A multi-technique study of CO2 adsorption on Fe3O4 magnetite

• Published in: The Journal of chemical physics Vol. 146; no. 1
• Main Authors: Pavelec, Jiri, Hulva, Jan, Halwidl, Daniel, Bliem, Roland, Gamba, Oscar, Jakub, Zdenek, Brunbauer, Florian, Schmid, Michael, Diebold, Ulrike, Parkinson, Gareth S.
• Format: Journal Article
• Published: 07.01.2017
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.4973241

The adsorption of CO2 on the Fe3O4(001)-( 2 × 2 )R45° surface was studied experimentally using temperature programmed desorption (TPD), photoelectron spectroscopies (UPS and XPS), and scanning tunneling microscopy. CO2 binds most strongly at defects related to Fe2+, including antiphase domain boundaries in the surface reconstruction and above incorporated Fe interstitials. At higher coverages,CO2 adsorbs at fivefold-coordinated Fe3+ sites with a binding energy of 0.4 eV. Above a coverage of 4 molecules per ( 2 × 2 )R45° unit cell, further adsorption results in a compression of the first monolayer up to a density approaching that of a CO2 ice layer. Surprisingly, desorption of the second monolayer occurs at a lower temperature (≈84 K) than CO2 multilayers (≈88 K), suggestive of a metastable phase or diffusion-limited island growth. The paper also discusses design considerations for a vacuum system optimized to study the surface chemistry of metal oxide single crystals, including the calibration and characterisation of a molecular beam source for quantitative TPD measurements.