The interfacial complexions, with distinct structures, are considered as quasi-two-dimensional phases, which undergo the structural and chemical changes associated with thermodynamic parameters [1-2]. We recently discovered the formation of gold-spinel interfacial complexions, with well-defined atomic structures, and the related growth of nominally stable spinel lattice underneath the gold nanoparticles after annealing [3-5]. As shown in Figure 1, the necking structure, which is tens of nanometers high, is detected under dewetted gold nanoparticles. Such necking structure has the same contrast with spinel substrate, maintains the spinel composition confirmed by the energy dispersive X-ray spectroscopy, and keeps an ideal epitaxial relationship with the substrate. In associated with the substrate growth, an interfacial bilayer with distinct crystalline structure forms between gold nanoparticles and the substrate. Further studies reveal that the formation and migration of the interfacial complexions are related to the defects at the interfaces, such as, the intersections of gold twinned planes and the interface (see details in Figure 2). In spite of their importance in synthesizing nanostructures, the atomic structures of interfacial complexions have not been fully elucidated yet.

Herein, in this paper, we investigated the detailed atomic models of such interfacial complexions in combination of atomic-resolution experimental images and first-principle computations. Experimentally, we synthesized a series of Au-MgAl₂O₄ samples within different annealing profiles and proposed the initial atomic models based on atomic-resolution scanning transmission electron microscopy (STEM) – high-angle annular dark-field (HAADF) images in Figure 3. Experimental images with two orthogonal crystallographic directions were selected to provide the three-dimensional structural information. A few possible atomic models, with different oxygen vacancies, were built through our MATLAB codes, and inputted into the density functional theory (DFT) computation. The relaxed atomic models, carried out with generalized gradient approximation (GGA) and Perdew-Burker-Ernzerhof (PBE) exchange-correlation density functional [6], were applied to simulate the HAADF images [7] in order to further verify the validity of the structures. Our results provide a new clue to the field of interfacial complexions, particularly to the structural origins of the abnormal phenomenon of self-assembled growth of oxide substrates underneath dewetted gold nanoparticles.

References:

[1] S. J. Dillon, et al, JOM 61(2009), p. 38-44.

[2] P. R. Cantwell, et al, Acta Materialia 62(2014), p. 1-48.

[3] G.-z. Zhu, et al, Applied Physics Letters 105(2014), p. 231607.

[4] F. Liu, et al, Materials Characterization 113(2016), p. 67-70.

[5] T. Majdi, et al, Applied Physics Letters 107(2015), p. 241601.

[6] J. P. Perdew, et al, Physical Review Letters 77(1996), p. 3865.

[7] E. J. Kirkland, Advanced Computing in Electron Microscopy, second ed. Springer Scieence & Business Media, 2010.

Acknowledgments

We acknowledge the financial support from the National Science Foundation of China (No. 51401124). 

Figures:

Figure 1. (a) The side-view morphology of gold nanoparticles. (b) The STEM-HAADF image shows the necking structure of substrate.

Figure 2. (a) The atomic structure of the Au-MgAl2O4 interfacial complexions after annealing at 900 ℃. The red lines stand for the twinned planes of gold nanoparticles.

Figure 1. The STEM-HAADF images of the Au-MgAl2O4 interface which were annealed at 1100 ℃from (a) <-110> zone axis and (b) <11-2> zone axis.

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EMC Abstracts - https://emc-proceedings.com/abstract/atomic-structures-of-interfacial-complexions-between-gold-nanoparticles-and-nominally-stable-spinel-substrate/