Abstract
The specular intensity of nearly mono-energetic helium atom beams (Ei = (7 ÷ 20) meV) has been measured during epitaxial deposition of Pb films on Pb(111) and Cu(111) surfaces. For Pb on Pb(111) regular monotonically damped oscillations are observed indicating monolayer by monolayer growth. For Pb on Cu(111) a more complicated modulated structure was found indicating an alternation between single- and double-layer growth mechanisms where in the double-layer regions the reflectivity was largest. The thickness at which double-layer growth predominates is found to coincide with predictions involving the dimensions of potential wells and electronic states normal to the surface. The lack of complex structures for Pb on Pb(111) system confirms the requirement of an internal boundary and appears to rule out other possible explanations.