| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Thursday Sessions |
| Session SS+AS+EM+EN-ThA |
| Session: | Atomistic Modeling of Surface Phenomena & Semiconductor Surfaces and Interfaces - II |
| Presenter: | Josue Morales-Cifuentes, University of Maryland, College Park |
| Authors: | J.R. Morales-Cifuentes, University of Maryland, College Park T.L. Einstein, University of Maryland, College Park A. Pimpinelli, Rice University |
| Correspondent: | Click to Email |
In studies of epitaxial growth, a major goal is to assess the size of the smallest stable cluster (with i + 1 monomers, where i is the critical nucleus size). This is accomplished by analyzing either the capture zone distribution (CZD), the scaling of incident flux F to the density of stable islands N or the island-size distribution (ISD). For CZD, generalized Wigner distributions (GWD) have proven useful, [1,2] with successful applications to, non-comprehensively: polar-conjugated molecule Alq3 on passivated Si(100), self-assembled Ge/Si(001) nanoislands and para-Hexaphenyl (6P) films on amorphous mica. [3] We concentrate on the last, for which the Winkler group found that i ≈ 3.
Scaling of N usually follows N ∝ Fα, where α is the growth exponent. For 6P films, a difference in scaling behaviors at small and large F is attributed to DLA and ALA dynamics (i.e. i = 5 ± 2, and i = 7 ± 2, respectively). [4] This discrepancy motivates our current work, where transient mobility effects modify scaling non-trivially. [5]
Consider that monomers begin in a (ballistic) hot precursor state before thermalizing (random walk). The competing times of ballistic monomers becoming thermalized vs. being captured by an island naturally define a “thermalization” scale for the system. We obtain an analytic solution and elaborate on the physical meaning behind the energies and dimensionless parameters used. Novel scaling regimes are retrieved for which power-law scaling applies, with non-monotonic crossovers between them and the growth exponent exclusively dependent on i. Applying the model to the 6P films results in good agreement for the scaling and the activation energies: experimental values of the activation energies of 0.26eV (high-T) and 0.04eV (low-T) match model predictions of 0.3eV (high-T) and 0.04eV (low-T). Furthermore, the high-flux regime is interpreted not as ALA (attachment-limited aggregation) or HMA (hot monomer aggregation) but rather as an intermediate scaling regime related to DLA (diffusion-limited aggregation). Lastly, we discuss a simplifying approximation for the model and connections to some capture zone distribution considerations of α. [6]
[1] T.L. Einstein, A. Pimpinelli, D. González, J. Cryst. Growth 401, 67 (2014)
[2] T.L. Einstein, A. Pimpinelli, D. González, and J. R. Morales-Cifuentes, Proc. CCP2014, J. Phys.: Conf. Series (2015), in press.
[3] T. Potocar, G. Lorbek, D. Nabok et al. 2011 Phys. Rev. B 83 075423
[4] L. Tumbek & A. Winkler, Surf. Sci. 606, L55 (2012)
[5] J. R. Morales-Cifuentes, T. L. Einstein, and A. Pimpinelli. Phys. Rev. Lett. 113, 246101(2014)
[6] J. R. Morales-Cifuentes, T. L. Einstein, and A. Pimpinelli (in preparation)