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Nearly dislocation-free semipolar AlGaN templates are achieved on c-plane sapphire substrate through controlled nanowire coalescence by selective-area epitaxy. The coalesced Mg-doped AlGaN layers exhibit superior charge-carrier-transport properties. Semipolar-AlGaN ultraviolet light-emitting diodes demonstrate excellent performance. This work establishes the use of engineered nanowire structures as a viable architecture to achieve large-area, dislocation-free planar photonic and electronic devices.

International audience; The segregation of solutes to austenite/ferrite transformation interfaces during decarburization/denitriding of Fe-Mn-C, Fe-Mn-N, and Fe-Si-C ternary alloys was studied by using atom probe tomography. Manganese was found to segregate noticeably to the transformation interface in the presence of carbon, while no segregation could be detected in the presence of nitrogen. This result might indicate that manganese interacts little with the interface itself and that its interaction with the interstitial controls its segregation behavior. In the case of Fe-Si-C, the experiments were complicated by interface motion during quenching. Preliminary results suggest that silicon was depleted at the interface in contrast to the commonly observed segregation behavior of silicon at grain boundaries of ferrite and austenite. This observation could be explained by taking into account the repulsive interaction between silicon and carbon along with the intense segregation of carbon to the interface. This would lead to a net repulsive interaction of silicon with the interface even when considering the intrinsic tendency of silicon to segregate to the boundary in the absence of carbon. The results presented here emphasize the need to account for the interaction of all solutes present at the interface in ferrite growth models.

Pulsed laser deposition (PLD) was used to prepare substitutionaly disordered Pt3Sc. Deposition was performed by using a crossed-beam PLD setup and the laser intensity on the Pt and Sc targets was adjusted to reach the desired composition (Pt:Sc 3:1). Deposition was performed in vacuum, 133 Pa He and 133 Pa Ar, on both Cu and Si substrates. It was shown that a homogeneous and substitutionaly disordered Pt3Sc alloy is formed when deposition is performed in vacuum and 133 Pa Ar on a Cu substrate. Alternatively, a non-homogeneous and multilayered deposit is formed when deposition is performed in vacuum on a Si substrate. This is believed to arise as a consequence of re-sputtering (and decomposition) of the native silicon oxide when highly energetic ablated species impinge on the substrate. The kinetic energy of the ablated species is reduced by increasing the pressure of Ar in the deposition chamber, yielding to an increased stability of the native silicon oxide layer and the formation of a porous deposit made of substitutionaly disordered Pt3Sc. The same phenomenon is observed when deposition is performed on a Ti substrate.

The C 1s inner shell excitation spectra of individual metallic and semiconducting single-walled carbon nanotubes (SWCNTs) were measured using high-resolution electron energy loss spectroscopy in an aberration-corrected transmission electron microscope (TEM-EELS). On the basis of its diameter, the metallic SWCNT is most likely a (10,10) sample, whereas (11,12) and a number of other chiral vectors are consistent with the diameter of the semiconducting SWCNTs. The C 1s X-ray absorption spectra of the same electronically pure SWCNT materials were measured as individual bundles or agglomerations of bundles by scanning transmission X-ray microscopy. Spectral differences in the C 1s → π* transitions of metallic and semiconducting species, related to differences in the van Hove singularities in their unoccupied states, are observed by both methods. The fine structure of the C 1s → π* transitions is similar to that recently reported from nonspatially resolved X-ray absorption spectroscopy of ensemble samples of high-purity metallic and semiconducting SWCNTs. The quality of the TEM-EELS spectra of individual SWCNTs is such that the line shape can be used to identify if they are metallic or semiconducting, thereby opening up the possibility to interrogate the electronic state of single-SWCNT devices. A strong X-ray linear dichroism in the C 1s → π* band of both types of SWCNTs was observed.

We examined the formation of the ternary complex hydride phase Mg2FeH6 during the thermal hydrogen absorption of a ball-milled powder mixture of MgH2 and Fe. Analytical measurements, scanning trans...

A simple and accessible method of probing the nature of bonding on the very surface of a material is reported, using transmission electron microscopy: the technologically important compound strontium titanate is examined as an example. This paper reports a simple and accessible method of probing the nature of bonding on the very surface of a material, using technologically important strontium titanate as an example. The authors generated a wedge-shaped sample, so that the thickness of the sample decreases as a transmission electron microscope tracks across it collecting spectroscopic information. In this way, the contribution of the signal from the bulk material decreases and that from the surface increases. The relative weights of the surface and bulk signals can be estimated from a series of spectral acquisitions, allowing the surface component of the data to be extracted. The determination of the atomic structure and the retrieval of information about reconstruction and bonding of metal oxide surfaces is challenging owing to the highly defective structure and insulating properties of these surfaces. Transmission electron microscopy (TEM) offers extremely high spatial resolution (less than one angstrom) and the ability to provide systematic information from both real and reciprocal space. However, very few TEM studies1,2,3 have been carried out on surfaces because the information from the bulk dominates the very weak signals originating from surfaces. Here we report an experimental approach to extract surface information effectively from a thickness series of electron energy-loss spectra containing different weights of surface signals, using a wedge-shaped sample. Using the (001) surface of the technologically important compound strontium titanate, SrTiO3 (refs 4, 5, 6), as a model system for validation, our method shows that surface spectra are sensitive to the atomic reconstruction and indicate bonding and crystal-field changes surrounding the surface Ti cations. Very good agreement can be achieved between the experimental surface spectra and crystal-field multiplet calculations based on the proposed atomic surface structure optimized by density functional calculations3. The distorted TiO6−x units indicated by the proposed model can be viewed directly in our high-resolution scanning TEM images. We suggest that this approach be used as a general method to extract valuable spectroscopic information from surface atoms in parallel with high-resolution images in TEM.

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.

We have synthesized and investigated the anisotropic growth of interesting silver nanorice. Its growth is kinetically controlled at 100 degrees C, and both oriented attachment and Ostwald ripening are involved, with the former growth mode dominating the anisotropic growth of the nanorice along the direction. This one-directional growth is initiated by an indispensable seed-selection process, in which oxygen plays a critical role in oxidatively etching twinned silver crystals. The inhibition of this process by removing oxygen essentially blocks the nanorice growth. Although increasing reaction temperature to 120 degrees C accelerates the one-dimensional growth along the direction, further temperature increase to 160 degrees C makes the oriented attachment dominated one-directional growth disappear; instead, the diffusion-controlled two-dimensional growth leads to the emergence of highly faceted truncated triangular and hexagonal plates mainly bound by low energy faces of {111}. Interestingly, we also found that the longitudinal surface plasmon resonance of the nanorice structures is highly sensitive to the refractive index of surrounding dielectric media, which predicts their promising applications as chemical or biological sensors. Moreover, the multipolar plasmonic resonances in these individual nanorice structures are visualized in real space, using high-resolution electron energy-loss spectroscopy. (Less)

The composition and structure of the surface film formed on pure Mg exposed at the corrosion potential in pure water for 48 h was investigated using a FIB cross-section and STEM–EDS. The surface film formed is duplex in nature, consisting of a thinner, more-porous, nano-crystalline MgO-rich inner layer, and a thicker, less-porous Mg(OH) 2 -rich outer platelet layer. The results are consistent with the theory that a chemical breakdown (hydration) of the bulk inner MgO layer (native oxide) is a necessary precursor step to the corrosion process that leads to the significant thickening of the partially protective outer Mg(OH) 2 layer.

1 Institute of Chemical Engineering and High Temperature Chemical Processes-Patras, FORTH, 26500 Patras, Greece 2 Institute of Food Technology, Faculty of Agriculture, University of Belgrade, 11080 Belgrade, Serbia 3 Institute of Theoretical Chemistry, Ulm University, 89081 Ulm, Germany 4Department of Material Science and Engineering and Canadian Centre for Electron Microscopy, McMaster University, Hamilton ON, Canada L8S4M1

Momentum resolved electron energy loss (EELS) spectra of multi-walled carbon nanotubes (MWCNT) have been measured at the C 1s edge in a transmission electron microscope (TEM). We demonstrate that structurally sensitive electron linear dichroic (ELD) signals analogous to X-ray linear dichroic (XLD) signals (Najafi et al., 2008) [17] can be measured by TEM-EELS from individual MWCNT if sample tilt and deflection of the inelastic scattering signal relative to the EELS spectrometer entrance aperture are used. This method is used to map defects in MWCNT at higher spatial resolution than is currently possible with X-ray microscopy.

We created a bimetallic chromium vanadium hydrogen sorption catalyst for magnesium hydride (MgH 2). The catalyst allows for significant room-temperature hydrogen uptake, over 10 cycles, at absorption pressures as low as 2 bar. This is something that has never been previously achieved. The catalyst also allowed for ultrarapid and kinetically stable hydrogenation cycling (over 225 cycles) at 200 and at 300 °C. Transmission electron microscopy analysis of the postcycled samples revealed a nanoscale dispersion of Cr-V nanocrystallites within the Mg or MgH 2 matrix. TEM analysis of the partially absorbed specimens revealed that even at a high absorption pressure, that is, a high driving force, relatively few hydride nuclei are formed at the surface of the pre-existing magnesium, ruling out the presence of any contracting volume (also termed contracting envelope or core shell) type growth. HRTEM of the cycled and desorbed powder sample demonstrated that the bcc Cr-V phase is crystalline and nanoscale. We experimentally demonstrated that the activation energy for hydrogen absorption is not constant but rather evolves with the driving force. This finding sheds new insight regarding the origins of the wide discrepancy in the literature - reported values of the hydrogenation activation energy in magnesium hydride and in related metal hydride systems. © 2011 American Chemical Society.

Nanocrystalline metals are often produced in a state of stress which can adversely affect certain properties, e.g. corrosion resistance, wear, fatigue strength, etc. This stress is referred to as internal or “intrinsic” stress since it is not directly caused by applied loads. The structural causes of these stresses in nanocrystalline materials are not fully understood and are therefore an area of particular interest. The internal stresses of nanocrystalline Ni and Ni-16wt%Fe were measured and found to increase with the addition of iron. Characterization using HR-TEM revealed no signs of porosity, second phase particles, or a high density of dislocations. Both materials possessed well defined high-angle grain boundaries. The main structural difference between the two materials was found to be grain size and correspondingly, a decrease in grain size resulted in an increase in internal stress which supports the applicability of the coalescence theory. The current study also provides evidence to rule out the effect of voids (or porosity), dislocations, and second phases as possible causes of internal stress.

In this work we investigate methods of statistical processing and background fitting of atomic resolution electron energy loss spectrum image (SI) data. Application of principal component analysis to SI data has been analyzed in terms of the spectral signal-to-noise ratio (SNR) and was found to improve both the spectral SNR and its standard deviation over the SI, though only the latter was found to improve significantly and consistently across all data sets analyzed. The influence of the number of principal components used in the reconstructed data set on the SNR and resultant elemental maps has been analyzed and the experimental results are compared to theoretical calculations.

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.

A novel PtRu catalyst consisting of a Ru-rich core and a Pt-rich shell was synthesized using a two-step microwave irradiation technique. The synthesized PtRu/C catalysts were characterized by X-ray diffraction (XRD), extended X-ray absorption finestructure (EXAFS), transmission electron microscopy (TEM) as well as energy dispersive X-ray spectrometry (EDXS). The produced PtRu/C catalysts showed identical crystalline structure and diffraction peaks to Pt itself, but with negligible higher 2 shift degrees, indicating the formation of a specific composite structure rather than alloy formation. This novel structure of PtRu/C catalyst was also further verified via X-ray absorption spectroscopy. The particle size of PtRu catalysts identified by TEM was less than 5 nm. In order to investigate the CO tolerance in the hydrogen oxidation reaction (HOR), H2 streams with six different concentrations of CO (0, 10, 50, 100, 300, and 500 ppm) were used. The electrocatalytic activity thus obtained was not only better than that of Pt/C catalyst in HOR, but also showed a better CO tolerance in various CO concentrations.

This paper presents results on the synthesis of Cu–Pd alloy thin films on Ti substrates by co-electrodeposition of Pd and Cu from nitrate-base electrolytic baths. The deposition rates of Cu and Pd were determined by Electrochemical Quartz Crystal Microbalance as a function of the electrode potential and Cu +2 and Pd +2 concentrations. It is shown that electrodeposition of copper and palladium occurs simultaneously at −0.50 V vs. SCE and that Cu–Pd thin films over the entire composition range were obtained by changing the composition of the solution. X-ray diffraction analyses indicated that these films have a nanocrystalline single-phase face-centered cubic structure and scanning electron microscopy analyses showed that potentiostatically deposited films are rough and porous, which is appropriate for electrocatalysis applications. In an attempt to get denser deposits as required for H 2 purification applications, pulsed potential co-electrodeposition was performed and the effect of the deposition conditions on the roughness of the films was assessed by double layer capacitance measurements. It was shown that smooth Cu–Pd films (with R f value as low as 8, as opposed to more than 120 for films prepared in the potentiostatic mode) could be obtained with a proper choice on the deposition conditions.

New metastable olivine phases of sodium metal phosphates, Na[Mn1–xMx]PO4 (M = Fe, Ca, Mg), nanorods are synthesized by a simple solid-state reaction at low temperature (≤100 °C) by means of a topotactic molten salt reaction that converts NH4[Mn1–xMx]PO4•H2O (M = Fe, Ca, Mg) to Na[Mn1–xMx]PO4. Their crystal structures are characterized via XRD Rietveld refinement and electron diffraction. A full range of solid solution behavior was observed for olivine Na1–xMn0.5Fe0.5PO4, in contrast to that of LiMPO4 (M = Fe, Mn) olivine materials, and is ascribed to ion size effects. The solid solution behavior of NaMn0.5Fe0.5PO4 was confirmed by electrochemical characterization.

Full-color, catalyst-free InGaN/GaN dot-in-a-wire light-emitting diodes (LEDs) were monolithically grown on Si(111) by molecular beam epitaxy, with the emission characteristics controlled by the dot properties in a single epitaxial growth step. With the use of p-type modulation doping in the dot-in-a-wire heterostructures, we have demonstrated the most efficient phosphor-free white LEDs ever reported, which exhibit an internal quantum efficiency of ∼56.8%, nearly unaltered CIE chromaticity coordinates with increasing injection current, and virtually zero efficiency droop at current densities up to ∼640 A/cm(2). The remarkable performance is attributed to the superior three-dimensional carrier confinement provided by the electronically coupled dot-in-a-wire heterostructures, the nearly defect- and strain-free GaN nanowires, and the significantly enhanced hole transport due to the p-type modulation doping.

Integration of multiple materials in a controllably programmed manner on the nanoscale has led to the evolution of the next generation of nanoparticles. We have explored the formation of bifunctional europium sulfide − cadmium chalcogenide composite nanostructures, as both of the semiconductor materials exhibit intriguing physical characteristics, suggesting that architectural tunability of these hybrid structures could have interesting effects on their collective properties. A two step synthetic procedure has been devised, where CdSe or CdS nanorods were used as a platform for the growth of the secondary material domains. An eight-coordinate lanthanide based single-source precursor, Eu(Ddtc)3(Bipy), was implemented as the material source for the selective growth of spherical EuS nanocrystals on the tips of cadmium chalcogenide nanorods. The composition and structure of these hybrid particles have been analyzed by high-resolution TEM. The nanoheterostrucutre has a type III, or broken band alignment, which...

Multi-layer InAs quantum wires were grown on, and embedded in In0.53Ga0.47−xAlxAs (with x=0, 0.1, 0.3 and 0.48) barrier/spacer layers lattice matched to an InP substrate. Correlated stacking of the quantum wire arrays were observed with aluminum content of 0 and 0.1. The quantum wire stacks became anti-correlated as the aluminum content was increased to 0.3 and 0.48. The origin of such stacking pattern variation was investigated by finite element calculations of the chemical potential distribution for indium on the growth front surface of the capping spacer layer. It is shown that the stacking pattern transition is determined by the combined effect of strain and surface morphology on the growth front of the spacer layers.

Mo 3 Sb 7− x Te x was earlier reported to be a promising p -type thermoelectric material for high temperature applications, with Ni 0.06 Mo 3 Sb 5.4 Te 1.6 achieving a ZT of 0.93 at 1023 K. In order to investigate the effect of using different transition metal atoms and to further improve the thermoelectric properties, a variety of transition metal atoms (Mn, Fe, Co and Ni) were intercalated into the voids of empty Sb atom cubes. Our results indicate that Fe 0.05 Mo 3 Sb 5.4 Te 1.6 and Ni 0.05 Mo 3 Sb 5.4 Te 1.6 exhibit a higher power factor than Mo 3 Sb 5.4 Te 1.6 . Fe 0.05 Mo 3 Sb 5.4 Te 1.6 demonstrates the highest ZT value at 673 K ( ZT = 0.31), significantly higher than Mo 3 Sb 5.4 Te 1.6 . Thermal analysis proves Ni 0.05 Mo 3 Sb 5.4 Te 1.6 to be phase stable at least until 1250 K in an inert atmosphere, an important prerequisite for high temperature applications.

The great interest of shifting towards biodiesel from vegetable oils or waste fats results in a tremendous increase of glycerol production as an inevitable by-product. This waste sparked the need for glycerol valorization to justify biodiesel as alternative for diesel from petroleum. Our research efforts are to partially electro-oxidize glycerol into value-added chemicals in order to make biodiesel production more environmentally benign with added financial benefits. The primary objective of this project is the identification of an active and stable electro-catalyst that can affect the selective electrooxidation of glycerol to value-added products without C-C-C bond cleavage leads to the formation of a large number of high value-added chemicals [1]. The control of catalyst selectivity and activity could be achieved through formulation of novel, nanostructured electrocatalysts [2]. Nickel is an attractive material for glycerol electrooxidation in alkaline media [3, 4], due to its natural abundance and good stability in alkaline media. Designing nanostructured 3D Ni electrodes could enhance the catalytic activity of Ni, whereas its selectivity could be altered by addition of small amounts of the second metal [5]. Monometallic Ni nanoparticles were synthesized using modified polyol method. Change of NaOH concentration resulted in the variation of Ni nanoparticles (NPs) shape: triangular NiNPs were synthesized at lower concentrations while Ni NPs of urchin-like structure were fabricated at higher NaOH concentration. Bi-metallic NixPdx-1 (x=95,90 and 80 at.%) were also synthesized by hydrazine reduction in the presence of ethylene glycol. The synthesised nanoparticles were characterized by XRD, SEM, TEM, EDS mapping and HAADF imaging. In this work, electro-oxidation of glycerol reaction (GEOR) is investigated in detail on mono- and bimetallic Ni nanoparticles in alkaline medium. In order to better understand the role of the nickel surface on GEOR, electrochemical measurements have been carried out on synthesized unsupported nickel nanoparticles using different electrochemical tests such as cyclic voltammetry (CV), chronoamperometry (CA) and linear sweep voltammetry (LSV). Results indicated that the Ni was able to catalyze the GEOR at the NiOOH surface, well known as the active species. Ni80Pd20 displays the highest activity toward glycerol electro-oxidation. Chronoamperommetry coupled with in-situ polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) for the simultaneous analysis of products on the Ni surface and in the bulk solution showed that the main reaction products on Ni surface are glyceraldehyde, carbonyl, carboxylate ions and some carbon dioxide. The correlation of electrocatalytic activity and selectivity with nanoparticle shape, size, surface and bulk composition, as well as structure of Ni-based nanoparticles will be discussed in terms of mass activities and product distribution during GEOR. References Behr, J. Eilting, K. Irawadi, J. Leschinski, F. Lindner, Green Chemistry 10 (2008) 13. M. Simoes, S. Baranton, C. Coutanceau, Applied Catalysis B: Environmental110 (2011) 40. M.S.E. Houache, E. Cossar, S. Ntais, E.A. Baranova, J. Power Sources 375 (2018) 310. V.L. Oliveira, C. Morais, K. Servat, T.W. Napporn, G. Tremiliosi-Filho, K.B. Kokoh, Electrochim.Acta. 117 (2014) 255. M. Simoes, S. Baranton, C. Coutanceau, ChemSusChem 5 (2012) 2106.

Atomic resolved elemental mapping is demonstrated at 80 keV with an aberration-corrected scanning transmission electron microscope on specimens of SrTiO 3 and BaTiO 3 /SrTiO 3 . The maps were acquired with acquisition times as short as 30 ms per pixel (limited by the spectrometer speed), and show very high signal-to-noise ratio and very good detection limits. The features in the elemental maps are interpreted with the help of elastic–inelastic multislice calculations, which show good agreement with experimental images. The elemental maps of Ti, Sr and Ba and their contrast at the interface between BaTiO 3 and SrTiO 3 are discussed, following a comparison with calculations, assuming an atomically sharp interface. The features in the energy-filtered maps and the background intensities, and the influence of the energy position of the integration windows are discussed in terms of the origins of the signals and the features with respect to the details shown in the high-angle annular dark-field images. The benefits of elemental mapping at 80 keV as compared to 200 keV are also discussed in terms of electron beam damage. Finally, applications of elemental mapping to the detection of La atoms in solid solution in Ba 3.25 La 0.75 Ti 3 O 12 films are also shown.

The Ti oxidation state of a series mixed-valence BaTi1−xNbxO3 compound (where x=0.002, 0.004, 0.02, 0.10, 0.20 and 0.50) is investigated using high resolution electron energy loss spectroscopy (EELS). The energy loss near edge structure (ELNES) of the Ti-L2,3 and O-K edges was recorded with high energy resolution. The fraction of Ti4+ and Ti3+ components is determined in each compound by linear profile fitting with Ti4+ and Ti3+ standard spectra obtained from reference compounds within the series. The fitting results indicate an increase in the fraction of the Ti3+ component as the Nb content increases. A deviation from the expected Ti3+ valence fraction based on the charge balance across the series was detected and discussed. By considering all detailed features on the spectra obtained with high energy resolution, this linear fitting method can be used to determine the oxidation state of transition metal oxides, especially for the early transition metals where conventional methods based on the L2,3 edge ratio have shown to fail. The potential of this method to provide insight to mixed valence systems, vacancies and properties of oxides is discussed.

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.

We have discovered two novel types of planar defects that appear in heteroepitaxial YBa2Cu3O7-delta(YBCO123) thin films, grown by pulsed-laser deposition (PLD) either with or without a La2/3Ca1/3MnO3 (LCMO) overlayer, using the combination of highangle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging and electron energy loss spectroscopy (EELS) mapping for unambiguous identification. These planar lattice defects are based on the intergrowth of either a BaO plane between two CuO chains or multiple Y-O layers between two CuO2 planes, resulting in non-stoichiometric layer sequences that could directly impact the high-Tc superconductivity. (C) 2018 Author(s).

The environmental stability of the layered semiconductor black phosphorus (bP) remains a challenge. Passivation of the bP surface with phosphorus oxide, POx, grown by a reactive ion etch with oxygen plasma is known to improve photoluminescence efficiency of exfoliated bP flakes. We apply phosphorus oxide passivation in the fabrication of bP field effect transistors using a gate stack consisting of a POx layer grown by reactive ion etching followed by atomic layer deposition of Al2O3. We observe room temperature top-gate mobilities of 115 cm2 V−1 s−1 in ambient conditions, which we attribute to the low defect density of the bP/POx interface.

CO2 conversion methods to remediate anthropogenic emissions appear promising, as they offer the potential to produce liquid and gaseous fuels for use either in the aeronautics industry, or as a chemical storage method for intermittent energy produced by windmills and photovoltaic panels. Fuel synthesis may be achieved via either the production of a syngas mixture (H2 and CO) through the water gas shift reaction and subsequent conversion into hydrocarbon fuel, or by direct electrochemical reduction of CO2. Direct electrochemical conversion of CO2 into value-added products is a low-temperature process, with the advantage of requiring relatively simple equipment. Formic acid, or formate salts, are used in a variety of chemical processes such as electrowinning, leather tanning, and aircraft de-icing. Alternatively, formic acid and formate salts may be considered as a hydrogen storage medium. On top of that, direct formic acid, and more recently direct formate, fuel cells, have been investigated as they demonstrate significant benefits over methanol fuel cells, including higher open circuit voltage and lower crossover. Pb and Bi are promising catalysts with good selectivity for formate. In the case of lead, it can be prepared in the form of dendrites with nanometre-sized tips. Local high electric fields can exist at the tip of these dendrites that can induce a concentration of electrolytes which in turn leads to improve electroreduction of CO2 [[1]]. Bismuth is non-toxic and has negligible environmental impact. It has few commercial applications, and its price has been low and relatively stable in recent years. In this work, we studied the activity and stability for CO2 electroreduction onto high surface area metallic Pb films. The latter Pb films were further functionalized by Bi overlayers to enhance CO2 reduction properties. For both materials, the material films were prepared through a potentiostatic method. Both types of films were extensively characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM) and x-ray diffraction (XRD), while electrochemical activities were characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and potentiostatic measurements. [1] M. Fang, S. Garbarino, G.A. Botton, A.C. Tavares and D. Guay, J. Mater. Chem A 5 (2017) 20747-20756

A conjugated tertiary amine-functionalized polymer, poly(9,9-bis(diethylaminopropyl)-2,7-fluorene-co-1,4-phenylene), was synthesized and employed in the supramolecular functionalization of single-walled carbon nanotubes. The formation of stable solutions in organic solvents, as well as in water upon protonation of the amine groups, indicates strong supramolecular interactions between the polymers and the carbon nanotube surface. UV−vis absorption spectroscopy and Raman spectroscopy were utilized to characterize the resulting functionalized nanotubes and it was found that the nanotube structure was unchanged due to the nature of noncovalent functionalization, thus preserving the nanotube’s inherent properties. Electrophoretic deposition techniques were developed to create uniform films of this polymer and also a mixture of the polymer with the supramolecularly functionalized carbon nanotubes. The deposition mechanism involves the electrophoresis of the charged polymer species in an acid solution followed b...

Arrays of well aligned Ru nanowires and nanotubes were prepared by electrodeposition through porous anodic aluminum oxide membranes. It is shown that Ru nanowires are formed at low cathodic deposition overpotential, while nanotubes are prepared at higher cathodic overpotential. The inner diameter of the nanotube can be controlled by the deposition potential, and it varies from 0 to 70% of the outer diameter as the deposition potential is changed from -0.30 to -0.45 V vs SCE.

Deep levels in lattice-matched undoped and Si-doped InAlN/GaN grown by plasma-assisted molecular beam epitaxy have been identified and characterized by capacitance and photocapacitance measurements. From x-ray diffraction, reflectance measurements, electron energy loss spectroscopy and high-resolution transmission electron microscopy it is evident that the material has two distinct phases with different compositions. These correspond to In compositions of 18.1% and 25.8%, with corresponding bandgaps of 4.6 eV and 4.1 eV, respectively. The lower bandgap material is present as columnar microstructures in the form of quantum wires. A dominant electron trap with an activation energy of 0.293 ± 0.01 eV, a small capture cross-section of (1.54 ± 0.25) × 10−18 cm2, and density increasing linearly with Si doping density is identified in all the samples. The characteristics of the electron trap and variation of diode capacitance are discussed in the context of carrier dynamics involving the dominant trap level and the quantum wires.

Shape- and size-controlled supported metal and intermetallic nanocrystallites are of increasing interest because of their catalytic and electrocatalytic properties. In particular, intermetallics PtX (X 5 Bi, Pb, Pd, Ru) are very attractive because of their high activity as fuel-cell anode catalysts for formic acid or methanol oxidation. These are normally synthesized using high-temperature techniques, but rigorous size control is very challenging. Even low-temperature techniques typically produce nanoparticles with dimensions much greater than the optimum

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

Bulk irradiation of crystalline α-quartz was performed with ∼170-fs laser pulses with a wavelength of 800 nm focused below the sample surface. Investigations were carried out using transmission electron microscopy on a cross-sectional specimen prepared using focused ion beam techniques. We observed alternating amorphous–crystalline structures with sharp transitions and associated density changes, surrounded by a highly strained crystalline structure. The alternating sub-surface structures are parallel to the laser’s electric field polarization and exhibit a spacing which is close to the laser wavelength in air. Cracking was also observed in the near proximity of these structures.

Irradiation of Si(1 0 0), Si(1 1 1), Si(1 1 0), Ge(1 0 0), and Ge(1 1 1) is compared for 150 fs, 800 nm wavelength pulses in a rough vacuum atmosphere. The surface crystalline orientation of the material is found to affect the final morphology, with (1 1 1)- and (1 1 0)-surface orientations exhibiting a much higher tendency for conical structure formation under multiple-pulse irradiation. Using cross-sectional transmission electron microscopy, the structures on Si(1 1 1) are found to have primarily crystalline cores with the same crystalline orientation as the substrate. The results show that the crystalline orientation of the target should be considered in laser machining applications.

The (100) surface of MgAl2O4 is evaluated as a substrate for the thin film deposition of the relaxor ferroelectric PbMg1/3Nb2/3O3(65%)–PbTiO3(35%). With a lattice mismatch of less than 0.5%, this film-substrate combination presents a geometrical template for growth that is far superior to that formed with other commercially available oxide substrates. Films were deposited using the pulsed laser deposition technique and were characterized in terms of their crystallographic, microstructural, and dielectric properties. From a crystallographic perspective the films show excellent cube-on-cube epitaxy, are highly oriented, and show no evidence of the frequently observed parasitic pyrochlore phase. With the exception of a few faceted surface structures, the film’s microstructure is single-crystal-like, exhibiting a sharp film-substrate interface, a smooth top surface, and no discernable granularity. The dielectric response shows the frequency-dependent diffuse phase transition characteristic of a relaxor material, but with less frequency dispersion and a smaller maximum in the dielectric constant. Taken together, the results suggest that the (100) MgAl2O4 substrate could prove to be an effective substrate material, not only for the PbMg1/3Nb2/3O3(65%)–PbTiO3(35%) system, but also for a number of other important lattice-matched ferroelectric, relaxor, and ferroelectric superlattice systems.

Surface-initiated atom transfer radical polymerization (si-ATRP) technique was successfully employed to modify Ni nanoparticles with polymer shells. ATRP initiators were covalently bonded onto Ni nanoparticle surfaces by a combination of ligand exchange and condensation reactions. Various kinds of polymers including poly(methyl methacrylate) (PMMA) and poly( n -isopropylacrylamide) (PNIPAM) were grafted from the immobilized initiators. The grated polymer shells gave Ni nanoparticles exceptionally good dispersion and stability in solvents. Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and transmission electron spectroscopy (TEM) were employed to confirm the grafting and to characterize the nanoparticle core–shell structure. Gel permeation chromatography (GPC) studies of cleaved polymer chains revealed that the grafting polymerization was well controlled. The magnetic properties of Ni- g -polymer nanoparticles were also studied.

The multiferroic behavior of epitaxial γ-Fe 2 O 3 ―BiFeO 3 (composite)/Bi 3.25 La 0.75 Ti 3 O 12 bi-layered heterostructures grown on SrRuO 3 /SrTiO 3 (111) substrates has been studied using piezoresponse force microscopy, magnetic force microscopy and magnetometry. The ferroelectric domain structure is ascribed to the BiFe0 3 phase while the magnetism originates in the γ-Fe 2 O 3 phase of the composite layer. Our studies demonstrate the presence and switching of magnetic and ferroelectric domains within the same area of the sample. This confirms the presence of multiferroic behavior at the nanoscale in our γ-Fe 2 O 3 ―BiFeO 3 nanocomposite thin films.

Epitaxial (0 0 1)-oriented films of the metallic oxide (Ba 1− y Sr y )Ti 0.5 Nb 0.5 O 3 , with y =0, 0.4, 0.5 and 0.6, are deposited onto (0 0 1) MgAl 2 O 4 substrates using the pulsed laser deposition technique. The strontium for barium substitution gives rise to a decrease in the lattice constant, without altering the conductivity of the film. X-ray diffraction measurements show a significant number of [1 1 1], [0 1 1] and [2 2 1] misoriented grains that are not present for the y =0.6 composition. Transmission electron microscopy images of the film–substrate interface obtained for the y =0.6 composition show a sharp interface with flawless epitaxy. We attribute the improvements to a decrease in the lattice misfit strain made possible through the superior lattice match to the substrate obtained through strontium substitution.

Palladium nanoparticles (Pd-NPs) were prepared by a single-phase reduction of palladium acetate in the presence of different organic thiol ligands. Sizes, size distributions and crystallinity of the Pd-NPs were determined by high resolution transmission electron microscopy (HR-TEM) and powder X-ray diffraction (XRD) while thermogravimetric analysis coupled with mass spectroscopy (TGA-MS) was employed to measure their organic ligand to palladium ratios and to quantify contaminants. No systematic effect of the different ligands on the size and purity of the Pd-NPs was observed but 1st-generation Frechet dendron thiols had an about 4 times larger foot-print at the surface of the NPs than the other thiol ligands.

We report on a theoretical and experimental investigation of Au–Pt nanoparticles (NPs). The Au–Pt miscibility gap is theoretically reevaluated for NPs of various sizes. The model includes a composition-dependent surface energy evaluated by considering surface segregation. Using precise quantitative energy-dispersive X-ray spectroscopy (EDXS) and high-resolution electron microscopy (HREM), the structural evolution of ∼20 nm Au(core)–Pt(shell) NPs upon annealing at various temperatures (300–800 °C) is studied. At low temperatures, only interdiffusion occurs between the core and the shell, while above ∼600 °C, the NPs evolve into Au- and Pt-rich crystals, separated by an interface. At these temperatures, the Au solubility in the Pt-rich phase is found to be 5–10% higher than the bulk phase diagram and agrees qualitatively with the theoretical model. Based on the EDXS and HREM results, the nature of the interface separating the Au- and Pt-rich phases within a NP is discussed and an estimate of its energy is obtained.

The interaction between single-walled carbon nanotubes and two anionic conjugated polyelectrolytes, poly[2,5-bis(3-sulfonatopropoxy)-1,4-phenylene-alt-1,4-phenylene) sodium salt and poly[2,5-bis(3-sulfonatopropoxy)-1,4-ethynylphenylene-alt-1,4-ethynylphenylene] sodium salt, was investigated. It was found that the supramolecular polymer−nanotube assembly occurred efficiently and produced stable complexes that could be purified from excess free polymer in solution. These complexes were characterized using absorption spectroscopy, fluorescence spectroscopy, Raman spectroscopy, and electron microscopy. It was further found that patterning of these polymer−nanotube complexes could be accomplished by utilizing electrostatic attraction with a prepatterned, cationically charged surface. Patterned features were found to be electrically conducting with a measured sheet resistance value of 0.68 ± 0.01 MΩ for features having a thickness on the order of several nanometers.

This paper reports on the TEM characterization of the surface oxide layer forming on Co nanocrystals (NCs) prepared using a standard method [Puntes, V.F., Krishnan, K.M., Alivisatos, P., 2001. Synthesis, self-assembly, and magnetic behavior of a two-dimensional superlattice of single-crystal epsilon-Co nanoparticles. Appl. Phys. Lett. 78 (15), 2187-2189]. Complementary transmission electron microscopy (TEM)-related techniques presented direct evidence of a 1.5-3nm CoO shell forming on epsilon-Co NCs. The crystalline structure of the Co NCs was confirmed by selected area diffraction study while the nature of the shell was probed by energy-loss near-edge spectroscopy and energy-filtered TEM. Based on these results, we comment on the detection of nanoscale feature with energy-filtered imaging.

In the last 20 years, synchrotron-based soft X-ray microscopy has emerged as a powerful technique for chemical microanalysis. By efficiently measuring near-edge X-ray absorption spectroscopy (NEXAFS) at high spatial resolution, it produces information analogous to that delivered by electron energy loss spectroscopy in a transmission electron microscope (TEM-EELS). NEXAFS microscopy has significant advantages for studies of soft matter, which is typically a challenge for TEM-EELS due to radiation damage. It provides unique capabilities for studying wet samples. Here, we describe current state-of-the-art soft X-ray microscopy instrumentation and techniques (including the recently commissioned spectromicroscopy facility at the Canadian Light Source in Saskatoon), provide brief descriptions of a few recent applications, and make explicit comparisons of the strengths and limitations of NEXAFS microscopy - in particular, scanning transmission X-ray microscopy (STXM) - relative to TEM-EELS for spatially resolved materials analysis by inner shell spectroscopy.

The room temperature cation valency distribution in the single-phase cubic spinel Cu 1.2 Mn 1.8 O 4 was extracted using EELS. Analysis of the Cu and Mn L 2,3 core-loss edges revealed that all Cu was present as Cu 2+ and that a multi-valent Mn ground state existed with the valence fractions: 55% Mn 4+ , 37% Mn 3+ and 8% Mn 2+ . The pre-peak of the ELNES on the O–K edge confirmed the dominant Mn 4+ component whilst the features in the ELNES are identical to those observed in other spinel compounds.

We present the results of 800 and 400 nm wavelength, femtosecond laser pulse irradiation of a sample consisting of a metal film on thermally-grown oxide on silicon. On selected sites, cross-sectional transmission electron microscopy was performed to provide information on sub-surface changes not observable with surface scanning electron microscopy. A range of pulse energies in single-pulse irradiation exists for which the metal film was removed but the oxide was not appreciably thinned. For a sufficiently high pulse energy within this range, substantial defects were observed in the underlying silicon. Five infrared pulses of a relatively high fluence created significant defects, as well as producing polycrystalline material on top of the original oxide and metal. We discuss various factors which may play a role in the formation of the observed features.