It is known that Au(100), Au(110), and Au(111) single crystal surfaces undergo reconstruction in vacuum by raising temperature and that similar reconstruction of the Au surfaces takes place in electrolyte solution, depending on the electrode potential.. These surface reconstructions are rationalized by lowering of surface energy. On the other hand, it has been accepted that the crystal habit owes to relative growth rate of crystallographic planes in vacuum as well as in solution, that is, the crystal habit is a kinetic phenomenon. Taking these facts into account, an interesting question may arise that whether the crystal habit of Au particles is influenced by the potential of electrode on which the particles grow. By using Au mesh for transmission electron microscopy (TEM) as an electrode, not only Au but also other metal particles deposited on it under the controlled potential were observed by TEM. It was found that multiply twinned particles (MTPs) of Au are formed at negative potential (vs. SCE) but the fcc single crystalline Au particles are predominantly grown at positive potential (vs. SCE). This phenomenon suggests that the shape of Au particles can be controlled by the electrode potential which may regulate the surface energy. It is known that the reconstruction of Au surfaces accompanies the lattice shortening, and the excess negative charge at the surface is responsible for the lattice shortening. We inferred that the similar lattice shortening might occur on the fcc metal surfaces at negative potential although the reconstruction is known only on Au and Pt surfaces. It was confirmed that the other fcc metals (Pt, Pd, Ag, Cu, Ir, Rh and Ni) also form MTPs at negative elecrode potential. AuCu alloyed particles take more readily multiply twinned shape than that of Au particles, that is, MTPs of AuCu alloy are formed at positive potential at which no MTPs of Au are formed. This phenomenon is explained by the underpotential deposition of Cu+ ion on Au surface.
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