Doping-Induced Surface and Grain Boundary Effects in Ni-Rich Layered Cathode Materials.

In this work, the effects of dopant size and oxidation state on the structure and electrochemical performance of LiNi0.8Co0.1Mn0.1O2 (NCM811) are investigated. It is shown that doping with boron (B) which has a small ionic radius and an oxidation state of 3+, leads to the formation of a boron oxide-containing surface coating (probably Li3BO3), mainly on the outer surface of the secondary particles. Due to this effect, boron only slightly affects the size of the primary particle and the initial capacity, but significantly improves the capacity retention. On the other hand, the dopant ruthenium (Ru) with a larger ionic radius and a higher oxidation state of 5+ can be stabilized within the secondary particles and does not experience a segregation to the outer agglomerate surface. However, the Ru dopant preferentially occupies incoherent grain boundary sites, resulting in smaller primary particle size and initial capacity than for the B-doped and pristine NCM811. This work demonstrates that a small percentage of dopant (2 mol%) cannot significantly affect bulk properties, but it can strongly influence the surface and/or grain boundary properties of microstructure and thus the overall performance of cathode materials.

A Novel 3D High Resolution Imaging Method Using Correlative X-Ray and Electron Microscopy to Study Neodymium-Doped Yttrium Aluminum Garnet Laser-Induced Defects in Intraocular Lenses.

INTRODUCTION: Cataract extraction is the most frequently performed ophthalmological procedure worldwide. Posterior capsule opacification remains the most common consequence after cataract surgery and can lead to deterioration of the visual performance with cloudy, blurred vision and halo, glare effects. Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser capsulotomy is the gold standard treatment and a very effective, safe and fast procedure in removing the cloudy posterior capsule. Damaging the intraocular lens (IOL) during the treatment may occur due to wrong focus of the laser beam. These YAG-pits may lead to a permanent impairment of the visual quality. METHODS: In an experimental study, we intentionally induced YAG pits in hydrophilic and hydrophobic acrylic IOLs using a photodisruption laser with 2.6 mJ. This experimental study established a novel 3D imaging method using correlative X-ray and scanning electron microscopy (SEM) to characterize these damages. By integrating the information obtained from both X-ray microscopy and SEM, a comprehensive picture of the materials structure and performance could be established. RESULTS: It could be revealed that although the exact same energies were used to all samples, the observed defects in the tested lenses showed severe differences in shape and depth. While YAG pits in hydrophilic samples range from 100 to 180 µm depth with a round shape tip, very sharp tipped defects up to 250 µm in depth were found in hydrophobic samples. In all samples, particles/fragments of the IOL material were found on the surface that were blasted out as a result of the laser shelling. CONCLUSION: Defects in hydrophilic and hydrophobic acrylic materials differ. Material particles can detach from the IOL and were found on the surface of the samples. The results of the laboratory study illustrate the importance of a precise and careful approach to Nd:YAG capsulotomy in order to avoid permanent damage to the IOL. The use of an appropriate contact glass and posterior offset setting to increase safety should be carried out routinely.

Direct Visualization of Distorted Twin Boundaries in Ce-Doped GdFeO3.

Utilizing advanced transmission electron microscopy (TEM), the structure at the (110)-type twin boundary (TB) of Ce-doped GdFeO3 (C-GFO) has been investigated with picometer precision. Such a TB is promising to generate local ferroelectricity within a paraelectric system, while precise knowledge about its structure is still largely missing. In this work, a direct measurement of the cation off-centering with respect to the neighboring oxygen is enabled by integrated differential phase contrast (iDPC) imaging, and up to 30 pm Gd off-centering is highly localized at the TB. Further electron energy loss spectroscopy (EELS) analysis demonstrates a slight accumulation of oxygen vacancies at the TB, a self-balanced behavior of Ce at the Gd sites, and a mixed occupation of Fe2+ and Fe3+ at the Fe sites. Our results provide an informative picture with atomic details at the TB of C-GFO, which is indispensable to further push the potential of grain boundary engineering.

Photocatalytic solid-phase degradation of polyethylene with fluoride-doped titania under low consumption ultraviolet radiation.

Photodegradation of plastic in solid-phase requires the polymer to be composited with an efficient photocatalyst. We report herein the successful synthesis and characterization of fluoride-doped-TiO2 and its applicability, for the first time, on solid-phase photodegradation of polyethylene films. Nearly half weight loss of polyethylene, containing only 2% of the photocatalyst, is eliminated after three weeks of ultraviolet A radiation using a low consumption light emitting diode lamp, defeating previously reported data. The half-life time of the plastic was around 3 weeks, highlighting the viability of this process for real applications. Results were compared to raw PE and PE composite with well-known TiO2, resulting in, respectively, 0 and 26% of weight loss. The degradation process was monitored by optical microscopy, scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Fourier transform infrared and X-ray photoelectron spectroscopy, which revealed the formation of plastic cracks, loss of polyethylene crystallinity and thus stability, the oxidation of C-H bonds and the oxidized state of the surface compounds during photodegradation. The obtained results open a path for the future production of cleaner and self-photodegradable plastics, where the photocatalyst would be introduced in all the manufactured plastics, making possible the quicker photodegradation of the plastics that end up on the environment and the plastics reaching wastewater treatment plants.

Boron-Mediated Grain Boundary Engineering Enables Simultaneous Improvement of Thermoelectric and Mechanical Properties in N-Type Bi2 Te3.

Powder metallurgy introduces small structures of high-density grain boundaries into Bi2 Te3 -based alloys, which promises to enhance their mechanical and thermoelectric performance. However, due to the strong donor-like effect induced by the increased surface, Te vacancies form in the powder-metallurgy process. Hence, the as-sintered n-type Bi2 Te3 -based alloys show a lower figure of merit (ZT) value than their p-type counterparts and the commercial zone-melted (ZM) ingots. Here, boron is added to one-step-sintered n-type Bi2 Te3 -based alloys to inhibit grain growth and to suppress the donor-like effect, simultaneously improving the mechanical and thermoelectric (TE) performance. Due to the alleviated donor-like effect and the carrier mobility maintained in our n-type Bi2 Te2.7 Se0.3 alloys upon the addition of boron, the maximum and average ZT values within 298-473 K can be enhanced to 1.03 and 0.91, respectively, which are even slightly higher than that of n-type ZM ingots. Moreover, the addition of boron greatly improves the mechanical strength such as Vickers hardness and compressive strength due to the synergetic effects of Hall-Petch grain-boundary strengthening and boron dispersion strengthening. This facile and cost-effective grain boundary engineering by adding boron facilitates the practical application of Bi2 Te3 -based alloys and can also be popularized in other thermoelectric materials.

Migration Kinetics of Surface Ions in Oxygen-Deficient Perovskite During Topotactic Transitions.

Oxygen diffusivity and surface exchange kinetics underpin the ionic, electronic, and catalytic functionalities of complex multivalent oxides. Towards understanding and controlling the kinetics of oxygen transport in emerging technologies, it is highly desirable to reveal the underlying lattice dynamics and ionic activities related to oxygen variation. In this study, the evolution of oxygen content is identified in real-time during the progress of a topotactic phase transition in La0.7 Sr0.3 MnO3-δ epitaxial thin films, both at the surface and throughout the bulk. Using polarized neutron reflectometry, a quantitative depth profile of the oxygen content gradient is achieved, which, alongside atomic-resolution scanning transmission electron microscopy, uniquely reveals the formation of a novel structural phase near the surface. Surface-sensitive X-ray spectroscopies further confirm a significant change of the electronic structure accompanying the transition. The anisotropic features of this novel phase enable a distinct oxygen diffusion pathway in contrast to conventional observation of oxygen motion at moderate temperatures. The results provide insights furthering the design of solid oxygen ion conductors within the framework of topotactic phase transitions.

Atomic scale imaging of magnetic circular dichroism by achromatic electron microscopy.

In order to obtain a fundamental understanding of the interplay between charge, spin, orbital and lattice degrees of freedom in magnetic materials and to predict and control their physical properties1-3, experimental techniques are required that are capable of accessing local magnetic information with atomic-scale spatial resolution. Here, we show that a combination of electron energy-loss magnetic chiral dichroism 4 and chromatic-aberration-corrected transmission electron microscopy, which reduces the focal spread of inelastically scattered electrons by orders of magnitude when compared with the use of spherical aberration correction alone, can achieve atomic-scale imaging of magnetic circular dichroism and provide element-selective orbital and spin magnetic moments atomic plane by atomic plane. This unique capability, which we demonstrate for Sr2FeMoO6, opens the door to local atomic-level studies of spin configurations in a multitude of materials that exhibit different types of magnetic coupling, thereby contributing to a detailed understanding of the physical origins of magnetic properties of materials at the highest spatial resolution.

Publisher Correction: Atomic scale imaging of magnetic circular dichroism by achromatic electron microscopy.

In Fig. 1 of the version of this Letter originally published, the word 'Subtract' was missing from the green box to the left of panel f. This has now been corrected in all versions of the Letter.

Size-Tailored Biocompatible FePt Nanoparticles for Dual T1/T2 Magnetic Resonance Imaging Contrast Enhancement.

The development of new contrast agents (CAs) for magnetic resonance imaging (MRI) is of high interest, especially because of the increased concerns of patient safety and quick clearance of clinically used gadolinium and iron oxide-based CAs, respectively. Here, a two-step synthesis of superparamagnetic water-soluble iron platinum (FePt) nanoparticles (NPs) with core sizes between 2 and 8 nm for use as CAs in MRI is reported. First, wet-chemical organometallic NPs are synthesized by thermal decomposition in the presence of stabilizing oleic acid and oleylamine. Second, the hydrophobic NPs are coated with an amphiphilic polymer and transferred into aqueous media. Their magnetization values and relaxation rates exceed those published for CAs already used for clinical application. Their saturation magnetization increases with the core size to approximately 82 A·m2/kgFe. For 8 nm NPs, the T2 relaxivity of approximately 221 (mM·s)-1 is 5 times larger than that for the ferumoxides, and for 6 nm NPs, the T1 relaxivity of approximately 12 (mM·s)-1 is slightly higher than that of ultrasmall gadolinium oxide NPs. The 6 nm FePt NPs are identified as excellent CAs for both T1 and T2 imaging. Most importantly, because of their coating, significantly low cytotoxicity is achieved. FePt NPs prove to be a promising alternative to gadolinium and iron oxide NPs showing high-quality CA characteristics for both T1- and T2-weighted images.

Local crystallographic shear structures in a[201] extended mixed dislocations of SrTiO3 unraveled by atomic-scale imaging using transmission electron microscopy and spectroscopy.

Recently, extended mixed dislocations were observed at a [001]/(100) low-angle tilt grain boundary of a SrTiO3 bicrystal because of a slight twist between the two crystal parts. The b = a[201]/(100) mixed dislocations at the grain boundary dissociate into three dislocations with Burgers vector b of a/2[101], a[100], and a/2[101], respectively. A structure model has been proposed in particular for the dislocation cores of the two partials with b = a/2[101] based on the high-angle annular dark-field (HAADF) images acquired by scanning transmission electron microscopy (STEM). However, the details of the atomic structure and the chemical composition of the dislocation cores remain unexplored, especially for the b = a[100] dislocation that is evidently disassociated into two b = a/2[101] partial dislocations. In this work, we study the further atomic details of the extended mixed dislocations, in particular the local chemistry, in a SrTiO3 bicrystal using STEM, electron energy loss spectroscopy (EELS), and energy dispersive X-ray (EDX) spectroscopy techniques. By these atomic-scale imaging techniques, we reveal a unique feature for the atomic structure of the b = a[201]/(100) extended mixed dislocation, which we named as local crystallographic shear (LCS) structures. In addition, we identify a rock salt FCC-type TiOx (x = 0.66-1.24) phase at the locations of the extended mixed dislocations. In contrast to the insulating TiO2 phases, the TiOx phase is known to exhibit very low electrical resistivity of only several µΩ cm. In this regard, the extended mixed dislocations of SrTiO3 comprising the FCC TiOx phase may function as the conducting filament in resistive switching processes by completion and disruption of the TiOx phase along the dislocation cores through electrically stimulated redox reactions.

Oxygen diffusion in amorphous and partially crystalline gallium oxide.

Oxygen transport in amorphous (a-GaO1.5) and partially crystalline (a/c-GaO1.5) gallium oxide was studied by means of 18O/16O isotope exchange experiments and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Thin films of a-GaO1.5 were deposited by pulsed laser deposition (PLD) on alumina substrates at room temperature in an oxygen atmosphere. Oxygen tracer diffusion coefficients D* and oxygen surface exchange coefficients k* were determined as a function of temperature, 300 ≤ T/°C ≤ 370, and as a function of oxygen partial pressure, 2 ≤ p(O2)/mbar ≤ 500 at a temperature of T = 330 °C. The activation energy of oxygen tracer diffusion in amorphous gallium oxide was found to be EA = 0.8 eV. In addition, the time-temperature-transformation (TTT) diagram of crystallisation of amorphous gallium oxide was determined.

Controlled Crystal Growth of Indium Selenide, In2Se3, and the Crystal Structures of α-In2Se3.

In2Se3 has been known for over 100 years and recently attracted interest as a promising candidate for a variety of applications, such as solar cells, photodiodes, and phase-change memories. Despite the broad concern for possible uses, its polymorphism and structure are poorly characterized. By combining X-ray diffraction, transmission electron microscopy, and quantum-chemical calculations, we present here the crystal structures of two layered room-temperature polytypes: 3R and 2H In2Se3. Both polymorphs are stacking variants of the same Se-In-Se-In-Se layers comprising two coordination environments for the In atoms, one tetrahedral and one octahedral. By using chemical-bonding analysis, we look at the different In positions in α-In2Se3 and compare them to those in the metastable ß-phase.

3D Structures of Responsive Nanocompartmentalized Microgels.

Compartmentalization in soft matter is important for segregating and coordinating chemical reactions, sequestering (re)active components, and integrating multifunctionality. Advances depend crucially on quantitative 3D visualization in situ with high spatiotemporal resolution. Here, we show the direct visualization of different compartments within adaptive microgels using a combination of in situ electron and super-resolved fluorescence microscopy. We unravel new levels of structural details and address the challenge of reconstructing 3D information from 2D projections for nonuniform soft matter as opposed to monodisperse proteins. Moreover, we visualize the thermally induced shrinkage of responsive core-shell microgels live in water. This strategy opens doors for systematic in situ studies of soft matter systems and their application as smart materials.

Unexpected Ge-Ge Contacts in the Two-Dimensional Ge4 Se3 Te Phase and Analysis of Their Chemical Cause with the Density of Energy (DOE) Function.

A hexagonal phase in the ternary Ge-Se-Te system with an approximate composition of GeSe0.75 Te0.25 has been known since the 1960s but its structure has remained unknown. We have succeeded in growing single crystals by chemical transport as a prerequisite to solve and refine the Ge4 Se3 Te structure. It consists of layers that are held together by van der Waals type weak chalcogenide-chalcogenide interactions but also display unexpected Ge-Ge contacts, as confirmed by electron microscopy analysis. The nature of the electronic structure of Ge4 Se3 Te was characterized by chemical bonding analysis, in particular by the newly introduced density of energy (DOE) function. The Ge-Ge bonding interactions serve to hold electrons that would otherwise go into antibonding Ge-Te contacts.

Exploring the detection limits of infrared near-field microscopy regarding small buried structures and pushing them by exploiting superlens-related effects.

We present a study on subsurface imaging with an infrared scattering-type scanning near-field optical microscope (s-SNOM). The depth-limitation for the visibility of gold nanoparticles with a diameter of 50 nm under Si3N4 is determined to about 50 nm. We first investigate spot size and signal strength concerning their particle-size dependence for a dielectric cover layer with positive permittivity. The experimental results are confirmed by model calculations and a comparison to TEM images. In the next step, we investigate spectroscopically also the regime of negative permittivity of the capping layer and its influence on lateral resolution and signal strength in experiment and simulations. The explanation of this observation combines subsurface imaging and superlensing, and shows up limitations of the latter regarding small structure sizes.

Shape without Structure: An Intriguing Formation Mechanism in the Solvothermal Synthesis of the Phase-Change Material Sb2 Te3.

We introduce a novel solvothermal synthesis of individual single crystalline Sb2 Te3 micro- and nanocrystals as a model material for phase-change switching. We identified different intermediates along the reaction path to the final Sb2 Te3 hexagonal platelets (HPs) and discuss their forming mechanism. By means of nanodiffraction (ND) in a scanning transmission electron microscope we demonstrate that the intermediates follow a hexagonal shape evolution in the amorphous state. In situ nanomanipulator measurements reveal electrical phase-change switching properties of the individual Sb2 Te3 hexagonal platelets.

Determination of the Young's modulus of the epicuticle of the smooth adhesive organs of Carausius morosus using tensile testing.

Adhesive organs like arolia of insects allow these animals to climb on different substrates by creating high adhesion forces. According to the Dahlquist criterion, adhesive organs must be very soft, exhibiting an effective Young's modulus of below 100 kPa to adhere well to substrates. Such a low effective Young's modulus allows the adhesive organs to make almost direct contact with the substrate and results in van der Waals forces along with capillary forces. In previous studies, the effective Young's moduli of adhesive organs were determined using indentation tests, revealing their structure to be very soft. However, adhesive organs show a layered structure, thus the measured values comprise the effective Young's moduli of several layers of the adhesive organs. In this study, a new approach is illustrated to measure the Young's modulus of the outermost layer of the arolium, i.e. of the epicuticle, of the stick insect Carausius morosus. As a result of the epicuticle being supported by upright fibres, tensile tests allow the determination of the Young's modulus of the epicuticle with hardly influence from subjacent layers. In our tensile tests, arolia of stick insects adhering on a latex membrane were stretched by stretching the membrane while the elongation of the contact area between an arolium and the membrane was recorded. For analysis, mathematical models of the mechanical system were developed. When fed with the observed elongations, these models yield estimates for the Young's modulus of the epicuticle of approximately 100 MPa. Thus, in arolia, a very thin layer (~225 nm) of a rather stiff material, which is less susceptible to abrasion, makes contact with the substrates, whereas the inner fibrous structure of arolia is responsible for their softness.

Influence of the Ba2+/Sr2+ content and oxygen vacancies on the stability of cubic Ba(x)Sr(1-x)Co(0.75)Fe(0.25)O(3-δ).

We present a theoretical and experimental study on the influence of the Ba/Sr and Co/Fe ratios as well as the oxygen-non-stoichiometry on the stability of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF). Thin-layer depositions are analysed by looking at TEM images and EDX spectra. Bond-analytical calculations are performed to explain the stability difference between hexagonal and cubic BSCF. Finally, annealing experiments analysed using XRD give an insight into the differences of phase-fraction growth with respect to the Ba/Sr ratio.

Studies of local structural distortions in strained ultrathin BaTiO3 films using scanning transmission electron microscopy.

Ultrathin ferroelectric heterostructures (SrTiO3/BaTiO3/BaRuO3/SrRuO3) were studied by scanning transmission electron microscopy (STEM) in terms of structural distortions and atomic displacements. The TiO2-termination at the top interface of the BaTiO3 layer was changed into a BaO-termination by adding an additional BaRuO3 layer. High-angle annular dark-field (HAADF) imaging by aberration-corrected STEM revealed that an artificially introduced BaO-termination can be achieved by this interface engineering. By using fast sequential imaging and frame-by-frame drift correction, the effect of the specimen drift was significantly reduced and the signal-to-noise ratio of the HAADF images was improved. Thus, a quantitative analysis of the HAADF images was feasible, and an in-plane and out-of-plane lattice spacing of the BaTiO3 layer of 3.90 and 4.22 Å were determined. A 25 pm shift of the Ti columns from the center of the unit cell of BaTiO3 along the c-axis was observed. By spatially resolved electron energy-loss spectroscopy studies, a reduction of the crystal field splitting (CFS, ΔL3=1.93 eV) and an asymmetric broadening of the eg peak were observed in the BaTiO3 film. These results verify the presence of a ferroelectric polarization in the ultrathin BaTiO3 film.