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Surface Science 429 (1999) 113 www.elsevier.nl/locate/susc Coverage grating template for the study of surface diffusion

Summary: Surface Science 429 (1999) 1­13 www.elsevier.nl/locate/susc
Coverage grating template for the study of surface diffusion:
K coadsorbed with CO on Re(001)
W. Zhao, M. Asscher *
Department of Physical Chemistry and the Farkas Center for Light Induced Processes, The Hebrew University, Jerusalem 91904, Israel
Received 10 October 1998; accepted for publication 26 January 1999
The coverage grating method as a template for coadsorbates is introduced for the study of surface diffusion. The
effect of coadsorbed CO inside coverage troughs formed by laser induced thermal desorption (LITD) on potassium
surface diffusion on Re(001) has been investigated using the coverage grating optical second harmonic diffraction
method. Enhancement of the first-order diffraction peak at a certain CO coadsorption coverage, observed for the first
time, demonstrates the very strong electronic interaction between these coadsorbates. The activation energy for K
surface diffusion and the pre-exponential factor significantly increase with CO coverage. At initial potassium coverage
of 1.0 ML, the activation energy for potassium diffusion increases from 5.0 kcal/mol on the clean rhenium surface to
15.0 kcal/mol in the presence of 0.065 ML CO, and the pre-exponential factor increases from 5.6×10-3 to
2.0×102 cm2/s. The activation energy doubles for potassium coverages of 0.9 ML and 0.8 ML as a result of the same
CO coverage. TPD measurements indicate that strong attractive interactions exist between CO and K on Re(001).
Coadsorbed CO and K stabilize each other while forming K
­CO surface complexes which slow down the potassium


Source: Asscher, Micha - Institute of Chemistry, Hebrew University of Jerusalem


Collections: Chemistry