Growth of composition-modulated Ag/Co wires on Pt(997) - art. no. 045404

Sequential deposition of Ag and Co on a Pt(111) stepped surface has been in vestigated as a means to obtain composition-modulated atomic wires. Thermal energy He atom scattering in grazing incidence conditions allows us to con trol and characterize the growth of Ag/Co wires on Pt(997) as a function of the substrate coverage and temperature. When Co is deposited first, Ag and Co atoms arrange themselves into regular stripes parallel to the Pt steps. A disordered phase is obtained when Ag is deposited first. We have carried out calculations based on semiempirical potentials to study the equilibriu m configuration of a Ag/Co mixture on Pt(997). The experimental observation s agree with ground-state calculations of the atomic structure, indicating that the first pure Co row in contact with the Pt step edge is very stable while the second row is occupied by Ag atoms. Free-energy minimization usin g a mean-field Ising approach at finite temperature of equimolar binary mix tures leads to very consistent results for the Ag/Co system, namely the pre ferential sequence with nearly pure Co and Ag wires in the first and second rows at the step. Predictive extensions to Co/Cu and Ag/Cu systems are dis cussed within the same approach. A preferential ordering with Co (Cu) occup ying the first row and Cu (Ag) the second row is clearly obtained from the calculations, although the Ag/Cu system can also be frozen in reverse order .