Preparation of Pt-Co Alloy Films

Thin films were prepared by physical vapor deposition in ultra-high vacuum (UHV) as described previously. A doser was constructed by tightly winding wires of the Pt and Co metals in small segments around a Ta filament. The filament is heated resistively at a current sufficiently high to initiate sublimation of subject metals onto a cold (Ru or Mo) substrate the latter is located close to the doser to enable a controllable deposition rate. 

Calibration of the dosing (film-formation) rate was conducted via an XPS breakpoint analysi In this procedure, a plot of the XPS intensity is obtained as a function of dosing time (Fig. 2) from submonolayer to full-monolayer coverages, the intensity-versus-time plot has a fixed slope. The point at which the slope changes marks the time at which a second monolayer begins to form it is also taken as the total time (/ml) required to deposit one full monolayer. In the preparation of an n-ML film, the total dosing time was simply equated to ( x 7ml). At the end of each deposition, the alloy films were annealed at 900 K for 20 minutes to ensure that Pt and Co had become alloyed. Prior to and subsequent to the electrochemical experiments, interfacial composition was determined by LEISS, XPS or TPD, and surface structure by LEED. 

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