Highly Uniform Colloids of Metallic and Intermetallic Nanocrystals
It is difficult to overestimate the importance of metals and alloys, and nanoscale dimensionality adds even more functions and unicity to these materials. Captured by unfolding and rich application space, our research group studies metallic and intermetallic nanocrystals in the form highly uniform colloids. Specifically, we have developed several monoatomic nanocrystals (e.g., Bismuth, Indium, and Gallium) with unprecedented quality for size control and monodispersity[1],[2],[3] and studied their colloidal synthesis by in-situ synchrotron-based methods.[4] Our synthetic efforts have provided a pathfinder for a range of applications, including 3D self-assemblies, stamped electrodes, or Li-ion battery anodes.[1],[2],[5] Recently, we have extended beyond monoatomic metals and developed the first universal approach for high-quality intermetallic nanocrystals (Figure 1).[6] Our method employs an amalgamation reaction at the surface of nanocrystals and unlocks up to a 1000 of new intermetallic nanocrystals with unprecedented quality for size uniformity, composition control, and phase purity. Starting from monometallic seeds (e.g., Ni, Cu, Pd, Ag, or Au), we carry out a thermal decomposition of metal-amides (e.g., Ga, In, or Zn amides) to dispatch low-melting metals to the surface of nanocrystals. This is followed up by the amalgamation process, i.e., an efficient way of alloy formation, in which a liquid metal diffuses into solid metal forming a bimetallic composition or intermetallic compound. One of the highlights is the remarkable kinetics of metal alloying during amalgamation, taking advantage of the high diffusivity of liquid metal component. Therefore, the amalgamation reaction is fast, convenient, and it takes only a couple of minutes to form homogeneous bimetallic nanocrystal. Consequently, the amalgamation synthesis is faster than detrimental mass transfer processes, such as Ostwald ripening. Thus, particle sizes and size uniformity of intermetallic nanocrystals are directly inherited from the high-quality monometallic seeds. Furthermore, the nanoscale amalgamation reaction shows excellent universality for Zn, In and Ga bimetallic nanocrystals and our method allows reaching various phases within the same bimetallic composition. Taking the example of Au-Ga, we were able to synthesize a wide range of compositions.[5] We prepare nanocrystals of Ga-doped fcc-Au, hexagonal Au7Ga2, low-symmetry AuGa, and cubic AuGa2phases simply by tuning the amount of added liquid Ga (i.e., the amount of Ga amide salt). Interestingly, we also observe two-phase samples, indicating miscibility gaps in bimetallic phase diagrams and providing means to reconstruct thermodynamic phase equilibria at the nanoscale.[7]
Figure 1: Schematics of nanoscale amalgamation reaction for high-quality intermetallic nanocrystals.
[1] M. Yarema*, M.V. Kovalenko, G. Hesser, D.V. Talapin, and W. Heiss; J. Am. Chem. Soc. 2010, 132, 15158-15159.
[2] M. Yarema, S. Pichler, D. Kriegner, J. Stangl, O. Yarema, R. Kirchschlager, S. Tollabimazraehno, M. Humer, D. Häringer, M. Kohl, G. Chen, and W. Heiss; ACS Nano 2012, 6, 4113-4121.
[3] M. Yarema, M. Wörle, M.D. Rossell, R. Erni, R. Caputo, L. Protesescu, K.V. Kravchyk, D.N. Dirin, K. Lienau, F. von Rohr, A. Schilling, M. Nachtegaal, and M.V. Kovalenko; J. Am. Chem. Soc. 2014, 136, 12422-12430.
[4] F. M. Schenk, S. Wintersteller, J. Clarysse, H. He, J.-M. von Mentlen, N. Yazdani, M. Wied, V. Wood, C. Prehal, and M. Yarema*; J. Am. Chem. Soc. 2025, 147, 14, 12105-12114.
[5] M. G. Boebinger, O. Yarema, M. Yarema, K. A. Unocic, R. R. Unocic, V. Wood, and M. T. McDowell; Nature Nanotech. 2020, 15, 475-481.
[6] J. Clarysse, A. Moser, O. Yarema, V. Wood, and M. Yarema*; Sci. Adv. 2021, 7, eabg1934.
[7] O. Yarema, A. Moser, C.-W. Chang, J. Clarysse, F. M. Schenk, E. Egüz, H. Vemulapalli, N. Mittal, E. Edison, Y.-H. Wu, D. A. Kuznetsov, C. R. Müller, M. Niederberger, C. M. Franck, V. Wood, and M. Yarema*; Adv. Funct. Mater. 2024, 34, 2309018.