HALOGEN ADSORPTION ON FE(100) .1. ADSORPTION OF CL2 STUDIED BY AES, LEED, WORK FUNCTION CHANGE AND THERMAL-DESORPTION

The initial sticking probability of chlorine on Fe(100) at room temperature is calculated to be 0.13, and there is evidence to suggest that the chlorine adsorbs into a short lived mobile precursor state above the surface. The work function change, Δφ, is proportional to coverage and reaches a maximum value of 1.43 eV at saturation. At this coverage a c(2 × 4) LEED pattern is formed. On heating, chlorine is lost from the surface, but the mechanism is such that no detectable loss is incurred at a constant elevated temperature. The c(2 × 4) pattern is shown to be a coincidence structure formed from a ( 1 2 3 -1 2 3) net of chlorine atoms on the Fe(100) substrate. This structure is a special case of the more general ( 1 2 tanα -1 2 tanα) structure formed at lower concentrations of chlorine. The c(2 × 4) is formed when α = 56.31°, which gives the chlorine atoms a hard sphere diameter of 0.345 nm and a concentration of 0.75 atoms per four-fold site. © 1979.