Role of Elastic Scattering in Electron Dynamics at Ordered Alkali Overlayers on Cu(111)

Scanning tunneling spectroscopy of $p(2\times 2)$ Cs and Na ordered overlayers on Cu(111) reveals similar line widths of quasi-two-dimensional quantum well states despite largely different binding energies. Detailed calculations show that 50% of the line widths are due to electron-phonon scattering while inelastic electron-electron scattering is negligible. The mechanism of enhanced elastic scattering due to Brillouin zone backfolding contributes the remaining width.

Figure 1

Comparison between measured (dots) and calculated (lines) $dI/dV$ curves for $p(2\times 2)$ structures of (a) Cs and (b) Na on Cu(111). The solid lines include both the elastic and inelastic contributions to the energy width, while the dashed lines include only the inelastic one.

Figure 2

Dispersion of $p(2\times 2)$ Na and Cs quantum well states in the $\overline{\Gamma }\mathrm{\text{−}}\overline{M}$ direction. Dark gray indicates bulk Cu states of the $(1\times 1)$ SBZ, while light gray shows the closing of the gap around $\overline{\Gamma }$ after backfolding from the $\overline{M}\mathrm{\text{−}}{\overline{M}}_{\mathrm{Cu}}$ and ${\overline{M}}_{\mathrm{Cu}}\mathrm{\text{−}}{\overline{K}}^{\prime }$ directions onto $\overline{\Gamma }\mathrm{\text{−}}\overline{M}$ defined in the inset.