S T R U C T U R E O F M A T E R I A L S

S C I E N T I F I C H I G H L I G H T S

1 2 0 H I G H L I G H T S 2 0 2 2 I

Fig. 111: Double-stage diamond anvil cell. To generate ultra- high pressures, the top surface of the primary 40 µm-diameter diamond anvil (top left) was modified with a focused ion beam. This reduced the contact area from 40 µm to 10 µm (top right). To increase the strength of the anvil, a nanocrystalline diamond

semiball (1) was added to it as a second stage anvil (2).

PRINCIPAL PUBLICATION AND AUTHORS

Materials synthesis at terapascal static pressures, L. Dubrovinsky (a), S. Khandarkhaeva (a,b), T. Fedotenko (c), D. Laniel (b), M. Bykov (d), C. Giacobbe (e), E. Lawrence Bright (e), P. Sedmak (e), S. Chariton (f), V. Prakapenka (f), A.V. Ponomareva (g), E.A. Smirnova (g), M.P. Belov (g), F. Tasnádi (h), N. Shulumba (h), F. Trybel (h), I.A. Abrikosov (h), N. Dubrovinskaia (b,h), Nature 605, 274-278 (2022); https:/doi.org/10.1038/s41586-022-04550-2 (a) Bayerisches Geoinstitut, University of Bayreuth (Germany) (b) Material Physics and Technology at Extreme Conditions, Laboratory of Crystallography University of Bayreuth (Germany) (c) Deutsches Elektronen-Synchrotron DESY, Hamburg (Germany) (d) Institute of Inorganic Chemistry, University of Cologne (Germany) (e) ESRF (f) Center for Advanced Radiation Sources, The University of Chicago, Illinois (USA) (g) Materials Modeling and Development Laboratory, National University of Science and Technology MISIS , Moscow (Russia) (h) Theoretical Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University (Sweden)

This work presents a solution: to generate ultra-high pressures, the top surface of the primary diamond anvil with a diameter of 40 µm was modified using a focused ion beam. As a result, the contact area was reduced from 40 µm to 10 µm (Figure 111). To increase the strength of the anvil, a semi-ball made of nanocrystalline diamond was added on the top as a second-stage anvil. This new device (called a double-stage diamond anvil cell) makes it possible to achieve pressures of around 1000 GPa. Moreover, by applying a specially designed laser-heated setup at the University of Bayreuth, heating of the samples over 3000 K was realised at such pressures.

The generation of pressures and temperatures is not an ultimate goal of the experiments a crucial part is the analysis of products of the reactions in the pressure chamber. This has become possible at beamline ID11, which is specialised in spatially resolved diffraction. ID11 has a very small beam (~0.4 x 0.4 µm2 in these experiments) and incredibly high resolution. Due to this work, ID11 has become the first beamline that has a proven record of single-crystal X-ray diffraction data collection on sub-micron-size samples in diamond anvil cells. The results of the data processing are crystal structures and chemical compositions of the materials synthesised at multimegabar pressures (Figure 112). The novel rhenium nitride Re7N3 has become the first complex material to

be fully structurally characterised under compression conditions that were previously inaccessible. Notably, the synthesis of rhenium nitride and Re-N alloys has made it possible to prove the theory that predicted their existence only under such extreme conditions.

Fig. 112: Determination of the crystal structure. The X-ray diffraction pattern (left) generated from a very small crystal in a double-stage diamond anvil cell using synchrotron radiation can be evaluated using single-crystal crystallography software. The result is a model of the crystal structure (right). Blue spheres show the positions of nitrogen atoms. Small grey spheres are rhenium atoms at the corners of trigonal prisms in the crystal structure model.