Panagiotis Grammatikopoulos1 Kengo Aranishi1 Vidyadhar Singh1 Evropi Toulkeridou1 Leonardo Lari2 Mukhles Sowwan1

1, OIST, Okinawa, , Japan
2, University of York, York, , United Kingdom

Recently we reported on the formation of metastable configurations of Ag-Cu NPs grown by concurrent magnetron sputtering inert-gas condensation from neighbouring sputtering targets, and showed that energetically unfavourable structures can be generated as a result of nanoparticle coalescence at a later stage of the nucleation and growth process, away from the target and the hot plasma region surrounding it [1]. Ag and Cu form a eutectic system with a pronounced miscibility gap; as such, the two materials are not prone to mix upon coalescence, forming core-satellite or Janus structures, or, in the case of Cu-rich structures of ~5%Ag, a patterned core-partial shell structure which we named ukidama, after traditional Japanese glass floats.
A question that was naturally raised, based on this study, was what would happen if the system was a miscible one. Would it behave in the same way, or would the atoms of the two elements actually mix, as expected from thermodynamics considerations?
To answer this question, we performed a similar study, using the same experimental setup, for the Ni-Pt system; in parallel, we developed nanophase diagrams using thermodynamics considerations. Ni-Pt is a well-established miscible system, as it satisfies all Hume-Rothery criteria: the atomic radii difference is only ~10%, both elements form FCC crystalline structures and have comparable valency and electronegativity values. We found that both stable solid solution and metastable segregated configurations were possible, which we attributed to the frequency of coalescence events. We also observed the existence of ukidama structures, similar to those for the eutectic Ag-Cu system, which can be explained using our previously reported extended cluster heating model of nanoparticle coalescence [2].
[1] “Kinetic trapping through coalescence and the formation of patterned Ag-Cu nanoparticles”
P. Grammatikopoulos, J. Kioseoglou, A. Galea, J. Vernieres, M. Benelmekki, R. E. Diaz, M. Sowwan
Nanoscale 8 (2016) 9780-9790.
[2] “Simple analytical model of nanocluster coalescence for porous thin film design”
P. Grammatikopoulos, E. Toulkeridou, K. Nordlund, M. Sowwan
Modelling Simul Mater Sci Eng 23 (2015) 015008.