On the Sub-Nanometer Resolution of Scanning Electron and Helium Ion Microscopes

Abstract

All forms of microscopy are being pushed to the limit by nanotechnology. This is especially true for high-resolution scanning electron and helium ion microscopes, which are proving to be extremely useful for nanometer-scale imaging, characterization, and dimensional measurements. Excellent resolution is essential for imaging nanomaterials. Hence, there is a relentless quest to achieve better and better resolution with various electron and ion microscopes and to monitor and maintain these instruments to achieve the best possible performance levels.The ability to resolve fine details with a microscope has greatly improved over the past 20 years. The resolution achievable with the newest scanning electron microscopes (SEMs) can now be at or below 0.4 nm and for the scanning helium ion microscope (HeIM), 0.24 nm has been reported. To put this into perspective, the {111} crystal plane in silicon (Si) has 0.32 nm lattice spacing, so one cubic nanometer in the Si crystal contains only a few atoms. Therefore, an instrument must be performing at the highest level possible to resolve routinely the finest structures. Clearly, the instrument operator must also be functioning at a high level as well to achieve the best resolution and to prove that the instrument is capable of doing the work.

To see or not to see: Imaging surfactant coated nano-particles using HIM and SEM

“…This method is very successful in this research field as it is minimal invasive and can achieve the required resolution of a few nano-meters down into the sub-nanometer * Correspondence to: e.s.kooij@utwente.nl 1 These authors contributed equally to the manuscript range [11]. With the advent of new detectors that allow energy filtering and separation of the different contributions to the signal as well as the possibility to use ultra-low acceleration voltages, the surface sensitivity of the method has also increased substantially.…”

“…Alternatively, a new charged particle scanning beam microscopy method has entered the market a few years ago. Helium Ion Microscopy (HIM) [12] has an ultimate resolution as small as 0.29 nm [11,13] and a very high surface sensitivity [14]. It uses helium ions to generate a multitude of signals including secondary electrons (SE), backscattered helium (BSHe) and photons.…”

Nanopillar growth by focused helium ion-beam-induced deposition

“…Compared to scanning electron microscopy, HIM has the advantage of a smaller interaction volume in the substrate and a predominance of type-1 secondary electron emission (SE 1 ) [10][11][12][13][14][15]. A helium ion microscope can also be used for nanofabrication.…”

Nanofabrication with a helium ion microscope

“…Until recently, the imaging tools have been limited to AFM and TEM. Helium ion microscopy (HIM) is a relative new high-resolution surface imaging technique [1,2]. It deploys a sub-nanometer sized spot that scans the surface of the sample with high sensitivity and high speed.…”

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ABSTRACTThe recently introduced helium ion microscope (HIM) is capable of imaging and fabrication of nanostructures thanks to its sub-nanometer sized ion probe [1,2]. The unique interaction of the helium ions with the sample material provides very localized secondary electron emission, thus providing a valuable signal for high-resolution imaging as well as a mechanism for very precise nanofabrication [3].

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