The phase separation occurring in Fe-Ni thin films near the Invar composition is studied by using high-resolution spectromicroscopy techniques and density functional theory calculations. Annealed at temperatures around 300 C, Fe0.70Ni0.30 films on W(110) break into micron-sized bcc and fcc domains with compositions in agreement with the bulk Fe-Ni phase diagram. Ni is found to be the diffusing species in forming the chemical heterogeneity. The experimentally determined energy barrier of 1.59 +- 0.09 eV is identified as the vacancy formation energy via density functional theory calculations. Thus, the principal role of the surface in the phase separation process is attributed to vacancy creation without interstitials.
@article{arxiv.1608.07969,
title = {Vacancy-mediated fcc/bcc phase separation in Fe1-xNix ultrathin films},
author = {T. O. Mentes and N. Stojic and E. Vescovo and J. M. Ablett and M. A. Nino and A. Locatelli},
journal= {arXiv preprint arXiv:1608.07969},
year = {2016}
}