Heterogeneous bimetallic
nanocrystals featuring explicit spatial
configurations and abundant twin defects can simultaneously enable
geometric and ligand effects to enhance catalytic and photonic applications.
Herein, we report two growth patterns of Au atoms on penta-twinned
Pd decahedra, involving twin proliferation to generate asymmetric
Pd–Au Janus icosahedra and twin elongation to produce anisotropic
Pd@Au core–shell starfishes, respectively. Mechanistic analysis
indicates that the injection rate determines the lower-limit number
(nlow) of Au(III) ions in the steady state
and thus controls the growth pattern. Whennlow≤ 5.5, the kinetic rate is slow enough to initiate
asymmetrical one-side growth but fast enough to outpace surface diffusion;
Au tetrahedral subunits are successively proliferated along the axial
⟨110⟩ direction of Pd decahedra to form Pd–Au
Janus icosahedra. Composed of five Pd and 15 Au tetrahedral subunits,
such a heterogeneous icosahedron supports high (2.2 GPa) tensile strain
and high strain difference up to +21.9%. In contrast, whennlow> 5.5, the fast reduction kinetics promotes
symmetric growth with inadequate surface diffusion. As such, Au atoms
are laterally deposited along five high-indexed ⟨211⟩
ridges of Pd decahedra to generate concave Pd@Au core–shell
starfishes with tunable sizes (28–40 nm), twin elongation ratios
(33.82–162.08%), and lattice expansion ratios (8.82–20.10%).