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PURPOSE Respiration induces temporal variations of the main magnetic field B0 along the spinal cord. These variations are typically not compensated for in velocity quantifications using phase-contrast MRI. The goal of this study was to analyze errors caused by respiration-induced B0 variations in real-time phase-contrast echo planar imaging (PCEPI) of cervical cerebrospinal fluid (CSF) velocity measurements and to evaluate this effect for various sequence parameters using numerical simulations. METHODS Real-time B0 measurements with double gradient echo sequence and PCEPI measurements were acquired in the cervical CSF of 10 healthy subjects. Dynamic phase offsets attributed to respiration-induced B0 variations were analyzed by quantifying amplitudes and comparing the temporal behavior with respiratory signals. In experiments and simulations, the influence of the echo time (TE) and the delay between PCEPI images (Δt) with respect to respiration on the dynamic phase offsets were investigated. RESULTS A good agreement was found between phase offsets extracted from both acquisition types. Furthermore, respiratory signals qualitatively matched the temporal behavior of the measured phase offsets showing a dependency on subject-dependent local B0 distribution and respiration physiology. Simulations revealed residual background phases in PCEPI velocity quantification varying with TE and Δt. CONCLUSION Respiration-induced B0 variations result in dynamic background phases in real-time PCEPI velocity quantifications of the CSF in the cervical spine. The current work underlines that these background phases need to be corrected to avoid confounding effects.

A multistep synthesis procedure for the homogeneous coating of a complex porous conductive oxide with small Ir nanoparticles is introduced to obtain a highly active electrocatalyst for water oxidation. At first, inverse opal macroporous Sb doped SnO2 (ATO) microparticles with defined pore size, composition, and open‐porous morphology are synthesized that reach a conductivity of ≈3.6 S cm$^{−1}$ and are further used as catalyst support. ATO‐supported iridium catalysts with a controlled amount of active material are prepared by solvothermal reduction of an IrO$_x$ colloid in the presence of the porous ATO particles, whereby homogeneous coating of the complete outer and inner surface of the particles with nanodispersed metallic Ir is achieved. Thermal oxidation leads to the formation of ATO‐supported IrO$_2$ nanoparticles with a void volume fraction of ≈89% calculated for catalyst thin films based on scanning transmission electron microscope tomography data and microparticle size distribution. A remarkably low Ir bulk density of ≈0.08 g cm$^{−3}$ for this supported oxide catalyst architecture with 25 wt% Ir is determined. This highly efficient oxygen evolution reaction catalyst reaches a current density of 63 A g$_{Ir}$$^{−1}$ at an overpotential of 300 mV versus reversible hydrogen electrode, significantly exceeding a commercial TiO$_2$‐supported IrO$_2$ reference catalyst under the same measurement conditions.

Germanium holds great potential as an anode material for lithium ion batteries due to its high specific capacity and its favorable properties such as good lithium ion diffusivity and electronic conductivity. However, the high cost of germanium and large volume changes during cycling, which lead to a rapid capacity fading for bulk Ge materials, demand for nanostructured thin film devices. Herein we report the preparation and electrochemical properties of thin films of porous, inverse opal structured Ge anodes obtained via a simple, up-scalable wet-chemical route utilizing [Ge9]4− Zintl ions. In the absence of conductive additives, they show high initial capacities of >1300 mA h g−1 and promisingly high coulombic efficiencies of up to 99.3% and deliver over 73% of their initial capacity after 100 cycles when cycled vs. metallic lithium. In contrast to many other porous structured Ge electrodes, they show very little to almost no capacity fading after an initial drop, which makes them promising candidates for long life applications.

Spray coating, a cost-effective and scalable technique, has been employed for fabricating titania films for solid-state dye-sensitized solar cells (ssDSSCs). The spray deposition of films is inherently based on kinetic processes with great complexity, which poses great challenges in its understanding. In the present work, the kinetics of the structure evolution of deposited films are investigated by in situ grazing-incidence small-angle x-ray scattering during spray deposition. The spray-solution is prepared via a polystyrene-block-polyethylene oxide (PS-b-PEO) template assisted sol-gel synthesis. It is turned into nanostructured titania/PS-b-PEO composite films via spray deposition. The information about nanostructure length scales of the composite film is obtained in real-time and in situ, revealing the morphological evolution during the spray deposition. The resulting mesoporous titania films serve as photoanodes of ssDSSCs, which couple with the solution-cast hole transport layer to form the active layers. The well working ssDSSCs demonstrate the successful use of spray deposition as a large-scale manufacturing process for photoanodes.

The degradation of poly(3-hexylthiophene) (P3HT)–titania-based solid-state dye-sensitized solar cells (ssDSSCs) is studied to better understand device aging mechanisms. The correlation of temporal evolution between P3HT crystallite structures and device performance is discussed for the first time using in situ measurements. For comparison, two types of mesoporous titania photoanodes with different pore sizes are prepared. Grazing incidence wide-angle X-ray scattering is used in situ under continuous solar illumination to obtain information about the impact of pore size on P3HT crystalline order and on temporal evolution of the P3HT crystallites. The development of the photovoltaic characteristics is explored in parallel. The lattice constants, crystal sizes, and volume fraction of crystalline P3HT in the large-pore active layer remain stable over 30 min, while the volume fraction of crystalline P3HT decreases in the small-pore active layer. Thus, the pore size of titania photoanodes is important for the s...

MRI (Magnetic Resonance Imaging) measurements and CFD (Computational Fluid Dynamics) simulations for blood flow in intracranial aneurysms are compared for a benchmark problem. In particular, it is shown that noise and other artifacts in the MRI measurements have an influence on certain properties of the flow field, e.g., on the boundary flow and mass conservation.

'Black' TiO2 -in the widest sense, TiO2 reduced by various treatments-has attracted tremendous scientific interest in recent years because of some outstanding properties; most remarkably in photocatalysis. While the material effects visible light absorption (the blacker, the better), black titania produced by high pressure hydrogenation was recently reported to show another highly interesting feature; noble-metal-free photocatalytic H2 generation. In a systematic investigation of high-temperature hydrogen treatments of anatase nanoparticles, TEM, XRD, EPR, XPS, and photoelectrochemistry are used to characterize different degrees of surface hydrogenation, surface termination, electrical conductivity, and structural defects in the differently treated materials. The materials' intrinsic activity for photocatalytic hydrogen evolution is coupled neither with their visible light absorption behavior nor the formation of amorphous material, but rather must be ascribed to optimized and specific defect formation (gray is better than black). This finding is further confirmed by using a mesoporous anatase matrix as a hydrogenation precursor, which, after conversion to the gray state, even further enhances the overall photocatalytic hydrogen evolution activity.

Nanostructured transparent conducting oxide (TCO) layers gain increasing importance as high surface area electrodes enabling incorporation of functional redox species with high loading. The fabrication of porous TCO films, namely, antimony-doped tin oxide (ATO), is reported using the self-assembly of preformed ATO nanocrystals with poly(ethylene oxide-b-hexyl acrylate) (PEO-b-PHA) block copolymer. The high molar mass of the polymer and tunable solution processing conditions enable the fabrication of TCO electrodes with pore sizes ranging from mesopores to macropores. Particularly notable is access to uniform macroporous films with a nominal pore size of around 80 nm, which is difficult to obtain by other techniques. The combination of tunable porosity with a large conducting interface makes the obtained layers versatile current collectors with adjustable performance. While all the obtained electrodes incorporate a large amount of small redox molecules such as molybdenum polyoxometalate, only the electrodes with sufficiently large macropores are able to accommodate high amounts of bulky photoactive photosystem I (PSI) protein complexes. The 11-fold enhancement of the current response of PSI modified macroporous ATO electrodes compared to PSI on planar indium tin oxide (ITO), makes this type of electrodes promising candidates for the development of biohybrid devices.

The n-type semiconducting spinel zinc ferrite (ZnFe2O4) is used as a photoabsorber material for light-driven water-splitting. It is prepared for the first time by atomic layer deposition. Using the resulting well-defined thin films as a model system, the performance of ZnFe2O4 in photoelectrochemical water oxidation is characterized. Compared to benchmark α-Fe2O3 (hematite) films, ZnFe2O4 thin films achieve a lower photocurrent at the reversible potential. However, the oxidation onset potential of ZnFe2O4 is 200 mV more cathodic, allowing the water-splitting reaction to proceed at a lower external bias and resulting in a maximum applied-bias power efficiency (ABPE) similar to that of Fe2O3. The kinetics of the water oxidation reaction are examined by intensity-modulated photocurrent spectroscopy. The data indicate a considerably higher charge transfer efficiency of ZnFe2O4 at potentials between 0.8 and 1.3 V versus the reversible hydrogen electrode, attributable to significantly slower surface charge recombination. Finally, nanostructured ZnFe2O4 photoanodes employing a macroporous antimony-doped tin oxide current collector reach a five times higher photocurrent than the flat films. The maximum ABPE of these host–guest photoanodes is similarly increased.

Spray coating, a simple and low‐cost technique for large‐scale film deposition, is employed to fabricate mesoporous titania films, which are electron‐transporting layers in all‐solid‐state dye‐sensitized solar cells (DSSCs). To optimize solar cell performance, presynthesized crystalline titania nanoparticles are introduced into the mesoporous titania films. The composite film morphology is examined with scanning electron microscopy, grazing incidence small‐angle X‐ray scattering, and nitrogen adsorption–desorption isotherms. The crystal phase and crystallite sizes are verified by X‐ray diffraction measurements. The photovoltaic performance of all‐solid‐state DSSCs is investigated. The findings reveal that an optimal active layer of the all‐solid‐state DSSC is obtained by including 50 wt% titania nanoparticles, showing a foam‐like morphology with an average pore size of 20 nm, featuring an anatase phase, and presenting a surface area of 225.2 m2 g−1. The optimized morphology obtained by adding 50 wt% presynthesized crystalline titania nanoparticles yields, correspondingly, the best solar cell efficiency of 2.7 ± 0.1%., Financial support by TUM.solar in the context of the Bavarian Collaborative Research Project “Solar Technologies Go Hybrid” (SolTech), by the GreenTech Initiative (Interface Science for Photovoltaics – ISPV) of the EuroTech Universities and by the Nanosystems Initiative Munich (NIM) is gratefully acknowledged. V.K. thanks the Bavarian State Ministry of Sciences, Research and Arts for funding this research work via project “Energy Valley Bavaria.” L.S., W.W., and Y.Y. acknowledge the China Scholarship Council (CSC).

Assemblies of undoped and antimony-doped tin oxide nanoparticles synthesized via a nonaqueous sol–gel procedure, pressed into pellets, and annealed under various conditions were investigated using time-domain terahertz spectroscopy, scanning electron microscopy, atomic force microscopy, and dc conductivity measurements. Combination of these methods made it possible to resolve the conductivity limitations imposed by intrinsic properties of the material and by the morphology of the samples. Percolation of the nanoparticles was confirmed in all samples. The undoped samples exhibit a weak hopping conductivity, whereas bandlike conduction of charges partially confined in the nanoparticles dominates in the doped samples. The conductivity of nanoparticles and their connectivity can be greatly controlled during the sample preparation, namely by the calcination temperature and by the order of technological steps. A substantial increase of the conductivity inside nanoparticles and of the charge transport between th...

We describe the fabrication of crystalline electrically conducting antimony-doped tin oxide (ATO) nanoparticles highly dispersible in polar solvents such as water and ethanol without any stabilizing agents. Nonagglomerated monodisperse ATO nanoparticles with different doping levels are obtained by a facile solvothermal reaction in tert-butanol, leading to the formation of monodisperse nanocrystals with a size of about 3 nm directly after synthesis. Electrical conductivity of ATO nanoparticles strongly increases due to the substitutional doping with antimony, reaching 6.8 × 10-2 S cm-1 for the as-synthesized nanoparticles prepared with 3-5 mol % Sb. This increase stems from transition from hopping in the undoped samples to band-like conduction in the doped samples as revealed by terahertz (THz) spectroscopy measurements describing transport on nanometer distances. The dc conductivity of the doped nanoparticles increases by about 3 orders of magnitude up to 62 S cm-1 after annealing in air at 500 °C. The electrical conductivity, crystallinity, small size, and high dispersibility in polar solvents make the obtained ATO nanoparticles promising building blocks for the direct assembly of more complex conducting architectures using polymer templates that could be damaged in organic solvents. We illustrate the benefits of the water-dispersible ATO nanoparticles by their assembly to periodic macroporous electrodes using poly(methyl methacrylate) (PMMA) beads as the porosity templates. Aqueous dispersion of ATO nanoparticles can be directly combined with PMMA beads that are easily removed by calcination, enabling a facile deposition of 3D-macroporous ATO electrodes featuring optical transparency and a large periodically ordered conducting interface.

Tin oxide-based materials attract increasing attention as anodes in lithium-ion batteries due to their high theoretical capacity, low cost, and high abundance. Composites of such materials with a carbonaceous matrix such as graphene are particularly promising, as they can overcome the limitations of the individual materials. The fabrication of antimony-doped tin oxide (ATO)/graphene hybrid nanocomposites is described with high reversible capacity and superior rate performance using a microwave assisted in situ synthesis in tert-butyl alcohol. This reaction enables the growth of ultrasmall ATO nanoparticles with sizes below 3 nm on the surface of graphene, providing a composite anode material with a high electric conductivity and high structural stability. Antimony doping results in greatly increased lithium insertion rates of this conversion-type anode and an improved cycling stability, presumably due to the increased electrical conductivity. The uniform composites feature gravimetric capacity of 1226 mAh g(-1) at the charging rate 1C and still a high capacity of 577 mAh g(-1) at very high charging rates of up to 60C, as compared to 93 mAh g(-1) at 60C for the undoped composite synthesized in a similar way. At the same time, the antimony-doped anodes demonstrate excellent stability with a capacity retention of 77% after 1000 cycles.

Using terahertz spectroscopy we investigate the charge transport in Sb-doped SnO 2 nanoparticles pressed into pellets. Doped and undoped samples are shown to have different mechanisms of intrinsic conductivity. We systematically study the influence of annealing on intra- and inter-nanoparticle charge transport.

We report on the fabrication of a complex electrode architecture for efficient direct bioelectrocatalysis. In the developed procedure, the redox enzyme pyrroloquinoline quinone-dependent glucose dehydrogenase entrapped in a sulfonated polyaniline [poly(2-methoxyaniline-5-sulfonic acid)-co-aniline] was immobilized on macroporous indium tin oxide (macroITO) electrodes. The use of the 3D-conducting scaffold with a large surface area in combination with the conductive polymer enables immobilization of large amounts of enzyme and its efficient communication with the electrode, leading to enhanced direct bioelectrocatalysis. In the presence of glucose, the fabricated bioelectrodes show an exceptionally high direct bioelectrocatalytical response without any additional mediator. The catalytic current is increased more than 200-fold compared to planar ITO electrodes. Together with a high long-term stability (the current response is maintained for >90% of the initial value even after 2 weeks of storage), the transparent 3D macroITO structure with a conductive polymer represents a valuable basis for the construction of highly efficient bioelectronic units, which are useful as indicators for processes liberating glucose and allowing optical and electrochemical transduction.

Therapy with high intensity focused ultrasound (HIFU) has been shown to be both safe and clinically practical in a growing number of patient studies for a variety of different target organs. Especially in cancer therapy there are comparable ablation methods like radio frequency (RFA) or laser (LITT) ablation, which are clinically more accepted. In an ongoing study we compare HIFU with RF‐ and laser ablation under MRI guidance in a perfused organ model. All evaluated techniques were appropriate to induce defined and localized ablation necrosis in the renal cortex. Our HIFU system and the laser system were completely MRI compatible. The tested RF‐ system showed local needle artefacts and disturbed the MR images during operation. The ablation rate of HIFU using a spot scanning technique was clearly lower compared to the other ablation techniques. However, advanced HIFU scanning methods might overcome this limitation. In addition HIFU is the only complete non‐invasive ablation technique.

High intensity focused ultrasound (HIFU) under magnetic resonance imaging (MRI) guidance is an attractive instrument to ablate tissue non‐invasively. The aim of this work was to investigate the coagulation volume and the perfusion changes after HIFU‐ablation in an isolated kidney model using MRI. Ablation was performed at least at two regions of the renal cortex. Morphological T1‐/T2‐weighted, temperature sensitive images and contrast‐enhanced perfusion measurements were performed. The detection of single HIFU induced coagulation necroses and HIFU induced tissue cavities was feasible. Perfusion changes could only be detected in few experiments because of relatively inhomogeneous kidney perfusion patterns. MR‐imaging is a sensitive method to detect and to quantify the HIFU‐focus. Moreover, MRI is a valuable approach for the detection of HIFU induced coagulation necroses. The investigation of perfusion changes, particularly important in tumor treatment, was sometimes hampered due to limitations in the used organ model. However, in patients MR perfusion imaging as well as volumetric and morphological imaging can be used to control the outcome of HIFU‐therapy.