Revealing crystal orientation and defects in the Helium Ion Microscope using channeling

Helium Ion Microscopy (HIM) is well known for its exceptional imaging and nanofabrication capabilities [1]⁠. HIM has an unprecedented surface sensitivity, and channeling can be utilized to maximize the signal to noise ratio, obtain information on the crystal structure and reveal defects such as dislocation networks.
Using a poly crystalline gold sample we show how channeling can be used to obtain crystallographic information in the HIM [2]⁠.
We demonstrate the resolving power of this technique using a thin (2 ML) silver layer on Pt(111). This is is representative example of a surface confined alloy widely studied in the field surface science. The obtained HIM results are compared to results obtained by low energy electron microscopy, spot profile analysis low energy electron diffraction (SPA-LEED), and atomic force microscopy phase contrast. In HIM single atom layer high steps can be visualized as a result of a work function change—across the otherwise atomically flat terraces—of only 20 meV. By utilizing the dechanneling contrast [3]⁠ mechanism also the surface reconstruction of this thin surface layer can be revealed. We find a threefold periodic structure of channeling (fcc stacking) and dechanneling (hcp stacking) areas. The periodicity of this structure—measured along the <11-2> surface directions—is 6.65 nm [4]⁠. This is in excellent agreement with values obtained by SPA-LEED.