화학공학소재연구정보센터
Applied Surface Science, Vol.258, No.7, 2255-2265, 2012
Growth of epitaxially oriented Ag nanoislands on air-oxidized Si(111)-(7 x 7) surfaces: Influence of short-range order on the substrate
Clean Si(1 1 1)-(7 x 7) 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 (7 x 7) order on the air-oxidized surface. Comparison with FTs of STM images from a clean Si(1 1 1)-(7 x 7) surface shows that only the 1/7th order spots are present on the air-oxidized surface. The oxide layer is similar to 2-3 nm thick, as revealed by cross-sectional transmission electron microscopy (XTEM). Growth of Ag islands on these air-oxidized Si(1 1 1)-(7 x 7) 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 degrees C face centered cubic Ag nanoislands grow with a predominant epitaxial orientation [1 (1) over bar0](Ag)parallel to[1 (1) over bar0](Si), (1 1 1)(Ag) parallel to (1 1 1)(Si) along with its twin [(1) over bar 1 0](Ag)parallel to[1 (1) over bar 0](Si), (1 1 1)(Ag) parallel to (1 1 1)(Si), as observedfor epitaxial growth of Ag on Si(1 1 1) surfaces. The twins are thus rotated by a 180 degrees rotation of the Ag unit cell about the Si[1 1 1] axis. It is intriguing that Ag nanoislands follow an epitaxial relationship with the Si(1 1 1) 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. (C) 2011 Elsevier B. V. All rights reserved.