Growth of Metastable High-Order Commensurate Overlayers of Pb on Cu(001)

We studied the growth and ordering of a Pb layer deposited on Cu(001) at 150 K. Contrary to the case of adsorption of Pb at room temperature, islands readily form. These islands order in a high-order commensurate structure of symmetry ( sqrt(61) x sqrt(61) ) R arctan(5/6). We followed the growth of these islands using atom beam scattering. From the measurement of the island diffraction peak profiles we found a power growth law for the mean island- size versus coverage. Upon increasing the coverage another high-order commensurate structure is formed, (5 x 5) R arctan(3/4). All the ordered phases obtained by adsorption at low temperature are metastable.