Johannes Müller (Berlin / DE), Marcel Schloz (Berlin / DE), Julian Schmehr (Hamburg / DE), Jin Cao (Hamburg / DE), Christian Mirek (Berlin / DE), Benedikt Haas (Berlin / DE), Sherjeel Shabih (Berlin / DE), Wouter van den Broek (Berlin / DE), Julian Becker (Hamburg / DE), Christoph T. Koch (Berlin / DE)
Abstract text (incl. figure legends and references)
1. Introduction
A wide range of diffraction-based techniques have recently been developed for 4D-STEM [1], many of these techniques can also be employed in conventional SEMs by inserting a fast camera below the electron-transparent sample. We developed two different camera-based sub-stages to realize 4D-STEM in SEMs, which can acquire transmission diffraction patterns with up to 2000 fps. Compared to dedicated transmission electron microscopes, using SEMs as a base platform allows for simpler, more easily customizable, and more economical systems. In addition, the lower acceleration voltage of 0.5kV to 30kV results in stronger scattering (beneficial, e.g. in 2D materials) as well as reduced knock-on damage. We will present our two SEM sub-stages and show a summary of our implemented methods and applications.
2. Objectives
Our goal is to add 4D-STEM to SEMs and FIB/SEMs to expand their vast range of applications, we ultimately aim for enabling ptychography [2] in SEM to increase their spatial resolution well beyond the instruments limit.
3. Material & methods
The two different camera-based transmission diffraction sub-stages are mountable to the SEM stage within our Zeiss GeminiSEM 500. The first setup consists of a Medipix 3 direct electron detector [3] and the second setup utilizes a compact 2.5x2.5x1.1cm³ CMOS camera with a fiber-coupled scintillator mounted inside a hexapod stage.
We merged the hard- and software in-house, giving us full control over the whole system. This enables us to implement new methods, like live-feedback systems, and existing 4D-STEM-based methods.
4. Results
We applied our SEM diffraction setups to map material properties like layer thickness, crystal orientations, crystallite size, crystallinity and other crystallographic information.
We also looked into improving the stability between sample and electron beam to apply more advanced methods like ptychography by investigating unwanted shifts resulting from floor vibrations, acoustic and electro-magnetic noise. For that purpose, we implemented a proof of concept feedback system using shadow images of a hole in a carbon TEM grid to minimize the relative movement between electron beam and sample.
5. Conclusion
4D-STEM in SEMs with direct and scintillator-based cameras is a feasible and well-working tool to investigate thin bulk and low-dimensional materials in SEMs, adding to their versatility.
Having full control over the microscope setup also allows for implementing new methods like live-feedback systems. Minimizing unwanted movement between sample and electron beam, will allow for ptychography in standard SEMs increasing the spatial resolution well beyond the instrument limit and increasing their application range.
References:
[1] C. Ophus, Microscopy and Microanalysis, Vol. 25, Issue 3, June 2019, pp. 563-582 (2019)
[2] M. Schloz, et al, Optics Express, Vol. 28, Issue 19, pp. 28306-28323 (2020)
[3] https://x-spectrum.de
[4] LiberTEM, DOI: 10.5281/zenodo.6927963
We acknowledge financial support by the German Research Foundation (DFG grant nrs. KO 2911/12-1, KO 2911/13-1, BR 5095/2-1 and Projektnummer 182087777 - SFB951) and by the Volkswagen Foundation (Initiative: "Experiment!", Project "Beyond mechanical stiffness").
We thank Harald Niebel, Björn Gamm, Markus Boese from Carl Zeiss Microscopy GmbH for help with controlling the SEM.