The morphology and adsorption energetics for Ag and Ni vapor deposited onto a graphene monolayer grown on Ni(111) were studied using low-energy ion scattering (LEIS) and single crystal adsorption calorimetry (SCAC). Both metals grew initially as 3D nanoparticles on the graphene. We observed a particle density for Ag of ~4×1015 particles/m2 at 300K and ~1.0×1016 particles/m2 at 100K. SCAC shows an initial heat of 240 kJ/mol at 300K and the differential heat of adsorption quickly reaches Ag’s bulk sublimation enthalpy of 285 kJ/mol (within 0.5ML at 300K). The sticking probability was lower than unity at both studied temperatures (~80% at 300K and ~90% at 100K). These results suggest a very weak interaction of Ag monomers and Ag nanoparticles with the substrate. Nickel grew with slightly higher particle densities of ~7×1015 particles/m2 at 300K and ~1.5×1016 particles/m2 at 100K on the same substrate. However, the Ni heats of adsorption increased much more slowly taking &gt;2ML to reach the Ni bulk sublimation enthalpy of 430 kJ/mol, and sticking probabilities remained high (&gt;90%) at both temperatures studied. These results indicate a much stronger bonding of Ni to the graphene. Combining the LEIS and SCAC results, we estimated the effective particle diameter during the SCAC measurements using the hemispherical cap model. These data provided the metal chemical potential for Ag or Ni on graphene/Ni(111) as a function of particle size and the adhesion energies of Ag and Ni to graphene.

Energetics and morphology of Ag and Ni on graphene / Ni(111) by adsorption calorimetry and ion scattering spectroscopy

ACS Spring 2022

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