ADSORPTION AND COADSORPTION OF LEAD AND 1,3-BUTADIENE ON PLATINUM (111) - AN AES, LEED AND DELTA-PHI-STUDY

The vapour deposition of Pb on Pt(111) has been characterized by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), measurements of work-function changes (DELTA-phi) and crystal current measurements (i(c)). Lead growth occurs in two stages: the completion of a dense monolayer (ML) followed by the growth of an intermixed region at the Pb/Pt interface. The interaction of 1,3-butadiene with Pb-precovered Pt(111) was examined by AES, LEED and DELTA-phi measurements. The butadiene chemisorption capacity decays linearly with increasing lead coverage and is completely suppressed above 0.7 ML. Lead acts as an inert site blocker. An in situ calibration of the carbon Auger signals shows that an ensemble of 4.3 +/- 0.2 platinum atoms is necessary to chemisorb each molecule.