91HIGHLIGHTS 2020

Probing the chemistry of CdS paints in The Scream by in situ non-invasive spectroscopies and synchrotron radiation x-ray techniques, L. Monico (a,b,c), L. Cartechini (a,b), F. Rosi (a,b), A. Chieli (a,b), C. Grazia (a,b), S. De Meyer (c), G. Nuyts (c), F. Vanmeert (c), K. Janssens (c,d), M. Cotte (e,f), W. De Nolf (f), G. Falkenberg (g), I. Sandu (h), E. Storevik Tveit (h), J. Mass (i, j), R. Pereira de Freitas (a,k), A. Romani (a,b) and C. Miliani (a,b,l), Sci. Adv. 6, eaay3514

(2020); https://doi.org/10.1126/sciadv. aay3514. (a) CNR-SCITEC, Perugia (Italy) (b) SMAArt Centre and Department of Chemistry, Biology and Biotechnology, University of Perugia (Italy) (c) AXES Research Group, NANOlab Centre of Excellence, University of Antwerp (Belgium) (d) Rijksmuseum, Amsterdam (The Netherlands) (e) ESRF

(f) LAMS, CNRS UMR 8220, Sorbonne Université, Paris (France) (g) DESY, Hamburg (Germany) (h) Munch Museum, Oslo (Norway) (i) Bard Graduate Center, New York (USA) (j) Scientific Analysis of Fine Art, LLC, Berwyn (USA) (k) LISComp Laboratory, Federal Institute of Rio de Janeiro (Brazil) (l) CNR-ISPC, Napoli (Italy)

[1] T. Froysaker et al. (Eds), Public Paintings by Edvard Munch and His Contemporaries: Change and Conservation Challenges (Archetype Publications Ltd: London), pp. 3-35, 52-71, 204-216, 294-324 (2015). [2] L. Monico et al., Chemistry A European Journal 24, 11584-11593 (2018).

NEW ATTRACTION FOR HEAT-HARVESTING DEVICES EXPLOITING MAGNETISM

The combination of X-ray resonant scattering with X-ray nanobeam diffraction has revealed the role of magnetic domains on thermoelectric conversion in new spin caloritronic nanomaterials, which exploit magnons to convert waste heat into usable electricity. The observed spin texture is found to inhibit the thermoelectric conversion and is a first step towards highly efficient next-generation spintronics.

PRINCIPAL PUBLICATION AND AUTHORS

REFERENCES

yellow surface of the lake region, were studied by µ-XRD, µ-XRF and µ-XANES spectroscopy at beamline ID21. µ-XRD mapping revealed that the microflakes consist of poorly crystalline hexagonal-CdS and contain significant abundances of CdCO3 (Figure 75a). Clear evidence of the presence of sulfates and minor abundances of sulfites (Na2SO3) were found inside the CdS-paint via sulfur-oxidation state mapping and S K-edge µ-XANES spectroscopy (Figures 75b,d). Sulfate-species, present as agglomerates, are made up of Na2SO4 and varying amounts of CdSO4 (also revealed by μ-XRD as shown in Figure 75a). Cl K-edge μ-XANES measurements (Figures 75c,e) showed the local presence of Cd(OH)Cl (identified by μ-XRD as shown in Figure 75a) along with NaCl and KCl particles (Figures 75f,g).

These observations, combined with the findings obtained from artificially aged paint mock-ups, led to the conclusion that the sulfates and sulfites can be interpreted as degradation products of the paint. Significantly, it was demonstrated that in high moisture conditions

(i.e., at a relative humidity of 95% and above) and in the presence of cadmium chlorides, the original CdS is oxidised to CdSO4. This takes place even in the absence of light and does not occur on chlorine-free oil paint mock-ups aged under similar conditions [2]. Moreover, upon exposure to moisture, secondary reactions involving dissolution, migration through the paint, and recrystallisation of water-soluble phases (e.g., Na2SO4 and Cd(OH)Cl) may have further promoted the formation of CdSO4 and various chloride compounds. The nature and distribution of such phases may contribute to explaining the instability and flaking of the yellow paint in the lake area of the painting.

The findings of this work are expected to have significant implications for the preventive conservation of The Scream (ca. 1910). To further mitigate degradation of the cadmium yellow paint, the masterpiece should not be exposed to moisture levels higher than 45% relative humidity, while lighting conditions should be kept at standard values foreseen for lightfast painting materials.

Spintronic devices exploit both the charge and spin properties of the electron, with a wide scope of applications accessible by coupling spin, charge and heat currents in the same material. One promising extension is thermoelectric

generation, broadly termed spin caloritronics [1]. If optimised, thermoelectric technologies can enable the direct conversion of thermal energy to electrical power. For efficient devices, good electric and poor thermal conductivity is