RESUMEN
The solid electrolyte interphase (SEI) that forms on Li-ion battery anodes is critical to their long-term performance, however observing SEI formation processes at the buried electrode-electrolyte interface is a significant challenge. Here we show that operando soft X-ray absorption spectroscopy in total electron yield mode can resolve the chemical evolution of the SEI during electrochemical formation in a Li-ion cell, with nm-scale interface sensitivity. O, F, and Si K-edge spectra, acquired as a function of potential, reveal when key reactions occur on high-capacity amorphous Si anodes cycled with and without fluoroethylene carbonate (FEC). The sequential formation of inorganic (LiF) and organic (-(C=O)O-) components is thereby revealed, and results in layering of the SEI. The addition of FEC leads to SEI formation at higher potentials which is implicated in the rapid healing of SEI defects and the improved cycling performance observed. Operando TEY-XAS offers new insights into the formation mechanisms of electrode-electrolyte interphases and their stability for a wide variety of electrode materials and electrolyte formulations.
RESUMEN
Vibrational modes affect fundamental physical properties such as the conduction of sound and heat and can be sensitive to nano- and atomic-scale structure. Probing the momentum transfer dependence of vibrational modes provides a wealth of information about a materials system; however, experimental work has been limited to essentially bulk and averaged surface approaches or to small wave vectors. We demonstrate a combined experimental and theoretical methodology for nanoscale mapping of optical and acoustic phonons across the first Brillouin zone, in the electron microscope, probing a volume ~1010 to 1020 times smaller than that of comparable bulk and surface techniques. In combination with more conventional electron microscopy techniques, the presented methodology should allow for direct correlation of nanoscale vibrational mode dispersions with atomic-scale structure and chemistry.
RESUMEN
Detonation nanodiamond particles (DND) contain highly-stable nitrogen-vacancy (N-V) centers, making it important for quantum-optical and biotechnology applications. However, due to the small particle size, the N-V concentrations are believed to be intrinsically very low, spawning efforts to understand the formation of N-V centers and vacancies, and increase their concentration. Here we show that vacancies in DND can be detected and quantified using simulation-aided electron energy loss spectroscopy. Despite the small particle size, we find that vacancies exist at concentrations of about 1 at%. Based on this experimental finding, we use ab initio calculations to predict that about one fifth of vacancies in DND form N-V centers. The ability to directly detect and quantify vacancies in DND, and predict the corresponding N-V formation probability, has a significant impact to those emerging technologies where higher concentrations and better dispersion of N-V centres are critically required.
RESUMEN
A combination of scanning transmission electron microscopy, electron energy loss spectroscopy, and ab initio calculations is used to describe the electronic structure modifications incurred by free-standing graphene through two types of single-atom doping. The N K and C K electron energy loss transitions show the presence of π* bonding states, which are highly localized around the N dopant. In contrast, the B K transition of a single B dopant atom shows an unusual broad asymmetric peak which is the result of delocalized π* states away from the B dopant. The asymmetry of the B K toward higher energies is attributed to highly localized σ* antibonding states. These experimental observations are then interpreted as direct fingerprints of the expected p- and n-type behavior of graphene doped in this fashion, through careful comparison with density functional theory calculations.
RESUMEN
Zirconium-based alloys are used in water-cooled nuclear reactors for both nuclear fuel cladding and structural components. Under this harsh environment, the main factor limiting the service life of zirconium cladding, and hence fuel burn-up efficiency, is water corrosion. This oxidation process has recently been linked to the presence of a sub-oxide phase with well-defined composition but unknown structure at the metal-oxide interface. In this paper, the combination of first-principles materials modeling and high-resolution electron microscopy is used to identify the structure of this sub-oxide phase, bringing us a step closer to developing strategies to mitigate aqueous oxidation in Zr alloys and prolong the operational lifetime of commercial fuel cladding alloys.
RESUMEN
We have correlated the elemental composition with the structure of multi-wall carbon nanotubes synthesised with nitrogen and phosphorus containing precursors and identified two chemically distinct dominant morphologies. The first type are cone-structured tubes and the second are nanotubes with fewer walls which can accommodate N2 gas along their inner channel and contain up to ten times more nitrogen than the cone-structured nanotubes. Phosphorus was present in the catalyst particles but was not detected within the walls of either type of nanotube. Elemental analysis combined with in situ electrical measurements has allowed us to monitor the evolution of the doped nanotubes when current is passed. The N2 gas becomes bonded immediately when current flows and the gas-containing nanotubes restructure more easily than the cone-structured ones. Since the inclusion of heteroatoms in multi-wall carbon nanotubes is generally inhomogeneous, understanding the distribution of elements across the sample is an important step towards the optimization of devices including gas sensors and components in electrical applications.
RESUMEN
Here we report a methodology combining TEM, STEM, Transmission-EBSD and EELS to analyse the structural and chemical properties of the metal-oxide interface of corroded Zr alloys in unprecedented detail. TEM, STEM and diffraction results revealed the complexity of the distribution of suboxide grains at the metal-oxide interface. EELS provided accurate quantitative analysis of the oxygen concentration across the interface, identifying the existence of local regions of stoichiometric ZrO and Zr3O2 with varying thickness. Transmission-EBSD confirmed that the suboxide grains can be indexed with the hexagonal ZrO structure predicted with ab initio by Nicholls et al. (2014). The t-EBSD analysis has also allowed for the mapping of a relatively large region of the metal-oxide interface, revealing the location and size distribution of the suboxide grains.
RESUMEN
BACKGROUND: Preventing and managing chemotherapy-induced nausea and vomiting (CINV) remain important goals. The objective of the Pan Australasian chemotherapy-induced emesis burden of illness (PrACTICE) study was to describe the incidence of CINV after highly or moderately emetogenic chemotherapy (HEC or MEC) for cancer in current clinical practice in Australia and five Asian countries (China, India, Singapore, South Korea, and Taiwan). STUDY DESIGN: This prospective, observational study of CINV was conducted at 31 sites in these six countries from August 2011 through September 2012 and enrolled male and female adult patients (≥18 years of age) naïve to HEC and MEC who were scheduled to receive at least two cycles of single-day chemotherapy. The primary effectiveness endpoint was complete response, defined as no vomiting or use of rescue therapy, during chemotherapy cycle 1 in the overall phase (0-120 h), acute phase (0-24 h), and delayed phase (>24-120 h). Study outcomes were analyzed descriptively. Primary outcomes, CINV incidence, and treatment patterns (chemotherapy, CINV prophylaxis, rescue medication prescription, and rescue medication use) were assessed by phase (overall, acute, delayed), by cycle (as appropriate), within and across countries, and by level of chemotherapy emetogenicity (HEC vs. MEC). The impact of CINV in cycle 1 on CINV in cycle 2 was analyzed for all patients with evaluable data for cycle 2. No site-specific analyses were performed. The remainder of this special series of papers reports on the results of this study.
Asunto(s)
Antieméticos/uso terapéutico , Náusea/tratamiento farmacológico , Vómitos/tratamiento farmacológico , Adulto , Anciano , Antineoplásicos/efectos adversos , Antineoplásicos/uso terapéutico , Australia/epidemiología , China/epidemiología , Costo de Enfermedad , Femenino , Humanos , Incidencia , India/epidemiología , Quimioterapia de Inducción , Masculino , Persona de Mediana Edad , Náusea/inducido químicamente , Náusea/epidemiología , Neoplasias/tratamiento farmacológico , Estudios Prospectivos , República de Corea/epidemiología , Encuestas y Cuestionarios , Vómitos/inducido químicamente , Vómitos/epidemiologíaRESUMEN
In this work it has been established that 3D nanoflowers of WS2 synthesised by chemical vapour deposition are composed of few layer WS2 along the edges of the petals. An experimental study in order to understand the evolution of these nanostructures shows the nucleation and growth along with the compositional changes they undergo.
RESUMEN
Hexagonal boron nitride (hBN) is a promising material for a range of applications including deep-ultraviolet light emission. Despite extensive experimental studies, some fundamental aspects of hBN remain unknown, such as the type of stacking faults likely to be present and their influence on electronic properties. In this paper, different stacking configurations of hBN are investigated using CASTEP, a pseudopotential density functional theory code. AB-b stacking faults, in which B atoms are positioned directly on top of one another while N atoms are located above the center of BN hexagons, are shown to be likely in conventional AB stacked hBN. Bandstructure calculations predict a single direct bandgap structure that may be responsible for the discrepancies in bandgap type observed experimentally. Calculations of the near edge structure showed that different stackings of hBN are distinguishable using measurements of core-loss edges in X-ray absorption and electron energy loss spectroscopy. AB stacking was found to best reproduce features in the experimental B and N K-edges. The calculations also show that splitting of the 1s to π* peak in the B K-edge, recently observed experimentally, may be accounted for by the presence of AB-b stacking faults.
RESUMEN
BACKGROUND: Ulcerative colitis is a lifelong, chronic, relapsing-remitting disease. OBJECTIVE: To assess the relationship between ulcerative colitis disease status and patient quality of life, and to determine the impact of ulcerative colitis on healthcare costs and work productivity, in the UK. METHODS: Clinicians assessed 173 adult patients' current disease status at a single study visit using the partial Mayo (pMayo) instrument. Patients completed the Euro Quality of Life 5-dimension, 5-level (EQ-5D-5L) questionnaire, the Work Productivity and Activity Impairment (WPAI) questionnaire. Healthcare resource use was determined from questionnaires and from patients' medical charts. RESULTS: Patients in remission had a significantly higher EQ-5D-5L scores (mean (SD) 0.86 (0.15)) than patients with active disease (0.71 (0.20); p<0.001). Patients with mild disease had significantly higher mean (SD) EQ-5D-5L scores than patients with moderate/severe disease: 0.77 (0.11) and 0.66 (0.24), respectively (p<0.001). The mean percent productivity impairment was greater for patients with active disease than for patients in remission on all items of the WPAI questionnaire: 24.6% vs 1.8% for work time missed, 34.1% vs 12.9% for impairment while working, 40.8% vs 14.4% for overall work impairment and 42.7% vs 13.0% for activity impairment (p<0.001 for all comparisons). The mean (SD) total cost of healthcare for ulcerative colitis in the prior 3â months was £1211 (1588). CONCLUSIONS: When compared with patients in remission, patients with active ulcerative colitis have significantly worse quality of life and significantly more work impairment. The healthcare costs of ulcerative colitis are considerable.
RESUMEN
NanoBuds exist in a variety of stable structures. Our studies show that engineering NanoBud geometries is indeed possible and we visualise the transformation of one Nanobud geometry to another using in situ aberration corrected imaging techniques. Such NanoBuds are precursors for generating nanotube junctions which could be used in composite and electronic applications.
Asunto(s)
Nanotubos de Carbono/química , Aerosoles/química , Electrones , Fulerenos/químicaRESUMEN
Precise control of graphene properties is an essential step toward the realization of future graphene devices. Defects, such as individual nitrogen atoms, can strongly influence the electronic structure of graphene. Therefore, state-of-the-art characterization techniques, in conjunction with modern modeling tools, are necessary to identify these defects and fully understand the synthesized material. We have directly visualized individual substitutional nitrogen dopant atoms in graphene using scanning transmission electron microscopy and conducted complementary electron energy loss spectroscopy experiments and modeling which demonstrates the influence of the nitrogen atom on the carbon K-edge.
RESUMEN
The "doping" of carbon nanotubes with heteroatoms is an established method of controlling their properties. However, variations in heteroatom concentration in multiwalled carbon nanotubes (MWCNTs) tend to produce nanotubes with different morphologies, and hence varying properties, within the same sample. Electron energy loss spectroscopy in conjunction with imaging using a scanning transmission electron microscope (STEM) is a powerful tool to precisely map the spatial variation and bonding state of heteroatoms, e.g., B, N, P, Si, or combinations of these, present in carbon nanotubes exhibiting different structures. TEM analysis revealed that B incorporation during MWCNT growth (B-MWCNTs) results in nanotube morphologies that can be divided into three different types. These include core-shell structures possessing a B-rich core of cones and a C outer layer, B-containing cone structures, and MWCNTs with an irregular inner channel. In situ studies were carried out using Nanofactory() holder experiments in order to investigate the properties of individual B-MWCNTs and to show that the three types of nanotubes undergo different current-induced breakdown. The inhomogeneity in composition, structure, and properties of B-MWCNTs could result from the variation in chemical composition and temperature within the furnace, and this work highlights the importance of developing synthesis techniques that can control the inclusion of heteroatoms into nanotubes.
Asunto(s)
Boro/química , Cristalización/métodos , Nanotubos/química , Nanotubos/ultraestructura , Sustancias Macromoleculares/química , Ensayo de Materiales , Conformación Molecular , Tamaño de la Partícula , Propiedades de SuperficieRESUMEN
If they could be easily exfoliated, layered materials would become a diverse source of two-dimensional crystals whose properties would be useful in applications ranging from electronics to energy storage. We show that layered compounds such as MoS(2), WS(2), MoSe(2), MoTe(2), TaSe(2), NbSe(2), NiTe(2), BN, and Bi(2)Te(3) can be efficiently dispersed in common solvents and can be deposited as individual flakes or formed into films. Electron microscopy strongly suggests that the material is exfoliated into individual layers. By blending this material with suspensions of other nanomaterials or polymer solutions, we can prepare hybrid dispersions or composites, which can be cast into films. We show that WS(2) and MoS(2) effectively reinforce polymers, whereas WS(2)/carbon nanotube hybrid films have high conductivity, leading to promising thermoelectric properties.
RESUMEN
In this paper, a chemically sensitive local characterization technique is used to characterize fullerene peapods containing two metal atoms within each fullerene. By combining bright-field imaging, high-angle annular dark-field imaging, and electron energy loss spectroscopy in a scanning transmission electron microscope, unambiguous identification of the metal atoms present is possible. Key to making this possible is aberration correction, which allows atomic resolution at lower beam energies. The peapods can be imaged for several consecutive scans at 80 keV beam energy, and the combination of techniques allows the position as well as the species of the encapsulated atoms to be identified. Movements of the encapsulated atoms are monitored.
RESUMEN
One-dimensional nanostructures based on the Mo-S-I system have recently aroused a lot of interest as a viable alternative to the ubiquitous carbon nanotube due to their uniform structure and electronic properties for a given composition. Previous research on the Mo(6)S(3)I(6) and Mo(6)S(4.5)I(4.5) stoichiometries has also shown them to be soluble in common solvents like water, acetone or isopropyl alcohol, and to debundle on dilution. Here, the solubility, debundling and composition of Mo(6)S(2)I(8) nanowires are presented. They were found to be most soluble in dimethylformamide, which retained 47 wt% of a 0.08 gl(-1) nanowire (NW) material dispersion as thin NW bundles after one week. Dispersions of 0.8 gl(-1) and 5 gl(-1) even retained 54 wt% and 66 wt%, respectively. However the NW material was completely insoluble in water, and the surface energy of Mo(6)S(2)I(8) NWs was deduced as 67 mJ m(-2), higher than for other Mo-S-I NWs. UV-vis-NIR spectroscopy showed nanowire peaks familiar from Mo(6)S(3)I(6) and Mo(6)S(4.5)I(4.5) spectra around 1.8 and 2.8 eV, as well as unforeseen ultraviolet peaks at 3.5 and 4.4 eV. These chemical differences suggest an alternate, more strongly bonded structure to that seen for Mo(6)S(3)I(6) and Mo(6)S(4.5)I(4.5) NWs. Films deposited from a range of concentrations were investigated using atomic force microscopy (AFM) to determine bundle diameter distributions. The average diameter and the spread in diameters were found to decrease somewhat with decreasing concentration. However extrapolation gave a finite bundle size at infinite dilution, and an extension of the existing debundling model is proposed to take this into account. To confirm the nominal stoichiometry of Mo(6)S(2)I(8), which does not follow the generic Mo(6)S(x)I(9-x) formula of previous stoichiometries, EDX was carried out. The composition of nanowire bundles was found to be Mo(6)S(2.3)I(8.6), supporting the nominal composition.
RESUMEN
A potential methodology is presented for the systematic prediction of EELS edges using DFT, suitable for codes that calculate ELNES for a specific atom in a unit cell. The method begins with the selection of a unit cell, chosen as the smallest cell that still provides a physically valid representation of the bulk material. Within this small cell, a single electron core-hole is included in the atom for which the EELS ionisation edge is to be calculated. The basis-set size and k-point mesh of the DFT calculation are converged specifically against the predicted EELS result. Subsequently, the cell size is increased until the theoretical core-holes no longer interfere. At this point one can then modify the exact core-hole approximation. This methodology was applied to the new EELS module of the CASTEP pseudopotential DFT code, as well as the all-electron code Wien2k. Aluminium K edges were investigated for various aluminium metal systems. It was observed that as the cell size was increased the predicted EELS result became less sensitive to the exact core-hole approximation used. It was noted however that due to high screening in metals a ground state single cell calculation is often acceptable. The semiconductor aluminium nitride (wurtzite form) was also investigated. It was observed that for both Wien2k and CASTEP, with careful convergence of the key DFT code parameters, single cell ground state calculations gave a reasonable agreement with experiment, contrary to what might be expected for a semiconductor with a large band gap. This was particularly true of the Wien2k result. Given the greater computational effort required for supercell calculations, these results are likely to form the beginnings of a detailed investigation into accepted methods of ELNES predictions.