How “Hot Precursors” Modify Island Nucleation: A Rate-Equation Model

We propose a novel island nucleation and growth model explicitly including transient (ballistic) mobility of the monomers deposited at rate $F$, assumed to be in a hot precursor state before thermalizing. In limiting regimes, corresponding to fast (diffusive) and slow (ballistic) thermalization, the island density $N$ obeys scaling $N\propto F^{\alpha }$. In between is found a rich, complex behavior, with various distinctive scaling regimes, characterized by effective exponents ${\alpha }_{\text{eff}}$ and activation energies that we compute exactly. Application to $N(F,T)$ of recent organic-molecule deposition experiments yields an excellent fit.