Silver Nanoparticles on Fe3O4(111): Energetics by Ag Adsorption Calorimetry and Structure by Surface Spectroscopies

The heat of adsorption of Ag atoms and the growth morphology of the resulting silver particles on the Fe3O4(111) surface at 300 K were studied by adsorption microcalorimetry, Auger electron spectroscopy (AES), and low energy ion scattering spectroscopy (LEIS). Thin films (similar to 6 nm thick) of Fe3O4(111) were grown on a Pt(111) single crystal. The changes in AES and LEIS signals versus Ag coverage during Ag vapor deposition onto Fe3O4(111) were indicative of Ag growing as 3D particles with a fixed density of similar to 4 x 10(12) particles/cm(2). The heat of Ag adsorption increased with Ag coverage from similar to 230 kJ/mol initially up to within a few percent of the heat of sublimation of bulk Ag (285 kJ/mol) by similar to 2 ML Ag. This corresponds to an increase in Ag atom stability (decrease in chemical potential) by similar to 55 kJ/mol as the Ag particle size grows from <1 to similar to 4 nm effective diameter on Fe3O4(111). The Ag(solid)/Fe3O4(111) adhesion energy for the 4 nm particles was estimated from the integral heat of adsorption to be 2.5 +/- 0.3 J/m(2). The sticking probability of Ag atoms was similar to 0.96 initially and increased to similar to 0.99 by similar to 1.0 ML and above.