Controlled Crystal Habit of Metal Particles and their Properties and Catalysis.

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So far, crystal habit has been recognized as a kinetic phenomenon which can be explained by relative growth rate of the crystal planes. When Au atoms are deposited on NaCl crystal surface in vacuum, a lot of icosahedral and/or decahedral particles, so called multi-twin particles, are formed. The outer most layer of the icosahedral and/or decahedral particles has a closed pack hexagonal array of Au atoms like the (111) plane. Although the surface energy of multi-twin particles may be low but. the strain is increased as the growth of particle size so that the multi-twin particles can not grow in large size. If this is correct, the formation of multi-twin particles is not the kinetic phenomenon but the thermodynamic or energetic phenomenon. On the other hand, Au (111), Au (110) and Au (100) surfaces undergo surface reconstruction forming hexagonal array of the topmost layer by heating in vacuum. It is known that Au surfaces undergo very similar reconstruction in electrolyte solution at a certain negative potential. We found the growth of multi-twin Au particles on electrode in solution when the electrode holds negative than this potential. These phenomena suggest that the surface energy can be controlled by electrode potential, and we could say that the crystal habit can be controlled by changing the surface energy. This new phenomenon is successfully extended to other fcc metals such as Cu, Ag, Ni, Pd, Pt, Rh, Ir, and Au-alloys. These results are reviewed in a book published from the Hokkaido University Press.