AVS 61st International Symposium & Exhibition
    Surface Science Wednesday Sessions
       Session SS+AS-WeM

Paper SS+AS-WeM11
Progress in Characterizing Submonolayer Island Growth: Capture-Zone Distributions, Growth Exponents, and Hot Precursors

Wednesday, November 12, 2014, 11:20 am, Room 312

Session: Atomistic Modeling of Surface Phenomena
Presenter: TheodoreL. Einstein, University of Maryland, College Park
Authors: T.L. Einstein, University of Maryland, College Park
J.R. Morales-Cifuentes, University of Maryland, College Park
A. Pimpinelli, Rice Quantum Institute
Correspondent: Click to Email
We review previous results for using the capture-zone [island proximity cell] distribution (CZD) in island growth to extract information about the critical nucleus size i.1 Over the experimentally accessible region, the CZD is well described by the generalized Wigner distribution Pβ(s) = aβ sβ exp(-bβs2), dependent only on the exponent β. For diffusion-limited aggregation (DLA), β ≈ i+2. We discuss recent experimental applications. For comparison with this approach, we consider the corresponding dependence of the growth exponent χ (stable island density N ~ Fχ, where F is the flux) for both DLA and attachment-limited aggregation (ALA). In either case, χβ = i, so that for ALA, where χ = 2i/(i+3), we find β = (i+3)/2.2 We compare with experiments depositing pentacene (5A) and p-hexaphenyl (6P) on sputtered mica.

Furthermore, recent experiments3 studying 5A on amorphous mica gave evidence of nucleation via a hot precursor state, with an unusual relationship between N and substrate temperature. Thus motivated, we examine a model of such behavior.4 We use rate equations and Walton's relation. We take deposited monomers to be hot initially, traveling ballistically with temperature-independent speed v until a time τ, when they thermalize. For the dimensionless combination z := v τ N-1/2 ≪ 1 rapid thermalization occurs, with consequent DLA nucleation. For z ≫ 1 we find the novel behavior for hot-monomer aggregation (HMA): χ has, unexpectedly, the same form as for ALA. We scrutinize behavior in both limits as well as in the crossover regime z ~ 1, in which behavior can be described using an effective χ. At low temperatures, the behavior becomes markedly non-Arrhenius, insensitive to temperature. We conclude a discussion of more general applications of this framework.

1T.L. Einstein, A. Pimpinelli, Diego Luis González, J. Crystal Growth (2014), http://dx.doi.org/10.1016/j.jcrysgro.2014.01.053.

2A. Pimpinelli, L. Tumbek, A. Winkler, J. Phys. Chem. Lett. 5 (2014) 995.

3A. Winkler, L. Tumbek, J. Phys. Chem. Lett. 4 (2013) 4080.

4A. Pimpinelli, J.R. Morales-Cifuentes, T.L. Einstein, preprint.