Iron oxide nanoparticles (FeO x -NP) are applied in medicine as contrast agents in magnetic resonance imaging (MRI) where they reduce the spin−spin relaxation time (T 2 -time) of absorbing tissue. Hence, control of their magnetic properties is essential for these applications. Magnetic properties strongly depend on the particle size and shape as well as the surface functionalization of the iron oxide nanoparticles. Especially, structural and magnetic disorder in the region close to the surface (1−2 nm) lead usually to a reduced magnetization compared to the corresponding bulk material. Therefore, X-ray magnetic circular dichroism (XMCD) in the total electron yield (TEY) mode is used to investigate local magnetic and electronic properties of the surface region of monodisperse, spherical FeO x -NPs (Fe 3 O 4 /γ-Fe 2 O 3 ) before and after the postsynthetic treatment in oxygen-rich environment. Charge transfer multiplet calculations of the XMCD spectra are performed to analyze the contributions of Fe 2+ and Fe 3+ at different lattice sites, i.e., either in octahedral or tetrahedral environment. The analysis of the XMCD data reveals that both, the magnetization of the nanoparticle surface region as well as their maghemite to magnetite ratio, are strongly increased after tempering in an oxidative environment, which likely causes rearrangement of their crystalline order. The magnitude and the kinetics of these variables depend strongly on the particle size. In addition, after thermal annealing a reduced spin canting is extrapolated from the lower magnetic coercivity, which confirms that a structural rearrangement takes place.

An experimental setup for low temperature thermal desorption spectroscopy (TDS) integrated in an ultrahigh vacuum-chamber housing a high-end scanning probe microscope for comprehensive multi-tool surface science analysis is described. This setup enables the characterization with TDS at low temperatures (T > 22 K) of portable sample designs, as is the case for scanning probe optimized setups or high-throughput experiments. This combination of techniques allows a direct correlation between surface morphology, local spectroscopy, and reactivity of model catalysts. The performance of the multi-tool setup is illustrated by measurements of a model catalyst. TDS of CO from Mo(001) and from Mo(001) supported MgO thin films were carried out and combined with scanning tunneling microscopy measurements.

Electron-assisted hydroxylation of single-crystalline silica bilayer films grown on Ru(0001) is studied by high-resolution electron energy loss spectroscopy (HREELS) and electron paramagnetic resonance (EPR) spectroscopy. The HREELS results reveal the formation of several hydroxyl species whose number and speciation depend on the defect structure of the film. For incomplete bilayer films, which exhibit nanometer-sized holes in the bilayer, the level of hydroxylation is significantly larger than for complete films. HREEL spectra taken in off-specular geometry provide evidence for the presence of hydroxyl groups with a transition dipole moment almost parallel to the surface for complete and incomplete bilayer films. Hydroxylation with isotopically labeled water (H2 18O) reveals a clear difference between the two casesOH species on the incomplete film almost exclusively contain oxygen from water, while the more ideal film exhibits OH groups with oxygen atoms stemming from both water and the silica film. These observations not only indicate that the degree of hydroxylation is significantly enhanced for the incomplete film but also that the reaction mechanism for hydroxylation at defect sites of this film is different. To gain insight into the reaction mechanism of electron-assisted hydroxylation, in situ EPR spectroscopy of electron-bombarded adsorbed ice layers was combined with infrared (IR) spectroscopy and mass spectrometry. We show that the electron bombardment removes a significant part of the water layer and produces different reactive paramagnetic species, namely, O2D, D, and solvated electrons, which may be trapped at low temperatures. The interaction of the silica film with such species may lead to splitting Si–O bonds even for covalently saturated silica structures as found in the ideal bilayer film and thus provide insight into possible reaction mechanisms.