Artificial chemical and magnetic structure at the domain walls of an epitaxial oxide.

Progress in nanotechnology requires new approaches to materials synthesis that make it possible to control material functionality down to the smallest scales. An objective of materials research is to achieve enhanced control over the physical properties of materials such as ferromagnets, ferroelectrics and superconductors. In this context, complex oxides and inorganic perovskites are attractive because slight adjustments of their atomic structures can produce large physical responses and result in multiple functionalities. In addition, these materials often contain ferroelastic domains. The intrinsic symmetry breaking that takes place at the domain walls can induce properties absent from the domains themselves, such as magnetic or ferroelectric order and other functionalities, as well as coupling between them. Moreover, large domain wall densities create intense strain gradients, which can also affect the material's properties. Here we show that, owing to large local stresses, domain walls can promote the formation of unusual phases. In this sense, the domain walls can function as nanoscale chemical reactors. We synthesize a two-dimensional ferromagnetic phase at the domain walls of the orthorhombic perovskite terbium manganite (TbMnO3), which was grown in thin layers under epitaxial strain on strontium titanate (SrTiO3) substrates. This phase is yet to be created by standard chemical routes. The density of the two-dimensional sheets can be tuned by changing the film thickness or the substrate lattice parameter (that is, the epitaxial strain), and the distance between sheets can be made as small as 5 nanometres in ultrathin films, such that the new phase at domain walls represents up to 25 per cent of the film volume. The general concept of using domain walls of epitaxial oxides to promote the formation of unusual phases may be applicable to other materials systems, thus giving access to new classes of nanoscale materials for applications in nanoelectronics and spintronics.

Electron microscopic investigation and elemental analysis of titanium dioxide in sun lotion.

OBJECTIVE: The objective of this research was to determine the size, shape and aggregation of titanium dioxide (TiO2 ) particles which are used in sun lotion as UV-blocker. METHODS: Overall, six sunscreens from various suppliers and two reference substances were analysed by electron microscopy (EM) techniques in combination with energy dispersive X-ray spectroscopy (EDS). Because of a high fat content in sun lotion, it was impossible to visualize the TiO2 particles without previous EM sample preparation. Different defatting methods for TiO2 from sun screens were tested. A novel sample preparation method was developed which allowed the characterization of TiO2 particles with the help of EM and EDS. RESULTS: Aggregates of titanium dioxide with the size of primary particles varying between 15 and 40 nm were observed only in five products. In the sun lotion with the highest SPF, only few small aggregates were found. In the sun screen with the lowest SPF, the largest aggregates of TiO2 particles were detected with sizes up to 1.6 µm. In one of the sun lotions, neither TiO2 nor ZnO was found in spite of the labelling. Instead, approx. 500 nm large diamond-shaped particles were observed. These particles are composed of an organic material as only carbon was detected by EDS. CONCLUSION: A novel defatting method for sample preparation of titanium dioxide nanoparticles used in sun cosmetics was developed. This method was applied to six different sun lotions with SPF between 30 and 50+. TiO2 particles were found in only five sunscreens. The sizes of the primary particles were below 100 nm and, according to the EU Cosmetic Regulation, have to be listed on the package with the term 'nano'.

[Robustness of Hospital Benchmarking with the Hospital Standardized Mortality Ratio (HSMR): An Analysis of Secondary Data from 37 German Hospitals]. / Robustheit eines Krankenhausvergleichs mit der Hospital Standardized Mortality Ratio (HSMR): eine Sekundärdatenanalyse von 37 deutschen Krankenhäusern.

Introduction: Internationally, the hospital standardized mortality ratio is increasingly used as a risk-adjusted simple measure for quality control. Goodness of fit of different risk models in Germany and robustness of hospital comparisons were evaluated with a secondary data analysis. Methods: Anonymized routine data from the year 2012 of 37 hospitals of the association Quality Indicators for Ecclesiastical Hospitals were used. 2 independent risk models and the observed mortality were compared, the risk models considered both the original and the adapted forms. Results: The risk models showed an area under curve between 0.906 [95% CI 0.904-0.908] and 0.920 [0.918-0.922]. There was a significant correlation between the risk models and the observed mortality with a correlation coefficient between 0.388 (p<0.05) and 0.936 (p<0.01). 26 hospitals had an identical assessment in all risk models comparing their HSMR with the group. 2 hospitals achieved a positive and a negative assessment taking into account the observed mortality. Conclusion: The quality of the risk models is high and the hospital comparison with the HSMR remained stable. However, it is unclear whether the differences are caused by quality-related issues or by different structures and case-mix. Therefore, the HSMR is primarily intended for quality management purposes within German hospitals.

Influence of metallic and dielectric nanowire arrays on the photoluminescence properties of P3HT thin films.

The optical properties of organic semiconductor thin films deposited on nanostructured surfaces are investigated using time-resolved two-photon photoluminescence (PL) microscopy. The surfaces consist of parallel aligned metallic or dielectric nanowires forming well-defined arrays on glass substrates. Keeping the nanowire dimensions constant and varying only their spacing from 40 to 400 nm, we study the range of different types of nanowire-semiconductor interactions. For silver nanowires and spacings below 100 nm, the PL intensity and lifetime of P3HT and MDMO-PPV decrease rapidly due to the short-ranged metal-induced quenching that dominates the PL response with respect to a possible plasmonic enhancement of optical transition rates. In the case of P3HT however, we observe an additional longer-ranged reduction of non-radiative losses for both metallic and dielectric nanowires that is not observed for MDMO-PPV. Excitation polarization dependent measurements indicate that this reduction is due to self-assembly of the P3HT polymer chains along the nanowires. In conclusion, nanostructured surfaces, when fabricated across large areas, could be used to control film morphologies and to improve energy transport and collection efficiencies in P3HT-based solar cells.

Nonreactive spreading at high temperature: molten metals and oxides on molybdenum.

The spontaneous spreading of small liquid metal (Cu, Ag, Au) and oxide drops on Mo substrates has been studied using a drop transfer setup combined with high-speed video. Under the experimental conditions used in this work, spreading occurs in the absence of interfacial reactions or ridging. The analysis of the spreading data indicates that dissipation at the triple junction (that can be described in terms of a triple-line friction) is playing a dominant role in the movement of the liquid front. This is due, in part, to the much stronger atomic interactions in high-temperature systems when compared to organic liquids. As a result of this analysis, a comprehensive view of spreading emerges in which the strength of the atomic interactions (solid-liquid, liquid-liquid) determines the relative roles of viscous impedance and dissipation at the triple junction in spreading kinetics.

Coccospheres confer mechanical protection: New evidence for an old hypothesis.

UNLABELLED: Emiliania huxleyi has evolved an extremely intricate coccosphere architecture. The coccosphere is comprised of interlocking coccoliths embedded in a polysaccharide matrix. In this work, we performed in-situ scanning electron microscopy based compression tests and conclude that coccospheres have a mechanical protection function. The coccosphere exhibits exceptional damage tolerance in terms of inelastic deformation, recovery and stable crack growth before catastrophic fracture, a feature, which is not found in monolithic ceramic structures. Some of the mechanical features of the coccospheres are due to their architecture, especially polysaccharide matrix that acts as a kind of bio-adhesive. Our data provide strong evidence for the mechanical protection-hypothesis of coccolithophore calcification, without excluding other functions of calcification such as various biochemical roles discussed in the literature. STATEMENT OF SIGNIFICANCE: Although bio-mechanics of shell structures like nacre have been studied over the past decade, coccospheres present an architecture that is quite distinct and complex. It is a porous cell structure evolved to protect the living algae cell inside it in the oceans, subjected to significant hydrostatic pressure. Despite being made of extremely brittle constituents like calcium carbonate, our study finds that coccospheres possess significant damage tolerance especially due to their interlocking coccolith architecture. This will have consequences in bio-mimetic design, especially relating to high pressure applications.

Coronary artery plaque disruption as cause of acute myocardial infarction during cesarean section with spinal anesthesia.

A 31-year-old parturient delivered twins at 35 weeks' gestation by cesarean section with spinal anesthesia. Following anesthesia induction, hypotension and bradycardia occurred, and were immediately treated with theodrenaline plus cafedrin (Akrinor) and atropine. Blood pressure and heart rate increased to 180/100 mmHg and 140 beats per minute, respectively. Several minutes later, the patient developed a myocardial infarction (MI) that she survived after intensive care treatment without sequelae. Although the coronary angiography showed normal coronary vessels, an intravascular ultrasound study demonstrated an atheroma in the left main coronary artery with ruptured fibrous cap. Laboratory screening for risk factors of coronary artery disease (CAD) showed hypercholesterinemia, increased factor VII activity, and hyperfibrogenemia. Angiographically normal coronary vessels are frequently found in pregnant patients who suffered MI. In these patients, coronary spasms have been discussed as the major mechanism of disease. Our case demonstrates that a significant CAD may be present despite angiographically normal findings. Plaque rupture was triggered by hypertension and led to MI as the first symptom of disease. On the basis of these findings, we believe that MI during pregnancy is more often caused by plaque rupture than may be expected, according to the current literature.

A 3D insight on the catalytic nanostructuration of few-layer graphene.

The catalytic cutting of few-layer graphene is nowadays a hot topic in materials research due to its potential applications in the catalysis field and the graphene nanoribbons fabrication. We show here a 3D analysis of the nanostructuration of few-layer graphene by iron-based nanoparticles under hydrogen flow. The nanoparticles located at the edges or attached to the steps on the FLG sheets create trenches and tunnels with orientations, lengths and morphologies defined by the crystallography and the topography of the carbon substrate. The cross-sectional analysis of the 3D volumes highlights the role of the active nanoparticle identity on the trench size and shape, with emphasis on the topographical stability of the basal planes within the resulting trenches and channels, no matter the obstacle encountered. The actual study gives a deep insight on the impact of nanoparticles morphology and support topography on the 3D character of nanostructures built up by catalytic cutting.

Hot electron attenuation of direct and scattered carriers across an epitaxial Schottky interface.

Hot electron transport of direct and scattered carriers across an epitaxial NiSi2/n-Si(111) interface, for different NiSi2 thickness, is studied using ballistic electron emission microscopy (BEEM). We find the BEEM transmission for the scattered hot electrons in NiSi2 to be significantly lower than that for the direct hot electrons, for all thicknesses. Interestingly, the attenuation length of the scattered hot electrons is found to be twice as large as that of the direct hot electrons. The lower BEEM transmission for the scattered hot electrons is due to inelastic scattering of the injected hot holes while the larger attenuation length of the scattered hot electrons is a consequence of the differences in the energy distribution of the injected and scattered hot electrons and the increasing attenuation length, at lower energies, of the direct hot electrons in NiSi2.

Ordered liquid aluminum at the interface with sapphire.

Understanding the nature of solid-liquid interfaces is important for many processes of technological interest, such as solidification, liquid-phase epitaxial growth, wetting, liquid-phase joining, crystal growth, and lubrication. Recent studies have reported on indirect evidence of density fluctuations at solid-liquid interfaces on the basis of x-ray scattering methods that have been complemented by atomistic simulations. We provide evidence for ordering of liquid atoms adjacent to an interface with a crystal, based on real-time high-temperature observations of alumina-aluminum solid-liquid interfaces at the atomic-length scale. In addition, crystal growth of alumina into liquid aluminum, facilitated by interfacial transport of oxygen from the microscope column, was observed in situ with the use of high-resolution transmission electron microscopy.

Electron energy-loss near-edge structure studies at the atomic level: reliability of the spatial difference technique.

The spatial difference technique was applied to determine the interface-specific components of electron energy-loss near-edge structures and the results are in good agreement to those obtained by atomic column resolved measurements averaged over one atomic layer. In previous studies an experimental set-up had been chosen where the scanning areas, which are used to measure electron energy-loss spectra, were symmetrical in respect to the location of the investigated interfaces. In the present study, an asymmetric setting of the scanning areas was applied, which allows the interfacial signals to be determined directly. Comparing the results of the different measurements shows that the spatial difference technique is valid and can be used to obtain information about the electronic structure of interfaces where single atomic column resolved measurements are not yet possible.

Successful application of spatial difference technique to electron energy-loss spectroscopy studies of Mo/SrTiO3 interfaces.

The electron energy-loss near-edge structure (ELNES) of Mo/SrTiO3 interfaces has been studied using high spatial resolution electron energy-loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope. Thin films of Mo with a thickness of 50 nm were grown on (001)-orientated SrTiO3 surfaces by molecular beam epitaxy at 600 degrees C. High-resolution transmission electron microscopy revealed that the interfaces were atomically abrupt with the (110)Mo plane parallel to the substrate surface. Ti-L2,3 ( approximately 460 eV), O-K ( approximately 530 eV), Sr-L2,3 ( approximately 1950 eV) and Mo-L2,3 ( approximately 2500 eV) absorption edges were acquired by using the Gatan Enfina parallel EELS system with a CCD detector. The interface-specific components of the ELNES were extracted by employing the spatial difference method. The interfacial Ti-L2,3 edge shifted to lower energy values and the splitting due to crystal field became less pronounced compared to bulk SrTiO3, which indicated that the Ti atoms at the interface were in a reduced oxidation state and that the symmetry of the TiO6 octahedra was disturbed. No interfacial Sr-L2,3 edge was observed, which may demonstrate that Sr atoms do not participate in the interfacial bonding. An evident interface-specific O-K edge was found, which differs from that of the bulk in both position (0.8 +/- 0.2 eV positive shift) and shape. In addition, a positive shift (0.9 +/- 0.3 eV) occurred for the interfacial Mo-L2,3, revealing an oxidized state of Mo at the interface. Our results indicated that at the interface SrTiO3 was terminated with TiO2. The validity of the spatial difference technique is discussed and examined by introducing subchannel drift intentionally.

Chemical reactions and morphological stability at the Cu/Al2O3 interface.

The microstructures of diffusion-bonded Cu/(0001)Al2O3 bicrystals annealed at 1000 degrees C at oxygen partial pressures of 0.02 or 32 Pa have been studied with various microscopy techniques ranging from optical microscopy to high-resolution transmission electron microscopy. The studies revealed that for both oxygen partial pressures a 20-35 nm thick interfacial CuAlO2 layer formed, which crystallises in the rhombohedral structure. However, the CuAlO2 layer is not continuous, but interrupted by many pores. In the samples annealed in the higher oxygen partial pressure an additional reaction phase with a needle-like structure was observed. The needles are several millimetres long, approximately 10 microm wide and approximately 1 microm thick. They consist of CuAlO2 with alternating rhombohedral and hexagonal structures. Solid-state contact angle measurements were performed to derive values for the work of adhesion. The results show that the adhesion is twice as good for the annealed specimen compared to the as-bonded sample.

[Myocardial infarction during pregnancy]. / Myokardinfarkte in der Schwangerschaft.

Up to now 136 cases of myocardial infarction during pregnancy have been reported, and angiography revealed normal findings in 47%. In these cases coronary spasms have been discussed as the major mechanism of the disease. In isolated cases coronary artery dissection may also present with a normal coronary angiography. The case of a 31-year-old pregnant women who developed myocardial infarction during a caesarean section under spinal anaesthesia gives rise to the assumption that an early stage of coronary artery disease may be the third cause that has to be considered. Probably as a consequence of phases of tachycardia and hypertension during the course of anaesthesia, the patient developed a myocardial infarction that she survived without sequelae. While coronary angiography showed normal coronary vessels, an intravascular ultrasound study (IVUS) demonstrated an atheroma in the left main coronary artery with a ruptured fibrous cap. Laboratory screening for risk factors of coronary artery disease (CAD) showed hypercholesterinemia, increased factor VII activity and hyperfibrinogenemia. Platelet aggregation was not inhibited by acetylsalicylic acid. It was pointed out recently that even in asymptomatic patients, plaques may be present in coronary vessels indicating an early stage of CAD that cannot be diagnosed by angiography. Plaque rupture is often triggered by hypertension and may lead to myocardial infarction, instable angina pectoris, or sudden ischemic death. As IVUS is a new diagnostic tool that allows diagnoses of even early stages of CAD we believe that myocardial infarction during pregnancy is more often caused by plaque rupture than may be expected according to the current literature.

Advances in EELS spectroscopy by using new detector and new specimen preparation technologies.

First results obtained with a Gatan UHV Enfina system, which was attached to a VG HB 501 UX dedicated STEM, are reported. The Enfina system is based on a CCD detector and offers, compared to the previously used photodiode array, a narrower point-spread function, higher sensitivity, and faster read-out capabilities. These improvements are demonstrated with electron energy-loss measurements on various oxides, such as Al2O3, TiO2 and SrTiO3. It is shown that a better energy resolution is achieved and that acquisition of high-energy absorption edges with a reasonable signal-to-noise ratio becomes possible. Furthermore, we report on the influence of the TEM specimen quality on the energy-loss spectra. Thin amorphous layers at the specimen surfaces, which are induced by ion-milling processes, can modify specific electron energy-loss near-edge structure features. We found that for the investigated ceramics the use of low-energy ion-milling systems is highly recommended, since the loss of energy-loss near-edge structure details by the presence of the amorphous layers is considerably reduced. This is especially true for very thin specimens.

Structures of BaF2-CaF2 heterolayers and their influences on ionic conductivity.

Recently, artificial ion conductors have been prepared by growing epitaxial heterolayers consisting of BaF2-CaF2 using molecular beam epitaxy. The ionic conductivity of these heterolayers shows a strong dependence on the layer thickness [N. Sata, S. Eberman, K. Eberl, and J. Maier, Nature 408, 996 (2000)]. In this paper three such heterolayers with different spacings (sample A: 80 nm, sample B: 10 nm, sample C: 1 nm) are investigated by conventional transmission electron microscopy and high-resolution transmission electron microscopy. The spacings are chosen such that they fall into the three conductivity regimes observed in N. Sata et al. (l > 50 nm; 8 < l < 50 nm; l < 8 nm). In accordance with conductivity studies, the samples with spacings of 10 nm or greater (A,B) are epitaxial and continuous, whereas in the case of extremely small spacing (C) the continuity of the layers is destroyed by formation of a column-like structure. Analytical electron microscopy reveals that, instead of forming multilayers, Ca and Ba separate in different columns in sample C. The structure properties of sample A (large l) are quite ideal: Planar interfaces with regular arrays of misfit dislocations with their Burgers vectors on the interface are observed. In the case of sample B (medium l) the lattice misfit is accommodated, in addition, by wavy interfaces associated with dislocations characterized by a Burgers vector that makes a large angle to the interfaces. The (111) lattice spacing very close to the interfaces is markedly changed due to this novel relaxation mechanism in the multilayer. The influences of the crystallographic defects on the ionic conductivity are also discussed.