Not quite sure if this is the place to ask this question, so feel free to
ignore me if it's appropriate :).
I'm doing some research on thin gold films on silicon substrates and I
need some material science/thermodynamics help.
As I understand it, spinodal decomposition is something that can be seen
in the miscibility gap of a phase diagram. It is something that arises
when there is no barrier to nucleation and it occurs when the enthalpy
of mixing is positive (and therfore the Gibbs free energy is positive)
and the temperature is around the critical temperature of the system in
question. My problem is that in the (bulk) Au-Si phase diagram
(http://liquids.deas.harvard.edu/oleg/presentations/AuSi_files/image001.jpg)
there is no miscibility gap seen, but rather, a line indicating a phase
transition around 376C. However, some papers cite they have found
evidence for spinodal decomposition with thin gold films and STM (Phys.
Rev. Lett. Vol, 91 article #066101) yet they give no explanation about the
discrepancy in the phase diagram (or did I not catch it?).
In short, I'm looking for an explanation as to how spinodal decomposition
can exist when not seen in a phase diagram yet observed in an experiment.
Also, if there is a way to know for certain from beginning and end
conditions if you underwent nucleation and growth or spinodal
decomposition.
If any of you interface science buffs or thermodynamicists can help me it
would be greatly appreciated. When I say spinodal decomposition around
here they all scatter like x-rays from electrons.