Gold and silver colloids and small particles are being used for various academic and commercial purposes. In this contribution we show analyses of shapes of recently prepared micro-crystals of these two metals. Gold micro- plates, -wires and -polyhedra were recently reported. [1] The gold plates have triangular or hexagonal shapes and their crystal facets represent flat and naturally grown (111) surfaces. Herein we report on a detail description of the shapes of the polyhedral crystals and wires. The former can be best described as derived from cube and octahedron. Various cuboctahedral, truncated cubeoctahedral, truncated octahedral and other crystals were observed in the products. These crystals are links between the two limiting forms, regular cube and octahedron. Regular cube consists of (100) and regular octahedron of (111) faces. Cuboctahedron, which is a combination of both basic geometrical objects, consists of both (111) and (100) crystallographic planes on its surface. This is a significant difference from a gold crystal micro-plates sample. Additionally, we found several crystals with more complicated shapes. Their geometrical analyses will be presented. A comparison of shapes of Ag micro‑crystals (plates, wires, polyhedra) with those of Au will be discussed. Ag wires of tens of micrometers in length and approximately one micrometer in diameter were prepared. The electrical conductivities of both Au and Ag wires are given. The elemental composition of superficial layers and stability of the samples toward air atmosphere were investigated using X-ray photoelectron spectroscopy. The surfaces of both Au and Ag microcrystalline objects were modified with sulphide ions or molecules of mercaptopropionic acid. These processes demonstrate the possibility of placing various functional groups onto the surface of these micro-crystals.
Ref.: [1] T. Base , Z. Bastl , M. Slouf , N. Murafa , J. Subrt , J. Plesek, M. G. S. Londesborough, O. Kriz, Surface Science, in press.
Acknowledgements: This work was supported by the Ministry of Education, Youth and Sports of the CR (grant nos. LC06041, LC06040 and KAN400480701) and by the AS CR (project nos. 1ET400400413, AVOZ40500505 and AV0Z240320502). |