Abstract: Monolithic nickel/carbon (Ni/C) composites were prepared from coal tar pitch-impregnated compressed expanded graphite pre-decorated with NiO particles (EGNiO) by pyrolysis at 550 °C and subsequent steam activation at 800 °C. The microstructural arrangement of the Ni-comprising nanoparticles in the composites was investigated using transmission electron microscopy. The specific surface area and porosity of the composites were analyzed by nitrogen adsorption. The catalytic activity of the composites was compared with the material obtained by the conventional H2 treatment of EGNiO using hydrocracking of 2,2,3-trimethylpentane as a model reaction.

Abstract: Si/Si(1 − x − y)GexCy superlattices are used in the construction of new microelectronic architectures such as multichannel transistors. The introduction of carbon in SiGe allows for compensation of the strain and to avoid plastic relaxation. However, the formation of incoherent β-SiC clusters during annealing limits the processability of SiGeC. This precipitation leads to a modification of the strain in the alloy due to the reduction of the substitutional carbon content. Here, we investigated the strain in annealed Si/Si0.744Ge0.244C0.012 superlattices grown by reduced pressure chemical vapour deposition using dark-field electron holography. The variation of the substitutional C content was calculated by correlating the results with finite-element simulations. The obtained values were then compared with Fourier-transformed infrared spectrometry measurements. It was shown that after annealing for 2 min at 1050 °C carbon no longer has any influence on strain in the superlattice, which behaves like pure SiGe. However, a significant proportion of substitutional C atoms remain in a third-nearest neighbour (3nn) configuration. It was deduced that the influence of 3nn C on strain is negligible and that only isolated atoms have a significant contribution. It was also proposed that the 3nn configuration is an intermediary step during the formation of SiC clusters.

Abstract: The speed and effectiveness of a conservation treatment used for stained glass windows have been investigated. Dark-coloured Mn-rich stains can be found in the alteration layer of ancient glass artefacts and cause the surface to turn brown/black: this phenomenon is known as Mn-browning or Mn-staining. While in glass manganese is present in the +II or +III oxidation states, in the Mn-rich bodies, manganese is in a higher oxidation state (+IV). In restoration practice, mildly reducing solutions are employed to eliminate the dark colour and restore the clear appearance of the glass. In this paper the effectiveness and side effects of the use of hydroxylamine hydrochloride for this purpose are assessed. Archaeological fragments of stained glass windows, dated to the 14th century and originating from Sidney Sussex College, Cambridge (UK), were examined by means of synchrotron radiation (SR) based microscopic X-ray Absorption Near-Edge Spectroscopy (μ-XANES) and microscopic X-Ray Fluorescence (μ-XRF) and with high resolution computed absorption tomography (μ-CT) before, during and after the treatment. The monitoring of the glass fragments during the treatment allows us to better understand the manner in which the process unfolds and its kinetics. The results obtained reveal that the hydroxylamine hydrochloride treatment is effective, but also that it has a number of unwanted side effects. These findings are useful for optimizing the time and other modalities of the Mn-reducing treatment as well as minimizing its unwanted results.

Abstract: In cultural heritage science, compositional data is traditionally obtained from works of art through the analysis of samples by means of various bench-top instruments (scanning electron microscope, Raman spectrometer, etc.). Alternatively, the object can be transported to a laboratory where it may be examined, usually by spectroscopic methods working in reflection mode. However, this paper describes how a complementary set of mobile and portable instruments was deployed in situ to gain a comprehensive view on the materials and related ageing compounds of an (almost) unmovable 15th-C polyptych, prior to and in preparation of the extraction of a limited number of samples. In line with the methodological approach discussed, PXRF was first employed as an efficient screening tool. The ensuing elemental data was supplemented by more specific information on both organic as inorganic materials supplied by reflection near- and mid-FTIR spectroscopy and fluorimetry. In completion, a limited number of diffraction patterns were collected with a mobile XRD instrument in order to identify the constituent crystalline phases in pigments, grounding materials and degradation products. In this way, it could be demonstrated how a rich array of colours was obtained by means of a limited palette of pigments: lead white, lead tin yellow, azurite, natural ultramarine, bone black, vermillion, madder lake, and a green copper-organo complex were detected and situated on the panels. Remarkably, next to chalk also gypsum was found in the ground layer(s) of this Western European easel painting. The relatively large surface of the background was covered with gold leaf; the analyses seem to point towards the labour-intensive water gilding technique. The versatility of this combination of analytical techniques was further illustrated by the accurate characterisation of degradation products affecting the readability and conservation of the painting: the overall presence of a calcium oxalate-based film of variable thickness was established. Nevertheless, further analysis of cross-sectioned samples was considered desirable in order to study the stratigraphy, to gain direct access to altered and sub-imposed layers and to allow highly detailed analysis of micrometric degradation products by state-of-the art techniques (i.e. synchrotron radiation).

Abstract: A modelling approach is presented that determines the most cost-effective set of reduction measures to reach an in-stream concentration target. The framework is based on the coupling of two models: the hydrological water quality model SWAT and an economic optimization model (Environmental Costing Model, ECM). SWAT is used to determine the relationship between the modelled in-stream concentration at the river basin outlet and the associated emission reduction. The ECM is used to set up marginal abatement cost curves for nutrients and oxygen demanding substances. Results for nitrogen are presented for the Grote Nete river basin in Belgium for the year 2006. Results show that the good status for total nitrogen can be reached in the study area. The most cost-effective measures are more productive dairy cattle, implementing basic measures as defined in the WFD, winter cover crops, improved efficiency of WWTP, enhanced fodder efficiency for pigs, further treatment of industrial waste water and tuned fertilization. (C) 2010 Elsevier Ltd. All rights reserved.

Abstract: The main goal of this work was to determine the chemical composition of building materials used in Turkey by utilizing energy dispersive X-ray fluorescence (EDXRF) spectrometry. Gas concrete, cement, sand, bricks, roofing tiles, marble, lime and gypsum materials were selected as building materials for this research. The chemical contents and their trace concentrations of the selected samples were determined. The most abundant oxides measured were generally SiO2, Al2O3, CaO, MgO, Fe2O3, K2O and SO3 for all samples. While the main chemical component of gas concrete, cement, sand and marble samples were SiO2 and CaO, brick and roofing tile mainly consisted of SiO2 and Al2O3. CaO and SO3 were major component of lime and gypsum samples, respectively. For U and Th concentrations in the samples, activities of 226Ra and 232Th were measured by utilizing gamma spectrometry. ANOVA and Pearson correlation analyses were performed on the studied data for statistical analysis.

Abstract: Solution derived La2Zr2O7 films have drawn much attention for potential applications as thermal barriers or low-cost buffer layers for coated conductor technology. Annealing and coating parameters strongly affect the microstructure of La2Zr2O7, but different film processing methods can yield similar microstructural features such as nanovoids and nanometer-sized La2Zr2O7 grains. Nanoporosity is a typical feature found in such films and the implications for the functionality of the films are investigated by a combination of scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS) and quantitative electron tomography. Chemical solution based La2Zr2O7 films deposited on flexible Ni5 at.%W substrates with a {100}lang001rang biaxial texture were prepared for an in-depth characterization. A sponge-like structure composed of nanometer-sized voids is revealed by high-angle annular dark-field scanning transmission electron microscopy in combination with electron tomography. A three-dimensional quantification of nanovoids in the La2Zr2O7 film is obtained on a local scale. Mostly non-interconnected highly faceted nanovoids compromise more than one-fifth of the investigated sample volume. The diffusion barrier efficiency of a 170 nm thick La2Zr2O7 film is investigated by STEM-EELS, yielding a 1.8 ± 0.2 nm oxide layer beyond which no significant nickel diffusion can be detected and intermixing is observed. This is of particular significance for the functionality of YBa2Cu3O7 − δ coated conductor architectures based on solution derived La2Zr2O7 films as diffusion barriers.

Abstract: Using a combination of the phenomenological GinzburgLandau theory and micromagnetic simulations, we study properties of a superconducting film with an array of soft magnetic dots on top. An external in-plane magnetic field gradually drives the magnets from an out-of-plane or magnetic vortex state to an in-plane single-domain state, which changes spatially the distribution of the superconducting condensate. If induced by the magnets, the vortexantivortex molecules exhibit rich transitions as a function of the applied in-plane field. At the same time, we show how the magnetic dots act as very effective dynamic pinning centers for vortices in an applied perpendicular magnetic field.

Abstract: We demonstrate for the first time a possibility to vary the anion content in perovskites over a wide range through a long-range-ordered arrangement of crystallographic shear (CS) planes. Anion-deficient perovskites (Pb,Bi)1−xFe1+xO3−y with incommensurately modulated structures were prepared as single phases in the compositional range from Pb0.857Bi0.094Fe1.049O2.572 to Pb0.409Bi0.567Fe1.025O2.796. Using a combination of electron diffraction and high-resolution scanning transmission electron microscopy, we constructed a superspace model describing a periodic arrangement of the CS planes. The model was verified by refinement of the Pb0.64Bi0.32Fe1.04O2.675 crystal structure from neutron powder diffraction data ((3 + 1)D S.G. X2/m(α0γ), X = [1/2,1/2,1/2,1/2], a = 3.9082(1) Å, b = 3.90333(8) Å, c = 4.0900(1) Å, β = 91.936(2)°, q = 0.05013(4)a* + 0.09170(3)c* at T = 700 K, RP = 0.036, RwP = 0.048). The (Pb,Bi)1−xFe1+xO3−y structures consist of perovskite blocks separated by CS planes confined to nearly the (509)p perovskite plane. Along the CS planes, the perovskite blocks are shifted with respect to each other over the 1/2[110]p vector that transforms the corner-sharing connectivity of the FeO6 octahedra in the perovskite framework to an edge-sharing connectivity of the FeO5 pyramids at the CS plane, thus reducing the oxygen content. Variation of the chemical composition in the (Pb,Bi)1−xFe1+xO3−y series occurs mainly because of a changing thickness of the perovskite block between the interfaces, that can be expressed through the components of the q vector as Pb6γ+2αBi1−7γ−αFe1+γ−αO3−3γ−α. The Pb, Bi, and Fe atoms are subjected to strong displacements occurring in antiparallel directions on both sides of the perovskite blocks, resulting in an antiferroelectric-type structure. This is corroborated by the temperature-, frequency-, and field-dependent complex permittivity measurements. Pb0.64Bi0.32Fe1.04O2.675 demonstrates a remarkably high resistivity >0.1 T Ω cm at room temperature and orders antiferromagnetically below TN = 608(10) K.

Abstract: We investigate the stability of circular monolayer graphene subjected to a radial load using non-equilibrium molecular dynamics simulations. When monolayer graphene is radially stressed, after some small circular strain (~0.4%) it buckles and bends into a new bowl-like shape. Young's modulus is calculated from the linear relation between stress and strain before the buckling threshold, which is in agreement with experimental results. The prediction of elasticity theory for the buckling threshold of a radially stressed plate is presented and its results are compared to the one of our atomistic simulation. The Jarzynski equality is used to estimate the difference between the free energy of the non-compressed states and the buckled states. From a calculation of the free energy we obtain the optimum radius for which the system feels the minimum boundary stress.

Abstract: The electron states in graphene-based magnetic dot and magnetic ring structures and combinations of both are investigated. The corresponding spectra are studied as a function of the radii, the strengths of the inhomogeneous magnetic field and of a uniform background field, the strength of an electrostatic barrier and the angular momentum quantum number. In the absence of an external magnetic field we have only long-lived quasi-bound and scattering states and we assess their influence on the density of states. In addition, we consider elastic electron scattering by a magnetic dot, whose average B vanishes, and show that the Hall and longitudinal resistivities, as a function of the Fermi energy, exhibit a pronounced oscillatory structure due to the presence of quasi-bound states. Depending on the dot parameters this oscillatory structure differs substantially for energies below and above the first Landau level.

Abstract: Iron is a widely used catalyst for the growth of carbon nanotubes (CNTs) or carbon nanofibers (CNFs) by catalytic chemical vapor deposition. However, both Fe and FeC compounds (generally, Fe3C) have been found to catalyze the growth of CNTs/CNFs, and a comparison study of their respective catalytic activities is still missing. Furthermore, the control of the crystal structure of iron-based catalysts, that is α-Fe or Fe3C, is still a challenge, which not only obscures our understanding of the growth mechanisms of CNTs/CNFs, but also complicates subsequent procedures, such as the removal of catalysts for better industrial applications. Here, we show a partial control of the phase of iron catalysts (α-Fe or Fe3C), obtained by varying the growth temperatures during the synthesis of carbon-based nanofibers/nanotubes in a plasma-enhanced chemical vapor deposition reactor. We also show that the structure of CNFs originating from Fe3C is bamboo-type, while that of CNFs originating from Fe is not. Moreover, we directly compare the growth rates of carbon-based nanofibers/nanotubes during the same experiments and find that CNFs/CNTs grown by α-Fe nanoparticles are longer than CNFs grown from Fe3C nanoparticles. The influence of the type of catalyst on the growth of CNFs is analyzed and the corresponding possible growth mechanisms, based on the different phases of the catalysts, are discussed.

Abstract: The new compounds NaLaFeTaO6, NaLaFeNbO6, NaLaMnTaO6, and NaLaMnNbO6 have been synthesized and characterized with a combination of transmission electron microscopy, X-ray powder diffraction (XRPD), neutron powder diffraction (NPD), and magnetization measurements. Through electron microscopy study, a local layered order of the A-cations has been detected without the typical occurrence of rock salt order at the B-cation site. Satellite reflections in the electron diffraction related to the local layered order are not visible on the XRPD or NPD patterns. The occurrence of local layered order is supported by pair distribution function analysis, which also reveals the presence of uncorrelated displacements of the Nb and Ta cations. The octahedra are tilted according to the system a−b+a−, and the coordinates were refined from XRPD and NPD with a disordered cation distribution in the space group Pnma. The magnetic exchange interactions in NaLaFeTaO6 and NaLaFeNbO6 are antiferromagnetic, while they are ferromagnetic in NaLaMnTaO6 and NaLaMnNbO6. Long-range magnetic ordering is not observed down to 4 K for any of the compositions.

Abstract: The (1 − x)BiFeO3−xLaFeO3 system has been investigated and characterized by room-temperature and high-temperature laboratory and synchrotron powder X-ray diffraction, electron diffraction, high-resolution transmission electron microscopy, differential scanning calorimetry, and magnetization measurements. At room temperature, the ferroelectric R3c phase is observed for 0.0 ≤ x ≤ 0.10. The PbZrO3-related √2ap × 2√2ap × 4ap superstructure (where ap is the parameter of the cubic perovskite subcell) is observed for Bi0.82La0.18FeO3, while an incommensurately modulated phase is formed for 0.19 ≤ x ≤ 0.30 with the √2ap × 2ap × √2ap basic unit cell. The GdFeO3-type phase with space group Pnma (√2ap × 2ap × √2ap) is stable at 0.50 ≤ x ≤ 1. Bi0.82La0.18FeO3 has no detectable homogeneity range (space group Pnam, a = 5.6004(1) Å, b = 11.2493(3) Å, c = 15.6179(3) Å). The incommensurately modulated Bi0.75La0.25FeO3 structure was solved from synchrotron X-ray powder diffraction data (Imma(00γ)s00 superspace group, a = 5.5956(1) Å, b = 7.8171(1) Å, c = 5.62055(8) Å, q = 0.4855(4)c*, RP = 0.023, RwP = 0.033). In this structure, cooperative displacements of the Bi and O atoms occur, which order within the (AO) (where A = Bi, La) layers, resulting in an antipolar structure. Local fluctuations of the intralayer antipolar ordering are compensated by an interaction with the neighboring (AO) layers. A coupling of the antipolar displacements with the cooperative tilting distortion of the perovskite octahedral framework is proposed as the origin of the incommensurability. All the phases transform to the GdFeO3-type structure at high temperatures. Bi0.82La0.18FeO3 shows an intermediate PbZrO3-type phase with √2ap × 2√2ap × 2ap (space group Pbam; a = 5.6154(2) Å, b = 11.2710(4) Å, and c = 7.8248(2) Å at 570 K). The compounds in the compositional range of 0.18 ≤ x ≤ 0.95 are canted antiferromagnets.