Cs-corrected, monochromated low-voltage TEM

Introduction

This article gives an overview of worldwide research in low-voltage aberration-corrected transmission and scanning transmission electron microscopy (TEM/STEM), evaluated on the basis of the scientific publications that appeared until the end of 2011. Low voltage here usually means TEM/STEM below 100 kV [1].

At Ulm University, the SALVE project developed a microscope for even lower voltages, down to 20 kV, together with Thermo Fisher Scientific. This development was made possible by the breakthroughs in aberration correction at the end of the last century (see the news articles 'Wolf Prize' and 'Historical Aspects of Hardware Aberration Correction'). The project has since grown into a permanent institution, the SALVE Microscopy Center, much as SuperSTEM at Daresbury began as a project and is today a national research facility. Similar surveys by others are found in [2]–[4].

Europe

Until 2011, Germany accounted for 51% of Europe’s papers on low-voltage aberration-corrected TEM/STEM and was thus a key country for both the application and the development of the method. The three leading institutions in Europe were Ulm University with its group Electron Microscopy of Materials Science (21%), the Leibniz Institute for Solid State and Materials Research (IFW) Dresden (16%) and the Department of Materials at the University of Oxford (14%). Together, the institutions in Germany and Great Britain provided 79% of Europe’s contribution. The remaining 21% were distributed as follows: the Netherlands (7%), Finland (5%), Switzerland and Belgium (3% together), Austria and Italy (1% together) and others (5% together, see the map).

Worldwide

Europe published 55% of all evaluated papers on low-voltage aberration-corrected TEM/STEM; the SALVE project alone contributed 15%. North America accounted for 30% and Asia for 15%.

Ranked by country, the publications until 2011 came from the USA (29%), Germany (28%), Great Britain (15%), Japan (11%), the Netherlands and Finland (3% each), Switzerland (2%) and Belgium, Canada, Taiwan, Israel, Austria, China, Australia, Italy and others (1% each).

Ranked by institution, the list was led by Ulm University (12%), Lawrence Berkeley National Laboratory (10%), IFW Dresden (9%), the University of Oxford (8%) and AIST (6%), followed by Harvard University (4%); the University of California, JEOL Ltd. and FEI Electron Optics (3% each); and the University of Helsinki, the University of Nottingham, the Max Planck Institute for Solid State Research Stuttgart, CEOS GmbH and Nion Corp. (2% each). FEI has been part of Thermo Fisher Scientific since 2016, and Nion part of Bruker since 2024. Others accounted for 34%; for details see the world map.

Methods

The share of the methods is taken from the SALVE trend database, which counts the papers on aberration-corrected TEM/STEM in leading journals year by year. At 20–80 kV, TEM accounted for 55% of the papers in 2011, STEM for 38% and combined TEM-STEM for 7%. Since then STEM has almost caught up: in 2024 the shares were 44% TEM, 42% STEM and 14% TEM-STEM. At 100–300 kV, STEM clearly dominates, with 61% of the papers in 2024, against 20% TEM and 19% TEM-STEM (Fig. 2). The first version of this article, based on a hand-compiled list of 123 publications up to 2011, had found 78% TEM, 12% TEM-STEM and only 10% STEM. That list came mainly from groups working in TEM mode; the larger trend database shows that STEM already accounted for more than a third of the papers in 2011.

Materials

The materials studied are taken from the same trend database (Fig. 3). At 20–80 kV, low-dimensional carbon materials led in 2011 with 26% of the papers, followed by functionalized graphene, carbon nanotubes and fullerenes (22%), test specimens and other materials (21%), low-dimensional inorganic materials (13%) and nanocrystals (8%); oxides and semiconductors had 5% each. By 2024, low-dimensional inorganic materials such as transition-metal dichalcogenides had become the largest class with 26%, while pristine carbon materials fell to 14%. Functionalized carbon materials kept their 22%, and oxides rose to 8%. At 100–300 kV the picture is quite different: oxides (40%), nanocrystals (23%) and semiconductors (16%) dominate, and the low-dimensional materials together account for only 9%. Low voltage thus remains the domain of beam-sensitive two-dimensional materials.

Since 2011

The map, the regional shares and the institution ranking describe the pioneering years up to 2011. How the field has grown since then is followed by SALVE’s own literature analysis: the SALVE trend database has counted the papers in leading journals year by year since 2012 and is shown in the trend graphics on the SALVE homepage, which many groups use as a reference for the field. A rough count in the open literature database OpenAlex is in good agreement: a search of the titles and abstracts of all publications for aberration correction together with low voltage finds 70 up to 2011 and 207 from 2012 to 2025, about three times as many. Up to 2011, Germany (25), Great Britain (23), the USA (16) and Japan (15) led, the same countries as in the evaluation above. From 2012 to 2025, the USA (56) led ahead of Japan (48), Germany (36), Great Britain (34), China (18), France (12) and South Korea (9); China accounted for only 1% of the papers until 2011. A publication counts once for every country among its authors’ affiliations. Because only titles and abstracts are searched, the counts show the trend rather than exact numbers. The methods have shifted as well: STEM, with techniques such as EELS, EDX, 4D-STEM and ptychography, has caught up with TEM at low voltage and dominates at medium voltage (Fig. 2).

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The map and the regional shares are based on the literature until the end of 2011, see the 'Publication list for AC-(S)TEM for 20–80 kV'.

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^*For more information about this study, please contact Ute A. Kaiser or EFP Berlin.