Nanoscale physics

On the Au-Ni equilibrium phase diagram for 6 nm sized nanoparticles
S. Bogatyrenko1, A. Kryshtal2, A. Minenkov1, A. Kruk2
1 Faculty of Physics and Technology, Karazin Kharkiv National University of the NAS of Ukraine. 4 Svobody Sq., Kharkiv, 61022, Ukraine.
E-mail: sib@univer.kharkov.ua
2 International Centre of Electron Microscopy for Material Science and Faculty of Metals Engineering and Industrial Computer Science, AGH University of Science and Technology. Al. Mickiewicza 30, Kraków, PL-30059, Poland.

The aim of this work is to establish new physical regularities of the solid-state interphase interactions in nanosized binary systems, namely, to study the evolution of an equilibrium phase diagram with decreasing characteristic size.
The object under research was a model system which was represented by flattened Au-Ni islands with a characteristic size of 6 nm. To form these objects, we deposited Ni on an a-C substrate heated to 350ºC in a vacuum of 1x10-7 Torr. As a result, the islet structure was formed. Then the Au was condensed on the Ni islands immediately after cooling the substrate to room temperature. The mass thickness of the films was ≈3 and ≈1 nm for Ni and Au, respectively, which corresponded to the overall composition of 30 at. % Au–Ni. The choice of the component’s ratio was motivated by the fact that the homogeneous solid solution of this composition has the highest formation temperature, i.e. lays on a very top of the miscibility gap for bulk samples.
The study of morphology and chemical elements distribution in binary nanosystems down to the atomic level was fulfilled in situ with a probe corrected FEI Titan3 G2 60-300 with ChemiSTEMTM system in the 20–450 ºC range. The kinetics of solid solution formation was investigated via electron diffraction technique by heating the samples directly in a PEM-125K transmission electron microscope.
New quantitative data on the kinetics of equilibrium solid solutions formation in nanosized Au-Ni system were obtained. Besides, the distribution of components in such solutions was investigated at the atomic scale. Experimental data on the size evolution of the components solid state mutual solubility in the Au-Ni system have been obtained. Based on these data, the solid-state region of the equilibrium phase diagram for the system under study was experimentally constructed.
This work was supported by the Ministry of Education and Science of Ukraine (0118U001772, 0118U002027) and by European Union's Horizon 2020 research and innovation program under grant agreement No. 823717ESTEEM3.