Electron Microscopy Sample Preparation: “The Future is Cold, Dynamic and Hybrid”

Interview with Staf van Tendeloo and Frédéric Leroux from the Leica Reference Site at EMAT (Electron Microscopy for Materials Science), University of Antwerp

October 22, 2015

In 2014, the renowned Electron Microscopy for Materials Science (EMAT) research lab at the University Antwerp, Belgium, and Leica Microsystems started a fruitful collaboration to establish a Leica Reference Site in Antwerp.

This site, officially opened in July 2014, is dedicated to specimen preparation for electron microscopy in materials science with a special focus on ion beam milling and recently also on carbon coating.

In this interview Prof Gustaf van Tendeloo, Director of EMAT, and Frédéric Leroux, TEM specimen preparation specialist, talk about research topics at EMAT, how the Leica reference site has evolved, and future trends for EM sample preparation.

Fig. 1: Frédéric Leroux, PhD, TEM specimen preparation specialist at EMAT, University of Antwerp, Belgium

What is the goal of the Collaborative Partner and Reference Site with Leica Microsystems?

Staf van Tendeloo: The EMAT research laboratory has a well-recognized world-wide reputation in advanced electron microscopy analysis. Daily, over 25 researchers acquire and analyze TEM data using one of our 9 electron microscopes of which the latest are aberration corrected. The introduction of Cs-corrected microscopes has drastically influenced and improved the applications of modern electron microscopy. It will take characterization of advanced materials to the ultimate atomic level. However, obtaining structural information down to the atomic scale requires high quality TEM specimens.

Frédéric Leroux: Indeed, the resolution and structural details in TEM images is greatly impacted by the quality of the TEM samples. Improving the quality of these samples is one of our main goals. We therefore expect that the partnership will enable us to develop and refine new applications that will push our current boundaries in materials science characterization. As scientists, we can’t wait to use the Leica instruments to their limits and see how EM sample preparation can be brought to the next level.

What are the benefits for users of the site?

Staf van Tendeloo: Since 1965, EMAT has built up a wide range of activities concerned with fundamental solid state physics, materials science, solid state chemistry and materials characterisation. With decreasing dimensions down to the nanometer and sub-nanometer scale, electron microscopy is a unique technique, being able to relate structural properties to physical or chemical properties.

Increased understanding of the basic phenomena involved in the "electron beam - material" interaction and improved computer power allow to better determine the local structure, the local composition and even the local electronic structure. This is applied to a wide field of materials such as semiconductors, superconductors, alloys, polymers catalysts and small particles, surface layers, multilayers and composite materials. 

Advanced electron microscopy not only involves resolution at the angstrom level: it also includes advanced diffraction techniques for determining the local structure and analysis of the inelastic scattered electrons to obtain compositional and electronic information. The strength of EMAT is that both theoretical and experimental know how is available for these different techniques.

Who can use the site?

Staf van Tendeloo: We clearly distinguish between fundamental research between research groups and industrial research. For industrial research there is a confidentiality agreement, a contract and the results totally belong to the company.

For fundamental research, all interesting projects are very welcome and can be discussed between both parties. Transnational access can be granted through the EC project “ESTEEM2” (www.esteem2.eu).

Which applications and research goals can be realized here?

Staf van Tendeloo: The interest of EMAT includes advanced electron diffraction to refine crystal structures, ultra high resolution at the sub-Angstrom level, electron tomography to reconstruct 3D morphologies at the nanoscale, energy filtered TEM for compositional mapping, electron energy loss spectroscopy (EELS) for electronic (bonding) analysis.

EMAT also has the necessary theoretical support for EM simulations and interpretation as well as for DFT calculations. The materials investigated cover a wide range, including alloys, ceramics, composites, but also nanoparticles, carbon based materials, porous materials, soft matter-hard matter and polymers. However a big focus is on nanostructured materials.

Fig. 2: TEM characterization of as-prepared and annealed α-Fe2O3 nanodeposits fabricated at 300°C. (2a) Cross-sectional HAADF-STEM image of the as-prepared sample, with EDX chemical map displayed in the inset. (2b) Cross-sectional HAADF-STEM micrograph of the annealed specimen. (2c) Bright-field TEM image of the FTO/ α-Fe2O3 interface for the as-prepared sample. Inset: ED pattern of the α-Fe2O3 nanodeposit. (2d) Representative HAADF-STEM image of α-Fe2O3 dendrites in the annealed specimen. White arrows mark the presence of some low-contrast pores. (2e) High resolution HAADF-STEM micrograph of an α-Fe2O3 dendrite in the annealed sample. The image is taken from the region marked by the white rectangle in 10d. (TEM images acquired by Dr. Stuart Turner, EMAT)

What highlights have there been since the start of the collaboration site?

Frédéric Leroux: We recently installed the Leica EM ACE600 carbon coater to improve our microscopy performance. When performing atomic scale analysis or SEM studies, every additional nanometer of amorphous carbon deposited on a sample which has no added benefits during analysis is detrimental for the signal-to-noise ratio of the obtained data. The unsurpassed reproducibility and accuracy of this coater enabled us to improve our results.

We are also currently optimizing argon ion beam milling of thin films using the Leica EM RES102. Here, we specifically aim at increasing the sample turnover without compromising the quality of the obtained specimens.

Why did you choose Leica Microsystems as a collaboration partner?

Frédéric Leroux: The major reason for the partnership is our long-term experience with the earlier versions of the Leica EM RES102 ion beam milling system and ultramicrotomes. The older models are still in use to this date and provided us with many solid solutions and an amazing flexibility ever since they were installed in our lab. Moreover, the instruments provide a high level of reproducibility, which is exactly what we were looking for. The instruments are made with extreme professionalism and with an in depth understanding of the subject.

Fig. 3: Plan view specimen of SrTiO3 prepared using the Leica EM RES102. In the according magnified STEM images one can see that the image contrast is homogeneous over the whole image and all atomic columns are resolved (STEM images acquired by Dr. Nicolas Gauquelin, EMAT).

What is your vision as director of the site? What are your goals, what do you expect?

Staf van Tendeloo: Electron microscopy is one of the few techniques that provide information on a nanoscale; even on an atomic scale. As technology is moving towards smaller and smaller dimensions, imaging at this scale becomes a must for technological progress.

Moreover electron microscopy has become a fully analytical technique, able to provide not only structural information, but also chemical and bonding information. All this not only in two dimensions, but recently in three dimensions. Essential though is to have a perfectly prepared and clean sample. Therefore TEM sample preparation will become even more important.

A glimpse into the future: How will sample preparation for electron microscopy evolve within the next 10 years?

Frédéric Leroux: I think the future is cold, dynamical and hybrid. Whereas much of the soft matter electron microscopy has been superseded in the last decade by less-damaging techniques such as confocal, two-photon, multi-photon, and near-field light microscopy by certain extents, there is still a major role for cryo TEM analysis of biomaterials, bio/inorganic interfaces, and nano-biological materials at near atomic scale. In the advent of this rapidly growing field manifold improvements in specimen preparation are necessary. Moreover, sample preparation developments for cryo TEM in combination with light microscopy are critical in order to achieve major progresses in this field.

There will be an increasing interest in analysing processes, more specifically interactions, growth, temperature-based structural transformations, etc. Although in situ observation of chemical processes is already feasible, both the time and spatial resolution will still improve. This is an important growth area where new parallel developments in electron microscopy instrumentation and sample preparation techniques will have a great impact.

The fabrication and analysis of composite hybrid materials is becoming more widespread. However soft and hard matter require different preparation approaches and instrumentation, all of which are dictated by their properties. Efforts will be necessary to provide and develop a specific toolbox to prepare and characterize these new types of materials.

The EMAT labs with the Leica EM ACE600 coater, the EM RES102 ion beam milling system, various microscopes and ultramicrotomes

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