Growth of epitaxially oriented Ag nanoislands on air-oxidized Si(111)-(7x7) surfaces: Influence of short range order on the substrate

Clean Si(111)-(7{x7) surfaces, followed by air-exposure, have been investigated by reflection high energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). Fourier transforms (FTs) of STM images show the presence of short range (7x7) order on the air-oxidized surface. Comparison with FTs of STM images from a clean Si(111)-(7x7) surface shows that only the 1/7th order spots are present on the air-oxidized surface. The oxide layer is ~ 2-3 nm thick, as revealed by cross-sectional transmission electron microscopy (XTEM). Growth of Ag islands on these air-oxidized Si(111)-(7x7) surfaces has been investigated by in-situ RHEED and STM and ex-situ XTEM and scanning electron microscopy. Ag deposition at room temperature leads to the growth of randomly oriented Ag islands while preferred orientation evolves when Ag is deposited at higher substrate temperatures. For deposition at 550{\deg}C face centered cubic Ag nanoislands grow with a predominant epitaxial orientation [1 -1 0]Ag || [1 -1 0]Si, (111)Ag || (111)Si along with its twin [-1 1 0]Ag || [1 -1 0]Si, (111)Ag || (111)Si, as observed for epitaxial growth of Ag on Si(111) surfaces. The twins are thus rotated by a 180{\deg} rotation of the Ag unit cell about the Si [111] axis. It is intriguing that Ag nanoislands follow an epitaxial relationship with the Si(111) substrate in spite of the presence of a 2-3 nm thick oxide layer between Ag and Si. Apparently the short range order on the oxide surface influences the crystallographic orientation of the Ag nanoislands.Comment: 10 figure

Self-organized metallic islands on nano-patterned silicon substrate

Combining the self-organized growth of nanometer size islands with the use of a pre-patterned substrate, the fabrication of a metallic nanoparticle array with sub-100 nm period is demonstrated. The array pattern is artificially defined through conventional lithography on a Si substrate. Two passivation steps are used first ex situ with a wet hydrogenation followed by the in situ formation under ultrahigh vacuum of an Au-Si wetting layer. This allows for the subsequent nucleation and growth of Au on an atomically clean surface. The long range order of the nanoparticle array is preserved over the whole millimeter-size patterned area

Nanostructured conducting polymer devices for tissue engineering.

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