to determine successful implantation is another issue, and here for the first time, the modulation of the cobalt implantation was imaged cross-sectionally by means of (scanning) transmission electron microscopy (TEM/STEM) and analytical TEM.

The researchers found the pattern of the AAO membrane to be well transferred into the substrate, making this technique a promising future tool for wide-area nanopatterning of embedded nanoparticles of various kinds of materials, whether for magnetic or optical applications.

A detailed description of the patterned implantation method can be found in the journal Nanotechnology.