Study of the growth and stability of ultra-thin films of Au deposited on Si(100) and Sill(111)

The growth and stability of ultra-thin films of Au deposited on Si(1 0 0)-2 x 1 and Si(1 1 1)-7 x 7 surfaces have been examined as a function of the quantity of Au deposited and substrate temperature using positron-annihilation-induced auger electron spectroscopy (PAES) in combination with electron-induced auger electron spectroscopy (EAES) and low energy electron diffraction. Previous studies have indicated that the PAES signal originates almost exclusively from the top-most atomic layer due to the trapping of the positron in an "image-correlation-well" at the surface before it annihilates. By making use of the selectivity of PAES for the top layer, it was possible to directly monitor the compositional changes in the topmost atomic layer for monolayer and submonolayer depositions of Au on Si(1 0 0) and Si(1 1 1). The PAES intensity was found to increase with increasing Au deposition and then saturate above similar to1 ML for depositions made at 173 K. Tn contrast, saturation did not occur until similar to2.5 ML when the deposition was performed at 303 K. Plots of the PAES intensity versus Au thickness show a "plateau" at similar to0.5 ML deposition. We interpret the saturation of the PAES signal from Au as an indication that the surface is completely covered by Au atoms after deposition of 1 ML at 173 K. The larger Au thickness required to achieve saturation and the plateau from similar to0.5 ML to 1 ML deposition are taken as an indication that, for 303 K deposition, a mixed alloy layer is formed first followed by the growth of a complete Au layer. A model for Au/Si interface formation in terms of Au and Si concentrations measured by PAES and EAES is presented. (C) 2001 Elsevier Science B.V. All rights reserved.