Island Size and Environment Dependence of Adatom Capture: Cu/Co Islands on Ru(0001)

We quantify the rate of capture by Co islands on Ru(0001) of additionally deposited Cu atoms, using scanning tunneling microscopy. The dependence of the capture rates on Co-island size is shown to reflect larger island-free areas surrounding bigger islands, a feature neglected in mean-field treatments. We also find a strong direction dependence in Cu adatom capture, reflecting the local environment of individual islands. These features are elucidated by simulations and diffusion equation analyses.