BONDING GEOMETRIES OF F AND CL ON SI(100)-2X1

Angle- and energy-resolved F+ and Cl+ electron-stimulated desorption d istributions are collected from Si(100)-2x1 surfaces exposed at room t emperature to XeF2 or Cl-2. These distributions are fit to a model tha t accounts for ion-surface interactions in order to extract bond angle information. It is found that both F and Cl chemisorb on the dangling bonds of intact Si dimers, at an angle of similar to 20 degrees from normal along the [011] azimuth. By annealing a chlorinated surface abo ve similar to 400 K, some normally oriented Si-Cl bonds are generated. In addition to determining bonding geometries, quantitative informati on is obtained regarding the image-charge interaction and neutralizati on for F+ and Cl+ interacting with Si.