Abstract
Surface Action Spectroscopy, a vibrational spectroscopy method developed in recent years at the Fritz Haber Institute is employed for structure determination of clean and H2O-dosed (111) magnetite surfaces. Surface structural information is revealed by using the microscopic surface vibrations as a fingerprint of the surface structure. Such vibrations involve just the topmost atomic layers, and therefore the structural information is truly surface related. Our results strongly support the view that regular Fe3O4(111)/Pt(111) is terminated by the so-called Fetet1 termination, that the biphase termination of Fe3O4(111)/Pt(111) consists of FeO and Fe3O4(111) terminated areas, and we show that the method can differentiate between different water structures in H2O-derived adsorbate layers on Fe3O4(111)/Pt(111). With this, we conclude that the method is a capable new member in the set of techniques providing crucial information to elucidate surface structures. The method does not rely on translational symmetry and can therefore also be applied to systems which are not well ordered. Even an application to rough surfaces is possible.
Highlights
Structure−reactivity relationships are important descriptors for the catalytic activity of surfaces
Via a comparison with vibrational spectra computed using density functional theory (DFT) for model surface terminations we show that Fe3O4(111) is terminated with Fetet[1], and that the method can differentiate between different water-derived species on Fe3O4(111)
The surface modes are highly sensitive to the structural arrangement of the surface atoms, and the surface vibrations represent a fingerprint of the surface structure
Summary
Structure−reactivity relationships are important descriptors for the catalytic activity of surfaces. Recording the messenger desorption rate as a function of the photon energy produces a vibrational spectrum.[4−6] We have applied such a procedure to messengers adsorbed on surfaces and demonstrated its usefulness in surface vibrational spectroscopy.[2,3] We use this method to measure vibrational spectra of different iron oxide layers in the range of about 300 to 700 cm−1, where a number of microscopic optical surface vibrations is situated. This is not the case for SAS since it is not based on diffraction, which is a relevant advantage with respect to the diffraction-based methods Scanning probe techniques such as STM (scanning tunneling microscopy) and AFM (atomic force microscopy) are suitable for surface structure determination, but they are not directly element sensitive and information about deeper layers is not revealed. We use a Fe3O4(111)-(1 × 1) surface unit cell adsorbing a single OH, one, and two H2O molecules
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