Abstract
We present a study of the transitional pathways between high-symmetry structural motifs for AgAu nanoparticles, with a specific focus on controlling the energetic barriers through chemical design. We show that the barriers can be altered by careful control of the elemental composition and chemical arrangement, with core@shell and vertex-decorated arrangements being specifically influential on the barrier heights. We also highlight the complexity of the potential and free energy landscapes for systems where there are low-symmetry geometric motifs that are energetically competitive to the high-symmetry arrangements. In particular, we highlight that some core@shell arrangements preferentially transition through multistep restructuring of low-symmetry truncated octahedra and rosette-icosahedra, instead of via the more straightforward square-diamond transformations, due to lower energy barriers and competitive energetic minima. Our results have promising implications for the continuing efforts in bespoke nanoparticle design for catalytic and plasmonic applications.
Highlights
Nanoparticles (NPs) consist of between a few and many thousands of atoms or molecules, interacting to form discrete particles.[1]
Recent research has shown that the nuclearity, composition and chemical ordering of bimetallic NPs can be well controlled during synthesis,[8−14] but it remains an experimental challenge to control the shape of these systems.[5,9,15]
Synthesis, characterization, and application of the NPs is generally performed under conditions that do not aid structure stabilization: A multitude of geometric arrangements coexist on most energy landscapes,[8,22,23] possibly with similar energies and separated by transition barriers that can be overcome at room temperature.[15,24,25]
Summary
Letter methods would be ideal, but there has been limited investigation of how to use NP composition to achieve this goal. Calculations of the SD and DS pathways for Ag1@Au146 give ΔE(CO → Ih) and ΔE(Ih → CO) as 1.19 and 2.22 eV, which are lower than the r-Ih route and similar to the other values for Ag-doped Au NPs. Analysis of the r-Ih transition pathway shows that the initial energy barriers are marginally lower than for the SD mechanism (Figure 2, top) and that the Ih and r-Ih motifs are close in energy. When calculations were repeated for Ag-decorated vertices on Au-rich NPs, rather different behavior was observed: Au135Ag12 has forward (SD) and backward (DS) barriers of 1.27 and 2.45 eV, that is, an increase in 0.13 and 0.12 eV, respectively, compared with Au147. We have shown that the transition pathway can be controlled via careful construction of the NP with respect to stoichiometry and chemical arrangements, by the use of vertex-doping to restrict surface-based structural transformations.
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