123HIGHLIGHTS 2020

Toward ultimate nonvolatile resistive memories: The mechanism behind ovonic threshold switching revealed, P. Noé (a), A. Verdy (a), F. d Acapito (b), J.-B. Dory (a), M. Bernard (a), J.-B. Jager (c), J. Gaudin (d) and J.-Y. Raty (a,e), Sci. Adv. 6, eaay2830 (2020); https://doi.org/10.1126/sciadv.

aay2830. (a) Université Grenoble Alpes, CEA, LETI, Grenoble (France) (b) CNR-IOM-OGG c/o ESRF, Grenoble, (Italy/ France) (c) Université Grenoble Alpes, CEA, IRIG, Grenoble (France)

(d) CELIA, Université de Bordeaux, CEA, CNRS, UMR 5107, Talence (France) (e) CESAM-Physics of Solids Interfaces and Nanostructures, Université de Liège, Sart- Tilman (Belgium)

[1] S.R. Ovshinsky, Phys. Rev. Lett. 21, 1450 (1968). [2] P. Noé & F. Hippert in Phase Change Memory, A. Redaelli (ed.) Springer Cham, 125-179 (2018). [3] J.-Y. Raty & P. Noé, Phys. Status Solidi RRL 14, 1900581 (2020). [4] M. Wuttig et al., Adv. Mater. 30, 1803777 (2018).

PRINCIPAL PUBLICATION AND AUTHORS

REFERENCES

TRACKING THE EVOLUTION OF Pt SINGLE SITES ON CeO2

Platinum single sites show excellent atom economy, but their role in the oxidation of pollutants (e.g, CO, CH4) is strongly discussed. This study used advanced operando infrared/hard X-ray techniques to localise these sites and to show that they are very dynamic and form small clusters/particles that are more active.

In heterogeneous catalysis, for example in emission control, the interaction of the support with the active noble metal can have a huge impact on the catalytic activity. In the case of platinum dispersed on ceria, the strong synergy between the two components can lead to the fine distribution possibly down to atomically dispersed species of Pt on the surface of the oxide under strongly oxidising conditions [1]. These single-atom catalysts are of high interest since

each individual noble metal atom is accessible and thus, potentially, an active site. This high atom efficiency would lead optimal noble metal usage. However, their real performance and the structure of these sites during the catalytic reaction (in particular stability, electronic state and fate) is still unclear.

Using a systematic and elaborate operando multi-technique approach, this study

Fig. 108: a) Schematics of HERDF-XANES setup at BM16. Photo: D. Testemale (CNRS). b) Operando HERDF-XANES spectra recorded for Pt single sites in CO oxidation reaction mixture. c) Reference spectra determined via MCR-ALS.

Figure credits: P. Dolcet, F. Maurer, M. Casapu, J.-D. Grunwaldt (KIT).

phase-change materials and those of the OTS family. In both systems, the bonding mechanism of MVB is responsible for the unique properties that led to the recent breakthrough

in NVMs. Finally, the main difference between PCM and OTS materials lies in their ability to stabilise the MVB mechanism and in the energy barrier to crystallisation.