“X-ray and electron spectroscopy investigation of the coreshell nanowires of ZnO:Mn”. Guda AA, Smolentsev N, Verbeeck J, Kaidashev EM, Zubavichus Y, Kravtsova AN, Polozhentsev OE, Soldatov AV, Solid state communications 151, 1314 (2011). http://doi.org/10.1016/j.ssc.2011.06.028
Abstract: ZnO/ZnO:Mn coreshell nanowires were studied by means of X-ray absorption spectroscopy of the Mn K- and L2,3-edges and electron energy loss spectroscopy of the O K-edge. The combination of conventional X-ray and nanofocused electron spectroscopies together with advanced theoretical analysis turned out to be fruitful for the clear identification of the Mn phase in the volume of the coreshell structures. Theoretical simulations of spectra, performed using the full-potential linear augmented plane wave approach, confirm that the shell of the nanowires, grown by the pulsed laser deposition method, is a real dilute magnetic semiconductor with Mn2+ atoms at the Zn sites, while the core is pure ZnO.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.554
Times cited: 12
DOI: 10.1016/j.ssc.2011.06.028
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“Zirconia-modified exfoliated graphite”. Afanasov IM, Van Tendeloo G, Inorganic materials 47, 603 (2011). http://doi.org/10.1134/S0020168511050013
Abstract: Zirconia has been incorporated into exfoliated graphite (EG) through the anodic polarization in the natural graphite-ZrO(NO3)2-HNO3-H2O system, followed by flash heating. The thermal properties of the oxidized graphites employed as precursors to EG have been studied by thermogravimetry in combination with differential scanning calorimetry, and the distribution of ZrO2 particles in the EG has been assessed by scanning and transmission electron microscopy. Conditions are described for the preparation of EG with bulk densities in the range 1.34.7 g/l and ZrO2 contents in the range 434 wt %.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 0.62
DOI: 10.1134/S0020168511050013
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“ZnO@ZIF-8 : stabilization of quantum confined ZnO nanoparticles by a zinc methylimidazolate framework and their surface structural characterization probed by CO2 adsorption”. Esken D, Noei H, Wang Y, Wiktor C, Turner S, Van Tendeloo G, Fischer RA, Journal of materials chemistry 21, 5907 (2011). http://doi.org/10.1039/c1jm10091b
Abstract: The microporous and activated zeolitic imidazolate framework (Zn(MeIM)2; MeIM = imidazolate-2-methyl; ZIF-8) was loaded with the MOCVD precursor diethyl zinc [Zn(C2H5)2]. Exposure of ZIF-8 to the vapour of the volatile organometallic molecule resulted in the formation of the inclusion compound [Zn(C2H5)2]0.38@ZIF-8 revealing two precursor molecules per cavity. In a second step the obtained material was treated with oxygen (5 vol% in argon) at various temperatures (oxidative annealing) to achieve the composite material ZnO0.35@ZIF-8. The new material was characterized with powder XRD, FT-IR, UV-vis, solid state NMR, elemental analysis, N2 sorption measurements, and transmission electron microscopy. The data give evidence for the presence of nano-sized ZnO particles stabilized by ZIF-8 showing a blue-shift of the UV-vis absorption caused by quantum size effect (QSE). The surface structure and reactivity of embedded ZnO nanoparticles were characterized via carbon dioxide adsorption at different temperatures monitored by ultra-high vacuum FTIR techniques. It was found that the surface of ZnO nanoparticles is dominated by polar OZnO and ZnZnO facets as well as by defect sites, which all exhibit high reactivity towards CO2 activation forming various adsorbed carbonate and chemisorbed CO2δ− species.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 76
DOI: 10.1039/c1jm10091b
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“Dark field electron holography for strain measurement”. Béché, A, Rouvière JL, Barnes JP, Cooper D, Ultramicroscopy 111, 227 (2011). http://doi.org/10.1016/J.ULTRAMIC.2010.11.030
Abstract: Dark field electron holography is a new TEM-based technique for measuring strain with nanometer scale resolution. Here we present the procedure to align a transmission electron microscope and obtain dark field holograms as well as the theoretical background necessary to reconstruct strain maps from holograms. A series of experimental parameters such as biprism voltage, sample thickness, exposure time, tilt angle and choice of diffracted beam are then investigated on a silicon-germanium layer epitaxially embedded in a silicon matrix in order to obtain optimal dark field holograms over a large field of view with good spatial resolution and strain sensitivity.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 31
DOI: 10.1016/J.ULTRAMIC.2010.11.030
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“Field mapping with nanometer-scale resolution for the next generation of electronic devices”. Cooper D, de la Peña F, Béché, A, Rouvière J-L, Servanton G, Pantel R, Morin P, Nano letters 11, 4585 (2011). http://doi.org/10.1021/NL201813W
Abstract: In order to improve the performance of todays nanoscaled semiconductor devices, characterization techniques that can provide information about the position and activity of dopant atoms and the strain fields are essential. Here we demonstrate that by using a modern transmission electron microscope it is possible to apply multiple techniques to advanced materials systems in order to provide information about the structure, fields, and composition with nanometer-scale resolution. Off-axis electron holography has been used to map the active dopant potentials in state-of-the-art semiconductor devices with 1 nm resolution. These dopant maps have been compared to electron energy loss spectroscopy maps that show the positions of the dopant atoms. The strain fields in the devices have been measured by both dark field electron holography and nanobeam electron diffraction.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 12.712
Times cited: 12
DOI: 10.1021/NL201813W
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“Quantitative strain mapping of InAs/InP quantum dots with 1 nm spatial resolution using dark field electron holography”. Cooper D, Rouvière J-L, Béché, A, Kadkhodazadeh S, Semenova ES, Dunin-Borkowsk R, Applied physics letters 99, 261911 (2011). http://doi.org/10.1063/1.3672194
Abstract: The optical properties of semiconductor quantum dots are greatly influenced by their strain state. Dark field electron holography has been used to measure the strain in InAsquantum dotsgrown in InP with a spatial resolution of 1 nm. A strain value of 5.4% ± 0.1% has been determined which is consistent with both measurements made by geometrical phase analysis of high angle annular dark field scanning transmission electron microscopy images and with simulations.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.411
Times cited: 26
DOI: 10.1063/1.3672194
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“The reduction of the substitutional C content in annealed Si/SiGeC superlattices studied by dark-field electron holography”. Denneulin T, Rouvière JL, Béché, A, Py M, Barnes JP, Rochat N, Hartmann JM, Cooper D, Semiconductor science and technology 26, 1 (2011). http://doi.org/10.1088/0268-1242/26/12/125010
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.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.305
DOI: 10.1088/0268-1242/26/12/125010
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“Degradation process of lead chromate in paintings by Vincent van Gogh studied by means of synchrotron X-ray spectromicroscopy and related methods : 1 : artificially aged model samples”. Monico L, van der Snickt G, Janssens K, de Nolf W, Miliani C, Verbeeck J, Tian H, Tan H, Dik J, Radepont M, Cotte M, Analytical chemistry 83, 1214 (2011). http://doi.org/10.1021/ac102424h
Abstract: On several paintings by artists of the end of the 19th century and the beginning of the 20th Century a darkening of the original yellow areas, painted with the chrome yellow pigment (PbCrO4, PbCrO4·xPbSO4, or PbCrO4·xPbO) is observed. The most famous of these are the various Sunflowers paintings Vincent van Gogh made during his career. In the first part of this work, we attempt to elucidate the degradation process of chrome yellow by studying artificially aged model samples. In view of the very thin (1−3 μm) alteration layers that are formed, high lateral resolution spectroscopic methods such as microscopic X-ray absorption near edge (μ-XANES), X-ray fluorescence spectrometry (μ-XRF), and electron energy loss spectrometry (EELS) were employed. Some of these use synchrotron radiation (SR). Additionally, microscopic SR X-ray diffraction (SR μ-XRD), μ-Raman, and mid-FTIR spectroscopy were employed to completely characterize the samples. The formation of Cr(III) compounds at the surface of the chrome yellow paint layers is particularly observed in one aged model sample taken from a historic paint tube (ca. 1914). About two-thirds of the chromium that is present at the surface has reduced from the hexavalent to the trivalent state. The EELS and μ-XANES spectra are consistent with the presence of Cr2O3·2H2O (viridian). Moreover, as demonstrated by μ-XANES, the presence of another Cr(III) compound, such as either Cr2(SO4)3·H2O or (CH3CO2)7Cr3(OH)2 [chromium(III) acetate hydroxide], is likely.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 6.32
Times cited: 113
DOI: 10.1021/ac102424h
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“Accurate pseudopotential description of the GW bandstructure of ZnO”. Dixit H, Saniz R, Lamoen D, Partoens B, Computer physics communications 182, 2029 (2011). http://doi.org/10.1016/j.cpc.2011.02.001
Abstract: We present the GW band structure of ZnO in its wurtzite (WZ), zincblende (ZB) and rocksalt (RS) phases at the Γ point, calculated within the GW approximation. We have used a Zn20+ pseudopotential which is essential for the adequate treatment of the exchange interaction in the self-energy. The accuracy of the pseudopotential used is also discussed. The effect of the pd hybridization on the GW corrections to the band gap is correlated by comparing the ZB and RS phase.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 3.936
Times cited: 18
DOI: 10.1016/j.cpc.2011.02.001
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“Electronic structure and band gap of zinc spinel oxides beyond LDA : ZnAl2O4, ZnGa2O4 and ZnIn2O4”. Dixit H, Tandon N, Cottenier S, Saniz R, Lamoen D, Partoens B, van Speybroeck V, Waroquier M, New journal of physics 13, 063002 (2011). http://doi.org/10.1088/1367-2630/13/6/063002
Abstract: We examine the electronic structure of the family of ternary zinc spinel oxides ZnX2O4 (X=Al, Ga and In). The band gap of ZnAl2O4 calculated using density functional theory (DFT) is 4.25 eV and is overestimated compared with the experimental value of 3.83.9 eV. The DFT band gap of ZnGa2O4 is 2.82 eV and is underestimated compared with the experimental value of 4.45.0 eV. Since DFT typically underestimates the band gap in the oxide system, the experimental measurements for ZnAl2O4 probably require a correction. We use two first-principles techniques capable of describing accurately the excited states of semiconductors, namely the GW approximation and the modified BeckeJohnson (MBJ) potential approximation, to calculate the band gap of ZnX2O4. The GW and MBJ band gaps are in good agreement with each other. In the case of ZnAl2O4, the predicted band gap values are >6 eV, i.e. ~2 eV larger than the only reported experimental value. We expect future experimental work to confirm our results. Our calculations of the electron effective masses and the second band gap indicate that these compounds are very good candidates to act as transparent conducting host materials.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 3.786
Times cited: 98
DOI: 10.1088/1367-2630/13/6/063002
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“Hydrogen impurities and native defects in CdO”. Amini MN, Saniz R, Lamoen D, Partoens B, Journal of applied physics 110, 063521 (2011). http://doi.org/10.1063/1.3641971
Abstract: We have used first-principles calculations based on density functional theory to study point defects in CdO within the local density approximation and beyond (LDA+U). Hydrogen interstitials and oxygen vacancies are found to act as shallow donors and can be interpreted as the cause of conductivity in CdO. Hydrogen can also occupy an oxygen vacancy in its substitutional form and also acts as a shallow donor. Similar to what was found for ZnO and MgO, hydrogen creates a multicenter bond with its six oxygen neighbors in CdO. The charge neutrality level for native defects and hydrogen impurities has been calculated. It is shown that in the case of native defects, it is not uniquely defined. Indeed, this level depends highly on the chemical potentials of the species and one can obtain different values for different end states in the experiment. Therefore, a comparison with experiment can only be made if the chemical potentials of the species in the experiment are well defined. However, for the hydrogen interstitial defect, since this level is independent of the chemical potential of hydrogen, one can obtain a unique value for the charge neutrality level. We find that the Fermi level stabilizes at 0.43 eV above the conduction band minimum in the case of the hydrogen interstitial defect, which is in good agreement with the experimentally reported value of 0.4 eV.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 2.068
Times cited: 13
DOI: 10.1063/1.3641971
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“Multiple Dirac particles in AA-stacked graphite and multilayers of graphene”. Lobato I, Partoens B, Physical review : B : condensed matter and materials physics 83, 165429 (2011). http://doi.org/10.1103/PhysRevB.83.165429
Abstract: Using the tight-binding formalism we show that in the recently experimentally realized AA-stacked graphite in essence two types of massless relativistic Dirac particles are present with a different effective speed of light. We also investigate how the electronic structure evolves from a single graphene sheet into AA-stacked graphite. It is shown that in contrast to AB-stacked graphene layers, the spectrum of AA-stacked graphene layers can be considered as a superposition of single-layer spectra and only particles with a linear spectrum at the Fermi energy around the K point are present. From the evolution of the band overlap we show that 6 multilayers of AA-stacked graphene already behave as AA-stacked graphite. The evolution of the effective speeds of light of the Dirac particles to their bulk values shows exactly the same behavior. The tight-binding parameters we use to describe AA-stacked graphite and multilayers of graphene are obtained by ab initio calculations.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 68
DOI: 10.1103/PhysRevB.83.165429
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“Tubular fullerenes inside carbon nanotubes : optimal molecular orientation versus tube radius”. Verberck B, Tarakina NV, European physical journal : B : condensed matter and complex systems 80, 355 (2011). http://doi.org/10.1140/epjb/e2011-10952-1
Abstract: We present an investigation of the orientations and positions of tubular fullerene molecules (C90, ..., C200) encapsulated in single-walled carbon nanotubes (SWCNT), a series of so-called fullerene nanopeapods. We find that increasing the tube radius leads to the following succession of energetically stable regimes: (1) lying molecules positioned on the tube's long axis; (2) tilted molecules on the tube's long axis; and (3) lying molecules shifted away from the tube's long axis. As opposed to C70 and C80 molecules encapsulated in a SWCNT, standing orientations do not develop. Our results are relevant for the possible application of molecular-orientation-dependent electronic properties of fullerene nanopeapods, and also for the interpretation of future experiments on double-walled carbon nanotube formation by annealing fullerene peapod systems.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 1.461
Times cited: 10
DOI: 10.1140/epjb/e2011-10952-1
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“Immersion calorimetry as a tool to evaluate the catalytic performance of titanosilicate materials in the epoxidation of cyclohexene”. Vernimmen J, Guidotti M, Silvestre-Albero J, Jardim EO, Mertens M, Lebedev OI, Van Tendeloo G, Psaro R, Rodríguez-Reinoso F, Meynen V, Cool P, Langmuir: the ACS journal of surfaces and colloids 27, 3618 (2011). http://doi.org/10.1021/la104808v
Abstract: Different types of titanosilicates are synthesized, structurally characterized, and subsequently catalytically tested in the liquid-phase epoxidation of cyclohexene. The performance of three types of combined zeolitic/mesoporous materials is compared with that of widely studied Ti-grafted-MCM-41 molecular sieve and the TS-1 microporous titanosilicate. The catalytic test results are correlated with the structural characteristics of the different catalysts. Moreover, for the first time, immersion calorimetry with the same substrate molecule as in the catalytic test reaction is applied as an extra means to interpret the catalytic results. A good correlation between catalytic performance and immersion calorimetry results is found. This work points out that the combination of catalytic testing and immersion calorimetry can lead to important insights into the influence of the materials structural characteristics on catalysis. Moreover, the potential of using immersion calorimetry as a screening tool for catalysts in epoxidation reactions is shown.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Laboratory of adsorption and catalysis (LADCA)
Impact Factor: 3.833
Times cited: 19
DOI: 10.1021/la104808v
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“New insights in the formation of combined zeolitic/mesoporous materials by using a one-pot templating synthesis”. Vernimmen J, Meynen V, Herregods SJF, Mertens M, Lebedev OI, Van Tendeloo G, Cool P, European journal of inorganic chemistry , 4234 (2011). http://doi.org/10.1002/ejic.201100268
Abstract: Zeolitic growth is often absent or occurs in separate phases when synthetic strategies based on the combination of zeolite templates and mesopore templating agents are applied. In this work, zeolitic growth and mesopore formation have been investigated at different temperatures by applying a one-pot templating approach, based on a TS-1 zeolite synthesis whereby part of the microtemplate (tetrapropylammonium hydroxide, TPAOH) is replaced by a mesotemplate (hexadecyltrimethylammonium bromide, CTMABr). Moreover, the synthesis duration and the molar ratio of the microtemplate/mesotemplate have also been studied. The different syntheses clearly show the inherent competitive mechanism between zeolitic growth and mesopore formation. These insights have led to the conclusion that by following a one-pot templating strategy with standard, nonexotic commercial templates, i.e. CTMABr and TPAOH, it is not possible to develop a true hierarchical mesoporous zeolite, meaning a mesoporous siliceous material with highly crystalline zeolitic walls. The resultant materials are instead combined zeolitic/mesoporous composite structures with, however, highly tuneable and controllable porosity characteristics.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Laboratory of adsorption and catalysis (LADCA)
Impact Factor: 2.444
Times cited: 7
DOI: 10.1002/ejic.201100268
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“Smart heating profiles for the synthesis of benzene bridged periodic mesoporous organosilicas”. Smeulders G, van Oers C, Van Havenbergh K, Houthoofd K, Mertens M, Martens JA, Bals S, Maes BUW, Meynen V, Cool P, Chemical engineering journal 175, 585 (2011). http://doi.org/10.1016/j.cej.2011.09.116
Abstract: In this study the effects of the heating rate and heating time on the formation of crystal-like benzene bridged periodic mesoporous organosilicas (PMOs) are investigated. The time needed to heat up an autoclave during the hydrothermal treatment has shown to be crucial in the synthesis of PMOs, while the total duration of heating gave rise to only minor differences. By choosing a smart heating profile, superior PMO materials can be obtained in a short time. Different heating profiles in a range from one minute to one hour are adopted by microwave equipment and compared with conventional heating methods. The heating rate has a large influence on the porosity characteristics and the uniformity of the obtained particles. Moreover, two new alternative synthetic strategies to adopt the smart heating profile are presented, in order to give some possible solutions for the expensive microwave equipment.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Laboratory of adsorption and catalysis (LADCA); Organic synthesis (ORSY)
Impact Factor: 6.216
Times cited: 7
DOI: 10.1016/j.cej.2011.09.116
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“Theoretical investigation of grain size tuning during prolonged bias-enhanced nucleation”. Eckert M, Mortet V, Zhang L, Neyts E, Verbeeck J, Haenen ken, Bogaerts A, Chemistry of materials 23, 1414 (2011). http://doi.org/10.1021/cm102481y
Abstract: In this paper, the effects of prolonged bias-enhanced nucleation (prolonged BEN) on the growth mechanisms of diamond are investigated by molecular dynamics (MD) and combined MD-Metropolis Monte Carlo (MD-MMC) simulations. First, cumulative impacts of CxHy+ and Hx+ on an a-C:H/nanodiamond composite were simulated; second, nonconsecutive impacts of the dominant ions were simulated in order to understand the observed phenomena in more detail. As stated in the existing literature, the growth of diamond structures during prolonged BEN is a process that takes place below the surface of the growing film. The investigation of the penetration behavior of CxHy+ and Hx+ species shows that the carbon-containing ions remain trapped within this amorphous phase where they dominate mechanisms like precipitation of sp3 carbon clusters. The H+ ions, however, penetrate into the crystalline phase at high bias voltages (>100 V), destroying the perfect diamond structure. The experimentally measured reduction of grain sizes at high bias voltage, reported in the literature, might thus be related to penetrating H+ ions. Furthermore, the CxHy+ ions are found to be the most efficient sputtering agents, preventing the build up of defective material.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 9.466
Times cited: 9
DOI: 10.1021/cm102481y
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“Fitting the momentum dependent loss function in EELS”. Bertoni G, Verbeeck J, Brosens F, Microscopy research and technique 74, 212 (2011). http://doi.org/10.1002/jemt.20894
Abstract: Momentum dependent inelastic plasmon scattering can be measured by electron energy loss in a transmission electron microscope. From energy filtered diffraction, the characteristic angle of scattering and the cutoff angle are measured, using a thin film of aluminum as a model test. Rather than deconvolving the data (as done in previous works), a fitting technique is used to extract the loss function from angular resolved spectra, starting from a simple model simulation.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Theory of quantum systems and complex systems
Impact Factor: 1.147
Times cited: 6
DOI: 10.1002/jemt.20894
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“Applying an information transmission approach to extract valence electron information from reconstructed exit waves”. Xu Q, Zandbergen HW, van Dyck D, Ultramicroscopy 111, 912 (2011). http://doi.org/10.1016/j.ultramic.2011.01.032
Abstract: The knowledge of the valence electron distribution is essential for understanding the properties of materials. However this information is difficult to obtain from HREM images because it is easily obscured by the large scattering contribution of core electrons and by the strong dynamical scattering process. In order to develop a sensitive method to extract the information of valence electrons, we have used an information transmission approach to describe the electron interaction with the object. The scattered electron wave is decomposed in a set of basic functions, which are the eigen functions of the Hamiltonian of the projected electrostatic object potential. Each basic function behaves as a communication channel that transfers the information of the object with its own transmission characteristic. By properly combining the components of the different channels, it is possible to design a scheme to extract the information of valence electron distribution from a series of exit waves. The method is described theoretically and demonstrated by means of computer simulations.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 1
DOI: 10.1016/j.ultramic.2011.01.032
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“Barrier efficiency of sponge-like La2Zr2O7 buffer layers for YBCO-coated conductors”. Molina L, Tan H, Biermans E, Batenburg KJ, Verbeeck J, Bals S, Van Tendeloo G, Superconductor science and technology 24, 065019 (2011). http://doi.org/10.1088/0953-2048/24/6/065019
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.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.878
Times cited: 31
DOI: 10.1088/0953-2048/24/6/065019
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“Exploring different inelastic projection mechanisms for electron tomography”. Goris B, Bals S, van den Broek W, Verbeeck J, Van Tendeloo G, Ultramicroscopy 111, 1262 (2011). http://doi.org/10.1016/j.ultramic.2011.02.007
Abstract: Several different projection mechanisms that all make use of inelastically scattered electrons are used for electron tomography. The advantages and the disadvantages of these methods are compared to HAADFSTEM tomography, which is considered as the standard electron tomography technique in materials science. The different inelastic setups used are energy filtered transmission electron microscopy (EFTEM), thickness mapping based on the log-ratio method and bulk plasmon mapping. We present a comparison that can be used to select the best inelastic signal for tomography, depending on different parameters such as the beam stability and nature of the sample. The appropriate signal will obviously also depend on the exact information which is requested.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 21
DOI: 10.1016/j.ultramic.2011.02.007
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“High precision measurements of atom column positions using model-based exit wave reconstruction”. de Backer A, Van Aert S, van Dyck D, Ultramicroscopy 111, 1475 (2011). http://doi.org/10.1016/j.ultramic.2011.07.002
Abstract: In this paper, it has been investigated how to measure atom column positions as accurately and precisely as possible using a focal series of images. In theory, it is expected that the precision would considerably improve using a maximum likelihood estimator based on the full series of focal images. As such, the theoretical lower bound on the variances of the unknown atom column positions can be attained. However, this approach is numerically demanding. Therefore, maximum likelihood estimation has been compared with the results obtained by fitting a model to a reconstructed exit wave rather than to the full series of focal images. Hence, a real space model-based exit wave reconstruction technique based on the channelling theory is introduced. Simulations show that the reconstructed complex exit wave contains the same amount of information concerning the atom column positions as the full series of focal images. Only for thin samples, which act as weak phase objects, this information can be retrieved from the phase of the reconstructed complex exit wave.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 8
DOI: 10.1016/j.ultramic.2011.07.002
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“A method to determine the local surface profile from reconstructed exit waves”. Wang A, Chen FR, Van Aert S, van Dyck D, Ultramicroscopy 111, 1352 (2011). http://doi.org/10.1016/j.ultramic.2011.04.005
Abstract: Reconstructed exit waves are useful to quantify unknown structure parameters such as the position and composition of the atom columns at atomic scale. Existing techniques provide a complex wave in a flat plane which is close to the plane where the electrons leave the atom columns. However, due to local deviation in the flatness of the exit surface, there will be an offset between the plane of reconstruction and the actual exit of a specific atom column. Using the channelling theory, it has been shown that this defocus offset can in principle be determined atom column-by-atom column. As such, the surface roughness could be quantified at atomic scale. However, the outcome strongly depends on the initial plane of reconstruction especially in a crystalline structure. If this plane is further away from the true exit, the waves of the atom columns become delocalized and interfere mutually which strongly complicates the interpretation of the exit wave in terms of the local structure. In this paper, we will study the delocalization with defocus using the channelling theory in a more systematic way.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 3
DOI: 10.1016/j.ultramic.2011.04.005
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“A practical method to determine the effective resolution in incoherent experimental electron tomography”. Heidari Mezerji H, van den Broek W, Bals S, Ultramicroscopy 111, 330 (2011). http://doi.org/10.1016/j.ultramic.2011.01.021
Abstract: It is not straightforward to determine resolution for a 3D reconstruction when performing an electron tomography experiment. Different contributions such as missing wedge and misalignment add up and often influence the final resolution in an anisotropic manner. The conventional resolution measures can not be used for all of the reconstruction techniques, especially for iterative techniques which are more commonly used for electron tomography in materials science. Here we define a quantitative resolution measure that determines the resolution in three orthogonal directions of the reconstruction. As an application we use this measure to determine the optimum number of simultaneous iterative reconstruction technique (SIRT) iterations to reconstruct the gold nanoparticles, based on a high angle annular dark field STEM (HAADF-STEM) tilt series.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 26
DOI: 10.1016/j.ultramic.2011.01.021
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“Three-dimensional atomic imaging of colloidal core-shell nanocrystals”. Bals S, Casavola M, van Huis MA, Van Aert S, Batenburg KJ, Van Tendeloo G, Vanmaekelbergh D, Nano letters 11, 3420 (2011). http://doi.org/10.1021/nl201826e
Abstract: Colloidal coreshell semiconductor nanocrystals form an important class of optoelectronic materials, in which the exciton wave functions can be tailored by the atomic configuration of the core, the interfacial layers, and the shell. Here, we provide a trustful 3D characterization at the atomic scale of a free-standing PbSe(core)CdSe(shell) nanocrystal by combining electron microscopy and discrete tomography. Our results yield unique insights for understanding the process of cation exchange, which is widely employed in the synthesis of coreshell nanocrystals. The study that we present is generally applicable to the broad range of colloidal heteronanocrystals that currently emerge as a new class of materials with technological importance.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 12.712
Times cited: 121
DOI: 10.1021/nl201826e
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“Three-dimensional atomic imaging of crystalline nanoparticles”. Van Aert S, Batenburg KJ, Rossell MD, Erni R, Van Tendeloo G, Nature 470, 374 (2011). http://doi.org/10.1038/nature09741
Abstract: Determining the three-dimensional (3D) arrangement of atoms in crystalline nanoparticles is important for nanometre-scale device engineering and also for applications involving nanoparticles, such as optoelectronics or catalysis. A nanoparticles physical and chemical properties are controlled by its exact 3D morphology, structure and composition1. Electron tomography enables the recovery of the shape of a nanoparticle from a series of projection images2, 3, 4. Although atomic-resolution electron microscopy has been feasible for nearly four decades, neither electron tomography nor any other experimental technique has yet demonstrated atomic resolution in three dimensions. Here we report the 3D reconstruction of a complex crystalline nanoparticle at atomic resolution. To achieve this, we combined aberration-corrected scanning transmission electron microscopy5, 6, 7, statistical parameter estimation theory8, 9 and discrete tomography10, 11. Unlike conventional electron tomography, only two images of the targeta silver nanoparticle embedded in an aluminium matrixare sufficient for the reconstruction when combined with available knowledge about the particles crystallographic structure. Additional projections confirm the reliability of the result. The results we present help close the gap between the atomic resolution achievable in two-dimensional electron micrographs and the coarser resolution that has hitherto been obtained by conventional electron tomography.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 40.137
Times cited: 341
DOI: 10.1038/nature09741
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“Ultra-high resolution electron tomography for materials science : a roadmap”. Batenburg KJ, Bals S, Van Aert S, Roelandts T, Sijbers J, Microscopy and microanalysis 17, 934 (2011). http://doi.org/10.1017/S143192761100554X
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 1.891
DOI: 10.1017/S143192761100554X
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“Throughput maximization of particle radius measurements by balancing size and current of the electron probe”. van den Broek W, Van Aert S, Goos P, van Dyck D, Ultramicroscopy 111, 940 (2011). http://doi.org/10.1016/j.ultramic.2010.11.025
Abstract: In thispaperweinvestigatewhichprobesizemaximizesthethroughputwhenmeasuringtheradiusof nanoparticlesinhighangleannulardarkfieldscanningtransmissionelectronmicroscopy(HAADFSTEM). The sizeandthecorrespondingcurrentoftheelectronprobedeterminetheprecisionoftheestimateofa particlesradius.Maximizingthroughputmeansthatamaximumnumberofparticlesshouldbeimaged withinagiventimeframe,sothataprespecifiedprecisionisattained.WeshowthatBayesianstatistical experimentaldesignisaveryusefulapproachtodeterminetheoptimalprobesizeusingacertainamount of priorknowledgeaboutthesample.Thedependenceoftheoptimalprobesizeonthedetectorgeometry and thediameter,variabilityandatomicnumberoftheparticlesisinvestigated.Anexpressionforthe optimalprobesizeintheabsenceofanykindofpriorknowledgeaboutthespecimenisderivedaswell.
Keywords: A1 Journal article; Engineering Management (ENM); Electron microscopy for materials research (EMAT); Vision lab
Impact Factor: 2.843
Times cited: 7
DOI: 10.1016/j.ultramic.2010.11.025
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“Analyzing a self-managed CHP system for greenhouse cultivation as a profitable way to reduce CO2-emissions”. Compernolle T, Witters N, Van Passel S, Thewys T, Energy 36, 1940 (2011). http://doi.org/10.1016/J.ENERGY.2010.02.045
Abstract: To counter global warming, a transition to a low-carbon economy is needed. The greenhouse sector can contribute by installing Combined Heat and Power (CHP) systems, known for their excellent energy efficiency. Due to the recent European liberalization of the energy market, glass horticulturists have the opportunity to sell excess electricity to the market and by tailored policy and support measures, regional governments can fill the lack of technical and economic knowledge, causing initial resistance. This research investigates the economic and environmental opportunities using two detailed cases applying a self managed cogeneration system. The Net Present Value is calculated to investigate the economic feasibility. The Primary Energy Saving, the CO2 Emission Reduction indicator and an Emission Balance are applied to quantify the environmental impact. The results demonstrate that a self-managed CHP system is economic viable and that CO2 emissions are reduced. (C) 2010 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology
Impact Factor: 4.52
Times cited: 19
DOI: 10.1016/J.ENERGY.2010.02.045
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“Insight to ternary complexes of co-adsorption of norfloxacin and Cu(II) onto montmorillonite at different pH using EXAFS”. Pei Z-G, Shan X-Q, Zhang S-Z, Kong J-J, Wen B, Zhang J, Zheng L-R, Xie Y-N, Janssens K, Journal of hazardous materials 186, 842 (2011). http://doi.org/10.1016/J.JHAZMAT.2010.11.076
Abstract: Co-adsorption of norfloxacin (Nor) and Cu(II) on montmorillonite at pH 4.5, 7.0 and 9.0 was studied by integrated batch adsorption experiments and extended X-ray absorption fine structure (EXAFS) spectroscopy. Under such pH conditions the dominant species of Nor are cation (Nor+), zwitterion (Nor±), and anion (Nor−), respectively. Results indicated that Nor sorption decreased with an increase of solution pH. The presence of Cu(II) slightly suppressed the Nor+ sorption at pH 4.5, while increased Nor± and Nor−sorption on montmorillonite at pH 7.0 and 9.0, respectively. In contrast, Nor increased Cu(II) adsorption at pH 4.5, but had little effect on the adsorption of Cu(II) on montmorillonite at pH 7.0 and 9.0. Spectroscopic results showed that, at pH 4.5, Nor+ was sorbed on montmorillonite by the formation of outer-sphere montmorilloniteNorCu(II) ternary surface complex. At pH 7.0, montmorilloniteNorCu(II) and montmorilloniteCu(II)Nor ternary surface complexes co-exist. At pH 9.0, montmorilloniteCu(II)Nor ternary surface complex was likely formed, which was different to Cu(II)(Nor)2 precipitate of the solution.
Keywords: A1 Journal article; Engineering sciences. Technology; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 6.065
Times cited: 25
DOI: 10.1016/J.JHAZMAT.2010.11.076
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