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“Thermal decomposition synthesis of Al-doped ZnO nanoparticles : an in-depth study”. Damm H, Kelchtermans A, Bertha A, Van den Broeck F, Elen K, Martins JC, Carleer R, D'Haen J, De Dobbelaere C, Hadermann J, Hardy A, Van Bael MK;, RSC advances 3, 23745 (2013). http://doi.org/10.1039/c3ra43328e
Abstract: Al-doped ZnO nanoparticles are synthesized by means of a heating up solution based thermal decomposition method. The synthesis involves a reaction of zinc acetylacetonate hydrate, aluminium acetylacetonate and 1,2-hexadecanediol in the presence of oleic acid and oleyl amine. A proposed reaction mechanism from reagents to monomers is corroborated by analysis of the evolving gases using headspace GC-MS analysis. The Al-doped ZnO nanoparticles synthesized are dynamically stabilized by adsorbed oleate ions, after deprotonation of oleic acid by oleyl amine, as was found by NOESY proton NMR and complementary FTIR spectroscopy. Precession electron diffraction shows a simultaneous increase in lattice parameters with Al concentration. This, together with HAADF-STEM and EDX maps, indicates the incorporation of Al into the ZnO nanoparticles. By the combination of complementary characterization methods during all stages of the synthesis, it is concluded that Al is incorporated into the ZnO wurtzite lattice as a dopant.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.108
Times cited: 10
DOI: 10.1039/c3ra43328e
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“R-phase transition and related mechanical properties controlled by low-temperature aging treatment in a Ti50.8 at.% Ni thin wire”. Wang X, Li K, Schryvers D, Verlinden B, Van Humbeeck J, Scripta materialia 72-73, 21 (2014). http://doi.org/10.1016/j.scriptamat.2013.10.006
Abstract: A cold-drawn Ti50.8 at.% Ni wire was annealed at 600 °C for 30 min, followed by aging at 250 °C for different times. A microstructure with small grains and nanoscaled precipitates was obtained. The thermally induced martensite transformation is suppressed in the samples aged for 4 h or longer, leaving a one-stage R-phase transition between −150 and +150 °C. The transformation behavior, work output and recovery stress associated with the R-phase transition are presented.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 3.747
Times cited: 27
DOI: 10.1016/j.scriptamat.2013.10.006
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“Creating arrays of electron vortices”. Niermann T, Verbeeck J, Lehmann M, Ultramicroscopy 136, 165 (2014). http://doi.org/10.1016/j.ultramic.2013.10.002
Abstract: We demonstrate the production of an ordered array of electron vortices making use of an electron optical setup consisting of two electrostatic biprisms. The biprism filaments are oriented nearly orthogonal with respect to each other in a transmission electron microscope. Matching the position of the filaments, we can choose to form different topological features in the electron wave. We outline the working principle of the setup and demonstrate fist experimental results. This setup partially bridges the gap between angular momentum carried by electron spin, which is intrinsic and therefore present in any position of the wave, and angular momentum carried by the vortex character of the wave, which can be extrinsic depending on the axis around which it is measured. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 9
DOI: 10.1016/j.ultramic.2013.10.002
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“Life cycle analyses of organic photovoltaics : a review”. Lizin S, Van Passel S, De Schepper E, Maes W, Lutsen L, Manca J, Vanderzande D, Energy &, Environmental Science 6, 3136 (2013). http://doi.org/10.1039/C3EE42653J
Abstract: This paper reviews the available life cycle analysis (LCA) literature on organic photovoltaics (OPVs). This branch of OPV research has focused on the environmental impact of single-junction bulk heterojunction polymer solar cells using a P3HT/PC60BM active layer blend processed on semi-industrial pilot lines in ambient surroundings. The environmental impact was found to be strongly decreasing through continuous innovation of the manufacturing procedures. The current top performing cell regarding environmental performance has a cumulative energy demand of 37.58 MJp m(-2) and an energy payback time in the order of months for cells having 2% efficiency, thereby rendering OPV cells one of the best performing PV technologies from an environmental point of view. Nevertheless, we find that LCA literature is lagging behind on the main body of OPV literature due to the lack of readily available input data. Still, LCA research has led us to believe that in the quest for higher efficiencies, environmental sustainability is being disregarded on the materials' side. Hence, we advise the scientific community to take the progress made on environmental sustainability aspects of OPV preparations into account not only because standard procedures put a bigger strain on the environment, but also because these methods may not be transferrable to an industrial process. Consequently, we recommend policy makers to subsidize research that bridges the gaps between fundamental materials research, stability, and scalability given that these constraints have to be fulfilled simultaneously if OPVs are ever to be successful on the market. Additionally, environmental sustainability will have to keep on being monitored to steer future developments in the right direction.
Keywords: A1 Journal article; Engineering sciences. Technology; Engineering Management (ENM)
Impact Factor: 29.518
Times cited: 124
DOI: 10.1039/C3EE42653J
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“Characterization and analysis of the adsorption immobilization mechanism of \beta-galactosidase on metal oxide powders”. Satyawali Y, Van Roy S, Roevens A, Meynen V, Mullens S, Jochems P, Doyen W, Cauwenberghs L, Dejonghe W, RSC advances 3, 24054 (2013). http://doi.org/10.1039/C3RA45107K
Abstract: Immobilization of the enzymes plays a vital role in enhancing their applicability in a wide range of applications, thus ensuring the use of sustainable enzymatic processes over the conventional chemical processes on an industrial scale. This study provides the background information for the selection and screening of inorganic metal oxide (MO) powders for their use as fillers in mixed matrix membranes for enzyme immobilization as the future aim. A total of 13 MOs, ranging in size from 0.01 μm to <5 μm, were tested for their performance as a support for enzyme (β-galactosidase) immobilization via adsorption. Alumina appeared to be the best performing MO with the amount and activity of the immobilized enzyme being 64 mg g−1 and up to 288 U g−1, respectively. The amount of immobilized enzyme on alumina (α-Al2O3 C and γ-Al2O3) was >3 times higher than ZrO2 (used as a reference MO in this study). Upon heat treatment at 900 °C, up to 15%, 52% and 42% decline was observed in the amount of immobilized enzyme in case of alumina metal oxides (MOs), ZrO2 and TiO2, respectively. The results suggested that both isoelectric point and surface area of the MO influence the immobilization. The most important observation in this study was that the bonding of the enzyme to the MO surface seems to be mediated by the bonding/interaction of the buffer to the enzyme.
Keywords: A1 Journal article; Laboratory of adsorption and catalysis (LADCA); Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1039/C3RA45107K
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“Ag nanoparticles on mixed Al2O3-Ga2O3 supports as catalysts for the N-alkylation of amines with alcohols”. Geukens I, Vermoortele F, Meledina M, Turner S, Van Tendeloo G, De Vos DE, Applied catalysis : A : general 469, 373 (2014). http://doi.org/10.1016/j.apcata.2013.09.044
Abstract: The combination of AgNO3 with NaH results in Ag nanoparticles that can selectively perform alcohol aminations under mild reaction conditions (110 °C). NaH not only serves as a reducing agent for the Ag salt, but also activates the alcohol for dehydrogenation to the corresponding ketone/aldehyde. The stability of the particles can be improved by immobilizing them onto mixed Al2O3Ga2O3 supports; the combination of Ga and Al provides materials with stronger Lewis acidic sites compared to pure alumina or gallium oxide supports. This leads to catalysts with enhanced activities, without the necessity of adding external Lewis acids. Detailed TEM characterization also reveals a close interaction between the Ag NPs and the gallium oxide phase. The obtained catalysts are recyclable and show activity for the alcohol amination using a variety of aliphatic and aromatic amines under mild conditions.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.339
Times cited: 24
DOI: 10.1016/j.apcata.2013.09.044
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“Discovery of a superhard iron tetraboride superconductor”. Gou H, Dubrovinskaia N, Bykova E, Tsirlin AA, Kasinathan D, Schnelle W, Richter A, Merlini M, Hanfland M, Abakumov AM, Batuk D, Van Tendeloo G, Nakajima Y, Kolmogorov AN, Dubrovinsky L;, Physical review letters 111, 157002 (2013). http://doi.org/10.1103/PhysRevLett.111.157002
Abstract: Single crystals of novel orthorhombic (space group Pnnm) iron tetraboride FeB4 were synthesized at pressures above 8 GPa and high temperatures. Magnetic susceptibility and heat capacity measurements demonstrate bulk superconductivity below 2.9 K. The putative isotope effect on the superconducting critical temperature and the analysis of specific heat data indicate that the superconductivity in FeB4 is likely phonon mediated, which is rare for Fe-based superconductors. The discovered iron tetraboride is highly incompressible and has the nanoindentation hardness of 62(5) GPa; thus, it opens a new class of highly desirable materials combining advanced mechanical properties and superconductivity.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.462
Times cited: 127
DOI: 10.1103/PhysRevLett.111.157002
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“Vortex states in nanoscale superconducting squares : the influence of quantum confinement”. Zhang L-F, Covaci L, Milošević, MV, Berdiyorov GR, Peeters FM, Physical review : B : condensed matter and materials physics 88, 144501 (2013). http://doi.org/10.1103/PhysRevB.88.144501
Abstract: Bogoliubov-de Gennes theory is used to investigate the effect of the size of a superconducting square on the vortex states in the quantum confinement regime. When the superconducting coherence length is comparable to the Fermi wavelength, the shape resonances of the superconducting order parameter have strong influence on the vortex configuration. Several unconventional vortex states, including asymmetric ones, giant-multivortex combinations, and states comprising giant antivortices, were found as ground states and their stability was found to be very sensitive on the value of k(F)xi(0), the size of the sample W, and the magnetic flux Phi. By increasing the temperature and/or enlarging the size of the sample, quantum confinement is suppressed and the conventional mesoscopic vortex states as predicted by the Ginzburg-Laudau (GL) theory are recovered. However, contrary to the GL results we found that the states containing symmetry-induced vortex-antivortex pairs are stable over the whole temperature range. It turns out that the inhomogeneous order parameter induced by quantum confinement favors vortex-antivortex molecules, as well as giant vortices with a rich structure in the vortex core-unattainable in the GL domain.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 19
DOI: 10.1103/PhysRevB.88.144501
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“Enhanced hydrogen production by photoreforming of renewable oxygenates through nanostructured Fe2O3 polymorphs”. Carraro G, Maccato C, Gasparotto A, Montini T, Turner S, Lebedev OI, Gombac V, Adami G, Van Tendeloo G, Barreca D, Fornasiero P;, Advanced functional materials 24, 372 (2014). http://doi.org/10.1002/adfm.201302043
Abstract: Sunlight-driven hydrogen production via photoreforming of aqueous solutions containing renewable compounds is an attractive option for sustainable energy generation with reduced carbon footprint. Nevertheless, the absence of photocatalysts combining high efficiency and stability upon solar light activation has up to date strongly hindered the development of this technology. Herein, two scarcely investigated iron(III) oxide polymorphs, β- and ε-Fe2O3, possessing a remarkable activity in sunlight-activated H2 generation from aqueous solutions of renewable oxygenates (i.e., ethanol, glycerol, glucose) are reported. For β-Fe2O3 and ε-Fe2O3, H2 production rates up to 225 and 125 mmol h−1 m−2 are obtained, with significantly superior performances with respect to the commonly investigated α-Fe2O3.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 12.124
Times cited: 95
DOI: 10.1002/adfm.201302043
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“Insights on growth and nanoscopic investigation of uncommon iron oxide polymorphs”. Carraro G, Maccato C, Bontempi E, Gasparotto A, Lebedev OI, Turner S, Depero LE, Van Tendeloo G, Barreca D, European journal of inorganic chemistry , 5454 (2013). http://doi.org/10.1002/ejic.201300873
Abstract: Si(100)-supported Fe2O3 nanomaterials were developed by a chemical vapor deposition (CVD) approach. The syntheses, which were performed at temperatures between 400 and 550 °C, selectively yielded the scarcely studied β- and ϵ-Fe2O3 polymorphs under O2 or O2 + H2O reaction environments, respectively. Correspondingly, the observed morphology underwent a progressive evolution from interconnected nanopyramids to vertically aligned nanorods. The present study aims to provide novel insights into Fe2O3 nano-organization by a systematic investigation of the system structure/morphology and of their interrelations with growth conditions. In particular, for the first time, the β- and ϵ-Fe2O3 preparation process has been accompanied by a thorough multitechnique investigation, which, beyond X-ray photoelectron spectroscopy (XPS) and field-emission scanning electron microscopy (FESEM), is carried out by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDXS), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), scanning TEM electron energy-loss spectroscopy (STEM-EELS), and high-angle annular dark-field STEM (HAADF-STEM). Remarkably, the target materials showed a high structural and compositional homogeneity throughout the whole thickness of the nanodeposit. In particular, spatially resolved EELS chemical maps through the spectrum imaging (SI) technique enabled us to gain important information on the local Fe coordination, which is of crucial importance in determining the system reactivity. The described preparation method is in fact a powerful tool to simultaneously tailor phase composition and morphology of iron(III) oxide nanomaterials, the potential applications of which include photocatalysis, magnetic devices, gas sensors, and anodes for Li-ion batteries.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.444
Times cited: 18
DOI: 10.1002/ejic.201300873
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“Polyhedral iron oxide coreshell nanoparticles in a biodegradable polymeric matrix : preparation, characterization and application in magnetic particle hyperthermia and drug delivery”. Filippousi M, Altantzis T, Stefanou G, Betsiou M, Bikiaris DN, Angelakeris M, Pavlidou E, Zamboulis D, Van Tendeloo G, RSC advances 3, 24367 (2013). http://doi.org/10.1039/c3ra43747g
Abstract: Polyhedral magnetic iron oxide nanocrystals with multiple facets have been embedded in biocompatible and biodegradable polymeric matrices in order to study their structural, magnetic features and alternating-current (AC) magnetic heating efficiency. The encapsulation of iron oxide nanoparticles into a polymer matrix was confirmed by transmission electron microscopy and further corroborated by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). HAADF-STEM tomography proved that the iron oxide nanocrystals consist of well-defined polyhedral structures with multiple facets. The magnetic features were found to be in good agreement with the structural and morphological features and are maintained even after encapsulation. Furthermore, the magnetic nanoparticles inside these matrices may be considered as good candidates for biomedical applications in hyperthermia treatments because of their high heating capacity exhibited under an alternating magnetic field. The anticancer Taxol drug was encapsulated in these nanoparticles and its physical state and release rate at 37 and 42 °C was studied.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.108
Times cited: 19
DOI: 10.1039/c3ra43747g
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“Characterisation of hydrous ferric oxides derived from iron-rich groundwaters and their contribution to the suspended sediment of streams”. Baken S, Sjostedt C, Gustafsson JP, Seuntjens P, Desmet N, De Schutter J, Smolders E, Applied geochemistry 39, 59 (2013). http://doi.org/10.1016/J.APGEOCHEM.2013.09.013
Abstract: When Fe(II) bearing groundwaters surface in streams, particulate authigenic Fe-rich material is produced by oxidation. Such freshly precipitated Fe minerals may be transported as suspended sediment and have a profound impact on the fate of trace metals and nutrients in rivers. The objective of this study was to monitor changes in mineralogy and composition of authigenic material from its source to streams of increasing order. Groundwaters, surface waters, and suspended sediment in streams of different order were sampled in the Kleine Nete catchment (Belgium), a lowland with Fe-rich groundwaters (3.5-53.8 mg Fe/L; pH 6.3-6.9). Fresh authigenic material (>0.45 mu m) was produced by oxidising filtered (<0.45 mu m) groundwater and surface water. This material contained, on average, 44% Fe, and smaller concentrations of C, P, and Ca. Iron EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy showed that the Fe was present as poorly crystalline hydrous ferric oxides with a structure similar to that of ferrihydrite. The Fe concentration in the suspended sediment samples decreased to 36-40% (stream order 2), and further to 18-26% (stream order 4 and 5). Conversely, the concentrations of organic C, Ca, Si, and trace metals increased with increasing stream order, suggesting mixing of authigenic material with suspended sediment from a different source. The Fe speciation in the suspended sediment was similar to that in fresh authigenic material, but more Fe-Fe interactions were observed, i.e. it was increasingly hydrolysed, suggesting ageing reactions. The suspended sediment in the streams of order 4 and 5 is estimated to contain between 31% and 59% of authigenic material, but more data are needed to refine this estimate. The authigenic material is an important sink for P in these streams which may alleviate the eutrophication risk in this catchment. (C) 2013 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Sustainable Energy, Air and Water Technology (DuEL)
DOI: 10.1016/J.APGEOCHEM.2013.09.013
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“Role of PdOx and RuOy clusters in oxygen exchange between nanocrystalline tin dioxide and the gas phase”. Marikutsa AV, Rumyantseva MN, Frolov DD, Morozov IV, Boltalin AI, Fedorova AA, Petukhov IA, Yashina LV, Konstantinova EA, Sadovskaya EM, Abakumov AM, Zubavichus YV, Gaskov AM;, The journal of physical chemistry: C : nanomaterials and interfaces 117, 23858 (2013). http://doi.org/10.1021/jp408646k
Abstract: The effect of palladium- and ruthenium-based clusters on nanocrystalline tin dioxide interaction with oxygen was studied by temperature-programmed oxygen isotopic exchange with mass-spectrometry detection. The modification of aqueous sol-gel prepared SnO2 by palladium and, to a larger extent, by ruthenium, increases surface oxygen concentration on the materials. The revealed effects on oxygen exchange-lowering the threshold temperature, separation of surface oxygen contribution to the process, increase of heteroexchange rate and oxygen diffusion coefficient, decrease of activation energies of exchange and diffusion-were more intensive for Ru-modified SnO2 than in the case of SnO2/Pd. The superior promoting activity of ruthenium on tin dioxide interaction with oxygen was interpreted by favoring the dissociative O-2 adsorption and increasing the oxygen mobility, taking into account the structure and chemical composition of the modifier clusters.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.536
Times cited: 20
DOI: 10.1021/jp408646k
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“Formation of metallic mercury during photodegradation/photodarkening of \alpha-HgS : electrochemical evidence”. Anaf W, Janssens K, De Wael K, Angewandte Chemie: international edition in English 52, 12568 (2013). http://doi.org/10.1002/ANIE.201303977
Abstract: Das rote Pigment α-HgS neigt in Gegenwart von Licht und Chloridionen zur Schwärzung. Als Grund für die Zersetzung und Entfärbung werden die Bildung von (schwarzem) β-HgS oder Quecksilbermetall vermutet, doch diese Substanzen wurden noch nicht auf natürlich oder künstlich zersetzter HgS-Farbe nachgewiesen. Elektrochemische Experimente belegen nun die Bildung von Quecksilbermetall in Gegenwart von Licht und Chloridionen.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 11.994
Times cited: 19
DOI: 10.1002/ANIE.201303977
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“Fluorine doped Fe2O3 nanostructures by a one-pot plasma-assisted strategy”. Carraro G, Gasparotto A, Maccato C, Bontempi E, Lebedev OI, Turner S, Sada C, Depero LE, Van Tendeloo G, Barreca D, RSC advances 3, 23762 (2013). http://doi.org/10.1039/c3ra43775b
Abstract: The present work reports on the synthesis of fluorine doped Fe2O3 nanomaterials by a single-step plasma enhanced-chemical vapor deposition (PE-CVD) strategy. In particular, Fe(hfa)2TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N′,N′-tetramethylethylenediamine) was used as molecular source for both Fe and F in Ar/O2 plasmas. The structure, morphology and chemical composition of the synthesized nanosystems were thoroughly analyzed by two-dimensional X-ray diffraction (XRD2), field emission-scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM). A suitable choice of processing parameters enabled the selective formation of α-Fe2O3 nanomaterials, characterized by an homogeneous F doping, even at 100 °C. Interestingly, a simultaneous control of the system nanoscale organization and fluorine content could be achieved by varying the sole growth temperature. The tailored properties of the resulting materials can be favourably exploited for several technological applications, ranging from photocatalysis, to photoelectrochemical cells and gas sensing.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.108
Times cited: 23
DOI: 10.1039/c3ra43775b
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“Ultrasonication induces oxygenated species and defects onto exfoliated graphene”. Skaltsas T, Ke X, Bittencourt C, Tagmatarchis N, The journal of physical chemistry: C : nanomaterials and interfaces 117, 23272 (2013). http://doi.org/10.1021/jp4057048
Abstract: The effect of ultrasonication parameters, such as time and power applied, to exfoliate graphite in o-dichlorobenzene (o-DCB) and N-methyl-1,2-pyrrolidone (NMP) was examined. It was found that the concentration of graphene was higher in o-DCB, while its dispersibility was increased when sonication was applied for a longer period and/or at higher power. However, spectroscopic examination by X-ray photoelectron spectroscopy (XPS) revealed that ultrasonication causes defects and induces oxygen functional groups in the form of carboxylic acids and ethers/epoxides onto the graphene lattice. Additional proof for the latter arose from Raman, IR, and thermogravimetry studies. The carboxylic acids and ethers/epoxides onto exfoliated graphene were derived from air during ultrasonication and found independent of the solvent used for the exfoliation and the power and/or time ultrasonication applied. Quantitative evaluation of the amount of oxygenated species present on exfoliated graphene as performed by high-resolution XPS revealed that the relative oxygen percentage was higher when exfoliation was performed in NMP. Finally, the sonication time and/or power affected the oxygen content on exfoliated graphene, since extended ultrasonication resulted in a decrease in the oxygen content on exfoliated graphene, with a simultaneous increase of defected sp(3) carbon atoms.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.536
Times cited: 65
DOI: 10.1021/jp4057048
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“Doping effect on the adsorption of NH3 molecule onto graphene quantum dot : from the physisorption to the chemisorption”. Seyed-Talebi SM, Beheshtian J, Neek-Amal M, Journal of applied physics 114, 124307 (2013). http://doi.org/10.1063/1.4822165
Abstract: The adsorption of ammonia molecule onto a graphene hexagonal flake, aluminum (Al) and boron (B) doped graphene flakes (graphene quantum dots, GQDs) are investigated using density functional theory. We found that NH3 molecule is absorbed to the hollow site through the physisorption mechanism without altering the electronic properties of GQD. However, the adsorption energy of NH3 molecule onto the Al- and B-doped GQDs increases with respect GQD resulting chemisorption. The adsorption of NH3 onto the Al-doped and B-doped GQDs makes graphene locally buckled, i.e., B-doped and Al-doped GQDs are not planar. The adsorption mechanism onto a GQD is different than that of graphene. This study reveals important features of the edge passivation and doping effects of the adsorption mechanism of external molecules onto the graphene quantum dots. (C) 2013 AIP Publishing LLC.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.068
Times cited: 10
DOI: 10.1063/1.4822165
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“Electronic structure of a hexagonal graphene flake subjected to triaxial stress”. Neek-Amal M, Covaci L, Shakouri K, Peeters FM, Physical review : B : condensed matter and materials physics 88, 115428 (2013). http://doi.org/10.1103/PhysRevB.88.115428
Abstract: The electronic properties of a triaxially strained hexagonal graphene flake with either armchair or zigzag edges are investigated using molecular dynamics simulations and tight-binding calculations. We found that (i) the pseudomagnetic field in strained graphene flakes is not uniform neither in the center nor at the edge of zigzag terminated flakes, (ii) the pseudomagnetic field is almost zero in the center of armchair terminated flakes but increases dramatically near the edges, (iii) the pseudomagnetic field increases linearly with strain, for strains lower than 15% but increases nonlinearly beyond it, (iv) the local density of states in the center of the zigzag hexagon exhibits pseudo-Landau levels with broken sublattice symmetry in the zeroth pseudo-Landau level, and in addition there is a shift in the Dirac cone due to strain induced scalar potentials, and (v) there is size effect in pseudomagnetic field. This study provides a realistic model of the electronic properties of inhomogeneously strained graphene where the relaxation of the atomic positions is correctly included together with strain induced modifications of the hopping terms up to next-nearest neighbors.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 46
DOI: 10.1103/PhysRevB.88.115428
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“Incommensurate modulation and luminescence in the CaGd2(1-x)Eu2x(MoO4)4(1-y)(WO)4y (0\leq x\leq1, 0\leq y\leq1) red phosphors”. Morozov VA, Bertha A, Meert KW, Van Rompaey S, Batuk D, Martinez GT, Van Aert S, Smet PF, Raskina MV, Poelman D, Abakumov AM, Hadermann J;, Chemistry of materials 25, 4387 (2013). http://doi.org/10.1021/cm402729r
Abstract: Scheelite related compounds (A',A '') [(B',B '')O-4], with B', B '' = W and/or Mo are promising new light-emitting materials for photonic applications, including phosphor converted LEDs (light-emitting diodes). In this paper, the creation and ordering of A-cation vacancies and the effect of cation substitutions in the scheelite-type framework are investigated as a factor for controlling the scheelite-type structure and luminescent properties. CaGd2(1-x)Eu2x(MoO4)(4(1-y))(WO4)(4y) (0 <= x <= 1, 0 <= y <= 1) solid solutions with scheelite-type structure were synthesized by a solid state method, and their structures were investigated using a combination of transmission electron microscopy techniques and powder X-ray diffraction. Within this series all complex molybdenum oxides have (3 + 2)D incommensurately modulated structures with superspace group I4(1)/a(alpha,beta,0)00(-beta,alpha,0)00, while the structures of all tungstates are (3 + 1)D incommensurately modulated with superspace group I2/b(alpha beta 0)00. In both cases the modulation arises because of cation-vacancy ordering at the A site. The prominent structural motif is formed by columns of A-site vacancies running along the c-axis. These vacant columns occur in rows of two or three aligned along the [110] direction of the scheelite subcell. The replacement of the smaller Gd3+ by the larger Eu3+ at the A-sublattice does not affect the nature of the incommensurate modulation, but an increasing replacement of Mo6+ by W6+ switches the modulation from (3 + 2)D to (3 + 1)D regime. Thus, these solid solutions can be considered as a model system where the incommensurate modulation can be monitored as a function of cation nature while the number of cation vacancies at the A sites remain constant upon the isovalent cation replacement. All compounds' luminescent properties were measured, and the optical properties were related to the structural properties of the materials. CaGd2(1-x)(MoO4)(4(1-y))(WO4)(4y) phosphors emit intense red light dominated by the D-5(0)-F-7(2) transition at 612 nm, along with other transitions from the D-5(1) and D-5(0) excited states. The intensity of the 5D0-7F2 transition reaches a maximum at x = 0.5 for y = 0 and 1.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 63
DOI: 10.1021/cm402729r
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“Perovskite transparent conducting oxides : an ab initio study”. Dabaghmanesh S, Saniz R, Amini MN, Lamoen D, Partoens B, Journal of physics : condensed matter 25, 415503 (2013). http://doi.org/10.1088/0953-8984/25/41/415503
Abstract: We present an ab initio study of the electronic structure and of the formation energies of various point defects in BaSnO3 and SrGeO3. We show that La and Y impurities substituting Ba or Sr are shallow donors with a preferred 1 + charge state. These defects have a low formation energy within all the suitable equilibrium growth conditions considered. Oxygen vacancies behave as shallow donors as well, preferring the 2 + charge state. Their formation energies, however, are higher in most growth conditions, indicating a limited contribution to conductivity. The calculated electron effective mass in BaSnO3, with a value of 0.21 me, and the very high mobility reported recently in La-doped BaSnO3 single-crystals, suggest that remarkably low scattering rates can be achieved in the latter. In the case of SrGeO3, our results point to carrier density and mobility values in the low range for typical polycrystalline TCOs, in line with experiment.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.649
Times cited: 17
DOI: 10.1088/0953-8984/25/41/415503
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“Soft vortex matter in a type-I/type-II superconducting bilayer”. Komendová, L, Milošević, MV, Peeters FM, Physical review : B : condensed matter and materials physics 88, 094515 (2013). http://doi.org/10.1103/PhysRevB.88.094515
Abstract: Magnetic flux patterns are known to strongly differ in the intermediate state of type-I and type-II superconductors. Using a type-I/type-II bilayer we demonstrate hybridization of these flux phases into a plethora of unique new ones. Owing to a complicated multibody interaction between individual fluxoids, many different intriguing patterns are possible under applied magnetic field, such as few-vortex clusters, vortex chains, mazes, or labyrinthal structures resembling the phenomena readily encountered in soft-matter physics. However, in our system the patterns are tunable by sample parameters, magnetic field, current, and temperature, which reveals transitions from short-range clustering to long-range ordered phases such as parallel chains, gels, glasses, and crystalline vortex lattices, or phases where lamellar type-I flux domains in one layer serve as a bedding potential for type-II vortices in the other, configurations clearly beyond the soft-matter analogy.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 27
DOI: 10.1103/PhysRevB.88.094515
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“Phase formation in intermixed NiGe thin films : influence of Ge content and low-temperature nucleation of hexagonal nickel germanides”. De Schutter B, Devulder W, Schrauwen A, van Stiphout K, Perkisas T, Bals S, Vantomme A, Detavernier C, Microelectronic engineering 120, 168 (2014). http://doi.org/10.1016/j.mee.2013.09.004
Abstract: In this study, we focus on phase formation in intermixed NiGe thin films as they represent a simplified model of the small intermixed interface layer that is believed to form upon deposition of Ni on Ge and where initial phase formation happens. A combinatorial sputter deposition technique was used to co-deposit a range of intermixed NiGe thin films with Ge concentrations varying between 0 and 50 at.%Ge in a single deposition on both Ge (100) and inert SiO2 substrates. In situ X-ray diffraction and transmission electron microscopy where used to study phase formation. In almost the entire composition range under investigation, crystalline phases where found to be present in the as-deposited films. Between 36 and 48 at.%Ge, high-temperature hexagonal nickel germanides were found to occur metastabily below 300 °C, both on SiO2 and Ge (100) substrates. For Ge concentrations in the range between 36 and 42 at.%, this hexagonal germanide phase was even found to be present at room temperature in the as-deposited films. The results obtained in this work could provide more insight in the phase sequence of a pure Ni film on Ge.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 1.806
Times cited: 9
DOI: 10.1016/j.mee.2013.09.004
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“An analysis of the physiologic parameters of intraoral wear: a review”. Lawson NC, Janyavula S, Çakir D, Burgess JO, Journal Of Physics D-Applied Physics 46, Unsp 404007 (2013). http://doi.org/10.1088/0022-3727/46/40/404007
Abstract: This paper reviews the conditions of in vivo mastication and describes a novel method of measuring in vitro wear. Methods: parameters of intraoral wear are reviewed in this analysis, including chewing force, tooth sliding distance, food abrasivity, saliva lubrication, and antagonist properties. Results: clinical measurement of mastication forces indicates a range of normal forces between 20 and 140 N for a single molar. During the sliding phase of mastication, horizontal movement has been measured between 0.9 and 2.86 mm. In vivo wear occurs by three-body abrasion when food particles are interposed between teeth and by two-body abrasion after food clearance. Analysis of food particles used in wear testing reveals that food particles are softer than enamel and large enough to separate enamel and restoration surfaces and act as a solid lubricant. In two-body wear, saliva acts as a boundary lubricant with a viscosity of 3 cP. Enamel is the most relevant antagonist material for wear testing. The shape of a palatal cusp has been estimated as a 0.6 mm diameter ball and the hardest region of a tooth is its enamel surface. pH values and temperatures have been shown to range between 2-7 and 5-55 degrees C in intraoral fluids, respectively. These intraoral parameters have been used to modify the Alabama wear testing method.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.588
DOI: 10.1088/0022-3727/46/40/404007
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“NEXAFS spectromicroscopy of suspended carbon nanohorns”. Bittencourt C, Ke X, Van Tendeloo G, Tagmatarchis N, Guttmann P, Chemical physics letters 587, 85 (2013). http://doi.org/10.1016/j.cplett.2013.09.034
Abstract: We demonstrate that near-edge X-ray-absorption fine-structure spectroscopy combined with full-field transmission X-ray microscopy can be used to study the electronic structure of suspended carbon nanohorns. Based on reports of electronic structure calculations additional spectral features observed in the π region of the NEXAFS spectrum recorded on the carbon nanohorns were associated to the presence of the pentagonal rings and the folding of the graphene sheet.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.815
Times cited: 4
DOI: 10.1016/j.cplett.2013.09.034
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“Synthesis and properties of charge-ordered thallium halide perovskites, CsTl0.5+Tl0.53+X3 (X = F or Cl) : theoretical precursors for superconductivity?”. Retuerto M, Emge T, Hadermann J, Stephens PW, Li MR, Yin ZP, Croft M, Ignatov A, Zhang SJ, Yuan Z, Jin C, Simonson JW, Aronson MC, Pan A, Basov DN, Kotliar G, Greenblatt M;, Chemistry of materials 25, 4071 (2013). http://doi.org/10.1021/cm402423x
Abstract: Recently, CsTlCl3 and CsTlF3 perovskites were theoretically predicted to be potential superconductors if they were optimally doped. The syntheses of these two compounds together with a complete characterization of the samples are reported. CsTlCl3 was obtained as orange crystals in two different polymorphs: a tetragonal phase (I4/m) and a cubic phase (Fm (3) over barm). CsTlF3 was formed as a light brown powder, and also as a double cubic perovskite (Fm (3) over barm). In all three CsTlX3 phases, Tl+ and Tl3+ were located in two different crystallographic positions that accommodate their different bond lengths. In CsTlCl3, some Tl vacancies were found in the Tl+ position. The charge ordering between Tl+ and Tl3+ was confirmed by X-ray absorption and Raman spectroscopy. The Raman spectroscopy of CsTlCl3 at high pressure (58 GPa) did not indicate any phase transition to a possible single Tl2+ state. However, the highly insulating material became less resistive with an increasing high pressure, while it underwent a change in its optical properties, from transparent to deeply opaque red, indicative of a decrease in the magnitude of the band gap. The theoretical design and experimental validation of the existence of CsTlF3 and CsTlCl3 cubic perovskites are the necessary first steps in confirming the theoretical prediction of superconductivity in these materials.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 28
DOI: 10.1021/cm402423x
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“Theoretical aspects of graphene-like group IV semiconductors”. Houssa M, van den Broek B, Scalise E, Ealet B, Pourtois G, Chiappe D, Cinquanta E, Grazianetti C, Fanciulli M, Molle A, Afanas’ev VV, Stesmans A;, Applied surface science 291, 98 (2014). http://doi.org/10.1016/j.apsusc.2013.09.062
Abstract: Silicene and germanene are the silicon and germanium counterparts of graphene, respectively. Recent experimental works have reported the growth of silicene on (1 1 1)Ag surfaces with different atomic configurations, depending on the growth temperature and surface coverage. We first theoretically study the structural and electronic properties of silicene on (1 1 1) Ag surfaces, focusing on the (4 x 4) silicene/Ag structure. Due to symmetry breaking in the silicene layer (nonequivalent number of top and bottom Si atoms), the corrugated silicene layer, with the Ag substrate removed, is predicted to be semiconducting, with a computed energy bandgap of about 0.3 eV. However, the hybridization between the Si 3p orbitals and the Ag 5s orbital in the silicene/(1 1 1)Ag slab model leads to an overall metallic system, with a distribution of local electronic density of states, which is related to the slightly disordered structure of the silicene layer on the (1 1 1)Ag surface. We next study the interaction of silicene and germanene with different hexagonal non-metallic substrates, namely ZnS and ZnSe. On reconstructed (0 0 0 1)ZnS or ZnSe surfaces, which should be more energetically stable for very thin layers, silicene and germanene are found to be semiconducting. Remarkably, the nature and magnitude of their energy bandgap can be controlled by an out-of-plane electric field, an important finding for the potential use of these materials in nanoelectronic devices. (C) 2013 Elsevier B. V. All rights reserved.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.387
Times cited: 20
DOI: 10.1016/j.apsusc.2013.09.062
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“Bilayer graphene Hall bar with a pn-junction”. Milovanovic SP, Masir MR, Peeters FM, Journal of applied physics 114, 113706 (2013). http://doi.org/10.1063/1.4821264
Abstract: We investigate the magnetic field dependence of the Hall and the bend resistances for a ballistic Hall bar structure containing a pn-junction sculptured from a bilayer of graphene. The electric response is obtained using the billiard model, and we investigate the cases of bilayer graphene with and without a band gap. Two different conduction regimes are possible: (i) both sides of the junction have the same carrier type and (ii) one side of the junction is n-type while the other one is p-type. The first case shows Hall plateau-like features in the Hall resistance that fade away as the band gap opens. The second case exhibits a bend resistance that is asymmetric in magnetic field as a consequence of snake states along the pn-interface, where the maximum is shifted away from zero magnetic field.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.068
Times cited: 3
DOI: 10.1063/1.4821264
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“First-principles electronic functionalization of silicene and germanene by adatom chemisorption”. van den Broek B, Houssa M, Scalise E, Pourtois G, Afanas'ev VV, Stesmans A, Applied surface science 291, 104 (2014). http://doi.org/10.1016/j.apsusc.2013.09.032
Abstract: This study presents first-principles results on the electronic functionalization of silicene and germanene monolayers by means of chemisorption of adatom species H, Li, F, Sc, Ti, V. Three general adatom-monolayer configurations are considered, each having its distinct effect on the electronic structure, yielding metallic or semiconducting dispersions depending on the adatom species and configuration. The induced bandgap is a (in)direct F gap ranging from 0.2 to 2.3 eV for both silicene and germanene. In general the alternating configuration was found to be the most energetically stable. The boatlike and chairlike conformers are degenerate with the former having anisotropic effective carrier masses. The top configuration leads to the planar monolayer and predominately to a gapped dispersion. The hollow configuration with V adatoms retains the Dirac cone, but with strong orbital planar hybridization at the Fermi level. We also observe a planar surface state the Fermi level for the latter systems. (C) 2013 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.387
Times cited: 32
DOI: 10.1016/j.apsusc.2013.09.032
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“A graphene oxide amplification platform tagged with tyrosinase-zinc oxide quantum dot hybrids for the electrochemical sensing of hydroxylated polychlorobiphenyls”. Rather JA, Pilehvar S, De Wael K, Sensors and actuators : B : chemical 190, 612 (2014). http://doi.org/10.1016/J.SNB.2013.09.018
Abstract: Graphene oxide can act as an amplification platform for the immobilization of a hybrid structure composed of tyrosinase (Tyr) and zinc oxide quantum dots (ZnO QDs). This article describes how this platform increases the sensitivity for the detection of hydroxylated polychlorobiphenyls (OH-PCBs). The adsorption of Tyr (with low isoelectric point) on the positively charged surface of ZnO QDs is based on electrostatic interactions. The scanning electron microscopic images and UVvis spectroscopic analysis demonstrated the adsorption of Tyr on ZnO QDs. The stepwise assembly process of the fabricated biosensor was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The synthesized ZnO QDs and graphene oxide were characterized by Raman spectroscopy, infrared spectroscopy, X-ray diffraction and scanning electron microscopic techniques. The determination of OH-PCBs was carried out by using square wave voltammetry over the concentration range of 2.827.65 μM with a detection limit of 0.15 μM with good reproducibility, selectivity and acceptable stability. The high value of surface coverage of ZnO QDs and small value of MichaelisMenten constant (View the MathML source) confirmed an excellent loading of the Tyr and a high affinity of the biosensor toward the detection of OH-PCBs. This biosensor and the described sensing platform offer a great potential for rapid, cost-effective and on-field analysis of OH-PCBs.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 5.401
Times cited: 26
DOI: 10.1016/J.SNB.2013.09.018
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“Nanoscale investigation of the degradation mechanism of a historical chrome yellow paint by quantitative electron energy loss spectroscopy mapping of chromium species”. Tan H, Tian H, Verbeeck J, Janssens K, Van Tendeloo G, Angewandte Chemie: international edition in English 52, 11360 (2013). http://doi.org/10.1002/anie.201305753
Abstract: Getting the picture: The investigation of 100 year old chrome yellow paint by transmission electron microscopy and spectroscopy has led to the identification of four types of coreshell particles. This nanoscale investigation has allowed a mechanism to be proposed for the darkening of some bright yellow colors in Van Gogh's paintings (e.g. in Falling leaves (Les Alyscamps), 1888).
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 11.994
Times cited: 29
DOI: 10.1002/anie.201305753
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