Fig. 3. (a) Schematic representation of the synthesis of p-Cu_1−xNNi_3−y/FeNiCu by solid–gas reactions of CuNNi₃ + Cu and NH₃ followed by Fe³⁺ etching. Reprinted with permission from ref. 99, copyright 2018, Nature Publishing Group (b) illustration of the formation of intermetallic FeSn₂ and close packing of the individual atomic layers of Fe and Sn (tetragonal, I4/mcm) via the Kirkendall process. Adapted with permission from ref. 102, copyright 2020, Wiley-VCH (c) synthesis and the fabrication procedure of FeNi₃/NC, Fe–FeNi₃/NC and Fe-enriched-FeNi₃/NC. Reprinted with permission from ref. 103, copyright 2020, Elsevier (d) illustrated synthesis protocol of NiMo-NGTs. Reprinted with permission from ref. 104, copyright 2016, American Chemical Society (e) synthesis of NiGe from the molecular bis(germylene)-Ni complex. Adapted with permission from ref. 105, copyright 2020, Wiley-VCH.