Potassium- and sodium-induced phonons on the reconstructed and unreconstructed copper (110) surface studied by high-resolution electron-energy-loss spectroscopy

The K- and Na-induced dipole-active vibrational modes on Cu(110) have been measured as a function of coverage at 90 and 300 K. On the reconstructed surface, in addition to the K- (Na-) substrate stretching mode, a dipole-active loss is found at 10 meV (11.5 meV). The observation of this mode even at coverages as low as Θ≃0.02 points to local reconstruction at the lowest alkali-metal coverages. The sequence of reconstructions does not change appreciably the Na-Cu stretching frequency.