COMPARISON OF THE INTERACTION OF CL-2 AND BR-2 WITH CU(100)

The adsorption, reaction and etching of Cu(100) by Cl-2 was studied us ing temperature programmed desorption (TPD) and low energy electron di ffraction (LEED), and the results were compared with recent results fo r Br-2. Although the general etching mechanism was the same for both g ases (adsorption rate limited Cu halide formation followed by halide s ublimation), significant differences between the behavior of Cl-2 and Br-2 were observed. The desorption of CuCl was characterized by a sing le zero order sublimation peak, independent of CuCl coverage, while li miting the CuBr coverage resulted in a desorption peak at temperatures lower than a prediction based on vapor pressure data of all known pha ses of CuBr. In addition, Cl-2 was found to be at least an order of ma gnitude less reactive than Br, towards halide formation. For both Cl-2 and Br-2, the halide formation rate reversibly decreased with increas ing reaction temperature. However, for Br-2, but not Cl-2, annealing a chemisorbed halogen layer prior to further reaction irreversibly incr eased the halide formation rate. Structural differences between CuCl a nd CuBr on Cu(100) were also observed. For CuCl, LEED data suggested t hat highly faceted crystallites form at 325 K and remain Stable until desorption, while LEED data for CuBr reveal a compressed epitaxial (11 1) layer that disorders below 400 K and then desorbs. The implications of these differences on etching and oxidation processes are discussed .