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J. Pavelec, J. Hulva, D. Halwidl, R. Bliem, O. Gamba Vasquez, Z. Jakub, F. Brunbauer, M. Schmid, U. Diebold, G. Parkinson:
"A multi-technique study of CO₂ adsorption on Fe₃O₄ magnetite";
Journal of Chemical Physics, 146 (2017), 0147011 - 01470110.

The adsorption of CO2 on the Fe3O4(001)-(p2 ⇥ p2)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 (p2 ⇥ p2)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