Observation of the adsorption and desorption kinetics of weakly bound CO on Si(001)-c(4×2) by means of reflectance difference spectroscopy

- Weakly bound CO exists on Si(001)-c(4x2) during CO exposure by reflectance difference spectroscopy.
- The life time of metastable CO species is evaluated, consistent with our previous study.
- The adsorption energies were evaluated from the life time using Arrhenius-type relation.
- The weakly bound CO can be assigned to the physisorbed structure according to theoretical calculations.
- The agglomeration process of CO is explained by van der Waals interaction.

The weak adsorption state of CO molecules on a Si(001)-c(4×2) surface at 110 K is investigated by means of reflectance difference spectroscopy (RDS). We observe repeated cycles of the increase and decrease in the RD intensity during CO exposure and after CO cessation. The decay process after CO cessation is analyzed by fitting the resulting data with an exponential function. The decay constant is evaluated to be ∼70-80 s, corresponding to the CO adsorption energies of ∼0.2-0.3 eV. The results indicate that a metastable species exists at 110 K during CO exposure. Theoretical calculations suggest that the physisorbed state is associated with this novel phenomenon.

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