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Simultaneously improving energy efficiency (EE) and material stability in electrochemical CO2 conversion remains an unsolved challenge. Among a series of ternary Sn-Ti-O electrocatalysts, 3D ordered mesoporous (3DOM) Sn0.3 Ti0.7 O2 achieves a trade-off between active-site exposure and structural stability, demonstrating up to 71.5 % half-cell EE over 200 hours, and a 94.5 % Faradaic efficiency for CO at an overpotential as low as 430 mV. DFT and X-ray absorption fine structure analyses reveal an electron density reconfiguration in the Sn-Ti-O system. A downshift of the orbital band center of Sn and a charge depletion of Ti collectively facilitate the dissociative adsorption of the desired intermediate COOH* for CO formation. It is also beneficial in maintaining a local alkaline environment to suppress H2 and formate formation, and in stabilizing oxygen atoms to prolong durability. These findings provide a new strategy in materials design for efficient CO2 conversion and beyond.

Micrometer-sized functional nucleic acid (FNA) superstructures (denoted as 3D DNA) were examined as a unique class of biorecognition elements to produce highly functional bioactive paper surfaces. 3D DNA containing repeating sequences of either a DNA aptamer or DNAzyme was created from long-chain products of rolling circle amplification followed by salt aging. The resulting 3D DNA retained its original spherical shape upon inkjet printing and adhered strongly to the paper surface via physisorption. 3D DNA paper sensors showed resistance to degradation by nucleases, suppressed nonspecific protein adsorption, and provided a much higher surface density of functional DNA relative to monomeric FNAs, making such species ideally suited for development of paper-based biosensors.

Syngas, the mixture of CO and H2, is a key feedstock to produce methanol and liquid fuels in industry, yet limited success has been made to develop clean syngas production using renewable solar energy. We demonstrated that syngas with a benchmark turnover number of 1330 and a desirable CO/H2 ratio of 1:2 could be attained from photoelectrochemical CO2 and H2O reduction in an aqueous medium by exploiting the synergistic co-catalytic effect between Cu and ZnO. The CO/H2 ratio in the syngas products was tuned in a large range between 2:1 and 1:4 with a total unity Faradaic efficiency. Moreover, a high Faradaic efficiency of 70 % for CO was acheived at underpotential of 180 mV, which is the lowest potential ever reported in an aqueous photoelectrochemical cell. It was found that the combination of Cu and ZnO offered complementary chemical properties that lead to special reaction channels not seen in Cu, or ZnO alone.

Highly {100} oriented Pt deposits were prepared by electrodeposition from a 10 mM HCl, 100 mM KCl and Na 2 PtCl 6 .xH 2 O electrolyte. The deposits were prepared in the form of thin fi lms and array of nanowires. A qualitative assessment of the proportion of {100} oriented Pt surfaces was obtained through X-ray diffraction measurements and cyclic voltammetry in 0.5 M H 2 SO 4 . The effect of the deposition potential, E dep , temperature of the electrolyte, T dep , platinum salt concentration [Na 2 PtCl 6 .xH 2 O], and nature of the substrate were investigated. It was shown that the proportion of {100} oriented Pt surfaces reaches a maximum for E dep = −0.35 V vs SCE. Moreover, this proportion increases steadily as T dep and [Na 2 PtCl 6 .xH 2 O] are decreased from 75 to 25 ° C and from 2.5 to 0.25 mM, respectively. Scanning electron microscopy and high-resolution transmission electron microscopy micrographs indicate that the more oriented samples are made of pine tree-like structures that are effectively single crystals, and that the growth facets appear to be close to the {001} plane. This observation also clearly indicates that the plane exposed during the CV experiment is also {001}. As suggested by these micrographs, the fi lms and nanowires are highly porous and roughness factors as large as 1000 were obtained on highly {100} oriented Pt nanowires. The predominance of {100} facets is attributed to their energetically favoured growth in the presence of hydrogen, and is shown to be signifi cantly enhanced when the mass transport of Pt 4 + is limited. Due to the predominance of {100} facets, the normalized electrocatalytic activity ( μ A cm − 2 Pt ) for the electro-oxidation of hydrazine and ammonia is higher than non-oriented polycrystalline Pt by a factor of 4 and 2.7, respectively.

Hierarchical structure porous MoS2/SiO2 microspheres were prepared by ultrasonic pyrolysis technique. The nanostructured MoS2/SiO2 materials were characterised by scanning electron micrograph (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), as well as nitrogen isotherm. The MoS2/SiO2 microspheres, synthesised using polystyrene latex spheres as a template, showed two pore sizes: 5.8 and 68 nm. The micro-, meso- and macropore volume was also calculated. Effect of PSL:SiO2 ratio on the hierarchical structure was also investigated. © 2011 Canadian Society for Chemical Engineering

The growth techniques which have enabled the realization of InGaN-based multi-quantum-well (MQW) structures with high internal quantum efficiencies (IQE) on 150mm (6-in.) silicon substrates are reviewed. InGaN/GaN MQWs are deposited onto GaN templates on large-area (111) silicon substrates, using AlGaN strain-mediating interlayers to inhibit thermal-induced cracking and wafer-bowing, and using a SiN x interlayer to reduce threading dislocation densities in the active region of the MQW structure. MQWs with high IQE approaching 60% have been demonstrated. Atomic resolution electron microscopy and EELS analysis have been used to study the nature of the important interface between the Si(111) substrate and the AlN nucleation layer. We demonstrate an amorphous SiN x interlayer at the interface about 2nm wide, which does not, however, prevent good epitaxy of the AlN on the Si(111) substrate. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

BaTiO3 and SrTiO3 perovskites of the A2+B4+O3 type form complete solid solution, Sr1−x BaxTiO3, which can accommodate a substantial amount of donor dopants, for example, La. At high oxygen partial pressure, La dopants in SrTiO3 are compensated by A-site vacancies, whereas in BaTiO3 they are compensated by B-site vacancies. Therefore, donor compensation in the Sr1−xBaxTiO3 solid solution should demonstrate a crossover from the A-site vacancies at x=0 to the B-site vacancies at x=1. One may expect, therefore, that at some critical concentration, xc, the free energy of the Sr1−xBaxTiO3 system can become invariant to the vacancy compensation regime. In other words, the system will adopt either A- or B-site vacancies depending on the target chemical composition. Based on the Rietveld refinement of X-ray diffraction patterns and their phase composition analysis as well as scanning electron microscopic and transmission electron microscopic data, we demonstrate that the 28% La-doped Sr1−xBaxTiO3 system equilibrated at 1400°C indeed becomes invariant to the vacancy-type compensation at xc≈0.25 and can accommodate A- and B-site vacancies at any given ratio. Finally, we propose a microscopic model based on the off-center Ti displacement and the partial covalency of Ti–O bond to explain the distinct difference in the vacancy compensation mechanisms in BaTiO3 and SrTiO3. These findings are important for a further understanding of the thermodynamics of the intrinsic point defects in perovskites as well as for the improvement of electrical performance of the solid oxide fuel cells, ferroelectric, and voltage-tunable ceramics.

Background: Understanding the interfacial reactions to synthetic bone regenerative scaffolds in vivo is fundamental for improving osseointegration and osteogenesis. Using transmission electron micr ...

A key feature in the understanding of the mechanisms of integration versus rejection of implanted materials is a deepened understanding of the elemental and molecular compositions of the interface zone between the surface of the synthetic man-made material and the biological components of tissue. Intact interfaces between metallic implants and tissues have not been able to image and analyse on the ultrastructural level with the common transmission electron microscopy (TEM) sample preparation techniques. By using focused ion beam microscopy for site-specific preparation of TEM samples, intact interfaces between metal implants and calcified tissue were imaged for the first time. The interface's elemental and crystallographic compositions were determined using energy dispersive X-ray mapping and electron diffraction. The developed technique fulfills a long-sought-for demand to correlate the surface properties of implanted metal prostheses with the fine structure and composition of preserved interfaces with tissues.

Poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA), a partially fluorinated polymer, was directly grafted from silicon wafer surfaces by a surface-initiated atom-transfer radical polymerization (ATRP). The polymer layer thickness increased linearly with monomer conversion and molecular weight of free polymers in solution. The thickness was mainly determined by the experimental conditions such as activator/deactivator ratio, monomer/catalyst ratio, and monomer concentration. PTFEMA layers of more than 100-nm thick were obtained. The grafted PTFEMA chains were “living” and allowed the extension of a second block of PMMA. X-ray photoelectron spectroscopy study showed that the chemical compositions at the surfaces agreed well with their theoretical values. A novel surface-attachable difunctional initiator was also synthesized and applied to the grafting of PTFEMA. The grafting density was doubled using this difunctional initiator, from 0.48 to 0.86 chains/nm2. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1252–1262, 2006

Solid solution of manganese in yttria-stabilized zirconia (YSZ) may occur in the electrolyte of solid oxide fuel cells. Possible changes in valence, coordination, and site occupancy of Mn in YSZ are of interest. Also, subsequent structural modification of the cubic YSZ, as well as the possible ordering of vacancies, has important consequences for the ionic conductivity. Electron energy loss spectroscopy was used to measure the O K and the Mn L edge of Mn in solid solution in a zirconia host lattice. The ratio Mn L3/L2was determined for some manganese oxides and for Mn in solid solution. It is shown that the L3/L2ratio does not simply reflect the oxidation state of the Mn ions in solid solution. Selected area diffraction experiments were also made in the TEM. This showed ordering of the cations and the anion vacancies at high doping levels. It is concluded that the number of O ions surrounding each Mn ion may be very important in interpreting the obtained L3/L2ratio.

The microstructure and the abrasive wear characteristics of two binderless carbides (WC-Mo2C and WC-TiC-TaC) have been studied. The microstructural analysis identified differences in the amount of mixing between the gamma-phase and WC. Mo2C and WC showed

A novel two-step surface modification method that includes atomic layer deposition (ALD) of TiO2 followed by post-annealing treatment on spinel LiNi0.5 Mn1.5 O4 (LNMO) cathode material is developed to optimize the performance. The performance improvement can be attributed to the formation of a TiMn2 O4 (TMO)-like spinel phase resulting from the reaction of TiO2 with the surface LNMO. The Ti incorporation into the tetrahedral sites helps to combat the impedance growth that stems from continuous irreversible structural transition. The TMO-like spinel phase also alleviates the electrolyte decomposition during electrochemical cycling. 25 ALD cycles of TiO2 growth are found to be the optimized parameter toward capacity, Coulombic efficiency, stability, and rate capability enhancement. A detailed understanding of this surface modification mechanism has been demonstrated. This work provides a new insight into the atomic-scale surface structural modification using ALD and post-treatment, which is of great importance for the future design of cathode materials.

Current state-of-the-art catalysts for polymer electrolyte membrane fuel cells, comprised of platinum nanoparticles on a high surface area carbon support, are susceptible to platinum dissolution and carbon support corrosion during operation. The use of transition metal oxides in the support material is proposed to stabilize the catalyst material by minimizing platinum dissolution and carbon corrosion. Here, the 3D structural changes are tracked for a hybrid Pt–Nb oxide on carbon catalyst before and after potential cycling utilizing identical location electron tomography. Pt dissolution is observed to varying degrees in both high and low Nb oxide content structures and appreciable carbon support corrosion in the high Nb oxide content structure but not in the low Nb oxide structure.

We compare experimentally observed electron energy loss spectra (EELS) of uranium dioxide UO 2 and nickel monoxide NiO with the results of ab-initio calculations carried out by using a method combining the local spin density approximation and the Hubbard U term (the LSDA + U method). We show that by taking better account of strong Coulomb correlations between electrons in the 5f shell of uranium ions in UO 2 and in the 3d shell of nickel ions in NiO it is possible to arrive at a better description of electron energy loss spectra, cohesive energies and elastic constants of both oxides compared with local spin density functional theory. For NiO we also compare the LSDA + U results and EELS spectra with a self-interaction corrected LSDA calculation.

This work uses electron energy loss spectroscopy (EELS) to study the excitation of interface and bulk plasmons in artificial, nonmagnetic metallic multilayers. We obtain EELS spectra for W/Si and Ta/Si multilayers with layer periodicity d using an off-axis acquisition technique and compare the results with dispersion relations and energy loss probability distributions predicted from dielectric theory. Our energy loss spectra, taken for a fixed out-of-plane wavevector kz = π/d and low in-plane wavevectors ky

SUMMARY We report changes in the iron L3/L2 white-line ratio of the electron energy-loss spectrum of a series of iron-copper multilayers which we discuss in terms of the lattice plane spacings present in the multilayer system. Momentum-resolved data from one multilayer is also considered.

SUMMARY The L3 to L2 white-line intensity ratios of Mn in solid solution in yttria-stabilized zirconia and in Mn oxide standards are measured using different approaches. We show that the L3/L2 ratio alone cannot be used as a means of deducing the oxidation state and that a combined analysis of this ratio and the normalized white-line intensity is required to retrieve the ionicity and magnetic state of the Mn dopant with respect to reference standards. Changes as a function of composition are measured and these are discussed in terms of variations in crystal field parameters associated with possible vacancy interaction. From the oxygen near-edge structure we analyse the localization of the extra electron charge introduced by the dopant and discuss the possible effects of the association of this extra charge with oxygen vacancies in relation to the macroscopic ion conductivity.

SUMMARY A method to determine the volume fraction of a dispersoid phase based on measurements carried out on thin foils is presented. The method involves the reconstruction of the shape and volume, by electron energy-loss spectroscopy thickness measurements, of the analysed foil and the determination of the volume of the dispersoids using more conventional electron microscopy imaging techniques. Hence the technique does not require the use of stereology theorems. The procedure to measure the total inelastic mean free path and the linearity of its measurement for thicknesses (t) relative to the mean free path (t/λ) up to t/λ ∼ 4 is described. A method allowing the conversion of one single experimental λ-value to various collection conditions either graphically or by parameterization is also outlined. Various imaging methods (CTEM, STEM and chemical mapping) were evaluated for their ability to retrieve the distribution of dispersoids and thus their volume. Artefacts of the technique and of the sample preparation method are also discussed. The possibility of applying such techniques using in-column and post-column imaging filters and the limitations of such methods are presented. Although the system has been applied to a relevant metallurgical system in the aluminium industry, it can be used for any other material provided that the values of the mean free path can be obtained.

The metastable oxygen-deficient title compound is characterized by powder X-ray and neutron diffraction and EELS.

SUMMARY The development of a parallel electron energy-loss spectrum imaging system is presented. The analytical performance of the imaging technique was investigated and the system applied to materials science problems. The system, which allows acquisition and storage of a parallel electron energy-loss spectrum at each pixel of an image, was developed by interfacing a multichannel analyser and a microscope to a computer workstation. In the experimental conditions used for imaging, detection limits and quantification errors were large and varied as a function of spatial resolution and the range of chemical elements of interest in the image. Applications of this imaging technique in materials science showed that quantitative chemical information is provided by the system and that the use of relative thickness maps and detailed statistical analysis of the spectrum-image allowed an unbiased interpretation of the images. As energy-loss spectra are available after processing, spectroscopic information about the analysed material can be used to provide supplementary information.

Metastable olivine phases of crystalline Na[Mn1-xMx]PO4 (M: Fe, Ca, Mg; 0 ≤ x ≤ 0.5) are formed by solid state topotactic reactions of NH4 [Mn1-xMx]PO4·H2O and excess NaOAc (65—100 °C).

The high temperature thermoelectric properties of the title compounds and Mo3Sb5.4Te1.6 are examined.

Coupling electron microscopy techniques with insitu heating ability allows us to study phase transformations on the single-nanoparticle level. We exploit this setup to study disorder-to-order transformation of Pt-Fe alloy nanoparticles, a material that is of great interest to fuel-cell electrocatalysis and ultrahigh density information storage. In contrast to earlier reports, we show that Fe (instead of Pt) segregates towards the particle surface during annealing and forms a Fe-rich FeOx outer shell over the alloy core. By combining both exsitu and insitu approaches to probe the interplay between ordering and surface-segregation phenomena, we illustrate that the surface segregation of Fe precedes the ordering process and affects the ordered phase evolution dramatically. We show that the ordering initiates preferably at the pre-existent Fe-rich shell than the particle core. While the material-specific findings from this study open interesting perspectives towards a controlled phase evolution of Pt-Fe nanoalloys, the characterization methodologies described are general and should prove useful to probing a wide-range of nanomaterials. Surface-segregation vs atomic-ordering: By using atomic-resolution imaging and electron energy loss spectroscopy and employing both exsitu and insitu approaches, an ongoing interplay between segregation and ordering during the thermal annealing of Pt - Fe alloy nanoparticles is studied. Findings reveal a surface segregation of Fe that is in contrast to earlier reports suggesting Pt surface segregation.