High Resolution Transmission Electron Microscopy

Coal fires typically have a variety of mineral and organic deposits associated with the venting emission gases. In addition to the tars typically found at the Ruth Mullins coal fire, Perry County, Kentucky, a sooty carbon, superficially similar to a carbon from a university-based stoker-fired power plant, was sampled in an August 2010 visit. Carbons in the soot include complex carbon particles, nanotubes encapsulating Hg, onionlike structures with polyhedral and quasi-spherical morphology with hollow centers, and metal-bearing multiwalled nanotubes. Mineral sublimates from the Ruth Mullins fire in abandoned underground and surface mines in the high volatile A bituminous Middle Pennsylvanian Hazard No. 7 coalbed, Perry County, Kentucky, were examined by optical mineralogy, X-ray diffraction (XRD), and high-resolution-transmission electron microscopy (HR-TEM). Optical examination revealed the presence of salammoniac and a fine, unidentified fibrous mineral. XRD also showed the presence of salammoniac, along with trace amounts of quartz, kaolinite, and, possibly, phengite. Both cubic and dendritic salammoniac forms were observed with HR-TEM. Gypsum, jarosite, with cubic pseudomorphs after pyrite, and Fe-minerals, including Cr-bearing hematite in association with jarosite, were observed with HR-TEM. Dehydration of jarosite can lead to the formation of less hydrous Fe-sulfates and hematite. Mineral and amorphous inorganic phases included glassy Al-Si spheres with associated Pb and Se; nanopyrite grains with trace As and Se; nanohematite with V 3+ ; salammoniac; quartz; Cr-and Pb-bearing jarosite; fibrous pickeringite with surficial natrojarosite; and Cd-, Co-, Mo-, Ni, V-, W-, and Zr-bearing nanospheres.

Previous investigations show that soot particle volume fraction and number density were significantly reduced by exhaust gas recirculation (EGR) diluents CO 2 and H 2 O. However, these investigations were often convoluted by their experimental flame configurations and primarily focused on soot volume fraction rather than soot inception. To isolate the effects on soot inception and the corresponding chemistry, the current study measured the reactivity of CO 2 (up to 9.5% volume fraction) for both C 2 H 2 (1.00% volume fraction) and CH 4 (1.85% volume fraction) fuels in homogeneous mixtures. Computed effect of H 2 O on these and other fuels are also presented. Experiments were performed at high temperature (1640 K and 1770 K) and high equivalence ratios (U = 55 and 75) to understand the effect of CO 2 on polycyclic aromatic hydrocarbons (PAH) and formation of nascent soot particles with negligible oxygen influence. Experimental results show that CO 2 enhanced the soot inception rate when added to C 2 H 2 but had an undetectable affect on CH 4. Gas chromatography confirmed that CO 2 increases CO mole fraction and reduces C 2 H 2 fuel concentration. Chemical kinetic simulations showed that the C 2 H 2 was being converted to soot precursors. CO 2 enhanced the soot inception rate for C 2 H 2 by producing OH radicals. Images of nascent soot particles produced in the presence of CO 2 were used to determine the size of PAH molecules in the particles and particle morphology. Both attributes were similar to particles formed without CO 2. CO 2 had little impact on the long reaction pathway from CH 4 to PAH molecules because H and CH 3 radicals propagated these reactions more readily than OH radicals.

In this work, we describe a kinetically controlled crystallization process assisted by an oriented attachment (OA) mechanism based on a nonaqueous sol-gel synthetic method (specifically, the reaction of titanium(IV) chloride (TiCl 4 ) with n-octanol) to prepare re-crystallized anatase TiO 2 mesocrystals (single crystal). The kinetics study revealed a multi-step and hierarchical process controlled by OA, and a high resolution transmission electron microscopy (HRTEM) analysis clearly shows that the synthesized mesocrystal presents a truncated bipyramidal Wulff shape, indicating that its surface is dominated by {101} facets. This shape is developed during the recrystallization step. The material developed here displayed superior photocatalytic activity under visible light irradiation compared to TiO 2 -P25 as a benchmarking.

Preliminary investigations revealed that beryllides like Be 12 Ti may be much more suitable for neutron multipliers in future fusion power plants than pure beryllium. With suitable mechanical alloying and hot pressing methods, beryllium and beryllium-titanium tablets with grain sizes of 5 lm have been produced and analyzed by means of scanning electron microscopy (SEM), X-ray diffractometry, transmission electron microscopy (TEM) and plasma emission spectrometry. The fabricated tablets of Be-7.7 at.%Ti, corresponding to a chemical composition of the Be 12 Ti phase, have been arcmelted in an oxygen-free atmosphere. X-ray diffractometry, scanning and high resolution transmission electron microscopy measurements revealed that the vast majority of the ingots consist of nearly pure Be 12 Ti phase. Nineteen specimens have been fabricated from the ingots and shipped to HFR-Petten for the HIDOBE benchmark irradiation program that started in June 2005 with an aim to achieve 6000 appm He in Be and Be alloys at blanket relevant irradiation temperatures.

Alumina (Al O )-carbon nanotube composite materials were synthesized by spraying a slurry of ferrocene (Fe(C H ) ) 2 3 5 5 2 and alumina in xylene, at 1000650 8C, using argon (#1.5 bar) as carrier gas. The as-prepared materials were formed in large flakes (ca. 2 cm) and consist of nanotubes intricately matted in a glassy alumina matrix. Based on the structural and microstructural investigations done by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), a possible growth mechanism has been suggested. 

High resolution transmission electron microscopy has been used to probe the microstructure of the n ‫؍‬ 2 Ruddlesden-Popper manganates Sr 2 LnMn 2 O 7 (Ln ‫؍‬ Y, La, Nd, Eu, Ho). Intergrowths of n ‫؍‬ 1 (K 2 NiF 4) are observed only for Ln ‫؍‬ La. Intergrowths with n55, essentially perovskite microdomains, are seen in the other compositions. The density of perovskite regions is greatest near the edges of the thin specimens, with the n ‫؍‬ 2 structure becoming established in the bulk. The complementarity of HRTEM and neutron diffraction is discussed.

New strontium titanyl phosphate Sr 2 TiO(PO 4) 2 (1) was synthesized and characterized by X ray powder diffraction, electron diffraction, high resolution electron microscopy, and band structure calculations. Titanyl phosphate 1 is isostructural with vanadyl phosphate Sr 2 VO(PO 4) 2 and has a layered structure. The titanium atoms are shifted from the centers of the TiO 6 octahedra and form short (1.74 Å) titanyl bonds. The structure of 1 is an unusual example of the disordered orientation of the chains formed by TiO 6 octahedra in complex titanium phosphates.

We report on sizable antiferromagnetic interlayer exchange coupling (AFC) of Fe(001) layers across epitaxial Si spacers, for which epitaxial growth of a pseudomorphic phase stabilized by the interface is confirmed by low-energy electron diffraction and high-resolution transmission electron microscopy. The coupling strength decays with spacer thickness on a length scale of a few Å and shows a negative temperature coefficient. Transport measurements of lithographically structured junctions in current-perpendicular-to-plane geometry show the validity of the three “Rowell criteria” for tunneling: (i) exponential increase of resistance R with thickness of the barrier, (ii) parabolic dI/dV-V curves, and (iii) slight decrease of R with increasing temperature. Therefore, AFC is mediated by non-conductive spacers, which in transport experiments act as tunneling barriers with a barrier height of several tenths of an eV. We discuss our data — in particular the strength, thickness and temperature dependence — in the context of two previously proposed models for AFC across non-conducting spacers. We find that neither the molecular-orbital model for heat-induced effective exchange coupling nor the quantum interference model extended to insulator spacers by introducing complex Fermi surfaces can account for the strong AFC across epitaxial Si spacers and its negative temperature coefficient. The recently proposed defect-assisted interlayer exchange coupling model, however, yields qualitative agreement with the enhanced AFC and the temperature dependence.

We report room temperature ferromagnetism in vacuum annealed ZnFe 2 O 4 ͑ZFO͒ nanoparticles. Upon vacuum and air annealing, ZFO nanoparticles show ferro and paramagnetic behavior, respectively. The well defined sextets along with doublet seen in the Mossbauer spectra confirms ferromagnetic coupling in vacuum annealed ZFO. After reannealing in air, the magnetization of vacuum annealed sample reduces from 62 to 1.5 emu/g. Both Mossbauer and micro-Raman results suggest that oxygen vacancies generated during vacuum annealing causes cation redistribution between the interstitial sites resulting in magnetic ordering. Our results show a unique possibility of switching the magnetic properties of ZFO between paramagnetic to ferromagnetic.

We have observed unusual ferromagnetic properties in single-crystalline CoSi nanowire ensemble, in marked contrast to the diamagnetic CoSi in bulk. High-density freestanding CoSi nanowires with B20 crystal structure are synthesized by a vapor-transport-based method. The reaction of cobalt chloride precursor with a Si substrate produces high-aspect-ratio CoSi nanowires. The high-resolution transmission electron microscopy and electron diffraction studies reveal superlattice structure in CoSi nanowires with twice the lattice parameter of simple cubic CoSi lattice. The zero-field-cooled and field-cooled (ZFC-FC) measurements from the nanowire ensemble show freezing of the disordered surface spins at low temperatures. The magnetoresistance (MR) measurements of single nanowire devices show a negative MR whose magnitude gets larger at lower temperatures.

Single-crystals of MnFe2O4 nanorods with an average diameter of 20 nm and length of 250 nm were synthesized by a hydrothermal process at 180 °C after 12 h. High-resolution transmission electron microscopy (HRTEM) and electron diffraction (ED) analysis revealed that the nanorods grow along the [110] axis, which is one of the easy magnetization axes of the material MnFe2O4. It was found that the nanorods exhibited a saturation magnetization (Ms) of 68.02 emu/g, which is much higher than that of quasi-spherical particles of MnFe2O4, prepared by other approaches such as solid-state reaction methods (Ms = 36.7 emu/g), and coprecipitation processes followed by annealing in vacuo at 400 °C (Ms = 24.4 emu/g). The oriented growth along the easy magnetization axis of MnFe2O4 was suggested to be responsible for the improvement of magnetic properties of MnFe2O4 nanorods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

A nonhydrolytic sol-gel process closely following that of Hyeon et al. for the synthesis of ZrO 2 nanocrystals (J. Am. Chem. Soc. 2003, 125, 6553-6557) was used to synthesize highly crystalline and monodisperse HfO 2 nanoparticles. Reactions of hafnium isopropoxide with hafnium halides at high temperature in a strongly coordinating solvent yield nanometersized particles of HfO 2 . The size, shape, and crystalline phase of the hafnia particles depend on both the reaction temperature and the halide. The nonhydrolytic cross-condensation method was also extended to the binary metal oxides nanocrystals, i.e., HfO 2 -ZrO 2 , ZrO 2 -TiO 2 , and HfO 2 -TiO 2 . Efforts to prepare nanocrystals of Hf x Zr 1-x O 2 over a wide range of x were successful; however, this method could not be used to prepare either Zr x Ti 1-x O 2 or Hf x Ti 1-x O 2 . In conjunction with X-ray powder diffraction and high-resolution transmission electron microscopy, Raman spectroscopy identifies the structural phase of the nanocrystals and also proves the formation of the Hf-Zr solid solution nanoparticles via the crosscondensation method. In the case of Hf x Zr 1-x O 2 , for x < 0.5, highly monodisperse, roughly spherical particles of tetragonal Hf x Zr 1-x O 2 were formed, while for x > 0.5, small nanorods of the monoclinic phase of the binary oxide were obtained.

CN x /ZrN multilayers were prepared by a dual-cathode unbalanced DC magnetron sputtering system. The results showed that under proper deposition conditions, the multilayer coatings were dense and fully crystalline with hardness exceeding 40 GPa and elastic modulus over 400 GPa. X-ray diffraction studies showed that there is a strong correlation between coating hardness and the occurrence of (111) texture of ZrN. Some crystalline regions going through the multilayers were clearly observed from the cross-sectional high resolution transmission electron microscopy image. Two extra d-spacings were obtained from the diffraction pattern that do not belong to any known d-spacing for ZrN, but match with two calculated d-spacings for b-C 3 N 4 . © 1997 Elsevier Science S.A.

Interfacial reactions in Ti/GaN contacts have been studied using conventional and high-resolution transmission electron microscopy ͑TEM͒, energy-filtered TEM ͑EFTEM͒, and x-ray diffraction. The thin film contacts were fabricated by evaporating Ti on n-GaN and subsequent rapid thermal annealing in argon. An x-ray result shows that the as-deposited Ti on GaN is an epitaxial hcp phase, whereas a fcc phase was identified from the as-deposited metal layer in cross-sectional TEM specimens. This phenomenon is interpreted as the transformation of hcp-Ti phase to fcc-TiH x phase by hydrogen incorporation during TEM specimen thinning. At elevated temperature, first gallium and then nitrogen diffused into the metal layer. The reaction front moved into the Ti layer, and after annealing at 700°C many voids were formed along the Ti/GaN interface at the GaN side. A sequence of phases GaN/TiN/Ti 2 GaN/Ti 3 Ga/Ti was identified in annealed contacts, and corresponds to the expected diffusion path. The ternary phase Ti 2 GaN was confirmed with electron diffraction and EFTEM. A planar TiN layer, which formed in direct contact to the GaN, presumably governs the electrical properties of the alloyed contact.

The microstructure and the composition of CVD silicon carbide films used as fiber coatings in composite materials were investigated by photoelectron spectroscopy and transmission electron microscopy. The films with a uniform thickness of 50 nm consisted of small SiC grains with a mean diameter of 15 nm and showed a stripe contrast in bright field images. Large grains with diameters in the dimension of the film thickness were used for imaging the lattice structure by high-resolution electron microscopy. The results are discussed as a polytype of cubic lamellae of a few nanometers and intermediate random stacking sequences of hexagonal structure.

Yttria-stabilized zirconia strengthened with lamellar flaky-shape Nb metal particles was obtained by hot-pressing at 1500°C for 1 h. The ZrO 2 -Nb interface has been studied by atomistic, first-principles calculations and by high-resolution transmission electron microscopy. The influence of the ceramic-metal interface on the crack growth resistance has been investigated. Crack growth is shown to occur with a rising resistance, governed by intact metal ligaments in the crack wake. Crack extension occurs by a combination of plastic deformation on the metal particles and interface debonding. The connection between the interface adhesion and this microstructural toughening mechanism has been evaluated.

Myxococcus xanthus, a common soil bacterium, plays an active role in the formation of spheroidal vaterite. Bacterial production of CO 2 and NH 3 and the transformation of the NH 3 to NH 4 þ and OH À , thus increasing solution pH and carbonate alkalinity, set the physicochemical conditions (high supersaturation) leading to vaterite precipitation in the microenvironment around cells, and directly onto the surface of bacterial cells. In the latter case, fossilization of bacteria occurs. Vaterite crystals formed by aggregation of oriented nanocrystals with c-axis normal to the bacterial cell-wall, or to the core of the spherulite when bacteria were not encapsulated. While preferred orientation of vaterite c-axis appears to be determined by electrostatic affinity (ionotropic effect) between vaterite crystal (0001) planes and the negatively charged functional groups of organic molecules on the bacterium cell-wall or on extracellular polymeric substances (EPS), analysis of the changes in the culture medium chemistry as well as high resolution transmission electron microscopy (HRTEM) observations point to polymorph selection by physicochemical (kinetic) factors (high supersaturation) and stabilization by organics, both connected with bacterial activity. The latter is in agreement with inorganic precipitation of vaterite induced by NH 3 and CO 2 addition in the protein-rich sterile culture medium. Our results as well as recent studies on vaterite precipitation in the presence of different types of bacteria suggest that bacterially mediated vaterite precipitation is not strain-specific, and could be more common than previously thought.

however, subtle processes which involve the specimen, the however, subtle processes which involve the specimen, the electron beam and any mobile species on the sample electron beam and any mobile species on the sample surface frequently cause the build up of hydrocarbon surface frequently cause the build up of hydrocarbon contamination layers. contamination layers.

In this investigation, the chemical and structural characteristics of Fe nanoparticles synthesized by high-energy ball milling have been explored. After the milling process the nanoparticles were collected using a magnetic field. The structure, morphology and composition of the powders were obtained using high-resolution electron microscopy. HREM images confirmed the nanoparticles’ presence with approximately 2–4 nm in size. It was found that using this method allowed the formation of nanoparticles in a smaller size range than other synthesis methods. Also, it was confirmed by HREM images that the obtained nanoparticles were mainly of the fcc nature and some of them of the MTP type.

Bacterial biofilms, i.e. surface-associated cells covered in hydrated extracellular polymeric substances (EPS), are often studied with highresolution electron microscopy (EM). However, conventional desiccation and high vacuum EM protocols collapse EPS matrices which, in turn, deform biofilm appearances. Alternatively, wet-mode environmental scanning electron microscopy (ESEM) is performed under a moderate vacuum and without biofilm drying. If completely untreated, however, EPS is not electron dense and thus is not resolved well in ESEM. Therefore, this study was towards adapting several conventional SEM staining protocols for improved resolution of biofilms and EPS using ESEM. Three different biofilm types were used: 1) Pseudomonas aeruginosa unsaturated biofilms cultured on membranes, 2) P. aeruginosa cultured in moist sand, and 3) mixed community biofilms cultured on substrates in an estuary. Working with the first specimen type, a staining protocol using ruthenium red, glutaraldehyde, osmium tetroxide and lysine was optimized for best topographic resolution. A quantitative image analysis tool that maps relief, newly adopted here for studying biofilms, was used to compare micrographs. When the optimized staining and ESEM protocols were applied to moist sand cultures and aquatic biofilms, the smoothening effect that bacterial biofilms have on rough sand, and the roughening that aquatic biofilms impart on initially smooth coupons, were each quantifiable. This study thus provides transferable staining and ESEM imaging protocols suitable for a wide range of biofilms, plus a novel tool for quantifying biofilm image data.

The relationships among the equivalent oxide thickness ͑EOT͒, nanochemistry, and nanostructure of atomic layer chemical-vapor-deposited ͑ALCVD͒ Hf-O-based films, with oxide and nitrided oxide interlayers on Si substrates, were studied using x-ray photoelectron spectroscopy ͑XPS͒, high-resolution transmission electron microscopy ͑HRTEM͒, scanning transmission electron microscopy ͑STEM͒ in annular dark-field imaging ͑ADF͒, and parallel electron energy-loss spectroscopy ͑PEELS͒, capacitance-voltage, and leakage-current-voltage measurements. The XPS (Hf 4 f binding energy shift͒ studies indicated the formation of Hf-O-Si bonds in as-deposited amorphous films, the amount of which was influenced by the interlayer composition and annealing conditions. After post-deposition annealing in N 2 and O 2 , the Hf-O layers were nanocrystalline. Although HRTEM images showed a structurally sharp interface between the Hf-O layer and the interlayer, angle-resolved XPS, ADF imaging, and PEELS in the STEM revealed a chemically diffused HfSiO x region in between. This interdiffusion was observed by the detection of Si ͑using Si L edge͒ and Hf ͑using Hf O 2,3 edge͒ in the Hf-O layer and the interlayer. For an annealed Hf-O/interlayer stack, with an ALCVD target thickness of 4.0 nm for the Hf-O layer on 1.2 nm of nitrided chemical oxide, the experimentally measured EOT and leakage current ͑at Ϫ1 V͒ were 1.52 nm and ϳ10 Ϫ8 A/cm 2. A three-layer ͑1.2 nm interlayer of nitrided chemical oxide/compositionally graded, 2 nm region of HfSiO x /2 nm HfO 2 layer͒ capacitor model was used to determine the respective contributions to the measured EOT, and the dielectric permittivity of the interlayer was found to be 6.06. These studies clearly indicate that a total EOT of 1 nm and below is attainable in the Hf-NO -Si/Si-NO system.

Nanoscale interfacial evolution in Cu-Al wire bonds during isothermal annealing from 175°C to 250°C was investigated by high resolution transmission electron microscopy (HRTEM). The native aluminum oxide film ($5 nm thick) of the Al pad migrates towards the Cu ball during annealing. The formation of intermetallic compounds (IMC) is controlled by Cu diffusion, where the kinetics obey a parabolic growth law until complete consumption of the Al pad. The activation energies to initiate crystallization of CuAl 2 and Cu 9 Al 4 are 60.66 kJ mol À1 and 75.61 kJ mol À1 , respectively. During IMC development, Cu 9 Al 4 emerges as a second layer and grows together with the initial CuAl 2 . When Al is completely consumed, CuAl 2 transforms to Cu 9 Al 4 , which is the terminal product. Unlike the excessive void growth in Au-Al bonds, only a few voids nucleate in Cu-Al bonds after long-term annealing at high temperatures (e.g., 250°C for 25 h), and their diameters are usually in the range of tens of nanometers. This is due to the lower oxidation rate and volumetric shrinkage of Cu-Al IMC compared with Au-Al IMC.

In Mexico, 70% of the land surface shows some degree of degradation. A substantial portion of these degraded soils are located in the central part of the country, where a high population density exerts unusual pressure on the land. The study of these degraded soils is important because of the ecological, social and economic consequence of this ecosystem component. Two types of degraded volcanic soils were studied in the present research: one coming from tepetates (a volcanic tuff, partially altered and ameliorated for production purposes) and the other, a highly eroded Acrisol developed from old volcanic materials. These soils have not been much studied and are here explored due to their potential to sequester carbon. In studies to focus the relationship between mineralogy and the carbon sequestration it will be necessary to clarify the characteristics of the fine fraction of the soil (b2 µm). Clays have been reported to show different mechanisms of association with soil organic matter, in accordance with their nature. In this paper, a mineralogical characterization was made of the fine (2-1 µm) and very fine (b 1 µm) fractions of these soils, considered to be the most active in the sequestration process. The characterization was initially developed by using X-ray diffraction (XRD). However, the results obtained with this technique were not conclusive. In addition, due to the fact that XRD sometimes requires tedious chemical treatments and take time, it is proposed here to use spectroscopical techniques other that the traditional ones to more accurately define the mineralogical characteristics of the studied fractions. The diffuse reflectance infrared Fourier transform (DRIFT), 27 Al magic angle spinning nuclear magnetic resonance ( 27 Al MAS NMR), 29 Si magic angle spinning nuclear magnetic resonance ( 29 Si MAS NMR), transmission electron microscopic (TEM), high resolution transmission electron microscopy (HRTEM) and Mössbauer spectroscopy were employed. The fine fractions (b 2 µm) of the degraded soils are made up of low activity clays: tubular halloysites in the Te-Tl tepetates and kaolinites in the Acrisol. The coarse (2-1 µm) ones in Te-Tl consist also of cristobalite and albite. In Ac-At, akaganeite, goethite and hematite are the principal Fe-mineral components. For this reason, the restoration techniques proposed for these degraded soils must be complemented with appropriate practices of fertilization providing basic elements (Ca, Mg, K and Na) to the soil that can be rapidly lost, and are associated with low activity of the fine fraction.

Nickel -zinc ferrite monodisperse nanoparticles are synthesized by forced hydrolysis in diethylenglycol. FC and ZFC susceptibility curves suggest that they present superparmagnetic behaviour with a blocking temperature between 63 and 15 K depending on the zinc content. The saturation magnetization of the nanocrystals at 5 K is very close to that of bulk materials, and very high compared to that of similar particles prepared by other chemical routes. High Resolution Transmission Electron Microscopy and In-field Mössbauer studies show clearly that these relatively high values are mainly due to: (i) the high crystalline quality of the particles and (ii) a cation distribution different from the classical distribution encountered in the bulk material. 2 Z. Beji et al.: Synthesis of nickel -zinc ferrite nanoparticles in polyol

spin-polarized currents. In recent years, however, the flow of pure spin currents has received much interest [1,2] in the quest of novel and low-energy consumption devices. [3] A key discovery was reported in 2013, when Nakayama et al. [4] and Hahn et al. [5] found out a new kind of magnetoresistance that appears in a nonmagnetic metal (NM) when placed in contact with a ferromagnetic insu-lator (FMI). It turned out that the resistance of the NM varies with the direction in which the FMI is magnetized. The observed effect relies on two ingredients. [6] The first one, so-called spin Hall effect (SHE), in which a charge current (J C), due to spin-orbit coupling, creates a flow of spins (J S) perpendicular to J C and produces a spin accumulation at sample edges with a polarization (σ) which is normal to both J C and J S (Figure 1a,b,e). The charge-to-spin current conversion is given by the spin Hall angle θ SH of the NM layer. Additionally, the created J S is converted back to J C by the inverse spin Hall effect (ISHE) which is the reciprocal effect to SHE, in which a spin current generates a transverse charge current. This is thus a second-order effect in θ SH that lowers the base resistivity of the NM layer with respect to its Drude resis-tivity. The second ingredient is the transport of spins across the NM/FMI interface, which is quantified by the spin-mixing interfacial conductance (G ↑↓). When a charge current is applied along the NM, the transverse spin current may be absorbed by the FMI depending on the direction of σ with respect to the direction of the magnetization (M) of the FMI. When σ is parallel to M, the spin current cannot be absorbed via spin transfer torque into the FMI and thus the electrical resistance of the NM layer remains unaltered; in contrast, when σ is perpendicular to M, spin torque occurs and J S is partially absorbed into the FMI (spin excitations) producing a loss of spin accumulation in the metal and thus a reduction of J C which is equivalent to an increase of resistance. Therefore, the resistance of the NM depends on the direction of M of the neighboring FMI, which can be controlled by appropriate external magnetic field, thus giving rise to the so-called spin Hall magnetoresistance (SMR) [4,7] (Figure 1a,b and Figure 2 (central panel)). Angular-dependent magnetore-sistance measurements (ADMR) and field-dependent magne-toresistance may allow observation of SMR. The magnitude of the observed SMR is determined by θ SH and G ↑↓. Spin currents have emerged as a new tool in spintronics, with promises of more efficient devices. A pure spin current can be generated in a nonmagnetic metallic (NM) layer by a charge current (spin Hall effect). When the NM layer is placed in contact with a magnetic material, a magnetoresistance (spin Hall magnetoresistance) develops in the former via the inverse spin Hall effect (ISHE). In other novel spin-dependent phenomena, such as spin pumping or spin Seebeck effect, spin currents are generated by magnetic resonance or thermal gradients and detected via ISHE in a neighboring normal metal layer. All cases involve spin transport across interfaces between nonmagnetic metallic layers and magnetic materials; quite commonly, magnetic insulators. The structural, compositional, and electronic differences between these materials and their integration to form an interface, challenge the control and understanding of the spin transport across it, which is known to be sensitive to sub-nanometric interface features. Here, the authors review the tremendous progress in material's science achieved during the last few years and illustrate how the spin Hall magnetoresistance can be used as a probe for surface magnetism. The authors end with some views on concerted actions that may allow further progress.

Carbon nanotube science is a new exciting subject for all the carbon community. We now have in hand 1D graphite prototypes opening a new field for basic research and increasing the technological potential of traditional carbon fibers. In addition to many open fundamental questions, one of the main difficulties resides on the technological side, since large scale synthesis, high purity samples, and manipulation at the nanoscale are not yet fully developed. In this paper, we present recent development on different nanotube aspects: preparation and purification, electronic transport properties, electron spin resonance, mechanical behaviour of individual nanotubes, and field-emission.

Composites of poly(methyl methacrylate) (PMMA) with multi-walled carbon nanotubes (MWCNT) of varying aspect ratio and carboxylic acid functionality were prepared using melt mixing. The extent of dispersion and distribution of the MWCNTs in the PMMA matrix was investigated using a combination of high-resolution transmission electron microscopy (HRTEM), wide-angle X-ray diffraction (XRD) and Raman spectroscopy. The electrical resistivity and oscillatory shear rheological properties of the composites were measured as a function of MWCNT geometry, functionality, and concentration. The fundamental ballistic conductance of the pristine free-standing MWCNTs was investigated using a mechanically controlled break-junction method. The electrical conductivity of PMMA was enhanced by up to 11 orders of magnitude for MWCNT concentrations below 0.5 wt.%. MWCNTs having higher aspect ratio, above 500, or functionalized with carboxylic acid groups readily formed rheological percolated networks with thresholds, determined from a power law relationship, of 1.52 and 2.06 wt.%, respectively. The onset of pseudo-solid-like behaviour and network formation is observed as G′, η∗, and tan δ−1 are independent of frequency as MWCNT loading increased. Sufficiently long and/or functionalized tubes are required to physically bridge or provide interfacial interactions with PMMA to alter polymer chain dynamics. Carboxylic acid functionalization disrupts the crystalline order of MWCNTs due to a loss of π-conjugation and electron de-localisation of sp2 C–C bonds resulting in non-ballistic electron transport in these tubes, irrespective of how highly dispersed they are in the PMMA matrix.

Glass transition temperatures (Tg) of amorphous sugar samples, prepared from 0% to 14% (wb) moisture content, were determined during both cooling and heating using differential scanning calorimetry (DSC). The DSC protocol used involved heating, cooling, and reheating the sugar samples, where Tg was obtained during both cooling and reheating steps. The Gordon-Taylor equation modeled the water plasticization effect, where the Tg of anhydrous solids and constant (k) values were determined simultaneously. No significant difference was found between the cooling and heating glass transition temperature values, with both values significantly influenced by sugar composition (p < 0.05). No significant effect of sugar composition was observed for the k values, resulting in discrepancies displayed by the Gordon-Taylor model for solid mass fractions below 0.84. Thus, k values should be estimated from measured Tg data at low solid mass fractions rather than extrapolated from high solid mass fractions, for prediction of Tg curve at high moisture contents.

Undoped and 2% Ga-doped ZnO films have been deposited by RF magnetron sputtering onto single crystal Si (1 0 0) substrates equivalent to the commercial Si solar cells. The same films were also grown on amorphous silica substrates to complete their characterization. The films have been characterized by X-ray diffraction, electrical and optical measurements, X-ray photoelectron spectroscopy, Raman microspectroscopy and scanning and high-resolution transmission electron microscopy. Films present a very good quality crystalline wurtzite structure with the c-axis perpendicular to the substrate, with continuity of the (0 0 0 2) planes along the whole film, as shown by transmission electron microscopy. The doped sample shows an increase of two orders of magnitude of the electrical conductivity, an optical transmittance bigger than 85% along the visible spectrum, a diminution of the grain size in the direction parallel to the substrate and a lower surface roughness. The Ga-cations act only as substitutional impurities, they are homogeneously distributed in the whole film, maintaining the wurtzite structure and increasing the carrier density. The formation of any spurious phase or segregation of Ga2O3 clusters that can act as carrier traps can be discarded. The characterization results allow us to conclude that the doped film has improved electrical and optical properties with respect to the undoped one. Therefore, the Ga-doped films are very suitable candidates as transparent conducting electrodes for solar cells, displays and other photoelectronic devices.High-resolution image of the interface between silicon substrate and the high-quality ZnO film. ► High quality ZnO and Ga:ZnO (2%at) films prepared by magnetron sputtering on Si (100) substrates. ► Both films show a continuity of the (0002) planes along the whole film. ► Ga cations act only as substitutional impurities, homogeneously distributed in the entire film. ► Ga-doping improves the electrical and optical properties of ZnO film.

Strain mapping is defined as a numerical image-processing technique that measures the local shifts of image details around a crystal defect with respect to the ideal, defect-free, positions in the bulk. Algorithms to map elastic strains from high-resolution transmission electron microscopy (HRTEM) images may be classified into two categories: those based on the detection of peaks of intensity in real space and the Geometric Phase approach, calculated in Fourier space. In this paper, we discuss both categories and propose an alternative real space algorithm (Peak Pairs) based on the detection of pairs of intensity maxima in an affine transformed space dependent on the reference area. In spite of the fact that it is a real space approach, the Peak Pairs algorithm exhibits good behaviour at heavily distorted defect cores, e.g. interfaces and dislocations. Quantitative results are reported from experiments to determine local strain in different types of semiconductor heterostructures. r

Highly thermally stable three-dimensional spongelike mesoporous Ce x Zr 1Àx O 2 solid solutions consisting of nanometer size particles with different Ce/Zr compositions were synthesized by a modified sol-gel procedure using a triethanolamine/water mixture as a solvent to be used in liquid Knoevenagel condensation reaction. These materials were investigated in detail by means of X-ray diffraction (XRD), Raman spectroscopy, chemical analysis, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and adsorption microcalorimetry. The XRD, HRTEM and XPS studies proved the presence of nanocrystalline Ce x Zr 1Àx O 2 solid solutions. These solid solutions showed excellent chemoselectivity in the classical Knoevenagel reaction. The large pore sizes (around 10 nm) highlight the possibility of using Ce x Zr 1Àx O 2 as a support material for versatile catalytic systems. The results obtained from NH 3 and SO 2 adsorption microcalorimetry experiments successfully demonstrated the incorporation of ZrO 2 into the CeO 2 lattice resulting in both acidic and basic surface sites in a mixed oxide matrix.

As-fabricated thermal barrier coating (TBC) systems generally consist of a superalloy substrate, a MCrAlY bond coat (M = Ni, Co, Fe), and a ceramic (usually partially stabilized zirconia) top coat. The conventional methods for producing the two coating layers generally derive from thermal spray and physical vapor deposition techniques. Thermal exposure leads to the formation of an additional layer: the thermally grown oxide (TGO) between the bond coat and top coat. In the present work, a TBC system is synthesized through the application of spark plasma sintering (SPS), which provides not only the opportunity to synthesize all three layers at once, but the process is quite rapid and can produce dense layers. More specifically, this paper describes the application of this method to an yttria-stabilized ZrO 2 (YSZ) top coat and a NiCrAlY bond coat on a Ni-base Hastelloy X substrate. A one-micron thick Al 2 O 3 TGO layer is also created from the reaction between an Al foil layer inserted in the stack prior to sintering and the ZrO 2 in the top coat. The effects of select process conditions are considered. The resulting multi-layer system is characterized with optical microscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDAX) and X-ray diffraction (XRD). Differential thermal analysis (DTA) is used to investigate the reaction between the Al foil and the YSZ top coat.

Recently designed advanced in-situ specimen holders for transmission electron microscopy (TEM) have been used in studies of gold nanoparticles. We report results of variable temperature TEM experiments in which structural transformations have been correlated with specimen temperature, allowing general trends to be identified. Transformation to a decahedral morphology for particles in the size range 5-12 nm was observed for the majority of particles regardless of their initial structure. Following in-situ annealing, decahedra were found to be stable at room temperature, confirming this as the equilibrium morphology, in agreement with recently calculated phase diagrams. Other transitions at low temperature in addition to surface roughening have also been observed and correlated with the same nanoscale phase diagram. Investigations of gold particles at high temperature have revealed evidence for co-existing solid and liquid phases. Overall, these results are important in a more precise understanding of the structure and action of catalytic gold nanoparticles and in the experimental verification of theoretical calculations.

Dry thermal oxidation of low defect density aluminum nitride single crystals was investigated by high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). Oxidation at 800 °C produced an amorphous oxide layer. In the AlN near the interface were many dislocations, stacking faults and domain boundaries, molecular nitrogen and oxygen. Oxidation at 1000 °C produced a crystalline, epitaxial oxide