Abstract
The adsorption energies of submonolayer amounts of one metal on the surface of another metal have been measured for decades by temperature programmed desorption. However, that method fails for metals that alloy. We report here the first measurement of the adsorption energy for any such metal-on-metal combination that forms a bulk alloy. The adsorption and interfacial energetics of vapor deposited Cu onto Pt(111) at 300K has been studied using single crystal adsorption calorimetry (SCAC) and X-ray photoelectron spectroscopy (XPS). The Cu grows as 2D pseudomorphic islands in the first layer and its heat of adsorption decreased linearly from 358 to 339kJ/mol. This is attributed to increasing lattice strain with island size, associated with the small lattice mismatch (8%). It adsorbs ~2kJ/mol more weakly in the 2nd layer than above 3ML, where it reaches the bulk heat of sublimation of Cu(solid), 337kJ/mol. The adhesion energy of multilayer Cu onto Pt(111) is 3.76J/m2. The extra stability of the first Cu monolayer compared to bulk Cu measured here is ~12kJ/mol, compared to a difference of ~83kJ/mol for underpotential deposition of Cu on a Pt(111) electrode, with the difference attributed to stronger bonding of Cu to the solvent and double layer compared to Pt.
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