ENERGIES CONTROLLING NUCLEATION AND GROWTH-PROCESSES - THE CASE OF AG/W(110)

The nucleation density N(x)(T) of Ag islands on the 2-monolayer-thick silver intermediate layer on W(110) is measured by UHV scanning electron microscopy and compared with kinetic nucleation equations. This yields a well-determined value of E(d) + 2E(b) = 0.65 +/- 0.03 eV, with pair-binding energy E(b) = 0.25 +/- 0.05, diffusion energy E(a) = 2.2 +/- 0.1 eV. Values for Ag/Ag (111) are calculated in effective-medium theory, giving E(a) = 2.23, E(b) = 0.28, E(d) = 0.12, and E(d) + 2E(b) = 0.68 eV. Observations on vicinal and impure surfaces are reported, and implications for defect binding energies discussed.