ESDIAD studies of fluorine and chlorine adsorption at Si(100)

Electron stimulated desorption ion angular distribution (ESDIAD) patterns are reported for fluorine and chlorine adsorbed at the silicon (100) surface. Analytical and numerical methods of establishing the degree of angular compression imposed by the sample bias frequently employed in ESDIAD measurements, are described. Measurements of the two halogen adsorbates contrast strongly, particularly with regard to their response to annealing in the temperature range 300 to 1000 K. In the case of F⁺ desorption, a minimum in ion intensity occurs along the surface normal. Maxima in the ion production are observed at a polar angle of 30°, and in registry with the principal crystal axes as reported by other workers. Cl⁺ ion angular distributions however, indicate a mixture of normal and off-normal emission for adsorption at ≤ 300 K. This pattern transforms, irreversibly, to a single maximum directed along the surface normal in response to annealing to 650 K. The transformation is linked to the thermal depopulation of one adsorption state, leaving a higher binding energy state intact.