6,564 research outputs found
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Thermal stress-induced charge and structure heterogeneity in emerging cathode materials
Nickel-rich layered oxide cathode materials are attractive near-term candidates for boosting the energy density of next generation lithium-ion batteries. The practical implementation of these materials is, however, hindered by unsatisfactory capacity retention, poor thermal stability, and oxygen release as a consequence of structural decomposition, which may have serious safety consequences. The undesired side reactions are often exothermic, causing complicated electro-chemo-mechanical interplay at elevated temperatures. In this work, we explore the effects of thermal exposure on chemically delithiated LiNi0.8Mn0.1Co0.1O2 (NMC-811) at a practical state-of-charge (50% Li content) and an over-charged state (25% Li content). A systematic study using a suite of advanced synchrotron radiation characterization tools reveals the dynamics of thermal behavior of the charged NMC-811, which involves sophisticated structural and chemical evolution; e.g. lattice phase transformation, transition metal (TM) cation migration and valence change, and lithium redistribution. These intertwined processes exhibit a complex 3D spatial heterogeneity and, collectively, form a valence state gradient throughout the particles. Our study sheds light on the response of NMC-811 to elevated temperature and highlights the importance of the cathode's thermal robustness for battery performance and safety
Tribological applications of surface analysis
For some years, surface analysis was used in fundamental studies of solid-solid contacts existing in tribological systems. Analysis was used to detect material transfer in sliding contacts. The effects of surface films on the adhesion of contacts was monitored. Finally electron spectroscopic analysis of interfaces has shed some light on the fundamental electronic nature of the interfacial bond. More recently, surface analysis was applied to many tribological engineering problems. In particular, identification of chemical films formed during the sliding contact of lubricated systems and study of the surface chemistry of lubricant additives were active areas of research. One or more of four properties of the analytical technique will be important in determining its utility. The four are: lateral resolution, specimen damage, depth resolution and the availability of chemical information. In each of the applications discussed here, the important factors are brought out
Accelerated Growth Plate Mineralization and Foreshortened Proximal Limb Bones in Fetuin-A Knockout Mice
PMCID: PMC3473050This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Conduction of topologically-protected charged ferroelectric domain walls
We report on the observation of nanoscale conduction at ferroelectric domain
walls in hexagonal HoMnO3 protected by the topology of multiferroic vortices
using in situ conductive atomic force microscopy, piezoresponse force
microscopy, and kelvin-probe force microscopy at low temperatures. In addition
to previously observed Schottky-like rectification at low bias [Phys. Rev.
Lett., 104, 217601 (2010)], conductance spectra reveal that negatively charged
tail-to-tail walls exhibit enhanced conduction at high forward bias, while
positively charged head-to-head walls exhibit suppressed conduction at high
reverse bias. Our results pave the way for understanding the semiconducting
properties of the domains and domain walls in small-gap ferroelectrics.Comment: 8 pages, 4 figure
Quantitative Chemically-Specific Coherent Diffractive Imaging of Buried Interfaces using a Tabletop EUV Nanoscope
Characterizing buried layers and interfaces is critical for a host of
applications in nanoscience and nano-manufacturing. Here we demonstrate
non-invasive, non-destructive imaging of buried interfaces using a tabletop,
extreme ultraviolet (EUV), coherent diffractive imaging (CDI) nanoscope. Copper
nanostructures inlaid in SiO2 are coated with 100 nm of aluminum, which is
opaque to visible light and thick enough that neither optical microscopy nor
atomic force microscopy can image the buried interfaces. Short wavelength (29
nm) high harmonic light can penetrate the aluminum layer, yielding
high-contrast images of the buried structures. Moreover, differences in the
absolute reflectivity of the interfaces before and after coating reveal the
formation of interstitial diffusion and oxidation layers at the Al-Cu and
Al-SiO2 boundaries. Finally, we show that EUV CDI provides a unique capability
for quantitative, chemically-specific imaging of buried structures, and the
material evolution that occurs at these buried interfaces, compared with all
other approaches.Comment: 12 pages, 8 figure
Advanced XPS characterization: XPS-based multi-technique analyses for comprehensive understanding of functional materials
X-ray photoelectron spectroscopy (XPS) has achieved maturity as an analytical technique in that it is a ubiquitous tool in the materials community, however as made apparent by recent reviews highlighting it's misuse as a means of chemical deduction, it is a practice which is greatly misunderstood even in its simplest form. Advanced XPS techniques, or a combination of XPS and a complementary surficial probe may elicit auxiliary information outside of the scope of the standard sphere of appreciation. This review aims to bring to the attention of the general materials audience a landscape of some atypical applications of lab-based XPS and combinatorial approaches of related surface analysis, such as ion scattering, ultraviolet photoelectron, electron energy loss and auger emission spectroscopies found on many lab-based instrument set-ups
Characterization of heterogeneity and spatial distribution of phases in complex solid dispersions by thermal analysis by structural characterization and X-ray micro computed tomography
Purpose: This study investigated the effect of drug-excipient miscibility on the heterogeneity and spatial distribution of phase separation in pharmaceutical solid dispersions at a micron-scale using two novel and complementary characterization techniques, thermal analysis by structural characterization (TASC) and X-ray micro-computed tomography (XCT) in conjunction with conventional characterization methods. Method: Complex dispersions containing felodipine, TPGS, PEG and PEO were prepared using hot melt extrusion-injection moulding. The phase separation behavior of the samples was characterized using TASC and XCT in conjunction with conventional thermal, microscopic and spectroscopic techniques. The in vitro drug release study was performed to demonstrate the impact of phase separation on dissolution of the dispersions. Results: The conventional characterization results indicated the phase separating nature of the carrier materials in the patches and the presence of crystalline drug in the patches with the highest drug loading (30% w/w). TASC and XCT where used to provide insight into the spatial configuration of the separate phases. TASC enabled assessment of the increased heterogeneity of the dispersions with increasing the drug loading. XCT allowed the visualization of the accumulation of phase separated (crystalline) drug clusters at the interface of air pockets in the patches with highest drug loading which led to poor dissolution performance. Semi-quantitative assessment of the phase separated drug clusters in the patches were attempted using XCT. Conclusion: TASC and XμCT can provide unique information regarding the phase separation behavior of solid dispersions which can be closely associated with important product quality indicators such as heterogeneity and microstructure
Intrinsic photoanode band engineering: enhanced solar water splitting efficiency mediated by surface segregation in Ti-doped hematite nanorods
Band engineering is thoroughly employed nowadays targeting technologically
scalable photoanodes for solar water splitting applications. Most often complex
and costly recipes are necessary, for average performances. Here we report very
simple photoanode growth and thermal annealing, with effective band engineering
results. Strongly enhanced photocurrent, of more than 200 %, is measured for
Ti-doped hematite nanorods grown from aqueous solutions and annealed under
Nitrogen atmosphere, compared to air annealed ones. Oxidized surface states and
increased density of charge carriers are found responsible for the enhanced
photoelectrochemical activity, as shown by electrochemical impedance
spectroscopy and synchrotron X-rays spectromicroscopies. They are found related
to oxygen vacancies, acting as n-dopants, and the formation of pseudo- brookite
clusters by surface Ti segregation. Spectro-ptychography is used for the first
time at Ti L3 absorption edge to isolate Ti chemical coordination arising from
pseudo-brookite clusters contribution. Correlated with electron microscopy
investigation and Density Functional Theory (DFT) calculations, our data
unambiguously prove the origin of the enhanced photoelectrochemical activity of
N2-annealed Ti-doped hematite nanorods. Finally, we present here a handy and
cheap surface engineering method beyond the known oxygen vacancy doping,
allowing a net gain in the photoelectrochemical activity for the hematite-based
photoanodes.Comment: 2 parts: first main manuscript with 39 pages, second supplementary
informations with 14 page
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Laboratory capture, isolation and analysis of microparticles in aerogel: Preparation for the return of Stardust
We present observations from the laboratory capture of particles in aerogel. The paper focuses on a possible extraction technique and the bulk mineral characterization of the captured material using non-destructive analytical techniques
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