Relationship Between Anisotropy of Specific Surface Free Energy and Surface Reconstruction

Abstract

Some surfaces reconstruct by changing their morphology such that new surface orientations are being exposed. From general considerations it is clear that the surface free energy of such a reconstructed surface will be lower than that of the non-reconstructed form. It can be shown, however, that surface reconstruction will only be energetically favorable if the anisotropy of the surface free energy in the orientational range involving the non-reconstructed surface is high. Two different experiments carried out on Pt{110} support this idea. Measurements of surface self-diffusion on Pt{110} in the 〈001〉 direction are consistent with an anisotropy in surface free energy, γ(θ) of 8–10% at T > 1400 K. Spectroscopic data of surface atom core level shifts (SCLS) of clean reconstructed and non-reconstructed Pt surfaces also yield anisotropics of γ(θ) in excess of 10% along the [11̄0] zone. Reconstruction of the Pt{110} surface to the 1×2 lowers that anisotropy drastically. Measurements of SCLS of CO-covered Pt surfaces are also evaluated in terms of changes in γ(θ). It is found that CO adsorption moves the lowest energy cusp from {111} to {110}, and further that the non-reconstructed {110} is more stable than the reconstructed surface. This explains why CO lifts the 1×2 reconstruction of Pt {110}.KeywordsSurface Free EnergySurface ReconstructionSurface OrientationProfile DecayCore Level ShiftThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.