Workshops > Non-equilibrium Interface and Surface Dynamics

Non-equilibrium Interface and Surface Dynamics

Directed Self Assembly of Nanostructures Kinetically: Patterning, the Ehrlich Schwoebel Barrier, and the Effect of a Critical Island Size*

Raymond Phaneuf

University of Maryland


In this talk I will compare the results of Kinetic Monte Carlo (KMC) simulations in a simple model system with molecular beam epitaxy (MBE) growth experiments on lithographically patterned GaAs(001) surfaces. Our previous work on epitaxial growth of GaAs on patterned GaAs(001) substrates suggested that an Ehrlich-Schwoebel barrier, which impedes diffusing atoms in crossing steps from above, might play a role in a transient growth instability [1-3]. Our recent KMC simulations suggest that the Ehrlich Schwoebel barrier can lead to self assembly of a variety of ordered arrangements of nanometer-sized ?mounds? during epitaxial growth on a patterned substrate. Strikingly, in different temperature windows of epitaxial growth, the pattern-mound interaction serves to assemble specific, nearly periodic mound arrangements. As the temperature is increased mounds arrange in structures with unit cells of dimensions.A/3 x A/3, A/√2 x A/√2 and AxA, where A is the pattern period. Our patterned growth experiments show that mound formation on patterned surfaces is indeed directed, with mounds forming in both 2-fold and 4-fold bridges between pits. Mound site selection for GaAs is more complex than in the KMC simulations: we find that the evolution of the pattern features during growth drives a change in the preferred mound positions. In addition, we see evidence that a critical island size, not included in our simulations, might lead to an observed size-selection in the amplification or decay of the pattern amplitude.

Joint work with C.-F. Lin1, A. B.-H. Hammouda, H.-C. Kan1, K. Subramaniam and C.J.K. Richardson

*Work supported by NSF #DMR0705447, The Laboratory for Physical Sciences and the UM-MRSEC # DMR0520471

[1] T. Tadayyon-Eslami, H.-C. Kan, L. C. Calhoun and R. J. Phaneuf, Physical Review Letters 97, 126101-1,-4 (2006)
[2] H.-C. Kan, R. Ankam, S. Shah, K.M. Micholsky, T. Tadayyon-Eslami, L. Calhoun, and R. J. Phaneuf, Physical Review B 73, 195410 (2006)
[3] H.-C. Kan, S. Shah, T.T. Tadayyon-Eslami and R.J. Phaneuf, Physical Review Letters 92, 146101 (2004)