Synthesis and Structural Analysis of High-Entropy Nano-Alloys

In this study it has been investigated the structure of the High-Entropy Nano-Alloys, materials that combine four or more metals in equiatomic composition. Mixing many elements at equiatomic composition in an alloy favors the formation of a solid solution crystallized in a cubic phase. The term "high entropy alloy" derives from the fact that this solid solution phase is stabilized by the high configurational entropy of the alloys. High-Entropy Alloys (HEA) have evolved to one of the most popular material classes in the last decades in both fundamental and applied material science. However research has been focused entirely on bulk HEA, ignoring HEA nanoalloys because of the absence of well controlled methods to synthetize such complex nanoparticles (NPs). The first aim of this study is to synthetize the High Entropy Nano-Alloys with two different synthesis methods: the Pulsed Laser Deposition (a pulsed laser beam ablates pure metallic targets forming a plasma that condenses on a heated substrate) and the Hot Injection (a wet chemical method in which all the metallic precursors are injected together in heated solution, in the solution the metallic precursors are reduced to favor the nucleation and growth of HEA NPs). The second aim is to study the structure and the composition of these futuristic materials at the single NP level. To achieve that it has been exploited the Transmission Electron Microscopy (TEM) facility present at the Laboratory Matériaux et Phénomènes Quantiques. This multifunctional tool permits to have atomic level resolution to study the crystal structure of single NPs and, thanks to the Energy Dispersive X-Rays spectroscopy (EDX), it is possible to perform chemical analyses to study the composition of single NPs. In this study it has been shown that it is possible to synthetize HEA NPs with these two techniques and that the equiatomic composition is a necessary condition to obtain well crystallized cubic solid solutions. It has been also confirmed that the TEM is one of the most powerful and complete tools to study nanomaterials.