Adsorption and desorption of lead on low-index and stepped copper surfaces

Abstract

Results from LEED, AES and isothermal desorption experiments are reported for monolayers of lead on low-index and stepped copper surfaces. Data for the (100), (711), (511), (311), (211) and (111) substrate orientations are discussed. Plots were made of the Auger peak-to-peak heights as a function of time during adsorption. These plots show breaks corresponding to the formation of dense monolayers and also earlier breaks due to changes in the sticking probability at the completion of submonolayer structures. The breaks permit a calibration of the spectrometer. For all substrate orientations LEED patterns were obtained with four-fold coincidence periodicities which are interpreted in terms of dense rows of lead atoms. For the stepped surfaces these rows are always parallel to the step directions. The desorption data (peak-to-peak heights as a function of time) show zero-order kinetics with initially a fast reaction and then a slow reaction that sets in at a coverage that depends on the orientation. The dominance of the fast reaction for (111) is related to the subsistence of islands of the compact monolayer arrangement down to low coverages.