PROMISES

Homepage of MSCA project funded by the European Union under GA No. 889546

"Properties of nanomaterials made from misfit-layered compounds revealed by electron microscopy and simulations"

Contents of this homepage:

• Embedded video "Misfit Nanotubes" created for dissemination purposes
• Summary of project
• Scientific publications
  
• Downloads

Summary

A way to reach many of the UN goals for sustainable development is a significant advancement in technology and material science. Although not an explicit goal, green energy is a key element that fuels the sustainable transformation of modern societies. One way to provide green energy is the generation of power from heat waste by thermoelectricity. One promising candidate for high-performance thermoelectric materials are the misfit layered compounds (MLCs). PROMISES focuses on the analysis of nanotubes made of this complex material system and related structures, with especial emphasis on in-situ studies, which allow investigation under application-relevant conditions.

The MLCs are based on layered materials, which possess a strong bonding in one plane and a weak bonding in the perpendicular direction, which causes their layered structure. In MLCs, atomic planes of two different layered materials stack up alternately. As each layered material possesses a different structure, atom positions from alternating layers are not identical, causing a misfit, giving the MLCs their name. This misfit makes bending of layered stacks favorable and facilitates the formation of tubular structures. MLCs are promising candidates for thermoelectric materials as they combine the properties of two different layered materials. However, MLCs are complex systems which require advanced characterization methods to shed light on their performance in potential applications, a main objective of PROMISES.

Therefore, nanotubular structures of MLCs and related materials are investigated by advanced transmission electron microscopy (TEM) for a better understanding of their structure, properties and the synthesis conditions of the material. A special focus is put on in-situ TEM studies, the second main objective, which allow to study (nano)materials under the influence of external stimuli such as heat or electrical currents. Technological development of in-situ TEM is necessary to solve the problem of sample preparation and contacting of individual nanomaterials especially for electrical in-situ analysis. An additional issue in TEM of very thin nanomaterials is the little contrast observed under focused conditions. A solution can be physical phase plates, which improve phase contrast of thin objects and the combination of aberration-corrected TEM with such phase plates was investigated

In the course of the project, several important findings on MLCs and other layered materials have allowed for a deeper understanding of their structure, properties, stability and the processes involved in the synthesis of these materials. Also, a novel preparation method has been developed to allow the in-situ studies of the stability and evolution of individual MLC nanotubes under the application of high electrical currents. As MLC is a promising candidate for thermoelectrical applications, the possibility of thermoelectrical characterization by in-situ TEM has been explored. As a conclusion, the results obtained in PROMISES have significantly improved the understanding of these materials as well as ameliorated and optimized in-situ TEM characterization approaches of nanomaterials beyond the state of the art.

Performed work

The work performed in PROMISES can be divided in two parts. The first part deals with the analysis of nanomaterials, synthesized by collaboration partners, by advanced transmission electron microscopy and related techniques. Numerous material systems have been investigated and the main results are summarized in the following: From the MLC material system class, nanotubes made of SrxCoO2-CoO2 have been analyzed and identified as promising candidates as interconnect material due to an extraordinary high ampacity. In a similar material system based on Ca instead of Sr, stable layered CoO2 nanoscrolls could be observed. The nanoscrolls are noteworthy as layered CoO2 is unstable in bulk form. A novel class of quaternary chalcogen-based MLC nanotubes (Sm,Y)S-TaS2 was studied. The analysis of many MLC nanotubes from a large study of a collaboration partner on stability and synthesis conditions for obtaining nanotubes of SmS-TaS2 and LaS-TaS2 showed that, e.g., nanotubes are only a meta-stable form. Related to MLCs, the study of nanotubes from the ternary system W(S,Se)2 showed that the band gap of the nanotubes can be tuned by the S/Se alloying degree, which could be useful for optoelectronic applications. A study of the epitaxial growth conditions of WS2 on sapphire showed that a metal pre-seeding step leads to the formation of an WO3 interface that facilitates the large-scale growth of WS2. For dissemination purposes, four scientific articles with results on the materials were published in peer-reviewed journals, two more have been submitted and at least two more are in preparation.

The second part of the work focused on methodological development of electron microscopy. The combination of aberration correction with Zernike phase plates was successfully studied. This is a very promising technique to enhance contrast and improve interpretability of TEM images of nanomaterials. Two scientific articles on phase plates were published in peer-reviewed journals. However, the main focus of methodological development was devoted to in-situ TEM analysis, especially for electrical characterization studies. Novel in-situ chips, which are the sample support for in-situ studies, were designed and fabricated. One design aimed to facilitate the thermoelectrical characterization of (nano)materials by in-situ TEM. Several proof-of-principle experiments showed the induction of a thermo-voltage and the general possibility of these analyses and a scientific article is in preparation. A second chip was designed for electrical characterization of materials in combination with the possibility to heat the sample. One of the main challenges for in-situ TEM is a clean preparation and contacting of the sample on the in-situ chip, especially for nanomaterials, whose structure has to be preserved throughout the process. A support-based transfer process was elaborated that provides a high reproducibility at minimum damage and contamination of the material. The process was sent as an investigation result to the office of technology transfer and a scientific article has been submitted. The technique was tested on various different nanomaterials, which subsequently were studied by in-situ TEM. Results have been obtained on the stability of LaS-TaS2 MLC under high electrical currents, which allows to study the breakdown mechanism. This breakdown mechanism differs largely between materials as have shown similar experiments on carbon-based materials. The results obtained by the in-situ studies require further analysis but several scientific publications are envisaged.

In addition to scientific articles, the results have been presented at five scientific conferences or seminars. Moreover, several dissemination activities during PROMISES aimed for the non-scientific public, including newspaper articles, the participation at the European Researchers' Night and the 2021 edition of Science is Wonderful.

Main progress

In the course of the PROMISES project, progress beyond the state of the art has been made in several areas. The advanced TEM and EELS data analysis conducted for different samples have represented a clear improvement of the knowledge and understanding of the studied systems. Two example data analyses, which were necessary for the study of the epitaxial growth conditions of WS2 on sapphire, are presented here: Firstly, the creation of an average map of the atomic configuration at the sapphire surface at different sample orientation allowed to adjust the model for density functional theory calculations and thus, to fully understand the structure of the interface made by WS2 and sapphire, by both theory and experiments. Secondly, the analysis by non-negative matrix factorization of the low-loss EELS data obtained at that interface yielded the clear identification of the different contributions of each of these materials. These examples illustrate that the improvement of TEM data analysis has a direct and critical impact on the materials' understanding.

In the area of methodological development of TEM, progress has clearly gone beyond the state of the art. For the first time, physical Zernike phase plates have been successfully combined with aberration-corrected TEM. It has been shown that the use of phase plates can strongly increase the information content in TEM images and also their interpretability. The developed support-based sample preparation of individual nanomaterials is the first process that guarantees high reproducibility with minimum damage and contamination of the materials. This sample preparation method allows, e.g., to study the behavior of materials under high electrical currents by in-situ TEM. Finally, for the first time, studies on thermoelectrical in-situ TEM have been performed, which potentially allows the direct analysis of the interplay between thermoelectrical properties and grain boundaries or dopants.

High-performance materials are a key element for sustainable progress in the modern society. The studies performed in the PROMISES project help to understand these materials in a better way.

Publications

S. Hettler, R. Arenal, Aberration-corrected transmission electron microscopy with Zernike phase plate. Ultramicroscopy 239, 113564 (2022). DOI.

M. Obermair, S. Hettler, M. Dries, M. Hugenschmidt, R. Spiecker, D. Gerthsen. Carbon-film-based Zernike phase plates with smooth thickness gradient for phase-contrast transmission electron microscopy with reduced fringing artifacts. Journal of Microscopy 287, 45-58 (2022). DOI.

K. Singha-Roy, S. Hettler, R. Arenal, L. Panchakarla, Strontium Deficient SrxCoO2-CoO2 Nanotubes as a High Ampacity and High Conductivity Material. Materials Horizon 9, 2115-2127 (2022). DOI.

M. B. Sreedhara, Y. Miroshnikov, K. Zheng, L. Houben, S. Hettler, R. Arenal, I. Pinkas, S.S. Sinha, I. E. Castelli, R. Tenne. Nanotubes from Ternary WS2(1−x)Se2x Alloys: Stoichiometry Modulated Tunable Optical Properties. JACS 144 (23), 10530-10541, 2022. DOI.

A. Bar-Hen, S. Hettler, A. Ramasubramaniam, R. Arenal, R. Bar-Ziv, M. Bar Sadan. Catalysts for the hydrogen evolution reaction in alkaline medium: Configuring a cooperative mechanism at the Ag-Ag2S-MoS2 interface. Journal of Energy Chemistry 74, 481-488 (2022). DOI.

A. Cohen, P. K. Mohapatra, S. Hettler, A. Patsha, K. V. L. V. Narayanachari, P. Shekhter, J. Cavin, J. M. Rondinelli, M. Bedzyk, O. Dieguez, R. Arenal, A. Ismach, Tungsten Oxide Mediated Quasi-van der Waals Epitaxy of WS2 on Sapphire ACS Nano 17, 5399-5411 (2023). DOI.

S. Pandey, S. Hettler, R. Arenal, C. Bouillet, A. Raman Moghe, S. Berciaud, J.Robert, J.-F. Dayen, D. Halley, Room-temperature anomalous Hall effect in graphene in interfacial magnetic proximity to EuO grown by topotactic reduction, Phys. Rev. B 108, 144423 (2023).

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