Scanning helium ion microscope

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Helium ion microscope by Zeiss
Comparison of SEM (top) and SHIM (bottom) images of mouse enamel. SHIM images have a superior depth of field, showing internal structure in enamel tunnels, which are dark spots in SEM images.[1]

A scanning helium ion microscope (SHIM, HeIM or HIM) is a high-resolution imaging instrument that uses a scanning helium ion beam to visualize at sub-nanometer resolution. It was developed in the mid-2000s for nanotechnology applications, and has been demonstrated to have a better surface resolution than scanning electron microscopes.

Description

Scanning helium ion microscope (SHIM) was developed in the mid-2000s as a new microscopy technique for nanotechnology applications.[2] It uses a focused beam of helium ions to scan a specimen's surface instead of electrons used in a scanning electron microscope (SEM).[3][4] It utilizes a gas field ionization source (GFIS), which is used to produce a highly focused beam of helium ions.[5]

The very high source brightness, and the short De Broglie wavelength of the helium ions, enables extremely small probe sizes.[4][5] Similar to other focused ion beam techniques, it allows to combine milling and cutting of samples with their observation at sub-nanometer resolution.[5][6] A surface resolution of 0.24 nanometers has been demonstrated by Zeiss.[7][8]

When the helium ions interact with a sample under visualization, it does not suffer from large excitation volume, and hence produces a much smaller interaction volume compared to electrons, leading to better surface sensitivity. These characteristics enable the SHIM to obtain qualitative data with a greater resolution that is not achievable with conventional microscopes which use photons or electrons as the emitting source.[4] The small interaction volume results in high contrast images, with a large depth of field on a wide range of materials.[2] The microscope is also better at imaging insulating materials because it causes less charging on interaction with such materials compared to electron beams.[4]

History

The SHIMs were made commercially available by Zeiss in 2007, and the first microscope was shipped to the National Institute of Standards and Technology.[9] However, it was discontinued by Zeiss in 2023.[10]

References

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