Add time:07/22/2019         Source:sciencedirect.com

Adsorption and desorption of CO from Ni nanostructures deposited on muscovite mica substrates have been studied by TPD and characterized by XPS and AFM. In agreement with previous reports it is found that CO does not adsorb on the bare mica substrate. The desorption spectra depend strongly on the Ni coverage on the mica substrate. Three coverage regimes have been found; for low Ni coverage of approximately 0.2 monolayers a dominant desorption peak is found near 400 K. For medium coverage of approximately 0.6 monolayers three distinct peaks appear in the temperature region from 250 to 550 K. For higher Ni coverage of approximately 3 monolayers a single peak is observed near 550 K. The high temperature peak was assigned to desorption from terrace sites, the medium temperature peak was assigned to step sites, and the low temperature peak was argued to stem from lateral interaction between adsorbed CO species and possible sites with low coordination, e.g. kink sites. Desorption parameters have been extracted from the low temperature part of the desorption spectra. Anomalous low values for the vibrational prefactors were obtained in the case of low Ni coverage. This is argued to be due to dissociation of CO.

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