Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, PO Box 217, 7500AE Enschede, The Netherlands.
Beilstein J Nanotechnol. 2012;3:507-12. doi: 10.3762/bjnano.3.58. Epub 2012 Jul 12.
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.
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.
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.
氦离子显微镜是一种新型的高性能扫描电子显微镜替代品。它通过使用二次电子提供更高的分辨率和高表面灵敏度。
我们报告了一种新的对比机制，该机制将通常在二次电子图像中实现的高表面灵敏度扩展到背散射氦图像。我们展示了如何通过背散射产额的变化，在较重元素衬底上可视化薄的有机和无机层以及自组装单层。重衬底上的轻元素薄层应该对背散射产额没有直接影响。然而，使用不透明晶体分数的简单几何计算，可以根据沟道概率的变化来解释在图像中观察到的对比度。
吸附的薄膜对离子进入晶体的抑制提供了 HIM 的一种新的对比机制。这种去沟道对比度特别适合于在较重衬底上可视化超薄的轻元素层。我们的结果还强调了适当的真空条件对于基于沟道的实验方法的重要性。
