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“Superconducting YBa2Cu3O7-δNanocomposites Using Preformed ZrO2Nanocrystals: Growth Mechanisms and Vortex Pinning Properties”. De Keukeleere K, Cayado P, Meledin A, Vallès F, De Roo J, Rijckaert H, Pollefeyt G, Bruneel E, Palau A, Coll M, Ricart S, Van Tendeloo G, Puig T, Obradors X, Van Driessche I, Advanced Electronic Materials 2, 1600161 (2016). http://doi.org/10.1002/aelm.201600161
Abstract: Although high temperature superconductors are promising for power applications, the production of low-cost coated conductors with high current densities—at high magnetic fields—remains challenging. A superior superconducting YBa2Cu3O7–δ nanocomposite is fabricated via chemical solution deposition (CSD) using preformed nanocrystals (NCs). Preformed, colloidally stable ZrO2 NCs are added to the trifluoroacetic acid based precursor solution and the NCs' stability is confirmed up to 50 mol% for at least 2.5 months. These NCs tend to disrupt the epitaxial growth of YBa2Cu3O7–δ, unless a thin seed layer is applied. A 10 mol% ZrO2 NC addition proved to be optimal, yielding a critical current density JC of 5 MA cm−2 at 77 K in self-field. Importantly, this new approach results in a smaller magnetic field decay of JC(H//c) for the nanocomposite compared to a pristine film. Furthermore, microstructural analysis of the YBa2Cu3O7–δ nanocomposite films reveals that different strain generation mechanisms may occur compared to the spontaneous segregation approach. Yet, the generated nanostrain in the YBa2Cu3O7–δ nanocomposite results in an improvement of the superconducting properties similar to the spontaneous segregation approach. This new approach, using preformed NCs in CSD coatings, can be of great potential for high magnetic field applications.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Times cited: 26
DOI: 10.1002/aelm.201600161
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“Enhanced optoelectronic performances of vertically aligned hexagonal boron nitride nanowalls-nanocrystalline diamond heterostructures”. Sankaran KJ, Hoang DQ, Kunuku S, Korneychuk S, Turner S, Pobedinskas P, Drijkoningen S, Van Bael MK, D' Haen J, Verbeeck J, Leou K-C, Lin I-N, Haenen K, Scientific reports 6, 29444 (2016). http://doi.org/10.1038/srep29444
Abstract: Field electron emission (FEE) properties of vertically aligned hexagonal boron nitride nanowalls (hBNNWs) grown on Si have been markedly enhanced through the use of nitrogen doped nanocrystalline diamond (nNCD) films as an interlayer. The FEE properties of hBNNWs-nNCD heterostructures show a low turn-on field of 15.2 V/mum, a high FEE current density of 1.48 mA/cm(2) and life-time up to a period of 248 min. These values are far superior to those for hBNNWs grown on Si substrates without the nNCD interlayer, which have a turn-on field of 46.6 V/mum with 0.21 mA/cm(2) FEE current density and life-time of 27 min. Cross-sectional TEM investigation reveals that the utilization of the diamond interlayer circumvented the formation of amorphous boron nitride prior to the growth of hexagonal boron nitride. Moreover, incorporation of carbon in hBNNWs improves the conductivity of hBNNWs. Such a unique combination of materials results in efficient electron transport crossing nNCD-to-hBNNWs interface and inside the hBNNWs that results in enhanced field emission of electrons. The prospective application of these materials is manifested by plasma illumination measurements with lower threshold voltage (370 V) and longer life-time, authorizing the role of hBNNWs-nNCD heterostructures in the enhancement of electron emission.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.259
Times cited: 15
DOI: 10.1038/srep29444
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“The effect of molecular structure of organic compound on the direct high-pressure synthesis of boron-doped nanodiamond: Effect of organic compound on synthesis of boron-doped nanodiamond”. Ekimov EA, Kudryavtsev OS, Turner S, Korneychuk S, Sirotinkin VP, Dolenko TA, Vervald AM, Vlasov II, Physica status solidi : A : applications and materials science 213, 2582 (2016). http://doi.org/10.1002/pssa.201600181
Abstract: Evolution of crystalline phases with temperature has been studied in materials produced by high-pressure high-temperature treatment of 9-borabicyclo[3.3.1]nonane dimer (9BBN), triphenylborane and trimesitylborane. The boron-doped diamond nanoparticles with a size below 10 nm were obtained at 8–9 GPa and temperatures 970–1250 °C from 9BBN only. Bridged structure and the presence of boron atom in the carbon cycle of 9BBN were revealed to be a key point for the direct synthesis of doped diamond nanocrystals. The diffusional transformation of the disordered carbon phase is suggested to be the main mechanism of the nanodiamond formation from 9BBN in the temperature range of 970–1400 °C. Aqueous suspensions of primary boron-doped diamond nanocrystals were prepared upon removal of non-diamond phases that opens wide opportunities for application of this new nanomaterial in electronics and biotechnologies.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.775
Times cited: 8
DOI: 10.1002/pssa.201600181
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“Direct imaging of boron segregation at dislocations in B:diamond heteroepitaxial films”. Turner S, Idrissi H, Sartori AF, Korneychuck S, Lu Y-G, Verbeeck J, Schreck M, Van Tendeloo G, Nanoscale 8, 2212 (2016). http://doi.org/10.1039/c5nr07535a
Abstract: A thin film of heavily B-doped diamond has been grown epitaxially by microwave plasma chemical vapor deposition on an undoped diamond layer, on top of a Ir/YSZ/Si(001) substrate stack, to study the boron segregation and boron environment at the dislocations present in the film. The density and nature of the dislocations were investigated by conventional and weak-beam dark-field transmission electron microscopy techniques, revealing the presence of two types of dislocations: edge and mixed-type 45 degrees dislocations. The presence and distribution of B in the sample was studied using annular dark-field scanning transmission electron microscopy and spatially resolved electron energy-loss spectroscopy. Using these techniques, a segregation of B at the dislocations in the film is evidenced, which is shown to be intermittent along the dislocation. A single edge-type dislocation was selected to study the distribution of the boron surrounding the dislocation core. By imaging this defect at atomic resolution, the boron is revealed to segregate towards the tensile strain field surrounding the edge-type dislocations. An investigation of the fine structure of the B-K edge at the dislocation core shows that the boron is partially substitutionally incorporated into the diamond lattice and partially present in a lower coordination (sp(2)-like hybridization).
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 15
DOI: 10.1039/c5nr07535a
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“Bending Gold Nanorods with Light”. Babynina A, Fedoruk M, Kuhler P, Meledin A, Doblinger M, Lohmueller T, Nano letters 16, 6485 (2016). http://doi.org/10.1021/acs.nanolett.6b03029
Abstract: V-shaped gold nanoantennas are the functional components of plasmonic metasurfaces, which are capable of manipulating light in unprecedented ways. Designing a metasurface requires the custom arrangement of individual antennas with controlled shape and orientation. Here, we show how highly crystalline gold nanorods in solution can be bend, one-by one, into a V-shaped geometry and printed to the surface of a solid support through a combination of plasmonic heating and optical force. Significantly, we demonstrate that both the bending angle and the orientation of each rod-antenna can be adjusted independent from each other by tuning the laser intensity and polarization. This approach is applicable for the patterning of V-shaped plasmonic antennas on almost any substrate, which holds great potential for the fabrication of ultrathin optical components and devices.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 12.712
Times cited: 24
DOI: 10.1021/acs.nanolett.6b03029
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“Three dimensional mapping of Fe dopants in ceria nanocrystals using direct spectroscopic electron tomography”. Goris B, Meledina M, Turner S, Zhong Z, Batenburg KJ, Bals S, Ultramicroscopy 171, 55 (2016). http://doi.org/10.1016/j.ultramic.2016.08.017
Abstract: Electron tomography is a powerful technique for the 3D characterization of the morphology of nanostructures. Nevertheless, resolving the chemical composition of complex nanostructures in 3D remains challenging and the number of studies in which electron energy loss spectroscopy (EELS) is combined with tomography is limited. During the last decade, dedicated reconstruction algorithms have been developed for HAADF-STEM tomography using prior knowledge about the investigated sample. Here, we will use the prior knowledge that the experimental spectrum of each reconstructed voxel is a linear combination of a well-known set of references spectra in a so-called direct spectroscopic tomography technique. Based on a simulation experiment, it is shown that this technique provides superior results in comparison to conventional reconstruction methods for spectroscopic data, especially for spectrum images containing a relatively low signal to noise ratio. Next, this technique is used to investigate the spatial distribution of Fe dopants in Fe:Ceria nanoparticles in 3D. It is shown that the presence of the Fe2+ dopants is correlated with a reduction of the Ce atoms from Ce4+ towards Ce3+. In addition, it is demonstrated that most of the Fe dopants are located near the voids inside the nanoparticle.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 13
DOI: 10.1016/j.ultramic.2016.08.017
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“Direct Observation of Ferroelectric Domain Walls in LiNbO3: Wall-Meanders, Kinks, and Local Electric Charges”. Gonnissen J, Batuk D, Nataf GF, Jones L, Abakumov AM, Van Aert S, Schryvers D, Salje EKH, Advanced functional materials 26, 7599 (2016). http://doi.org/10.1002/adfm.201603489
Abstract: Direct observations of the ferroelectric domain boundaries in LiNbO3 are performed using high-resolution high-angle annular dark field scanning transmission electron microscopy imaging, revealing a very narrow width of the domain wall between the 180° domains. The domain walls demonstrate local side-way meandering, which results in inclinations even when the overall wall orientation follows the ferroelectric polarization. These local meanders contain kinks with “head-to-head” and “tail-to-tail” dipolar configurations and are therefore locally charged. The charged meanders are confined to a few cation layers along the polarization direction and are separated by longer stretches of straight domain walls.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.124
Times cited: 23
DOI: 10.1002/adfm.201603489
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“Influence of defect distribution on the reducibility of CeO2-x nanoparticles”. Spadaro MC, Luches P, Bertoni G, Grillo V, Turner S, Van Tendeloo G, Valeri S, D'Addato S, Nanotechnology 27, 425705 (2016). http://doi.org/10.1088/0957-4484/27/42/425705
Abstract: Ceria nanoparticles (NPs) are fundamental in heterogeneous catalysis because of their ability to store or release oxygen depending on the ambient conditions. Their oxygen storage capacity is strictly related to the exposed planes, crystallinity, density and distribution of defects. In this work a study of ceria NPs produced with a ligand-free, physical synthesis method is presented. The NP films were grown by a magnetron sputtering based gas aggregation source and studied by high resolution- and scanning-transmission electron microscopy and x-ray photoelectron spectroscopy. In particular, the influence of the oxidation procedure on the NP reducibility has been investigated. The different reducibility has been correlated to the exposed planes, crystallinity and density and distribution of structural defects. The results obtained in this work represent a basis to obtain cerium oxide NP with desired oxygen transport properties.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.44
Times cited: 11
DOI: 10.1088/0957-4484/27/42/425705
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“A first-principles study of stable few-layer penta-silicene”. Aierken Y, Leenaerts O, Peeters FM, Physical chemistry, chemical physics 18, 18486 (2016). http://doi.org/10.1039/c6cp03200a
Abstract: Recently penta-graphene was proposed as a stable two-dimensional carbon allotrope consisting of a single layer of interconnected carbon pentagons [Zhang et al., PNAS, 2015, 112, 2372]. Its silicon counterpart, penta-silicene, however, is not stable. In this work, we show that multilayers of penta-silicene form stable materials with semiconducting or metallic properties, depending on the stacking mode. We demonstrate their dynamic stability through their phonon spectrum and using molecular dynamics. A particular type of bilayer penta-silicene is found to have lower energy than all of the known hexagonal silicene bilayers and forms therefore the most stable bilayer silicon material predicted so far. The electronic and mechanical properties of these new silicon allotropes are studied in detail and their behavior under strain is investigated. We demonstrate that strain can be used to tune its band gap.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 4.123
Times cited: 42
DOI: 10.1039/c6cp03200a
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“Accelerated removal of Fe-antisite defects while nanosizing hydrothermal LiFePO4 with Ca2+”. Paolella A, Turner S, Bertoni G, Hovington P, Flacau R, Boyer C, Feng Z, Colombo M, Marras S, Prato M, Manna L, Guerfi A, Demopoulos GP, Armand M, Zaghib K;, Nano letters 16, 2692 (2016). http://doi.org/10.1021/acs.nanolett.6b00334
Abstract: Based on neutron powder diffraction (NPD) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), we show that calcium ions help eliminate the Fe-antisite defects by controlling the nucleation and evolution of the LiFePO4 particles during their hydrothermal synthesis. This Ca-regulated formation of LiFePO4 particles has an overwhelming impact on the removal of their iron antisite defects during the subsequent carbon coating step since (i) almost all the Fe-antisite defects aggregate at the surface of the LiFePO4 crystal when the crystals are small enough and (ii) the concomitant increase of the surface area, which further exposes the Fe-antisite defects. Our results not only justify a low-cost, efficient and reliable hydrothermal synthesis method for LiFePO4 but also provide a promising alternative viewpoint on the mechanism controlling the nanosizing of LiFePO4, which leads to improved electrochemical performances.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 12.712
Times cited: 30
DOI: 10.1021/acs.nanolett.6b00334
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Meledina M (2016) Advanced electron microscopy characterization of catalysts. Antwerpen
Keywords: Doctoral thesis; Electron microscopy for materials research (EMAT)
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“BCS-BEC crossover in quantum confined superconductors”. Guidini A, Flammia L, Milošević, MV, Perali A, Journal of superconductivity and novel magnetism 29, 711 (2016). http://doi.org/10.1007/s10948-015-3308-y
Abstract: Ultranarrow superconductors are in the strong quantum confinement regime with formation of multiple coherent condensates associated with the many subbands of the electronic structure. Here, we analyze the multiband BCS-BEC crossover induced by the chemical potential tuned close to a subband bottom, in correspondence of a superconducting shape resonance. The evolution of the condensate fraction and of the pair correlation length in the ground state as functions of the chemical potential demonstrates the tunability of the BCS-BEC crossover for the condensate component of the selected subband. The extension of the crossover regime increases when the pairing strength and/or the characteristic energy of the interaction get larger. Our results indicate the coexistence of large and small Cooper pairs in the crossover regime, leading to the optimal parameter configuration for high transition temperature superconductivity.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.18
Times cited: 12
DOI: 10.1007/s10948-015-3308-y
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“Bilayer SnS2 : tunable stacking sequence by charging and loading pressure”. Bacaksiz C, Cahangirov S, Rubio A, Senger RT, Peeters FM, Sahin H, Physical review B 93, 125403 (2016). http://doi.org/10.1103/PhysRevB.93.125403
Abstract: Employing density functional theory-based methods, we investigate monolayer and bilayer structures of hexagonal SnS2, which is a recently synthesized monolayer metal dichalcogenide. Comparison of the 1H and 1T phases of monolayer SnS2 confirms the ground state to be the 1T phase. In its bilayer structure we examine different stacking configurations of the two layers. It is found that the interlayer coupling in bilayer SnS2 is weaker than that of typical transition-metal dichalcogenides so that alternative stacking orders have similar structural parameters and they are separated with low energy barriers. A possible signature of the stacking order in the SnS2 bilayer has been sought in the calculated absorbance and reflectivity spectra. We also study the effects of the external electric field, charging, and loading pressure on the characteristic properties of bilayer SnS2. It is found that (i) the electric field increases the coupling between the layers at its preferred stacking order, so the barrier height increases, (ii) the bang gap value can be tuned by the external E field and under sufficient E field, the bilayer SnS2 can become a semimetal, (iii) the most favorable stacking order can be switched by charging, and (iv) a loading pressure exceeding 3 GPa changes the stacking order. The E-field tunable band gap and easily tunable stacking sequence of SnS2 layers make this 2D crystal structure a good candidate for field effect transistor and nanoscale lubricant applications.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 38
DOI: 10.1103/PhysRevB.93.125403
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“Combined macroscopic, nanoscopic, and atomic-scale characterization of gold-ruthenium bimetallic catalysts for octanol oxidation”. Chinchilla LE, Olmos C, Kurttepeli M, Bals S, Van Tendeloo G, Villa A, Prati L, Blanco G, Calvino JJ, Chen X, Hungría AB, Particle and particle systems characterization 33, 419 (2016). http://doi.org/10.1002/ppsc.201600057
Abstract: A series of gold-ruthenium bimetallic catalysts of increasing Au:Ru molar ratios supported on a Ce0.62Zr0.38O2 mixed oxide are prepared and their structural and chemical features characterized by a combination of macroscopic and atomic-scale techniques based on scanning transmission electron microscopy. The influence of the temperature of the final reduction treatment used as activation step (350-700 degrees C range) is also investigated. The preparation method used allows catalysts to be successfully prepared where a major fraction of the metal nanoparticles is in the size range below 5 nm. The structural complexities characteristic of this type of catalysts are evidenced, as well as the capabilities and limitations of both the macroscopic and microscopic techniques in the characterization of the system of metal nanoparticles. A positive influence of the addition of Ru on both the resistance against sintering and the catalytic performance of the starting supported Au catalyst is evidenced.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 4.474
Times cited: 7
DOI: 10.1002/ppsc.201600057
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“Comment on “Creating in-plane pseudomagnetic fields in excess of 1000 T by misoriented stacking in a graphene bilayer””. Van der Donck M, Peeters FM, Van Duppen B, Physical review B 93, 247401 (2016). http://doi.org/10.1103/PhysRevB.93.247401
Abstract: In a recent paper [Phys. Rev. B 89, 125418 (2014)], the authors argue that it is possible to map the electronic properties of twisted bilayer graphene to those of bilayer graphene in an in-plane magnetic field. However, their description of the low-energy dynamics of twisted bilayer graphene is restricted to the extended zone scheme and therefore neglects the effects of the superperiodic structure. If the energy spectrum is studied in the supercell Brillouin zone, we find that the comparison with an in-plane magnetic field fails because (i) the energy spectra of the two situations exhibit different symmetries and (ii) the low-energy spectra are very different.
Keywords: Editorial; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 6
DOI: 10.1103/PhysRevB.93.247401
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“Comparison of short-channel effects in monolayer MoS2 based junctionless and inversion-mode field-effect transistors”. Agarwal T, Sorée B, Radu I, Raghavan P, Fiori G, Iannaccone G, Thean A, Heyns M, Dehaene W, Applied physics letters 108, 023506 (2016). http://doi.org/10.1063/1.4939933
Abstract: Conventional junctionless (JL) multi/gate (MuG) field-effect transistors (FETs) require extremely scaled channels to deliver high on-state current with low short-channel effect related leakage. In this letter, using ultra-thin 2D materials (e.g., monolayer MoS2), we present comparison of short-channel effects in JL, and inversion-mode (IM) FETs. We show that JL FETs exhibit better sub-threshold slope (S.S.) and drain-induced-barrier-lowering (DIBL) in comparison to IM FETs due to reduced peak electric field at the junctions. But, threshold voltage (VT) roll-off with channel length downscaling is found to be significantly higher in JL FETs than IM FETs, due to higher source/drain controlled charges (dE/dx) in the channel. Further, we show that although VT roll-off in JL FETs improves by increasing the gate control, i.e., by scaling the oxide, or channel thickness, the sensitivity of threshold voltage on structural parameters is found out to be high. (C) 2016 AIP Publishing LLC.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.411
Times cited: 13
DOI: 10.1063/1.4939933
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“Computing optical properties of ultra-thin crystals”. Sahin H, Torun E, Bacaksiz C, Horzum S, Kang J, Senger RT, Peeters FM, Wiley Interdisciplinary Reviews: Computational Molecular Science 6, 351 (2016). http://doi.org/10.1002/wcms.1252
Abstract: An overview is given of recent advances in experimental and theoretical understanding of optical properties of ultra-thin crystal structures (graphene, phosphorene, silicene, MoS2 , MoSe2, WS2, WSe2, h-AlN, h-BN, fluorographene, and graphane). Ultra-thin crystals are atomically thick-layered crystals that have unique properties which differ from their 3D counterpart. Because of the difficulties in the synthesis of few-atom-thick crystal structures, which are thought to be the main building blocks of future nanotechnology, reliable theoretical predictions of their electronic, vibrational, and optical properties are of great importance. Recent studies revealed the reliable predictive power of existing theoretical approaches based on density functional theory. (C) 2016 John Wiley & Sons, Ltd WIREs Comput Mol Sci 2016, 6:351-368. doi: 10.1002/wcms.1252 For further resources related to this article, please visit the .
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 14.016
Times cited: 14
DOI: 10.1002/wcms.1252
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“Deactivation study of Fe2O3-CeO2 during redox cycles for CO production from CO2”. Dharanipragada NVRA, Meledina M, Galvita VV, Poelman H, Turner S, Van Tendeloo G, Detavernier C, Marin GB, Industrial and engineering chemistry research 55, 5911 (2016). http://doi.org/10.1021/acs.iecr.6b00963
Abstract: Deactivation was investigated in Fe2O3-CeO2 oxygen storage materials during repeated H-2-reduction and CO2-reoxidation. In situ XRD, XAS, and TEM were used to identify phases, crystallite sizes, and morphological changes upon cycling operation. The effect of redox cycling was investigated both in Fe-rich (80 wt % Fe2O3-CeO2) and Ce-rich (10 wt %Fe2O3-CeO2) materials. The former consisted of 100 nm Fe2O3 particles decorated with 5-10 nm Ce1-xFexO2-x. The latter presented CeO2 with incorporated Fe, i.e. a solid solution of Ce1-xFexO2-x, as the main oxygen carrier. By modeling the EXAFS Ce-K signal for as-prepared 10 wt %Fe2O3-CeO2, the amount of Fe in CeO2 was determined as 21 mol %, corresponding to 86% of the total iron content. Sintering and solid solid transformations, the latter including both new phase formation and element segregation, were identified as deactivation pathways upon redox cycling. In Ce-rich material, perovskite (CeFeO3) was identified by XRD. This phase remained inert during reduction and reoxidation, resulting in an overall lower oxygen storage capacity. Further, Fe segregated from the solid solution, thereby decreasing its reducibility. In addition, an increase in crystallite size occurred for all phases. In Fe-rich material, sintering is the main deactivation pathway, although Fe segregation from the solid solution and perovskite formation cannot be excluded.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.843
Times cited: 26
DOI: 10.1021/acs.iecr.6b00963
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“Defect-modulated transistors and gas-enhanced photodetectors on ReS2 nanosheets”. Yang S, Kang J, Yue Q, Coey JMD, Jiang C, Advanced Materials Interfaces 3, 1500707 (2016). http://doi.org/10.1002/admi.201500707
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 4.279
Times cited: 22
DOI: 10.1002/admi.201500707
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“Dislocation and back stress dominated viscoplasticity in freestanding sub-micron Pd films”. Lemoine G, Delannay L, Idrissi H, Colla M-S, Pardoen T, Acta materialia 111, 10 (2016). http://doi.org/10.1016/j.actamat.2016.03.038
Abstract: A dislocation-based crystal plasticity model is developed in order to study the mechanical and creep/ relaxation behaviour of polycrystalline metallic thin films. The model accounts for the confinement of plasticity due to grain boundaries and for the anisotropy of individual grains, as well as for the significant viscoplastic effects associated to dislocation dominated thermally activated mechanisms. Numerical predictions are assessed based on experimental tensile test followed by relaxation on freestanding Pd films, based on an on-chip test technique. The dislocation-based mechanism assumption captures all the experimental trends, including the stress strain response, the relaxation behaviour and the dislocation density evolution, confirming the dominance of a dislocation driven deformation mechanism for the present Pd films with high defects density. The model has also been used to address some original experimental evidences involving back stresses, Bauschinger effect, backward creep and strain recovery. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
Times cited: 6
DOI: 10.1016/j.actamat.2016.03.038
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“Effect of crystal structure on the electronic transport properties of the organometallic perovskite CH3NH3PbI3”. Berdiyorov GR, Madjet ME, El-Mellouhi F, Peeters FM, Solar energy materials and solar cells
T2 –, 2nd International Renewable and Sustainable Energy Conference (IRSEC), OCT 17-19, 2014, Ouarzazate, MOROCCO 148, 60 (2016). http://doi.org/10.1016/j.solmat.2015.09.006
Abstract: Using density-functional theory in combination with the nonequilibrium Green's function formalism, we study the effect of the crystal lattice structure of organometallic perovskite CH3NH3PbI3 on its electronic transport properties. Both dispersive interactions and spin-orbit coupling are taken into account in describing structural and electronic properties of the system. We consider two different phases of the material, namely the orthorhombic and cubic lattice structures, which are energetically stable at low (< 160 K) and high (> 330 K) temperatures, respectively. The sizable geometrical differences between the two structures in term of lattice parameters, PbI6 octahedral tilts, rotation and deformations, have considerable impact on the transport properties of the material. For example, at zero bias and for all considered electron energies, the cubic phase has a larger transmission than the orthorhombic one, although both show similar electronic densities of states. Depending on the applied voltage, the current in the cubic system can be several orders of magnitude larger as compared to the one obtained for the orthorhombic sample. We attribute this enhancement in the transmission to the presence of extended states in the cubic phase due to the symmetrically shaped and ordered PbI6 octaherdra. (C) 2015 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 4.784
Times cited: 16
DOI: 10.1016/j.solmat.2015.09.006
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“Effect of halide-mixing on the electronic transport properties of organometallic perovskites”. Berdiyorov GR, El-Mellouhi F, Madjet ME, Alharbi FH, Peeters FM, Kais S, Solar energy materials and solar cells
T2 –, 2nd International Renewable and Sustainable Energy Conference (IRSEC), OCT 17-19, 2014, Ouarzazate, MOROCCO 148, 2 (2016). http://doi.org/10.1016/j.solmat.2015.11.023
Abstract: Using density-functional theory in combination with the nonequilibrium Green's function formalism, we study the effect of iodide/chloride and iodide/bromide mixing on the electronic transport in lead based organometallic perovskite CH3NH3PbI3, which is known to be an effective tool to tune the electronic and optical properties of such materials. We found that depending on the level and position of the halide mixing, the electronic transport can be increased by more than a factor of 4 for a given voltage biasing. The largest current is observed for small concentration of bromide substitutions located at the equatorial sites. However, full halide substitution has a negative effect on the transport properties of this material: the current drops by an order of magnitude for both CH3NH3PbCl3 and CH3NH3PbBr3 samples. (C) 2015 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 4.784
Times cited: 23
DOI: 10.1016/j.solmat.2015.11.023
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“Electric-field-driven Mott metal-insulator transition in correlated thin films : an inhomogeneous dynamical mean-field theory approach”. Bakalov P, Esfahani DN, Covaci L, Peeters FM, Tempere J, Locquet J-P, Physical review : B : condensed matter and materials physics 93, 165112 (2016). http://doi.org/10.1103/PhysRevB.93.165112
Abstract: Simulations are carried out based on the dynamical mean-field theory (DMFT) in order to investigate the properties of correlated thin films for various values of the chemical potential, temperature, interaction strength, and applied transverse electric field. Application of a sufficiently strong field to a thin film at half filling leads to the appearance of conducting regions near the surfaces of the film, whereas in doped slabs the application of a field leads to a conductivity enhancement on one side of the film and a gradual transition to the insulating state on the opposite side. In addition to the inhomogeneous DMFT, a local density approximation (LDA) is considered in which the particle density n, quasiparticle residue Z, and spectral weight at the Fermi level A(ω=0) of each layer are approximated by a homogeneous bulk environment. A systematic comparison between the two approaches reveals that the less expensive LDA results are in good agreement with the DMFT approach, except close to the metal-to-insulator transition points and in the layers immediately at the film surfaces. LDA values for n are overall more reliable than those for Z and A(ω=0). The hysteretic behavior (memory effect) characteristic of the bulk doping driven Mott transition persists in the slab.
Keywords: A1 Journal article; Theory of quantum systems and complex systems; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 5
DOI: 10.1103/PhysRevB.93.165112
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“Electronic states in an atomistic carbon quantum dot patterned in graphene”. Craco L, Carara SS, da Silva Pereira TA, Milošević, MV, Physical review B 93, 155417 (2016). http://doi.org/10.1103/PhysRevB.93.155417
Abstract: We reveal the emergence of metallicKondo clouds in an atomistic carbon quantum dot, realized as a single-atom junction in a suitably patterned graphene nanoflake. Using density functional dynamical mean-field theory (DFDMFT) we show how correlation effects lead to striking features in the electronic structure of our device, and how those are enhanced by the electron-electron interactions when graphene is patterned at the atomistic scale. Our setup provides a well-controlled environment to understand the principles behind the orbital-selective Kondo physics and the interplay between orbital and spin degrees of freedom in carbon-based nanomaterials, which indicate new pathways for spintronics in atomically patterned graphene.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 6
DOI: 10.1103/PhysRevB.93.155417
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“Energy levels of hybrid monolayer-bilayer graphene quantum dots”. Mirzakhani M, Zarenia M, Ketabi SA, da Costa DR, Peeters FM, Physical review B 93, 165410 (2016). http://doi.org/10.1103/PhysRevB.93.165410
Abstract: Often real samples of graphene consist of islands of both monolayer and bilayer graphene. Bound states in such hybrid quantum dots are investigated for (i) a circular single-layer graphene quantum dot surrounded by an infinite bilayer graphene sheet and (ii) a circular bilayer graphene quantum dot surrounded by an infinite single-layer graphene. Using the continuum model and applying zigzag boundary conditions at the single-layer-bilayer graphene interface, we obtain analytical results for the energy levels and the corresponding wave spinors. Their dependence on perpendicular magnetic and electric fields are studied for both types of quantum dots. The energy levels exhibit characteristics of interface states, and we find anticrossings and closing of the energy gap in the presence of a bias potential.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 26
DOI: 10.1103/PhysRevB.93.165410
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“First-principles thermodynamics and defect kinetics guidelines for engineering a tailored RRAM device”. Clima S, Chen YY, Chen CY, Goux L, Govoreanu B, Degraeve R, Fantini A, Jurczak M, Pourtois G, Journal of applied physics 119, 225107 (2016). http://doi.org/10.1063/1.4953673
Abstract: Resistive Random Access Memories are among the most promising candidates for the next generation of non-volatile memory. Transition metal oxides such as HfOx and TaOx attracted a lot of attention due to their CMOS compatibility. Furthermore, these materials do not require the inclusion of extrinsic conducting defects since their operation is based on intrinsic ones (oxygen vacancies). Using Density Functional Theory, we evaluated the thermodynamics of the defects formation and the kinetics of diffusion of the conducting species active in transition metal oxide RRAM materials. The gained insights based on the thermodynamics in the Top Electrode, Insulating Matrix and Bottom Electrode and at the interfaces are used to design a proper defect reservoir, which is needed for a low-energy reliable switching device. The defect reservoir has also a direct impact on the retention of the Low Resistance State due to the resulting thermodynamic driving forces. The kinetics of the diffusing conducting defects in the Insulating Matrix determine the switching dynamics and resistance retention. The interface at the Bottom Electrode has a significant impact on the low-current operation and long endurance of the memory cell. Our first-principles findings are confirmed by experimental measurements on fabricated RRAM devices. Published by AIP Publishing.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.068
Times cited: 17
DOI: 10.1063/1.4953673
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“Gas-phase synthesis of Mg-Ti nanoparticles for solid-state hydrogen storage”. Calizzi M, Venturi F, Ponthieu M, Cuevas F, Morandi V, Perkisas T, Bals S, Pasquini L, Physical chemistry, chemical physics 18, 141 (2016). http://doi.org/10.1039/c5cp03092g
Abstract: Mg-Ti nanostructured samples with different Ti contents were prepared via compaction of nanoparticles grown by inert gas condensation with independent Mg and Ti vapour sources. The growth set-up offered the option to perform in situ hydrogen absorption before compaction. Structural and morphological characterisation was carried out by X-ray diffraction, energy dispersive spectroscopy and electron microscopy. The formation of an extended metastable solid solution of Ti in hcp Mg was detected up to 15 at% Ti in the as-grown nanoparticles, while after in situ hydrogen absorption, phase separation between MgH2 and TiH2 was observed. At a Ti content of 22 at%, a metastable Mg-Ti-H fcc phase was observed after in situ hydrogen absorption. The co-evaporation of Mg and Ti inhibited nanoparticle coalescence and crystallite growth in comparison with the evaporation of Mg only. In situ hydrogen absorption was beneficial to subsequent hydrogen behaviour, studied by high pressure differential scanning calorimetry and isothermal kinetics. A transformed fraction of 90% was reached within 100 s at 300 degrees C during both hydrogen absorption and desorption. The enthalpy of hydride formation was not observed to differ from bulk MgH2.
Keywords: A1 Journal article; Engineering Management (ENM); Electron microscopy for materials research (EMAT)
Impact Factor: 4.123
Times cited: 31
DOI: 10.1039/c5cp03092g
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“Giant magnetic anisotropy in doped single layer molybdenum disulfide and fluorographene”. Sivek J, Sahin H, Partoens B, Peeters FM, Journal of physics : condensed matter 28, 195301 (2016). http://doi.org/10.1088/0953-8984/28/19/195301
Abstract: Stable monolayer materials based on existing, well known and stable two-dimensional crystal fluorographene and molybdenum disulfide are predicted to exhibit a huge magnetocrystalline anisotropy when functionalized with adsorbed transition metal atoms at vacant sides. Ab initio calculations within the density-functional theory formalism were performed to investigate the adsorption of the transitional metals in a single S (or F) vacancy of monolayer molybdenum disulfide (or fluorographene). We found strong bonding of the transitional metal atoms to the vacant sites with binding energies ranging from 2.5 to 5.2 eV. Our calculations revealed that these systems with adsorbed metal atoms exhibit a magnetic anisotropy, specifically the structures including Os and Ir show a giant magnetocrystalline anisotropy energy of 31-101 meV. Our results demonstrate the possibility of obtaining stable monolayer materials with huge magnetocrystalline anisotropy based on preexisting, well known and stable two-dimensional crystals: fluorographene and molybdenum disulfide. We believe that the results obtained here are useful not only for deeper understanding of the origin of magnetocrystalline anisotropy but also for the design of monolayer optoelectronic devices with novel functionalities.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.649
Times cited: 7
DOI: 10.1088/0953-8984/28/19/195301
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“Hexagonal-shaped monolayer-bilayer quantum disks in graphene : a tight-binding approach”. da Costa, Zarenia M, Chaves A, Pereira JM Jr, Farias GA, Peeters FM, Physical review B 94, 035415 (2016). http://doi.org/10.1103/PhysRevB.94.035415
Abstract: Using the tight-binding approach, we investigate confined states in two different hybrid monolayer-bilayer systems: (i) a hexagonal monolayer area surrounded by bilayer graphene in the presence of a perpendicularly applied electric field and (ii) a hexagonal bilayer graphene dot surrounded by monolayer graphene. The dependence of the energy levels on dot size and external magnetic field is calculated. We find that the energy spectrum for quantum dots with zigzag edges consists of states inside the gap which range from dot-localized states, edge states, to mixed states coexisting together, whereas for dots with armchair edges, only dot-localized states are observed.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 11
DOI: 10.1103/PhysRevB.94.035415
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“Highly efficient rutile TiO2 photocatalysts with single Cu(II) and Fe(III) surface catalytic sites”. Neubert S, Mitoraj D, Shevlin SA, Pulisova P, Heimann M, Du Y, Goh GKL, Pacia M, Kruczała K, Turner S, Macyk W, Guo ZX, Hocking RK, Beranek R;, Journal of materials chemistry A : materials for energy and sustainability 4, 3127 (2016). http://doi.org/10.1039/c5ta07036h
Abstract: Highly active photocatalysts were obtained by impregnation of nanocrystalline rutile TiO2 powders with small amounts of Cu(II) and Fe(III) ions, resulting in the enhancement of initial rates of photocatalytic degradation of 4-chlorophenol in water by factors of 7 and 4, compared to pristine rutile, respectively. Detailed structural analysis by EPR and X-ray absorption spectroscopy (EXAFS) revealed that Cu(II) and Fe(III) are present as single species on the rutile surface. The mechanism of the photoactivity enhancement was elucidated by a combination of DFT calculations and detailed experimental mechanistic studies including photoluminescence measurements, photocatalytic experiments using scavengers, OH radical detection, and photopotential transient measurements. The results demonstrate that the single Cu(II) and Fe(III) ions act as effective cocatalytic sites, enhancing the charge separation, catalyzing “dark” redox reactions at the interface, thus improving the normally very low quantum yields of UV light-activated TiO2 photocatalysts. The exact mechanism of the photoactivity enhancement differs depending on the nature of the cocatalyst. Cu(II)-decorated samples exhibit fast transfer of photogenerated electrons to Cu(II/I) sites, followed by enhanced catalysis of dioxygen reduction, resulting in improved charge separation and higher photocatalytic degradation rates. At Fe(III)-modified rutile the rate of dioxygen reduction is not improved and the photocatalytic enhancement is attributed to higher production of highly oxidizing hydroxyl radicals produced by alternative oxygen reduction pathways opened by the presence of catalytic Fe(III/II) sites. Importantly, it was demonstrated that excessive heat treatment (at 450 degrees C) of photocatalysts leads to loss of activity due to migration of Cu(II) and Fe(III) ions from TiO2 surface to the bulk, accompanied by formation of oxygen vacancies. The demonstrated variety of mechanisms of photoactivity enhancement at single site catalyst-modified photocatalysts holds promise for developing further tailored photocatalysts for various applications.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.867
Times cited: 44
DOI: 10.1039/c5ta07036h
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