We have observed and compared the growth of nanosize, self-assembled island
s in two strained heteroepitaxial systems, Ge on Si(001) and CoSi2 on Si(11
1). Island growth took place in a transmission electron microscope and in a
low-energy electron microscope, both of which had been modified to allow i
n situ deposition. The kinetics of island formation are substantially diffe
rent in the two systems, suggesting different growth mechanisms. We discuss
the two mechanisms and their implications for controlled island growth for
novel electronic devices.