Nanoanalysis of Interreactions
Nucleation of product phase at reactive diffusion of Co/Al
The reaction of Co/Al bi-layers was investigated by means of atomprobe tomography. For that, tip-shaped
reaction couples were produced by sputter deposition onto tungsten substrates. The reaction couple Co/Al is a
rather clear example, where the formation of a unique product (Al9Co2) is indicated
by two distinct heat releases in DSC traces. The nano-analysis directly proved the existence of two distinct
reaction stages, i) nucleation and lateral growth along the interface and ii) normal growth. Furthermore
interdiffusion on the length scale of only 3-4 nm has been proven as a precursor of the reaction for the
first time. The naïve picture of reaction step i) must be modified, since already in this state some thickness
growth takes place by interfacial transport along the product particle surface. By a quantitative analysis it was
shown that this behaviour leads to a thickness of about 10 nm when reaction stage i) is completed.
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