Modeling of segregation in the Fe (Au) alloy—from the bulk to thin films and nano-particles

Surface and interface segregations in the Fe(110)(Au)/Al₂O₃(0001) system have been simulated for the bulk Fe(Au) alloy, thin films and nano-particles by introducing a constrained condition of size effect in the modified Darken model [1]. The simulated results show that the equilibrium Au concentration at the Fe(110)(Au)/Al₂O₃(0001) interface: (a) exhibits a discontinuous transition (S-shaped segregation) with decreasing the bulk concentration/temperature for the thick Fe(Au) layer; (b) decreases with reducing the thickness of Fe(110)(Au) thin film and the size of Fe (Au) nano-particle, but approaches to a nearly constant value with increasing temperature. In particular, the simulated Au equilibrium concentration values at the Fe(110)(Au)/Al₂O₃(0001) interface, on the Fe(110) and Fe(100) nano-particle surfaces and in the Fe grain boundary at 1173K agree well with the experimental ones [2].

References

[1] J. Y. Wang, Equilibrium and kinetic surface segregation in binary alloy thin film. Applied Surface. Science, 252 (2006) 5347-5350.

[2] D. Amram, Y. Amouyal, E. Rabkin, Encapsulation by segregation- A multifaceted approach to gold segregation in iron particles on sapphire. Acta Materialia,102 (2016) 342-351.

Fig.1. Au equilibrium concentration at the Fe(110)(Au)/Al2O3(0001) interface as a function of temperature for different Au bulk concentrations at 1173K.

Fig.2. Au equilibrium concentration at the Fe(110)(Au)/Al2O3(0001) interface as a function of temperature for different Fe(110)(1.5at.%Au) thin films.

Fig.3. Au equilibrium concentration at the Fe(110)(Au)/Al2O3(0001) interface as a function of temperature for different cubic Fe(110)(1.5at.%Au) nano-particles.

Fig.4. Au equilibrium concentration values for the Fe(110)(1.5at.%Au) alloy at the Fe(110)(Au)/Al2O3(0001) interface, on the Fe(110) and Fe(100) nano-particle surfaces and in the Fe grain boundary at 1173K.