MEASUREMENT OF SURFACE ELECTRIC-FIELDS BY AN EXCITED-STATE ATOMIC-BEAM TECHNIQUE

Electric fields due to adsorbates on a metal surface are studied experimentally with highly excited atoms as probes. A beam containing Li Rydberg atoms, with principal quantum numbers in the range 20 less-than-or-similar-to 80, is detected after passing through a metal mesh having 6-mu-m square openings. Adsorbates at 10(-2) monolayer can produce 400 V/cm electric fields 0.6-mu-m from the surface. Fields of this magnitude can ionize Rydberg atoms in the atomic beam, reducing the flux through the mesh. Measurements of the excited-state atomic beam flux can thus yield information about the presence of adsorbates, including sticking probability, orientation and magnitude of electric dipole moment, and desorption energy. In the analysis of the experimental calibration, a relationship is obtained for the mesh transmission as a function of the adsorbate dipole-moment density. The measured desorption energies are compared with values reported in the literature.