Growth of Co Nanoclusters on SiC Honeycomb Templates
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Growth of Co Nanoclusters on SiC Honeycomb Templates Wei Chen, Kian Ping Loh Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore. 117543 Hai Xu, A.T.S. Wee Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore. 117542 Abstract A honeycomb-like SiC reconstructed surface with regular, periodic porosity in the nano-scale range has been used as an effective template for the formation of monodispersed Co nanoclusters. In-situ scanning tunneling microscopy (STM) was used to study the nucleation process of the Co nanoclusters on this template. The deposition of Co at different substrate temperature was investigated by STM. It is found that the failure in the deposition of Co nanoclusters on the SiC honeycomb template with substrate temperatures higher than room temperature (RT) might be due to the high desorption rate of the adsorbed Co atoms. Introduction: Well-ordered nano-templates have been used to successfully fabricate twodimensional nanostructure arrays by creating preferential binding sites for binding of adsorbates. Supramolecular structures formed by the self-assembly of molecules at surfaces,1~7 strain-relief patterns created by deposition of one or two monolayers of material on a substrate with a different lattice constant,8, 9 as well as the superstructures arising from the reconstructions on metal or semiconductor surfaces,10~13 have been shown to be effective nano-templates. The carbon-rich 6H-SiC(0001)- 6 3 × 6 3R30° honeycomb surface reconstruction has been used as an effective template for the growth of high density, monodispersed and uniform-sized Co nanoclusters.14 This 6 3 × 6 3R30° reconstructed 6H-SiC surface arises from the arrangement of segregated carbon atoms at 1100oC into a periodic, porous, honeycomb array resembling the anodized alumina template but at a smaller scale. It offers several advantages for the growth of monodispersed nanoclusters, including: (i) the honeycomb structures will constrain the diffusion of adsorbed atoms on the surface and thus favoring the formation of monodispersed nanoclusters; (ii) this carbon-rich honeycomb template may act as a barrier layer to prevent the Co nanoclusters from reacting with underlayer Si atoms to form cobalt silicide during cluster formation and annealing process. In this paper, the formation of Co nanoclusters on this honeycomb template is presented. The deposition of Co at different substrate temperatures is also investigated. Experiment: The experiments were carried out in a multi-chamber UHV system with a base pressure of 1×10-10 torr, allowing in-situ transfer between facilities for electron-beam evaporation, x-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), and the Omicron variable temperature scanning tunneling microscope (VTSTM).14,15 To prepare the SiC honeycomb template, a 6H-SiC substrate polished on the (0001) face was first coated with several layers of silicon by evaporating silicon in-situ from a resistively heated silicon wafe
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