“Multiple dot-in-rod PbS/CdS heterostructures with high photoluminescence quantum yield in the near-infrared”. Justo Y, Goris B, Sundar Kamal J, Geiregat P, Bals S, Hens Z, Journal of the American Chemical Society 134, 5484 (2012). http://doi.org/10.1021/ja300337d
Abstract: Pb cations in PbS quantum rods made from CdS quantum rods by successive complete cationic exchange reactions are partially re-exchanged for Cd cations. Using STEM-HAADF, we show that this leads to the formation of unique multiple dot-in-rod PbS/CdS heteronanostructures, with a photoluminescence quantum yield of 4555%. We argue that the formation of multiple dot-in-rods is related to the initial polycrystallinity of the PbS quantum rods, where each PbS crystallite transforms in a separate PbS/CdS dot-in-dot. Effective mass modeling indicates that electronic coupling between the different PbS conduction band states is feasible for the multiple dot-in-rod geometries obtained, while the hole states remain largely uncoupled.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 41
DOI: 10.1021/ja300337d
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“Nanoscale spectroscopy with polarized X-rays by NEXAFS-TXM”. Guttmann P, Bittencourt C, Rehbein S, Umek P, Ke X, Van Tendeloo G, Ewels CP, Schneider G, Nature photonics 6, 25 (2012). http://doi.org/10.1038/NPHOTON.2011.268
Abstract: Near-edge X-ray absorption spectroscopy (NEXAFS)1 is an essential analytical tool in material science. Combining NEXAFS with scanning transmission X-ray microscopy (STXM) adds spatial resolution and the possibility to study individual nanostructures2, 3. Here, we describe a full-field transmission X-ray microscope (TXM) that generates high-resolution, large-area NEXAFS data with a collection rate two orders of magnitude faster than is possible with STXM. The TXM optical design combines a spectral resolution of E/ΔE = 1 × 104 with a spatial resolution of 25 nm in a field of view of 1520 µm and a data acquisition time of ~1 s. As an example, we present image stacks and polarization-dependent NEXAFS spectra from individual anisotropic sodium and protonated titanate nanoribbons. Our NEXAFS-TXM technique has the advantage that one image stack visualizes a large number of nanostructures and therefore already contains statistical information. This new high-resolution NEXAFS-TXM technique opens the way to advanced nanoscale science studies.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 37.852
Times cited: 76
DOI: 10.1038/NPHOTON.2011.268
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“New insights into the early stages of nanoparticle electrodeposition”. Ustarroz J, Ke X, Hubin A, Bals S, Terryn H, The journal of physical chemistry: C : nanomaterials and interfaces 116, 2322 (2012). http://doi.org/10.1021/jp210276z
Abstract: Electrodeposition is an increasingly important method to synthesize supported nanoparticles, yet the early stages of electrochemical nanoparticle formation are not perfectly understood. In this paper, the early stages of silver nanoparticle electrodeposition on carbon substrates have been studied by aberration-corrected TEM, using carbon-coated TEM grids as electrochemical electrodes. In this manner we have access to as-deposited nanoparticle size distribution and structural characterization at the atomic scale combined with electrochemical measurements, which represents a breakthrough in a full understanding of the nanoparticle electrodeposition mechanisms. Whereas classical models, based upon characterization at the nanoscale, assume that electrochemical growth is only driven by direct attachment, the results reported hereafter indicate that early nanoparticle growth is mostly driven by nanocluster surface movement and aggregation. Hence, we conclude that electrochemical nulceation and growth models should be revised and that an electrochemical aggregative growth mechanism should be considered in the early stages of nanoparticle electrodeposition.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.536
Times cited: 104
DOI: 10.1021/jp210276z
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“A new way of producing electron vortex probes for STEM”. Verbeeck J, Tian H, Béché, A, Ultramicroscopy 113, 83 (2012). http://doi.org/10.1016/j.ultramic.2011.10.008
Abstract: A spiral holographic aperture is used in the condensor plane of a scanning transmission electron microscope to produce a focussed electron vortex probe carrying a topological charge of either −1, 0 or +1. The spiral aperture design has a major advantage over the previously used forked aperture in that the three beams with topological charge m=−1, 0, and 1 are not side by side in the specimen plane, but rather on top of each other, focussed at different heights. This allows us to have only one selected beam in focus on the sample while the others contribute only to a background signal. In this paper we describe the working principle as well as first experimental results demonstrating atomic resolution HAADF STEM images obtained with electron vortex probes. These results pave the way for atomic resolution magnetic information when combined with electron energy loss spectroscopy.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 62
DOI: 10.1016/j.ultramic.2011.10.008
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“Novel vortex generator and mode converter for electron beams”. Schattschneider P, Stoeger-Pollach M, Verbeeck J, Physical review letters 109, 084801 (2012). http://doi.org/10.1103/PhysRevLett.109.084801
Abstract: A mode converter for electron vortex beams is described. Numerical simulations, confirmed by experiment, show that the converter transforms a vortex beam with a topological charge m = +/- 1 into beams closely resembling Hermite-Gaussian HG(10) and HG(01) modes. The converter can be used as a mode discriminator or filter for electron vortex beams. Combining the converter with a phase plate turns a plane wave into modes with topological charge m = +/- 1. This combination serves as a generator of electron vortex beams of high brilliance.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.462
Times cited: 74
DOI: 10.1103/PhysRevLett.109.084801
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“Oxidation state and chemical shift investigation in transition metal oxides by EELS”. Tan H, Verbeeck J, Abakumov A, Van Tendeloo G, Ultramicroscopy 116, 24 (2012). http://doi.org/10.1016/j.ultramic.2012.03.002
Abstract: Transition metal L2,3 electron energy-loss spectra for a wide range of V-, Mn- and Fe-based oxides were recorded and carefully analyzed for their correlation with the formal oxidation states of the transition metal ions. Special attention is paid to obtain an accurate energy scale which provides absolute energy positions for all core-loss edges. The white-line ratio method, chemical shift method, ELNES fitting method, two-parameter method and other methods are compared and their validity is discussed. Both the ELNES fitting method and the chemical shift method have the advantage of a wide application range and good consistency but require special attention to accurately measure the core-loss edge position. The obtained conclusions are of fundamental importance, e.g., for obtaining atomic resolution oxidation state information in modern experiments.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 413
DOI: 10.1016/j.ultramic.2012.03.002
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“Oxygen exchange on nanocrystalline tin dioxide modified by palladium”. Frolov DD, Kotovshchikov YN, Morozov IV, Boltalin AI, Fedorova AA, Marikutsa AV, Rumyantseva MN, Gaskov AM, Sadovskaya EM, Abakumov AM, Journal of solid state chemistry 186, 1 (2012). http://doi.org/10.1016/j.jssc.2011.11.028
Abstract: Temperature-programmed oxygen isotopic exchange study was performed on nanocrystalline tin dioxide-based materials synthesized via sol-gel route and modified by palladium. Such materials are widely used as resistive gas sensors. The experiments were carried out in a flow-reactor up to complete isotopic substitution of oxygen. Substantial rates of isotopic exchange for SnO2 were observed from about 700 K. The distribution of isotopic molecules O-16(2). (OO)-O-16-O-18 and O-18(2) corresponds to simple dioxygen heteroexchange mechanism with single lattice oxygen atom. The modification of SnO2 by Pd introduced multiple heteroexchange mechanism with preliminary O-2 dissociation on the clusters surface. Spill-over of atomic oxygen from Pd to the surface of SnO2 and fast exchange with lattice oxygen result in more than 100% increase of apparent heteroexchange rate. The exchange on SnO2/Pd was shown to be a complex process involving partial deactivation of the catalytic centers at temperature higher than 750 K. (C) 2011 Elsevier Inc. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.299
Times cited: 34
DOI: 10.1016/j.jssc.2011.11.028
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“Phase selection enabled formation of abrupt axial heterojunctions in branched oxide nanowires”. Gao J, Lebedev OI, Turner S, Li YF, Lu YH, Feng YP, Boullay P, Prellier W, Van Tendeloo G, Wu T, Nano letters 12, 275 (2012). http://doi.org/10.1021/nl2035089
Abstract: Rational synthesis of nanowires via the vaporliquidsolid (VLS) mechanism with compositional and structural controls is vitally important for fabricating functional nanodevices from bottom up. Here, we show that branched indium tin oxide nanowires can be in situ seeded in vapor transport growth using tailored AuCu alloys as catalyst. Furthermore, we demonstrate that VLS synthesis gives unprecedented freedom to navigate the ternary InSnO phase diagram, and a rare and bulk-unstable cubic phase can be selectively stabilized in nanowires. The stabilized cubic fluorite phase possesses an unusual almost equimolar concentration of In and Sn, forming a defect-free epitaxial interface with the conventional bixbyite phase of tin-doped indium oxide that is the most employed transparent conducting oxide. This rational methodology of selecting phases and making abrupt axial heterojunctions in nanowires presents advantages over the conventional synthesis routes, promising novel composition-modulated nanomaterials.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 12.712
Times cited: 25
DOI: 10.1021/nl2035089
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“A polar corundum oxide displaying weak ferromagnetism at room temperature”. Li MR, Adem U, McMitchell SRC, Xu Z, Thomas CI, Warren JE, Giap DV, Niu H, Wan X, Palgrave RG, Schiffmann F, Cora F, Slater B, Burnett TL, Cain MG, Abakumov AM, Van Tendeloo G, Thomas MF, Rosseinsky MJ, Claridge JB;, Journal of the American Chemical Society 134, 3737 (2012). http://doi.org/10.1021/ja208395z
Abstract: Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO3 (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO3 has a weak ferromagnetic ground state below 356 K-this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO3.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 48
DOI: 10.1021/ja208395z
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“Preparation, microstructure characterization and catalytic performance of Cu/ZnO and ZnO/Cu composite nanoparticles for liquid phase methanol synthesis”. Sliem MA, Turner S, Heeskens D, Kalidindi SB, Van Tendeloo G, Muhler M, Fischer RA, Physical chemistry, chemical physics 14, 8170 (2012). http://doi.org/10.1039/c2cp40482f
Abstract: Stearate@Cu/ZnO nanocomposite particles with molar ratios of ZnO ∶ Cu = 2 and 5 are synthesized by reduction of the metalorganic Cu precursor [Cu{(OCH(CH3)CH2N(CH3)2)}2] in the presence of stearate@ZnO nanoparticles. In the case of ZnO ∶ Cu = 5, high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) combined with electron-energy-loss-spectroscopy (EELS) as well as attenuated total reflection Fourier transform infrared (ATR-IR) spectroscopy are used to localize the small amount of Cu deposited on the surface of 35 nm sized stearate@ZnO particles. For ZnO ∶ Cu = 2, the microstructure of the nanocomposites after catalytic activity testing is characterized by HAADF-STEM techniques. This reveals the construction of large Cu nanoparticles (2050 nm) decorated by small ZnO nanoparticles (35 nm). The catalytic activity of both composites for the synthesis of methanol from syn gas is evaluated.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.123
Times cited: 16
DOI: 10.1039/c2cp40482f
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“Preparation, structural and optical characterization of nanocrystalline ZnO doped with luminescent Ag-nanoclusters”. Kuznetsov AS, Lu Y-G, Turner S, Shestakov MV, Tikhomirov VK, Kirilenko D, Verbeeck J, Baranov AN, Moshchalkov VV, Optical materials express 2, 723 (2012). http://doi.org/10.1364/OME.2.000723
Abstract: Nanocrystalline ZnO doped with Ag-nanoclusters has been synthesized by a salt solid state reaction. Three overlapping broad emission bands due to the Ag nanoclusters have been detected at about 570, 750 and 900 nm. These emission bands are excited by an energy transfer from the exciton state of the ZnO host when pumped in the wavelength range from 250 to 400 nm. The 900 nm emission band shows characteristic orbital splitting into three components pointing out that the anisotropic crystalline wurtzite host of ZnO is responsible for this feature. Heat-treatment and temperature dependence studies confirm the origin of these emission bands. An energy level diagram for the emission process and a model for Ag nanoclusters sites are suggested. The emission of nanocrystalline ZnO doped with Ag nanoclusters may be applied for white light generation, displays driven by UV light, down-convertors for solar cells and luminescent lamps.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.591
DOI: 10.1364/OME.2.000723
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“Production of large graphene sheets by exfoliation of graphite under high power ultrasound in the presence of tiopronin”. Quintana M, Grzelczak M, Spyrou K, Kooi B, Bals S, Van Tendeloo G, Rudolf P, Prato M, Chemical communications 48, 12159 (2012). http://doi.org/10.1039/c2cc35298b
Abstract: Under ultrasonication, the production of high quality graphene layers by exfoliation of graphite was achieved via addition of tiopronin as an antioxidant.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 6.319
Times cited: 39
DOI: 10.1039/c2cc35298b
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“The role of phase compatibility in martensite”. Salman OU, Finel A, Delville R, Schryvers D, Journal of applied physics
T2 –, 22nd International Symposium on Integrated Functionalities (ISIF), JUN 13-16, 2010, San Juan, PR 111, 103517 (2012). http://doi.org/10.1063/1.4712629
Abstract: Shape memory alloys inherit their macroscopic properties from their mesoscale microstructure originated from the martensitic phase transformation. In a cubic to orthorhombic transition, a single variant of martensite can have a compatible (exact) interface with the austenite for some special lattice parameters in contrast to conventional austenite/twinned martensite interface with a transition layer. Experimentally, the phase compatibility results in a dramatic drop in thermal hysteresis and gives rise to very stable functional properties over cycling. Here, we investigate the microstructures observed in Ti50Ni50-xPdx alloys that undergo a cubic to orthorhombic martensitic transformation using a three-dimensional phase field approach. We will show that the simulation results are in very good agreement with transmission electron microscopy observations. However, the understanding of the drop in thermal hysteresis requires the coupling of phase transformation with plastic activity. We will discuss this point within the framework of thermoelasticity, which is a generic feature of the martensitic transformation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712629]
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.068
Times cited: 11
DOI: 10.1063/1.4712629
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“Seedless synthesis of single crystalline Au nanoparticles with unusual shapes and tunable LSPR in the near-IR”. Angelomé, PC, Heidari Mezerji H, Goris B, Pastoriza-Santos I, Pérez-Juste J, Bals S, Liz-Marzán LM, Chemistry of materials 24, 1393 (2012). http://doi.org/10.1021/cm3004479
Abstract: The plasmonic properties of metal nanoparticles have acquired great importance because of their potential applications in very diverse fields. Metal nanoparticles with localized surface plasmon resonances (LSPR) in the near-infrared (NIR, 7501300 nm) are of particular interest because tissues, blood, and water display low absorption in this spectral range, thus facilitating biomedical applications. Cetyltrimethylammonium chloride (CTAC) was used to induce the seedless formation of highly anisotropic, twisted single crystalline Au nanoparticles in a single step. The LSPR of the obtained particles can be tuned from 600 nm up to 1400 nm by simply changing the reaction temperature or the reagents concentrations. The tunability of the LSPR is closely associated with significant changes in the final particle morphology, which was studied by advanced electron microscopy techniques (3D Tomography and HAADF-STEM). Kinetic experiments were carried out to establish the growth mechanism, suggesting that slow kinetics together with the complexation of the gold salt precursor to CTAC are key factors favoring the formation of these anisotropic particles.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 42
DOI: 10.1021/cm3004479
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“Short-range order of Br and three-dimensional magnetism in (CuBr)LaNb2O7”. Tsirlin AA, Abakumov AM, Ritter C, Henry PF, Janson O, Rosner H, Physical review : B : condensed matter and materials physics 85, 214427 (2012). http://doi.org/10.1103/PhysRevB.85.214427
Abstract: We present a comprehensive study of the crystal structure, magnetic structure, and microscopic magnetic model of (CuBr)LaNb2O7, the Br analog of the spin-gap quantum magnet (CuCl) LaNb2O7. Despite similar crystal structures and spin lattices, the magnetic behavior and even peculiarities of the atomic arrangement in the Cl and Br compounds are very different. The high- resolution x-ray and neutron data reveal a split position of Br atoms in (CuBr) LaNb2O7. This splitting originates from two possible configurations developed by [CuBr] zigzag ribbons. While the Br atoms are locally ordered in the ab plane, their arrangement along the c direction remains partially disordered. The predominant and energetically more favorable configuration features an additional doubling of the c lattice parameter that was not observed in (CuCl) LaNb2O7. (CuBr) LaNb2O7 undergoes long-range antiferromagnetic ordering at T-N = 32 K, which is nearly 70% of the leading exchange coupling J4 similar or equal to 48 K. The Br compound does not show any experimental signatures of low-dimensional magnetism because the underlying spin lattice is three-dimensional. The coupling along the c direction is comparable to the couplings in the ab plane, even though the shortest Cu-Cu distance along c (11.69 angstrom) is three times larger than nearest-neighbor distances in the ab plane (3.55 angstrom). The stripe antiferromagnetic long-range order featuring columns of parallel spins in the ab plane and antiparallel spins along c is verified experimentally and confirmed by the microscopic analysis.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 5
DOI: 10.1103/PhysRevB.85.214427
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“A simple road for the transformation of few-layer graphene into MWNTs”. Quintana M, Grzelczak M, Spyrou K, Calvaresi M, Bals S, Kooi B, Van Tendeloo G, Rudolf P, Zerbetto F, Prato M, Journal of the American Chemical Society 134, 13310 (2012). http://doi.org/10.1021/ja303131j
Abstract: We report the direct formation of multiwalled carbon nanotubes (MWNT) by ultrasonication of graphite in dimethylformamide (DMF) upon addition of ferrocene aldehyde (Fc-CHO). The tubular structures appear exclusively at the edges of graphene layers and contain Fe clusters. Pc in conjunction with benzyl aldehyde, or other Fc derivatives, does not induce formation of NT. Higher amounts of Fc-CHO added to the dispersion do not increase significantly MWNT formation. Increasing the temperature reduces the amount of formation of MWNTs and shows the key role of ultrasound-induced cavitation energy. It is concluded that Fc-CHO first reduces the concentration of radical reactive species that slice graphene into small moieties, localizes itself at the edges of graphene, templates the rolling up of a sheet to form a nanoscroll, where it remains trapped, and finally accepts and donates unpaired electron to the graphene edges and converts the less stable scroll into a MWNT. This new methodology matches the long held notion that CNTs are rolled up graphene layers. The proposed mechanism is general and will lead to control the production of carbon nanostructures by simple ultrasonication treatments.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 13.858
Times cited: 56
DOI: 10.1021/ja303131j
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“Site-specific mapping of transition metal oxygen coordination in complex oxides”. Turner S, Egoavil R, Batuk M, Abakumov AA, Hadermann J, Verbeeck J, Van Tendeloo G, Applied physics letters 101, 241910 (2012). http://doi.org/10.1063/1.4770512
Abstract: We demonstrate site-specific mapping of the oxygen coordination number for transition metals in complex oxides using atomically resolved electron energy-loss spectroscopy in an aberration-corrected scanning transmission electron microscope. Pb2Sr2Bi2Fe6O16 contains iron with a constant Fe3+ valency in both octahedral and tetragonal pyramidal coordination and is selected to demonstrate the principle of site-specific coordination mapping. Analysis of the site-specific Fe-L2,3 data reveals distinct variations in the fine structure that are attributed to Fe in a six-fold (octahedron) or five-fold (distorted tetragonal pyramid) oxygen coordination. Using these variations, atomic resolution coordination maps are generated that are in excellent agreement with simulations.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.411
Times cited: 12
DOI: 10.1063/1.4770512
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“Spin-dependent on-site electron correlations and localization in itinerant f erromagnets”. Gotter R, Fratesi G, Bartynski RA, da Pieve F, Offi F, Ruocco A, Ugenti S, Trioni MI, Brivio GP, Stefani G, Physical review letters 109, 126401 (2012). http://doi.org/10.1103/PhysRevLett.109.126401
Abstract: Spin selectivity in angle-resolved Auger photoelectron coincidence spectroscopy (AR-APECS) is used to probe electron correlation in ferromagnetic thin films. In particular, exploiting the AR-APECS capability to discriminate Auger electron emission events characterized by valence hole pairs created either in the high or in the low total spin state, a strong correlation effect in the Fe M2,3VV Auger line shape (measured in coincidence with the Fe 3p photoelectrons) of Fe/Cu(001) thin films is detected and ascribed to interactions within the majority spin subband. Such an assignment follows from a close comparison of the experimental AR-APECS line shapes with the predictions of a model based on spin polarized density functional theory and the Cini-Sawatzky approach.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.462
Times cited: 9
DOI: 10.1103/PhysRevLett.109.126401
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“Stability and crystal structures of iron carbides : a comparison between the semi-empirical modified embedded atom method and quantum-mechanical DFT calculations”. Fang CM, van Huis MA, Thijsse BJ, Zandbergen HW, Physical review : B : condensed matter and materials physics 85, 054116 (2012). http://doi.org/10.1103/PhysRevB.85.054116
Abstract: Iron carbides play a crucial role in steel manufacturing and processing and to a large extent determine the physical properties of steel products. The modified embedded atom method (MEAM) in combination with Lee's Fe-C potential is a good candidate for molecular dynamics simulations on larger Fe-C systems. Here, we investigate the stability and crystal structures of pure iron and binary iron carbides using MEAM and compare them with the experimental data and quantum-mechanical density functional theory calculations. The analysis shows that the Fe-C potential gives reasonable results for the relative stability of iron and iron carbides. The performance of MEAM for the prediction of the potential energy and the calculated lattice parameters at elevated temperature for pure iron phases and cementite are investigated as well. The conclusion is that Lee's MEAM Fe-C potential provides a promising basis for further molecular dynamics simulations of Fe-C alloys and steels at lower temperatures (up to 800 K).
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 18
DOI: 10.1103/PhysRevB.85.054116
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“Stability and structures of the CFCC-TmC phases : a first-principles study”. Fang CM, van Huis MA, Zandbergen HW, Computational materials science 51, 146 (2012). http://doi.org/10.1016/j.commatsci.2011.07.017
Abstract: The η-M6C, γ-M23C6, and π-M11C2 phases (M = Cr, Mn and Fe) have complex cubic lattices with lattice parameters of approximately 1.0 nm. They belong to the CFCC-TmC family (complex face-centered cubic transition metal carbides), display a rich variety of crystal structures, and play in important role in iron alloys and steels. Here we show that first-principles calculations predict high stability for the γ-M23C6 and η-M6C phases, and instability for the π-M11C2 phases, taking into account various compositional and structural possibilities. The calculations also show a wide variety in magnetic properties. The Cr-containing phases were found to be non-magnetic and the Fe-phases to be ferromagnetic, while the Mn-containing phases were found to be either ferrimagnetic or non-magnetic. Details of the local atomic structures, and the formation and stability of these precipitates in alloys are discussed.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.292
Times cited: 18
DOI: 10.1016/j.commatsci.2011.07.017
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“Structural requirements in lithium cobalt oxides for the catalytic oxidation of water”. Gardner GP, Go YB, Robinson DM, Smith PF, Hadermann J, Abakumov A, Greenblatt M, Dismukes GC, Angewandte Chemie: international edition in English 51, 1616 (2012). http://doi.org/10.1002/anie.201107625
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 11.994
Times cited: 119
DOI: 10.1002/anie.201107625
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“Structure and high-temperature properties of the (Sr,Ca,Y)(Co,Mn)O3-y perovskites –, perspective cathode materials for IT-SOFC”. Napolsky PS, Drozhzhin OA, Istomin SY, Kazakov SM, Antipov EV, Galeeva AV, Gippius AA, Svensson G, Abakumov AM, Van Tendeloo G, Journal of solid state chemistry 192, 186 (2012). http://doi.org/10.1016/j.jssc.2012.03.056
Abstract: Oxygen deficient perovskites Sr0.75Y0.25Co1-xMnxO3-y, x=0.5 and 0.75, were prepared by using the citrate route at 1373-1573 K for 48 h. The cubic Pm-3m perovskite structure for x=0.5 was confirmed by electron diffraction study and refined using neutron powder diffraction (NPD) data. For x=0.75, the superstructure corresponding to a=root 2 x a(per), b=2 x a(per), c=root 2 x a(per) (a(0)b(-)b(-) tilt system, space group Imma) was revealed by electron diffraction. The solid solution Sr0.75-xCaxY0.25Co0.25Mn0.75O3-y, 0.1 <= x <= 0.6 and compound Ca0.75Y0.25Mn0.85Co0.15O2.92 were prepared in air at 1573 K for 48 h. The crystal structure of Ca0.75Y0.25Mn0.85Co0.15O2.92 was refined using NPD data (S.G. Pnma, a=5.36595(4), b=7.5091(6), c=5.2992(4) angstrom, R-p=0.057, R-wp=0.056, chi(2)=4.26). High-temperature thermal expansion properties of the prepared compounds were studied in air using both dilatometry and high-temperature X-ray powder diffraction data (HTXRPD). They expanding non-linearly at 298-1073 K due to the loss of oxygen at high temperatures. Calculated average thermal expansion coefficients (TECs) for Sr0.75Y0.25Co1-xMnxO3-y, x=0.5, 0.75 and Ca0.75Y0.25Mn0.85Co0.15O2.92(1) are 15.5, 15.1, and 13.8 ppm K-1, respectively. Anisotropy of the thermal expansion along different unit cell axes was observed for Sr0.15Ca0.6Y0.25Co0.25Mn0.75O3-y, and Ca0.75Y0.25Mn0.85Co0.15O2.92. Conductivity of Sr0.75Y0.25Co1-xMnxO3-y, x=0.5 and 0.75 increases with the temperature reaching 110 S/cm for x=0.5 and 44 S/cm for x=0.75 at 1173 K. Samples of Sr0.75-xCaxY0.25Co0.25Mn0.75O3-y, 0.1 <= y <= 0.6 were found to be n-type conductors at room temperature with the similar temperature dependence of the conductivity and demonstrated the increase of the sigma value from similar to 1 to similar to 50 S/cm as the temperature increases from 300 to 1173 K. Their conductivity is described in terms of the small polaron charge transport with the activation energy (E-p) increasing from 340 to 430 meV with an increase of the calcium content from x=0 to x=0.6. (C) 2012 Elsevier Inc. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.299
Times cited: 5
DOI: 10.1016/j.jssc.2012.03.056
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“Structures and magnetism of La1-xSrxMnO3-(0.5+x)/2 (0.67\leq x\leq1) phases”. Dixon E, Hadermann J, Hayward MA, Chemistry of materials 24, 1486 (2012). http://doi.org/10.1021/cm300199b
Abstract: Topotactic reduction of La1-xSrxMnO3 (0.67 <= x <= 1) phases with sodium hydride yields a series of isoelectronic materials of composition La1-xSrxMnO3-(0.5+x)/2. Lanthanum rich members of the series (0.67 <= x <= 0.83) adopt anion deficient perovskite structures with a 6-layer -OTOOT'O- stacking sequence of sheets of octahedra/square-based pyramids (O) and sheets of tetrahedra (T). The strontium rich members of the series (0.83 <= x <= 1) incorporate “step defects” into this 6-layer structure in which the OTOOT'O stacking sequence is converted into either OOTOOT' or TOOT'OO at a defect plane which runs perpendicular to the [201] lattice plane. The step defects appear to provide a mechanism to relieve lattice strain and accommodate additional anion deficiency in phases with x > 0.83. Magnetization and neutron diffraction data indicate La1-xSrxMnO3-(0.5+x)/2 phases adopt antiferromagnetically ordered states at low-temperature in which the ordered arrangement of magnetic spins is incommensurate with the crystallographic lattice.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 13
DOI: 10.1021/cm300199b
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“Study of the interaction between copper and carbon nanotubes”. Bittencourt C, Ke X, Van Tendeloo G, Thiess S, Drube W, Ghijsen J, Ewels CP, Chemical physics letters 535, 80 (2012). http://doi.org/10.1016/j.cplett.2012.03.045
Abstract: Copper deposited by thermal evaporation onto pristine and oxygen plasma treated carbon nanotubes (CNTs) diffuse over the CNT surface, coalescing and forming crystalline islands. The nucleation sites of the islands are preferentially defects, and more homogeneous island dispersion was observed at the CNT oxygen functionalized surface. The presence of weakly bound oxygen atoms at the CNT surface induces the formation of CuO bonds at the Cu/CNT interface, as described through density functional calculations. Exposure to air allows further oxidation to facetted crystalline Cu2O. Oxygen plasma pre-treatment represents a promising route for homogenous disperse Cu2O nanoparticle decoration of CNTs.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.815
Times cited: 27
DOI: 10.1016/j.cplett.2012.03.045
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“Sub-nanometer free electrons with topological charge”. Schattschneider P, Stöger-Pollach M, Löffler S, Steiger-Thirsfeld A, Hell J, Verbeeck J, Ultramicroscopy 115, 21 (2012). http://doi.org/10.1016/j.ultramic.2012.01.010
Abstract: The holographic mask technique is used to create freely moving electrons with quantized angular momentum. With electron optical elements they can be focused to vortices with diameters below the nanometer range. The understanding of these vortex beams is important for many applications. Here, we produce electron vortex beams and compare them to a theory of electrons with topological charge. The experimental results show excellent agreement with simulations. As an immediate application, fundamental experimental parameters like spherical aberration and partial coherence are determined. (C) 2012 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 24
DOI: 10.1016/j.ultramic.2012.01.010
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“Synthesis, crystal structure, transport, and magnetic properties of novel ternary copper phosphides, A2Cu6P5(A = Sr, Eu) and EuCu4P3”. Charkin DO, Urmanov AV, Kazakov SM, Batuk D, Abakumov AM, Knöner S, Gati E, Wolf B, Lang M, Shevelkov AV, Van Tendeloo G, Antipov EV;, Inorganic chemistry 51, 8948 (2012). http://doi.org/10.1021/ic301033h
Abstract: Three new ternary copper phosphides, Sr2Cu6P5, Eu2Cu6P5, and EuCu4P3, have been synthesized from the elements in evacuated silica capsules. Eu2Cu6P5 and Sr2Cu6P5 adopt the Ca2Cu6P5-type structure, while EuCu4P3 is isostructural to BaMg4Si3 and still remains the only representative of this structure type among the ternary Cu pnictides. All three materials show metallic conductivity in the temperature range 2 K <= T <= 290 K, with no indication for superconductivity. For Eu2Cu6P5 and EuCu4P3, long-range magnetic order was observed, governed by 4f local moments on the Eu atoms with predominant ferromagnetic interactions. While Eu2Cu6P5 shows a single ferromagnetic transition at T-C = 34 K, the magnetic behavior of EuCu4P3 is more complex, giving rise to three consecutive magnetic phase transitions at 70, 43, and 18 K.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.857
Times cited: 13
DOI: 10.1021/ic301033h
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“Tailoring CuO nanostructures for enhanced photocatalytic property”. Liu J, Jin J, Deng Z, Huang SZ, Hu ZY, Wang L, Wang C, Chen LH, Li Y, Van Tendeloo G, Su BL;, Journal of colloid and interface science 384, 1 (2012). http://doi.org/10.1016/j.jcis.2012.06.044
Abstract: We report on one-pot synthesis of various morphologies of CuO nanostructures. PEG200 as a structure directing reagent under the synergism of alkalinity by hydrothermal method has been employed to tailor the morphology of CuO nanostructures. The CuO products have been characterized by XRD, SEM, and TEM. The morphologies of the CuO nanostructures can be tuned from 10 (nanoseeds, nanoribbons) to 2D (nanoleaves) and to 3D (shuttle-like, shrimp-like, and nanoflowers) by changing the volume of PEG200 and the alkalinity in the reaction system. At neutral and relatively low alkalinity (OH-/Cu2+ <= 3), the addition of PEG200 can strongly influence the morphologies of the CuO nanostructures. At high alkalinity (OH/Cu2+ >= 4), PEG200 has no influence on the morphology of the CuO nanostructure. The different morphologies of the CuO nanostructures have been used for the photodecomposition of the pollutant rhodamine B (RhB) in water. The photocatalytic activity has been correlated with the different nanostructures of CuO. The 10 CuO nanoribbons exhibit the best performance on the RhB photodecomposition because of the exposed high surface energy {-121} crystal plane. The photocatalytic results show that the high energy surface planes of the CuO nanostructures mostly affect the photocatalytic activity rather than the morphology of the CuO nanostructures. Our synthesis method also shows it is possible to control the morphologies of nanostructures in a simple way. (C) 2012 Elsevier Inc. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.233
Times cited: 105
DOI: 10.1016/j.jcis.2012.06.044
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“Bi0.75Sr0.25FeO3-\delta : revealing order/disorder phenomena by combining diffraction techniques”. Pachoud E, Bréard Y, Martin C, Maignan A, Abakumov AM, Suard E, Smith RI, Suchomel MR, Solid state communications 152, 331 (2012). http://doi.org/10.1016/j.ssc.2011.12.023
Abstract: The local and long range structure of polycrystalline samples of Bi0.75Sr0.25FeO3-delta has been probed by neutron and synchrotron X-ray diffraction coupled with transmission electron microscopy. It is found that the long range structure on average can be described by the cubic space group Pm-3m (a(p) congruent to 3.951 angstrom). However, the refinements revealed large atomic displacements for the (Bi, Sr) cations and the oxygen atoms from their ideal positions. The electron microscopy study indicates the existence of local phenomena like local ordering of oxygen vacancies, which are segregated at the randomly spaced parallel (FeO2-delta) planes, or the existence of region of different symmetry, probably R3c. At room temperature, the compound exhibits G-type antiferromagnetism (T-N congruent to 650 K) with a magnetic moment of congruent to 3.7 mu(B). (C) 2012 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.554
Times cited: 6
DOI: 10.1016/j.ssc.2011.12.023
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“(CuCl)LaTa2O\text{7} and quantum phase transition in the (CuX)LaM2O7 family (X=Cl, Br, M=Nb, Ta)”. Tsirlin AA, Abakumov AM, Ritter C, Rosner H, Physical review : B : condensed matter and materials physics 86, 064440 (2012). http://doi.org/10.1103/PhysRevB.86.064440
Abstract: We apply neutron diffraction, high-resolution synchrotron x-ray diffraction, magnetization measurements, electronic structure calculations, and quantum Monte-Carlo simulations to unravel the structure and magnetism of (CuCl)LaTa2O7. Despite the pseudo-tetragonal crystallographic unit cell, this compound features an orthorhombic superstructure, similar to the Nb-containing (CuX)LaNb2O7 with X = Cl and Br. The spin lattice entails dimers formed by the antiferromagnetic fourth-neighbor coupling J(4), as well as a large number of nonequivalent interdimer couplings quantified by an effective exchange parameter J(eff). In (CuCl)LaTa2O7, the interdimer couplings are sufficiently strong to induce the long-range magnetic order with the Neel temperature T-N similar or equal to 7 K and the ordered magnetic moment of 0.53 mu(B), as measured with neutron diffraction. This magnetic behavior can be accounted for by J(eff)/J(4) similar or equal to 1.6 and J(4) similar or equal to 16 K. We further propose a general magnetic phase diagram for the (CuCl)LaNb2O7-type compounds, and explain the transition from the gapped spin-singlet (dimer) ground state in (CuCl)LaNb2O7 to the long-range antiferromagnetic order in (CuCl)LaTa2O7 and (CuBr)LaNb2O7 by an increase in the magnitude of the interdimer couplings J(eff)/J(4), with the (CuCl)LaM2O7 (M = Nb, Ta) compounds lying on different sides of the quantum critical point that separates the singlet and long-range-ordered magnetic ground states.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 6
DOI: 10.1103/PhysRevB.86.064440
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“Na2/7Gd4/7MoO4 : a modulated scheelite-type structure and conductivity properties”. Morozov V, Arakcheeva A, Redkin B, Sinitsyn V, Khasanov S, Kudrenko E, Raskina M, Lebedev O, Van Tendeloo G, Inorganic chemistry 51, 5313 (2012). http://doi.org/10.1021/ic300221m
Abstract: Scheelite-type compounds with the general formula (A1,A2)n[(B1,B2)O4]m (2/3 ≤ n/m ≤ 3/2) are the subject of large interest owing to their stability, relatively simple preparation, and optical properties. The creation of cation vacancies (□) in the scheelite-type framework and the ordering of A cations and vacancies can be a new factor in controlling the scheelite-type structure and properties. For a long time, cation-deficient Nd3+:M2/7Gd4/7□1/7MoO4 (M = Li, Na) compounds were considered as potential lasers with diode pumping. They have a defect scheelite-type 3D structure (space group I41/a) with a random distribution of Li+(Na+), Gd3+, and vacancies in the crystal. A Na2/7Gd4/7MoO4 single crystal with scheelite-type structure has been grown by the Czochralski method. Transmission electron microscopy revealed that Na2/7Gd4/7MoO4 has a (3 + 2)D incommensurately modulated structure. The (3 + 2)D incommensurately modulated scheelite-type cation-deficient structure of Na2/7Gd4/7MoO4 [super space group I4̅ (αβ0,βα0)00] has been solved from single-crystal diffraction data. The solution of the (3 + 2)D incommensurately modulated structure revealed the partially disordered distribution of vacancies and Na and Gd cations. High-temperature conductivity measurements performed along the [100] and [001] orientation of the single crystal revealed that the conductivity of Na2/7Gd4/7MoO4 at T = 973 K equals σ = 1.13 × 105 Ω1 cm1.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.857
Times cited: 37
DOI: 10.1021/ic300221m
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