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Gold cluster
Gold clusters in cluster chemistry are gold-derived materials that can either be discrete molecules or larger colloidal particles. Both types are described as nanoparticles, with diameters of less than one micrometer. A nanocluster is a collective group made up of a specific number of atoms or molecules held together by some interaction mechanism. Gold nanoclusters have potential applications in optoelectronics and catalysis.
==Structure==
Bulk gold exhibits a face-centered cubic (fcc) structure. As gold particle size decreases the fcc structure of gold transforms into a centered-icosahedral structure illustrated by Au13.〔 It can be shown that the fcc structure can be extended by a half unit cell in order to make it look like a cuboctahedral structure. The cuboctahedral structure maintains the cubic-closed pack and symmetry of fcc. This can be thought of as redefining the unit cell into a more complicated cell. Each edge of the cuboctahedron represents a peripheral Au–Au bond. The cuboctahedron has 24 edges while the icosahedron has 30 edges; the transition from cuboctahedron to icosahedron is favored since the increase in bonds contributes to the overall stability of the icosahedron structure.〔
The centered icosahedral cluster Au13 is the basis of constructing large gold nanoclusters. Au13 is the endpoint of atom-by-atom growth. In other words, starting with one gold atom up to Au12, each successful cluster is created by adding one additional atom. The icosahedral motif is found in many gold clusters through vertex sharing (Au25and Au36), face-fusion (Au23 and Au29), and interpenetrating biicosahedrons (Au19, Au23, Au26, and Au29).〔 Large gold nanoclusters can essentially be reduced to a series of icosahedrons connecting, overlapping, and/or surrounding each other. The crystallization process of gold nanoclusters involves the formation of surface segments that grow towards the center of the cluster. The cluster assumes an icosahedral structure because of the associated surface energy reduction.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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