Low-energy ${\mathrm{D}}^{+}$ scattering has been employed to explore the nature of the bonding of Na, K, and Cs adatoms on the Si(100), Ge(100), ${\mathrm{TiO}}_2$(110), Pt(111), and ${\mathrm{SiO}}_2$ surfaces in a low-coverage regime (<1.7×${10}^{14}$ adatoms/${\mathrm{cm}}^2$). The analysis, based on neutralization and inelastic scattering of the ${\mathrm{D}}^{+}$ ions, reveals that the alkali-metal adatoms are essentially neutral with significant covalency on the Pt(111) surface while those except for Na are ionized on the semiconductor surfaces. The charge state of Na is critical and we conclude that large ionicity occurs only on the ${\mathrm{TiO}}_2$(110) surface. The special nature of the Na charge state on the semiconductor surfaces is caused by a larger ionization energy for Na than for the other alkali-metal adatoms.

• Received 21 June 1993

DOI:https://doi.org/10.1103/PhysRevB.48.17255