Island morphologies and island separations were determined from the tw
o-dimensional diffraction patterns measured with high-resolution low-e
nergy electron diffraction during sub-monolayer homoepitaxy on the Cu(
001) surface. In the temperature range considered, islands were found
to have square shapes with edges along the [110] direction indicating
a low energy-barrier for diffusion along close packed step edges. By m
easuring the temperature dependence of the average island separation i
n the diffusion limited steady-state growth regime, the energy barrier
for adatom diffusion and the binding energy for small islands were de
termined.