It is known form Fick's phenomenological laws that in a diffusion couple the displacement of a plane with constant composition (or an abrupt interface) is proportional to t^1/2. However, we have shown first from computer simulations that this rule can be violated on the nanoscale either in completely [1] or restricted miscible systems [2]. This is strongly related to the discrete character of the system on the nanoscale and to the highly neglected fact in the literature that the diffusion coefficients or mobilities depend on the composition. As we have shown recently, these studies may help to understand the atomistic meaning of the kinetic transfer coefficient in solid state reactions. [3]

Computer simulations also have shown that on the nanoscale, for strongly composition-dependent diffusion coefficients, diffuse interfaces can sharpen rather broaden in completely miscible binary systems during annealing [4]. This sharpening is surprising, because the direction of diffusion is always opposite to the direction of the composition gradient. This phenomenon could provide a useful tool for the improvement of interfaces and offer a way to fabricate of e.g. better X-ray or neutron mirrors, microelectronic devices or GMR multilayers.

These phenomena predicted by computer simulations have been later proved experimentally as well [5-6]. This shows the efficiency and importance of the computer modeling in planning and fabrication of new devices.

[1] Z. Erdélyi, Ch. Girardeaux et al., Surf. Sci. 496, 129 (2002)
[2] Z. Erdélyi, G. L. Katona et al., Phys. Rev. B 69, 113407 (2004)
[3] D. L. Beke. Z. Erdélyi, Phys. Rev. B 73, 035426 (2006)
[4] Z. Erdélyi, I. A. Szabó et al., Phys. Rev. Lett. 89, 165901 (2002)
[5] G. L. Katona, Z. Erdélyi et al., Phys. Rev. B 71, 115432 (2005)
[6] Z. Erdélyi, M. Sladecek et al., SCIENCE 306, 1913 (2004)

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1. Investigating interdiffusion in Cu/Ni multilayers from x-ray diffraction and kinetic simulation