Here, amorphous silica nanoparticles (NPs), one of the most abundant nanomaterials, are used as an example to illustrate the utmost importance of surface coverage by functional groups which critically determines biocompatibility. Silica NPs are functionalized with increasing amounts of amino groups, and the number of surface exposed groups is quantified and characterized by detailed NMR and fluorescamine binding studies. Subsequent biocompatibility studies in the absence of serum demonstrate that, irrespective of surface modification, both plain and amine‐modified silica NPs trigger cell death in RAW 264.7 macrophages. The in vitro results can be confirmed in vivo and are predictive for the inflammatory potential in murine lungs. In the presence of serum proteins, on the other hand, a replacement of only 10% of surface‐active silanol groups by amines is sufficient to suppress cytotoxicity, emphasizing the relevance of exposure conditions. Mechanistic investigations identify a key role of lysosomal injury for cytotoxicity only in the presence, but not in the absence, of serum proteins. In conclusion, this work shows the critical need to rigorously characterize the surface coverage of NPs by their constituent functional groups, as well as the impact of serum, to reliably establish quantitative nanostructure activity relationships and develop safe nanomaterials.

Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−d (BSCF) compacts were prepared and annealed under application-relevant temperatures between 700 and 1000 °C for 100 h. The microstructure and chemical composition was investigated by electron microscopic techniques and energy dispersive X-ray spectroscopy (EDXS) to obtain a detailed insight into the formation of secondary phases which are involved in the degradation of the ionic conductivity of BSCF. Secondary phases are precipitated from the cubic BSCF phase at temperatures ≤900 °C. In addition to the well-known hexagonal phase, another secondary phase was identified which has the same crystal structure as Ba n+1 Co n O 3n+3 (Co 8 O 8 ) with n ≥ 2 which is denoted as a BCO-type phase. Regions with plate-like morphology are formed which contain thin lamellae of the cubic, hexagonal, and BCO-type phase. The negative impact of the secondary phases on the material performance is discussed.

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A fast method for determination of the Co-valence state by electron energy loss spectroscopy in a transmission electron microscope is presented. We suggest the distance between the Co-L3 and Co-L2 white-lines as a reliable property for the determination of Co-valence states between 2+ and 3+. The determination of the Co-L2,3 white-line distance can be automated and is therefore well suited for the evaluation of large data sets that are collected for line scans and mappings. Data with a low signal-to-noise due to short acquisition times can be processed by applying principal component analysis. The new technique was applied to study the Co-valence state of Ba0.5Sr0.5Co0.8Fe0.2O3-d (BSCF), which is hampered by the superposition of the Ba-M4,5 white-lines on the Co-L2,3 white-lines. The Co-valence state of the cubic BSCF phase was determined to be 2.2+ (±0.2) after annealing for 100 h at 650°C, compared to an increased valence state of 2.8+ (±0.2) for the hexagonal phase. These results support models that correlate the instability of the cubic BSCF phase with an increased Co-valence state at temperatures below 840°C.

Transmission electron microscopy (TEM) with low-energy electrons has been recognized as an important addition to the family of electron microscopies as it may avoid knock-on damage and increase the contrast of weakly scattering objects. Scanning electron microscopes (SEMs) are well suited for low-energy electron microscopy with maximum electron energies of 30 keV, but they are mainly used for topography imaging of bulk samples. Implementation of a scanning transmission electron microscopy (STEM) detector and a charge-coupled-device camera for the acquisition of on-axis transmission electron diffraction (TED) patterns, in combination with recent resolution improvements, make SEMs highly interesting for structure analysis of some electron-transparent specimens which are traditionally investigated by TEM. A new aspect is correlative SEM, STEM, and TED imaging from the same specimen region in a SEM which leads to a wealth of information. Simultaneous image acquisition gives information on surface topography, inner structure including crystal defects and qualitative material contrast. Lattice-fringe resolution is obtained in bright-field STEM imaging. The benefits of correlative SEM/STEM/TED imaging in a SEM are exemplified by structure analyses from representative sample classes such as nanoparticulates and bulk materials.

Transport measurements on the two-dimensional electron system in Al 2 O 3 /SrTiO 3 heterostructures indicate significant non-crystalline anisotropic behavior below T ≈ 30 K.Lattice dislocations in SrTiO 3 and interfacial steps are suggested to be the main sources for electronic anisotropy. Anisotropic defect scattering likewise alters magnetoresistance at low temperature remarkably and influences spin-orbit coupling significantly by the Elliot-Yafet mechanism of spin relaxation resulting in anisotropic weak localization. Applying a magnetic field parallel to the interface results in an additional field-induced anisotropy of the conductance, which can be attributed to Rashba spin-orbit interaction. Compared to LaAlO 3 /SrTiO 3 , Rashba coupling seems to be reduced indicating a weaker polarity in Al 2 O 3 /SrTiO 3 heterostructures.

The outstanding oxygen permeability of the perovskite Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ (BSCF) and its applicability as a cathode in solid oxide fuel cells are remarkable, yet have been hindered by the formation of secondary phases at T < 840 °C and the subsequent degradation. The other main drawback to BSCF is related to the formation of carbonates in the presence of CO 2 . These degrade its excellent oxygen surface-exchange kinetics. In this work, 10% Y-doped Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ (BSCF10Y) is electrochemically, microstructurally, and chemically characterized in O 2 -and CO 2 -containing atmospheres as porous cathodes in symmetrical cells with Gd-doped ceria as electrolyte. Experiments in oxygen/nitrogen gas mixtures (pO 2 = 0.02−0.40 atm) at T = 600−900 °C showed high performance with a cathode specific resistance of 49.9 mΩ cm 2 at 600 °C in air (pO 2 = 0.21 atm), which is very comparable to 47.8 mΩ cm 2 for undoped BSCF, but which deteriorates constantly under the same conditions. Moreover, adding significant amounts of CO 2 (from 1% to 3% vol) to air at 700 °C shows that BSCF10Y has a remarkably enhanced tolerance toward the adsorption of CO 2 molecules (compared to the undoped BSCF cathodes). The electrode microstructure was analyzed by focused ion beam (FIB) combined with scanning electron microscopy (SEM). The chemical composition was analyzed by scanning transmission electron spectroscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDXS). The presence of secondary phases in the BSCF10Y cathodes was strongly reduced or even suppressed compared to undoped BSCF, which explains the superior oxygen reduction reaction kinetics over time. Also, the segregated volume fraction of carbonates is greatly reduced after 50 h in 1% CO 2 . The improved stability of the cubic phase in BSCF10Y compared to BSCF is linked to the monovalent agent and higher radius of the Y-dopant, while the improved stability in CO 2 -containing atmospheres is attributed to the higher acidity of Y 3+ compared to the A-site cations and the high concentration of the Y-dopant, which is located on both the A-and B-sites of the perovskite.

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