Chemical Order and Electronic Structure in Alloys and Nanoalloys

We have used the Tight-Binding formalism, within the continued fraction technique, in order to study the stacking defect fcc vs hc as a function of electronic filling in the aim to make a general study concerning transition metals of the end of series (like Ir, Pt and Au). With this study we have demonstrated the importance of spd hybridization which affects the d band not only for very low and very high fillings (band borders) but also on all the energy range and therefore all the electronic filling range[21, 22]. We have further applied the same method to mixed systems of transition metals considering in particular CoAu. Applying this method to alloys required to determine first a rule of charge distribution as a function of concentration. Based on DFT calculations we have shown that this rule reduced to a local neutrality rule, per site, species and orbital. Applying this rule in self- consistent TB calculations, we were able to study in a first application, the d level shifts, as a function of concentration in an alloy, which can be associated to core level shifts measured in XPS experiments[23].

References :

[21] ”Role of spd hybridization in the formation of stacking defects at metal surfaces”, A. Jaafar, C. Goyhenex and G. Tréglia, Surf. Sci. 602, 2681 (2008).

[22] ”Formation of stacking defects at surfaces : From atomistic simulations to density functional theory calculations”, A. Jaafar and C. Goyhenex, Solid State Sciences 12, 172 (2010).

[23] ”Rules for Tight-Binding calculations in bi-metallic compounds based on Density Functional Theory : the Co-Au case”, A. Jaafar, C. Goyhenex and G. Tréglia, J. Phys. Cond. Matter 22, 505503 (2010).