Abstract
Background: Helium ion microscopy is a new high-performance alternative to classical scanning electron microscopy. It provides superior resolution and high surface sensitivity by using secondary electrons.Results: We report on a new contrast mechanism that extends the high surface sensitivity that is usually achieved in secondary electron images, to backscattered helium images. We demonstrate how thin organic and inorganic layers as well as self-assembled monolayers can be visualized on heavier element substrates by changes in the backscatter yield. Thin layers of light elements on heavy substrates should have a negligible direct influence on backscatter yields. However, using simple geometric calculations of the opaque crystal fraction, the contrast that is observed in the images can be interpreted in terms of changes in the channeling probability.Conclusion: The suppression of ion channeling into crystalline matter by adsorbed thin films provides a new contrast mechanism for HIM. This dechanneling contrast is particularly well suited for the visualization of ultrathin layers of light elements on heavier substrates. Our results also highlight the importance of proper vacuum conditions for channeling-based experimental methods.
Highlights
The helium ion microscope (HIM) has established itself as a high-performance alternative to the classic scanning electron microscope (SEM)
The suppression of ion channeling into crystalline matter by adsorbed thin films provides a new contrast mechanism for HIM
Our results highlight the importance of proper vacuum conditions for channeling-based experimental methods
Summary
The helium ion microscope (HIM) has established itself as a high-performance alternative to the classic scanning electron microscope (SEM). While images based on secondary electrons (SE) allow a resolution as good as 0.29 nm [2], backscattered helium (BSHe) images reveal the elemental composition of the specimen. We discuss how channeling can be utilized to gain unexpected contrast in BSHe images on ultrathin surface layers. HIM already provides superior surface sensitivity in SE-based images. We demonstrate how hard-to-visualize thin layers of light elements on top of heavier element substrates can be detected in BSHe mode by clever utilization of channeling into the substrate. Helium ion microscopy is a new high-performance alternative to classical scanning electron microscopy. It provides superior resolution and high surface sensitivity by using secondary electrons
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