Island Nucleation in a Reactive Two-Component System

The flux and temperature dependence of titanium silicide islands formed by reactive deposition near $500°\mathrm{C}$ indicate a critical nucleus containing 2 Ti atoms and a single activation energy of $E_d+\frac{1}{2}{E}_2=1.4\mathrm{}\pm 0.2\mathrm{eV}$, where $E_d$ and $E_2$ are the surface diffusion and cluster binding energies, respectively. These values are not consistent with STM observations of Ti dimer-vacancy hopping at lower temperatures and show that silicide island nucleation involves a different, highly mobile Ti species.