Scanning transmission helium ion microscopy on carbon nanomembranes.

Jörg K N Lindner,Nikolaus Meyerbröker,André Beyer,Daniel Emmrich,Annalena Wolff,Armin Gölzhäuser

doi:10.3762/bjnano.12.18

Jörg K N Lindner, Nikolaus Meyerbröker + Show 4 more

Open Access

https://doi.org/10.3762/bjnano.12.18

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Abstract

A dark-field scanning transmission ion microscopy detector was designed for the helium ion microscope. The detection principle is based on a secondary electron conversion holder with an exchangeable aperture strip allowing its acceptance angle to be tuned from 3 to 98 mrad. The contrast mechanism and performance were investigated using freestanding nanometer-thin carbon membranes. The results demonstrate that the detector can be optimized either for most efficient signal collection or for maximum image contrast. The designed setup allows for the imaging of thin low-density materials that otherwise provide little signal or contrast and for a clear end-point detection in the fabrication of nanopores. In addition, the detector is able to determine the thickness of membranes with sub-nanometer precision by quantitatively evaluating the image signal and comparing the results with Monte Carlo simulations. The thickness determined by the dark-field transmission detector is compared to X-ray photoelectron spectroscopy and energy-filtered transmission electron microscopy measurements.

Highlights

Throughout the past decade, the helium ion microscope (HIM) has emerged as a versatile instrument that is used to drive research across multiple disciplines
The results suggest that the Carbon nanomembranes (CNMs) thickness can be determined with sub-nanometer accuracy using dark-field scanning transmission ion microscopy (STIM) measurements
To test the validity of the determined thickness and the approach described above, the results from the STIM dark-field imaging are compared to X-ray photoelectron spectroscopy (XPS) and energy-filtered transmission electron microscopy (EFTEM) data, both being established techniques for the thickness measurement of thin films

Summary

Introduction

Throughout the past decade, the helium ion microscope (HIM) has emerged as a versatile instrument that is used to drive research across multiple disciplines. Depending on the resulting scattering angle, the transmitted ions hit different points on the conversion plate below the sample. A mechanically stable with α as the acceptance angle, h as the operational height of the holder (i.e., the distance between a thin membrane and the conversion plate) and r as the radius of the hole (Figure 1a).

Results

Conclusion