Ag grows on the Si(001) surface in the Stranski-Krastanov growth mode. We have studied the behavior for this system at elevated temperatures with scanning tunneling microscopy and low-energy electron diffraction, concentrating on early stages of growth where a two-dimensional (2D) layer is formed. This 2D layer is well ordered and its saturation coverage is determined to be 0.5 monolayers of Ag. The transition from 2D to 3D growth with increasing Ag deposition is unusual in that the 2D layer is observed to roughen before 3D islands start to grow. This is explained by the subsurface accommodation of Ag when its density exceeds the saturation coverage of the 2D layer.

• Received 8 February 1993

DOI:https://doi.org/10.1103/PhysRevB.47.10947