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Fast surface exchange processes determining local concentration profiles in heteroepitaxial nanometric islands

Francesco Montalenti 

University of Milano-Bicocca, Department of Materials Science, via Cozzi 53, Milano 20125, Italy

Abstract
Thin-film growth as determined by various experimental deposition techniques commonly takes place under non-equilibrium conditions. In order to build a comprehensive understanding of the phenomenon it is therefore fundamental to understand the actual kinetic scenario. This requires evaluating the activation energies for the most relevant diffusion events, after having determined possible diffusion paths. In the first half of this talk, I shall review some key methodology which was introduced within the last decade, allowing one to tackle the well-known problem of estimating the rates of (initially unknown) rare events.  Accelerated molecular dynamics [1], the Nudged Elastic Band Method [2], the Dimer Method [3], and Metadynamics [4] will be briefly reviewed. Afterwards, I shall present recent results exemplifying how exploiting state of the art methods it is possible to accurately characterize complex exchange-mediated diffusion events involving several atoms at the same time. Applications to popular Ge/Si systems (for both flat films and 3D islands) will be discussed [5,6], with the aim of understanding recent experimental results concerning the Si/Ge concentration profiles in nanoislands [7] .

I acknowledge financial support from the EU (STREP Project d-DOT-FET, contract 012150) and from the Cariplo Foundation (SIMBAD project).

[1] A.F. Voter, F. Montalenti, and T.C. Germann, Annu. Rev. Mater. Res. 32, 321 (2002).

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

[3] G. Henkelman and H. Jonsson, J. Chem. Phys. 111, 7010 (1999).

[4] A. Laio and M. Parrinello, PNAS 99, 12562 (2002).

[5] F. Zipoli, S. Cereda, M. Ceriotti, M. Bernasconi, L. Miglio, e F. Montalenti, Appl. Phys. Lett. 92, 191908 (2008).

[6] S. Cereda and F. Montalenti, in preparation.

[7] G. Medeiros-Ribeiro and R. Stanley Williams, Nano Lett. 7, 223 (2007).

 

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Presentation: Invited oral at E-MRS Fall Meeting 2008, Symposium G, by Francesco Montalenti
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-23 18:29
Revised:   2009-06-07 00:48