Exploiting channelling in Helium Ion Microscopy


Exploiting channelling in Helium Ion Microscopy

Hlawacek, G.

Helium ion Microscopy1⁠ is a versatile microscopy technique that provides high resolution imaging and nano-machining in combination with a high surface sensitivity and large depth of focus. It utilizes a narrow beam of He+ ions to achieve a lateral resolution of less than 0.5 nm. Backscattered Helium ions (BSHe) and secondary electrons (SE) can be used to obtain an image of the specimen. While the first one will provide information of the bulk the latter is extremely surface sensitive2⁠.
When using crystalline samples channeling of the particles can occur. This effect can be exploited in several ways in the HIM. First of all it is possible to map out the different channeling directions and intensities and thus obtain information on the crystal structure of the sample. A simple geometrical model is introduced that can predict the channeling directions and relative intensities observed in the HIM. Such a map of the channeling directions for a fcc metal is presented in figure 13⁠. Channeling is also important for many imaging applications. The contrast on thin surface layers in SE mode can be enhanced when channeling is considered. For BSHe images the situation is more complicated as the signal is dominated by the bulk. Only heavy element adlayers on light element substrates can easily be imaged in BSHe mode. However, the dechanneling contrast also allows the visualization of light elements on heavy element substrates4⁠. In figure 2 a thin organic layer on a silicon wafer is made visible in SE and BSHe mode. By exploiting channeling and making use of the dechanneling contrast thin surface adlayers can be made visible in SE as well BSHe images5⁠.

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  • Invited lecture (Conferences)
    EBSD 2015, 30.-31.03.2015, Glasgow, United Kingdom

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