3. Nanoscale effects in volume diffusion

In this chapter we will show that classical picture of the diffusion cannot be kept on the nanoscale. Different examples for diffusional nanoscale effects, we have discovered recently. Interface shift kinetics may be different form the ones predicted by continuum approximations (anomalous kinetics). Moreover we show that in solid state reactions, reaction layers form and start to grow highly off-stoichiometrically and an initially existing stoichiometric compound layer may dissolve then re-form off-stoichiometrically. Our findings are of primary importance for nanotechnologies where early stages of SSR are utilized. We also show that an initially diffused interface may sharpen even in completely miscible systems. 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 multilayers with giant magnetic resistance.

A variety of different experimental techniques (AES/XPS and synchrotron facilities) has been used to prove the above theoretical findings in different systems (e.g. Ni/Cu. Ni/Au, Si/Ge, Co/Si).