Modeling of Metal(100) Homepitaxial Film Growth at Very Low Temperatures

We model the growth of Ag films deposited on Ag(100) below 140K. Our recent VariableTemperature Scanning Tunneling Microscopy {VTSTM) studies reveal "smooth growth" from 120-140K, consistent with earlier diffraction studies. However, we also find rougher growth for lower temperatures. This unexpected behavior is modeled by describing the deposition dynamics using a "restricted downward funneling" model, wherein deposited atoms get caught on the sides of steep nanoprotrusions (which are prevalent below 120K), rather than always funneling down to lower four-fold hollow adsorption sites. At OK, where no thermal diffusion processes are .operative, this leads to the formation of overhangs and internal defects (or voids). Above 40K, low barrier interlayer diffusion processes become operative, producing the observed smooth growth by 120K. We also discuss how the apparent film morphology mapped out by the STM tip "smears" features of the actual film morphology (which are small at low temperature), and also can lead to underestimation of the roughness.