BROMINE ADSORPTION, REACTION, AND ETCHING OF CU(100)

The interaction of Br-2 with Cu(100) was characterized using temperatu re-programmed desorption (TPD) and low-energy electron diffraction (LE ED). Initial exposure to Br-2 resulted in the formation of a c(2 x 2) LEED pattern and CuBr desorption peaks at 870 and 1000 K. These desorp tion peaks saturated at a dose of approximately 5 L and were attribute d to Br chemisorption. Continued exposure to Br-2 resulted in the grow th of Cu3Br3 desorption peaks associated with the formation of bulk Cu Br. The Cu3Br3 desorption peaks exhibited a strong coverage dependence . At low CuBr coverages, desorption peaks at 450 and 485 K were observ ed, while at intermediate coverages a third peak at 540 K was observed , and at high coverages a single broad peak at 500 K was observed. Sim ilar results were obtained whether the CuBr layer was formed by exposu re to Br-2 or by deposition of Cu3Br3 onto a c(2 x 2) layer. The two h igher-temperature peaks were shown to be consistent with sublimation o f alpha and beta CuBr, while the lowest-temperature peak could not be associated with sublimation of any bulk phase of CuBr. The lowest-temp erature peak was attributed to either a grain-size effect or to the in teraction of CuBr with chemisorbed Br. At 325 K, growth of CuBr result ed in a hexagonal LEED pattern that disappeared upon annealing to 400 K. Again, the same results were obtained for CuBr formed by reaction w ith Br-2 and by vapor deposition of Cu3Br3, suggesting that the reacti on produces near-equilibrium structures. The hexagonal LEED pattern wa s attributed to compressed epitaxial CuBr(lll). The reaction of Br-2 w ith Cu(100) was characterized by a constant sticking coefficient, indi cating that the reaction is adsorption-rate limited over the range stu died. The sticking coefficient was found to depend on temperature in t wo distinct ways: (i) annealing the c(2 x 2) layer irreversibly increa ses the sticking coefficient, and (ii) the sticking coefficient revers ibly decreases with increasing reaction temperature. The first effect was attributed to structural changes in the chemisorbed layer.