(92d) Predicting and Controlling Self-Assembly in Al(110) Homoepitaxial Growth

Homoepitaxial growth on Al(110) exhibits nanoscale self-assembly [1] due to an interplay between the thermodynamic interactions between atoms and the kinetics of atomic diffusion and deposition. After 30 ML deposition with a flux of 1 ML/min at 450 K, 3D hut-shaped nanostructures called ?nanohuts? were seen in AFM images, which self-organize over the micron scale. Nanohuts have smooth and well-defined (100) and (111) facets and reach heights of up to 50 nm. Morphology during homoepitaxial growth under other conditions and structural evolution of nanohuts during deposition are presently not clear.

To explore surface morphologies under different growth conditions and identify the key mechanisms which govern them, we developed a 3D kinetic Monte Carlo model. The kinetic input to the model, in the form of energy barriers for atomic diffusion moves, were obtained by using the climbing-image nudged elastic band method [2] and first-principles total-energy calculations. We found several new mechanisms for adatom diffusion and refined the energy barriers obtained for the known mechanisms [3]. We found that the diffusion energy barriers are sensitive to the local environment due to atomic interactions at the initial and transition states. Under certain configurations, energy barriers for diffusion moves are significantly reduced in the presence of neighboring atoms. Thus, atoms assist each other to achieve moves that are kinetically difficult for single atoms, and lead to interesting self-assemblies.

We studied self-assembly under different deposition conditions in Al(110) homoepitaxial growth by modifying deposition flux and temperatures. Further, we propose innovative approaches to achieve the desired shapes and spatial distributions of nanostructures.

[1] F. Buatier de Mongeot, W. Zhu, A. Molle, R. Buzio, C. Boragno, U. Valbusa, E. Wang, and Z. Zhang, Phys. Rev. Lett. 91, 016102 (2003).

[2] G. Henkelman, B.P. Uberuaga, and H. Jonsson, J. Chem. Phys. 113, 9901 (2000).

[3] W. Zhu, F. Buatier de Mongeot, U. Valbusa, E. G. Wang, and Z. Y. Zhang, Phys. Rev. Lett. 92, 106102 (2004).