Neutral fractions are measured for 4 keV ${{}^{\mathrm{7}}\mathrm{L}\mathrm{i}}^{+}$ scattering from clean, hydrogen-covered, and cesiated Si surfaces. The neutral fraction in scattering from clean Si is $\sim 26\%$ and it decreases with hydrogen adsorption. When Cs is adsorbed on Si, the neutral fraction does not distinguish the local potential at the Cs sites from the Si sites, unless hydrogen is coadsorbed. These results demonstrate that resonant charge transfer occurs due to coupling of the Li ionization level with the dangling bond surface states, and that the influence of the dangling bonds extends beyond the local scattering sites.

• Received 29 March 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.196102