Medium-energy ion-scattering study of the temperature dependence of the structure of Cu(111)

We have studied the surface structure and vibrations of Cu(111) at temperatures between 300 and 1180 K using medium-energy ion scattering. At 300 K, first and second interlayer spacing contractions of -1.0% and -0.2%, respectively, relative to the bulk spacing are found. Above 1040 K, the first interlayer spacing expands significantly more rapidly than the bulk spacing, so that at 1180 K a +4.3% expansion is found. This expansion is smaller than the one previously determined for Ag(111), in agreement with predictions. Monte Carlo simulation of spectra show also that the vibration amplitudes of the Cu(111) surface atoms are enhanced by ∼30% below 910 K, and ∼100% at 1180 K, with respect to their bulk values.