Helium ion microscopy is a surface imaging technique that involves scanning a focused helium ion beam across a sample surface. The image is formed from secondary electron emission in a similar way to a scanning electron microscope (SEM), but the larger mass and therefore shorter de Broglie wavelength of a helium ion compared with that of an electron leads to a smaller interaction volume and a therefore a higher resolution compared with an SEM.

Higher resolution patterning

The helium ion microscope (HIM) can also be used as a milling tool to remove material directly from a surface in a similar way to a gallium focused ion beam (FIB). The low mass of helium compared with gallium results in a much reduced sputtering yield and therefore lower milling rates, with the more tightly focused beam leading to higher resolution patterning.

In the study, the group from the University of Southampton, UK, fabricated constricted domain wall spin valves that show considerable magneto-resistance when the Ni pads are switched by a magnetic field from an anti-parallel to a parallel configuration.

The implantation of He ions leads to sub-surface swelling, which limits the process to the fabrication of sub-30 nm device features and makes the tool complementary to e-beam lithography.

Group details

The Southampton Nanofabrication Centre run by the Nano Research Group is a state-of-the-art facility for micro-fabrication and high-spec nanofabrication, as well as a wide range of characterization capabilities housed in the new Mountbatten Complex at the University of Southampton. The scientists in the Nano Research Group focus on fabrication and engineering from the micro-scale down to the nanometre scale to produce a wide range of novel devices, materials and integrated systems. Current research topics include nano-magnetic materials and devices, nano-photonics, graphene electronics, biosensors, MEMS/NEMS devices, solar cells, new materials, as well as continuing work on ultimate MOS devices.

Full details can be found in the journal Nanotechnology.