Diffusion of CO on Pt(111) studied by an optical diffraction method

We have measured the diffusion of CO on flat and stepped Pt(111) surfaces using the linear optical diffraction method from an adsorbate grating. Measurements over a wide range of temperatures (133--313 K) and CO coverages (0.1--0.67 ML) indicate Arrhenius behavior with diffusion activation energies of 3.0--4.7 kcal/mol and 7.3--7.9 kcal/mol for flat and stepped surfaces, respectively. Comparisons of our measurements on flat and stepped (defected) surfaces with previous experiments by various groups using various techniques resolves several discrepancies and illustrates the importance of defect-induced effects on variations in measured diffusion parameters.