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“Engineering properties by long range symmetry propagation initiated at perovskite heterostructure interface”. Liao ZL, Green RJ, Gauquelin N, Gonnissen J, Van Aert S, Verbeeck J, et al, Advanced functional materials , 1 (2016)
Abstract: In epitaxial thin film systems, the crystal structure and its symmetry deviate from the bulk counterpart due to various mechanisms such as epitaxial strain and interfacial structural coupling, which induce an accompanying change in their properties. In perovskite materials, the crystal symmetry can be described by rotations of 6-fold coordinated transition metal oxygen octahedra, which are found to be altered at interfaces. Here, we unravel how the local oxygen octahedral coupling (OOC) at perovskite heterostructural interfaces initiates a different symmetry in epitaxial films and provide design rules to induce various symmetries in thin films by careful selecting appropriate combinations of substrate/buffer/film. Very interestingly we discovered that these combinations lead to symmetry changes throughout the full thickness of the film. Our results provide a deep insight into understanding the origin of induced crystal symmetry in a perovskite heterostructure and an intelligent route to achieve unique functional properties.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 12.124
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“Theoretical study of silicene and germanene”. Houssa M, van den Broek B, Scalise E, Pourtois G, Afanas'ev VV, Stesmans A, Graphene, Ge/iii-v, And Emerging Materials For Post Cmos Applications 5 (2013). http://doi.org/10.1149/05301.0051ECST
Abstract: The structural and electronic properties of silicene and germanene on metallic and non-metallic substrates are investigated theoretically, using first-principles simulations. We first study the interaction of silicene with Ag(111) surfaces, focusing on the (4x4) silicene/Ag structure. Due to symmetry breaking in the silicene layer (nonequivalent number of top and bottom Si atoms), silicene is predicted to be semiconducting, with a computed energy gap of about 0.3 eV. However, the charge transfer occurring at the silicene/Ag(111) interface leads to an overall metallic system. We next investigate the interaction of silicene and germanene with hexagonal non-metallic substrates, namely ZnS and ZnSe. On reconstructed (semiconducting) (0001) ZnS or ZnSe surfaces, silicene and germanene are found to be semiconducting. Remarkably, the nature (indirect or direct) and magnitude of their energy band gap can be controlled by an out-of-plane electric field.
Keywords: P1 Proceeding; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Times cited: 6
DOI: 10.1149/05301.0051ECST
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“Two-dimensional hexagonal tin : ab initio geometry, stability, electronic structure and functionalization”. van den Broek B, Houssa M, Scalise E, Pourtois G, Afanas'ev VV, Stesmans A, 2D materials 1, 021004 (2014). http://doi.org/10.1088/2053-1583/1/2/021004
Abstract: We study the structural, mechanical and electronic properties of the two-dimensional (2D) allotrope of tin: tinene/stanene using first-principles calculation within density functional theory, implemented in a set of computer codes. Continuing the trend of the group-IV 2D materials graphene, silicene and germanene; tinene is predicted to have a honeycomb lattice with lattice parameter of a(0) = 4.62 angstrom and a buckling of d(0) = 0.92 angstrom. The electronic dispersion shows a Dirac cone with zero gap at the Fermi energy and a Fermi velocity of v(F) = 0.97 x 10(6) m s(-1); including spin-orbit coupling yields a bandgap of 0.10 eV. The monolayer is thermally stable up to 700 K, as indicated by first-principles molecular dynamics, and has a phonon dispersion without imaginary frequencies. We explore applied electric field and applied strain as functionalization mechanisms. Combining these two mechanisms allows for an induced bandgap up to 0.21 eV, whilst retaining the linear dispersion, albeit with degraded electronic transport parameters.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 6.937
Times cited: 58
DOI: 10.1088/2053-1583/1/2/021004
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“Strong attachment of circadian pacemaker neurons on modified ultrananocrystalline diamond surfaces”. Voss A, Wei HY, Zhang Y, Turner S, Ceccone G, Reithmaier JP, Stengl M, Popov C, Materials science and engineering: part C: biomimetic materials 64, 278 (2016). http://doi.org/10.1016/j.msec.2016.03.092
Abstract: Diamond is a promising material for a number of bio-applications, including the fabrication of platforms for attachment and investigation of neurons and of neuroprostheses, such as retinal implants. In the current work ultrananocrystalline diamond (UNCD) films were deposited by microwave plasma chemical vapor deposition, modified by UV/O-3 treatment or NH3 plasma, and comprehensively characterized with respect to their bulk and surface properties, such as crystallinity, topography, composition and chemical bonding nature. The interactions of insect circadian pacemaker neurons with UNCD surfaces with H-, O- and NH2-terminations were investigated with respect to cell density and viability. The fast and strong attachment achieved without application of adhesion proteins allowed for advantageous modification of dispersion protocols for the preparation of primary cell cultures. Centrifugation steps, which are employed for pelletizing dispersed cells to separate them from dispersing enzymes, easily damage neurons. Now centrifugation can be avoided since dispersed neurons quickly and strongly attach to the UNCD surfaces. Enzyme solutions can be easily washed off without losing many of the dispersed cells. No adverse effects on the cell viability and physiological responses were observed as revealed by calcium imaging. Furthermore, the enhanced attachment of the neurons, especially on the modified UNCD surfaces, was especially advantageous for the immunocytochemical procedures with the cell cultures. The cell losses during washing steps were significantly reduced by one order of magnitude in comparison to controls. In addition, the integration of a titanium grid structure under the UNCD films allowed for individual assignment of physiologically characterized neurons to immunocytochemically stained cells. Thus, employing UNCD surfaces free of foreign proteins improves cell culture protocols and immunocytochemistry with cultured cells. The fast and strong attachment of neurons was attributed to a favorable combination of topography, surface chemistry and wettability. (C) 2016 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.164
Times cited: 7
DOI: 10.1016/j.msec.2016.03.092
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“Exceptional layered ordering of cobalt and iron in perovskites”. Lebedev OI, Turner S, Caignaert V, Cherepanov VA, Raveau B, Chemistry of materials 28, 2907 (2016). http://doi.org/10.1021/acs.chemmater.6b01046
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 4
DOI: 10.1021/acs.chemmater.6b01046
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“Incorporation and study of SiV centers in diamond nanopillars”. Felgen N, Naydenov B, Turner S, Jelezko F, Reithmaier JP, Popov C, Diamond and related materials 64, 64 (2016). http://doi.org/10.1016/j.diamond.2016.01.011
Abstract: We report on the incorporation of SiV centers during hot filament chemical vapor deposition of diamond on top of diamond nanopillars with diameters down to 100 nm. The nanopillars themselves were prepared from nano crystalline diamond films by applying electron beam lithography and inductively coupled plasma reactive ion etching. The optical investigations revealed the presence of ensembles of SiV color centers incorporated during the overgrowth step. (C) 2016 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.561
Times cited: 14
DOI: 10.1016/j.diamond.2016.01.011
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“Effect of the substitution Ba\leftrightarrow Sr on the Ga-1222 superstructure : an electron diffraction study”. Milat O, Van Tendeloo G, Amelinckx S, Wright AJ, Greaves C, Chemistry of materials 7, 1709 (1995). http://doi.org/10.1021/cm00057a021
Abstract: The superstructure of the RE(2)(Sr0.85-xBaxNd0.15)(2)GaCU2O9 compound is found to change significantly with increasing substitution of Ba for Sr. Most of the changes take place in the (Sr0.85-xBaxNd0.15)O-GaO-(Sr0.85-xBaxNd0.15)O lamella, the rest of the basic structure being hardly affected. The structural changes for O less than or equal to x less than or equal to 0.65 are studied by electron diffraction. The arrangement of the chains of GaO4 tetrahedra in the Ba-free compound becomes disordered at x > 0.25. At x similar to 0.65 a rearrangement of the chains in the GaO layers takes place; they form a meandering arrangement, which can be described on a 4a(p) x 2a(p) x c(p) superlattice. This rearrangement is accompanied by ordering of Ba and Sr atoms in the adjacent (ST0.85-xBaxNd0.15)O layers. A simple scheme is proposed to explain the influence of the substitution of Ba for Sr on the linking of the GaO4 tetrahedra and on the geometry of the ''chains'' in the GaO layer.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 8.354
DOI: 10.1021/cm00057a021
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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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“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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“Structural aspects of AuCu I or AuCu II and a cuboidal black configuration of f.c.c. disordered phase in AuCu-Pt and AuCu-Ag pseudobinary alloys”. Udoh K-I, El- Araby AM, Tanaka Y, Hisatsune K, Yasuda K, Van Tendeloo G, van Landuyt J, Materials science and engineering: part A: structural materials: properties, microstructure and processing 203, 154 (1995). http://doi.org/10.1016/0921-5093(95)09850-X
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.567
Times cited: 15
DOI: 10.1016/0921-5093(95)09850-X
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“Point defect reactions in silicon studies in situ by high flux electron irradiation in high voltage transmission electron microscope”. Vanhellemont J, Romano-Rodriguez A, Fedina L, van Landuyt J, Aseev A, Materials science and technology 11, 1194 (1995)
Keywords: A3 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 7
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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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“Solution-derived YBa2Cu3O7-\delta (YBCO) superconducting films with BaZrO3 (BZO) nanodots based on reverse micelle stabilized nanoparticles”. Bretos I, Schneller T, Falter M, Baecker M, Hollmann E, Woerdenweber R, Molina-Luna L, Van Tendeloo G, Eibl O, Journal of materials chemistry C : materials for optical and electronic devices 3, 3971 (2015). http://doi.org/10.1039/c4tc02543a
Abstract: Superconducting YBa2Cu3O7-delta (YBCO) films with artificial BaZrO3 (BZO) nanodots were prepared using a chemical solution deposition method involving hybrid solutions composed of trifluoroacetate-based YBCO precursors and reverse micelle stabilized BZO nanoparticle dispersions. Microemulsion-mediated synthesis was used to obtain nano-sized (similar to 12 nm) and mono-dispersed BZO nanoparticles that preserve their features once introduced into the YBCO solution, as revealed by dynamic light scattering. Phase pure, epitaxial YBCO films with randomly oriented BZO nanodots distributed over their whole microstructure were grown from the hybrid solutions on (100) LaAlO3 substrates. The morphology of the YBCO-BZO nanocomposite films was strongly influenced by the amount of nanoparticles incorporated into the system, with contents ranging from 5 to 40 mol%. Scanning electron microscopy showed a high density of isolated second-phase defects consisting of BZO nanodots in the nanocomposite film with 10 mol% of BZO. Furthermore, a direct observation and quantitative analysis of lattice defects in the form of interfacial edge dislocations directly induced by the BZO nanodots was evidenced by transmission electron microscopy. The superconducting properties (77 K) of the YBCO films improved considerably by the presence of such nanodots, which seem to enhance the morphology of the sample and therefore the intergranular critical properties. The incorporation of preformed second-phase defects (here, BZO) during the growth of the superconducting phase is the main innovation of this novel approach for the all-solution based low-cost fabrication of long-length coated conductors.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.256
Times cited: 19
DOI: 10.1039/c4tc02543a
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“Structural, electrochemical and magnetic properties of a novel KFeSO4F polymorph”. Lander L, Rousse G, Abakumov AM, Sougrati M, Van Tendeloo G, Tarascon J-M, Journal of materials chemistry A : materials for energy and sustainability 3, 19754 (2015). http://doi.org/10.1039/c5ta05548b
Abstract: In the quest for sustainable and low-cost positive electrode materials for Li-ion batteries, we discovered, as reported herein, a new low temperature polymorph of KFeSO4F. Contrary to the high temperature phase crystallizing in a KTiOPO4-like structure, this new phase adopts a complex layer-like structure built on FeO4F2 octahedra and SO4 tetrahedra, with potassium cations located in between the layers, as solved using neutron and synchrotron diffraction experiments coupled with electron diffraction. The detailed analysis of the structure reveals an alternation of edge-and corner-shared FeO4F2 octahedra leading to a large monoclinic cell of 1771.774(7) angstrom(3). The potassium atoms are mobile within the structure as deduced by ionic conductivity measurements and confirmed by the bond valence energy landscape approach thus enabling a partial electrochemical removal of K+ and uptake of Li+ at an average potential of 3.7 V vs. Li+/Li-0. Finally, neutron diffraction experiments coupled with SQUID measurements reveal a long range antiferromagnetic ordering of the Fe2+ magnetic moments below 22 K with a possible magnetoelectric behavior.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 8.867
Times cited: 11
DOI: 10.1039/c5ta05548b
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“Diffusion of fluorine on and between graphene layers”. Sadeghi A, Neek-Amal M, Berdiyorov GR, Peeters FM, Physical review : B : condensed matter and materials physics 91, 014304 (2015). http://doi.org/10.1103/PhysRevB.91.014304
Abstract: Using first-principles calculations and reactive force field molecular dynamics simulations, we study the structural properties and dynamics of a fluorine (F) atom, either adsorbed on the surface of single layer graphene (F/GE) or between the layers of AB stacked bilayer graphene (F@ bilayer graphene). It is found that the diffusion of the F atom is very different in those cases, and that the mobility of the F atom increases by about an order of magnitude when inserted between two graphene layers. The obtained diffusion constant for F/GE is twice larger than that experimentally found for gold adatom and theoretically found for C-60 molecule on graphene. Our study provides important physical insights into the dynamics of fluorine atoms between and on graphene layers and explains the mechanism behind the separation of graphite layers due to intercalation of F atoms.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 15
DOI: 10.1103/PhysRevB.91.014304
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“Electronic properties of triangular and hexagonal MoS2 quantum dots”. Pavlović, S, Peeters FM, Physical review : B : condensed matter and materials physics 91, 155410 (2015). http://doi.org/10.1103/PhysRevB.91.155410
Abstract: Using the tight-binding approach, we calculate the electronic structure of triangular and hexagonal MoS2 quantum dots. Due to the orbital asymmetry we show that it is possible to form quantum dots with the same shape but having different electronic properties. The electronic states of triangular and hexagonal quantum dots are explored, as well as the local and total density of states and the convergence towards the bulk spectrum with dot size is investigated. Our calculations show that: (1) edge states appear in the band gap, (2) that there are a larger number of electronic states in the conduction band as compared to the valence band, and (3) the relative number of edge states decreases with increasing dot size.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 44
DOI: 10.1103/PhysRevB.91.155410
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“Theory of anharmonic phonons in two-dimensional crystals”. Michel KH, Costamagna, Peeters FM, Physical review : B : condensed matter and materials physics 91, 134302 (2015). http://doi.org/10.1103/PhysRevB.91.134302
Abstract: Anharmonic effects in an atomic monolayer thin crystal with honeycomb lattice structure are investigated by analytical and numerical lattice dynamical methods. Starting from a semiempirical model for anharmonic couplings of third and fourth orders, we study the in-plane and out-of-plane (flexural) mode components of the generalized wave vector dependent Gruneisen parameters, the thermal tension and the thermal expansion coefficients as a function of temperature and crystal size. From the resonances of the displacement-displacement correlation functions, we obtain the renormalization and decay rate of in-plane and flexural phonons as a function of temperature, wave vector, and crystal size in the classical and in the quantum regime. Quantitative results are presented for graphene. There, we find that the transition temperature T-alpha from negative to positive thermal expansion is lowered with smaller system size. Renormalization of the flexural mode has the opposite effect and leads to values of T-alpha approximate to 300 K for systems of macroscopic size. Extensive numerical analysis throughout the Brillouin zone explores various decay and scattering channels. The relative importance of normal and umklapp processes is investigated. The work is complementary to crystalline membrane theory and computational studies of anharmonic effects in two-dimensional crystals.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 38
DOI: 10.1103/PhysRevB.91.134302
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“Anisotropic exciton Stark shift in black phosphorus”. Chaves A, Low T, Avouris P, Çakir D, Peeters FM, Physical review : B : condensed matter and materials physics 91, 155311 (2015). http://doi.org/10.1103/PhysRevB.91.155311
Abstract: We calculate the excitonic spectrum of few-layer black phosphorus by direct diagonalization of the effective mass Hamiltonian in the presence of an applied in-plane electric field. The strong attractive interaction between electrons and holes in this system allows one to investigate the Stark effect up to very high ionizing fields, including also the excited states. Our results show that the band anisotropy in black phosphorus becomes evident in the direction-dependent field-induced polarizability of the exciton.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 88
DOI: 10.1103/PhysRevB.91.155311
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“Majorana zero-energy modes and spin current evolution in mesoscopic superconducting loop systems with spin-orbit interaction”. Zha G-Q, Covaci L, Peeters FM, Zhou S-P, Physical review : B : condensed matter and materials physics 92, 094516 (2015). http://doi.org/10.1103/PhysRevB.92.094516
Abstract: The Majorana zero modes and persistent spin current in mesoscopic d-wave-superconducting loops with spin-orbit (SO) interaction are investigated by numerically solving the spin-generalized Bogoliubov-de Gennes equations self-consistently. For some appropriate strength of the SO coupling, Majorana zero-energy states and sharp jumps of the spin-polarized currents can be observed when the highest energy levels cross the Fermi energy in the spectrum, leading to spin currents with opposite chirality flowing near the inner and outer edges of the sample. When the threaded magnetic flux turns on, four flux-dependent patterns of the persistent spin current with step-like features show up, accompanied by Majorana edge modes at flux values where the energy gap closes. Moreover, the Majorana zero mode is highly influenced by the direction of the Zeeman field. A finite in-plane field can lead to the gap opening since the inversion symmetry is broken. Remarkably, multiple Majorana zero-energy states occur in the presence of an out-of-plane field h(z), and the number of steps in the spin current evolution can be effectively tuned by the field strength due to the shift of Majorana zero modes. Finally, when the loop sample contains surface indentation defects, zero-energy modes can always show up in the presence of an appropriate h(z). Interestingly, multiple Majorana states may be present in the system with a corner defect even if h(z) = 0.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 11
DOI: 10.1103/PhysRevB.92.094516
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“Multilayer MoS2 growth by metal and metal oxide sulfurization”. Heyne MH, Chiappe D, Meersschaut J, Nuytten T, Conard T, Bender H, Huyghebaert C, Radu IP, Caymax M, de Marneffe JF, Neyts EC, De Gendt S;, Journal of materials chemistry C : materials for optical and electronic devices 4, 1295 (2016). http://doi.org/10.1039/c5tc04063a
Abstract: We investigated the deposition of MoS2 multilayers on large area substrates. The pre-deposition of metal or metal oxide with subsequent sulfurization is a promising technique to achieve layered films. We distinguish a different reaction behavior in metal oxide and metallic films and investigate the effect of the temperature, the H2S/H-2 gas mixture composition, and the role of the underlying substrate on the material quality. The results of the experiments suggest a MoS2 growth mechanism consisting of two subsequent process steps. At first, the reaction of the sulfur precursor with the metal or metal oxide occurs, requiring higher temperatures in the case of metallic film compared to metal oxide. At this stage, the basal planes assemble towards the diffusion direction of the reaction educts and products. After the sulfurization reaction, the material recrystallizes and the basal planes rearrange parallel to the substrate to minimize the surface energy. Therefore, substrates with low roughness show basal plane assembly parallel to the substrate. These results indicate that the substrate character has a significant impact on the assembly of low dimensional MoS2 films.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 5.256
DOI: 10.1039/c5tc04063a
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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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“Self-assembly of gas-phase synthesized magnesium nanoparticles on room temperature substrates”. Venturi F, Calizzi M, Bals S, Perkisas T, Pasquini L, Materials research express 2, 015007 (2015). http://doi.org/10.1088/2053-1591/2/1/015007
Abstract: Magnesium nanoparticles (NPs) with initial size in the 10-50 nmrange were synthesized by inert gas condensation under helium flow and deposited on room temperature substrates. The morphology and crystal structure of the NPs ensemble were investigated as a function of the deposition time by complementary electron microscopy techniques, including high resolution imaging and chemical mapping. With increasing amount of material, strong coarsening phenomena were observed at room temperature: small NPs disappeared while large faceted NPs developed, leading to a 5-fold increase of the average NPs size within a few minutes. The extent of coarsening and the final morphology depended also on the nature of the substrate. Furthermore, large single-crystal NPs were seen to arise from the self-organization of primary NPs units, providing a mechanism for crystal growth. The dynamics of the self-assembly process involves the basic steps of NPs sticking, diffusion on substrate, coordinated rotation and attachment/coalescence. Key features are the surface energy anisotropy, reflected by the faceted shape of the NPs, and the low melting point of the material. The observed phenomena have strong implications in relation to the synthesis and stability of nanostructures based on Mg or other elements with similar features.
Keywords: A1 Journal article; Engineering Management (ENM); Electron microscopy for materials research (EMAT)
Impact Factor: 1.068
Times cited: 14
DOI: 10.1088/2053-1591/2/1/015007
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“In-situ TEM study of the Ni5Al3 to B2 + L12 decomposition in Ni65Al35”. Schryvers D, Ma Y, Materials letters 23, 105 (1995). http://doi.org/10.1016/0167-577X(95)00030-5
Abstract: Homogenised and quenched Ni65Al35 samples were heated and studied in situ in a CM20 electron microscope up to 900 degrees C. The Ni5Al3 phase first forming around 550 degrees C in the quenched L1(0) microtwinned martensite starts to decompose around 800 degrees C yielding B2 precipitates in a twinned L1(2) matrix. The latter twinning is a remainder of the microtwinning in the original room temperature martensite. Also the crystallographic relations between precipitates and matrix can be traced back to the original formation of twinned martensite plates within the austenite. Some aspects of the dynamics of the process are discussed on the basis of snap shots and video recordings.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.489
Times cited: 5
DOI: 10.1016/0167-577X(95)00030-5
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“Electronic and magnetic properties of 1T-TiSe2 nanoribbons”. Ozaydin HD, Sahin H, Kang J, Peeters FM, Senger RT, 2D materials 2, 044002 (2015). http://doi.org/10.1088/2053-1583/2/4/044002
Abstract: Motivated by the recent synthesis of single layer TiSe2, we used state-of-the-art density functional theory calculations, to investigate the structural and electronic properties of zigzag and armchair-edged nanoribbons (NRs) of this material. Our analysis reveals that, differing from ribbons of other ultra-thin materials such as graphene, TiSe2 NRs have some distinctive properties. The electronic band gap of the NRs decreases exponentially with the width and vanishes for ribbons wider than 20 angstrom. For ultranarrow zigzag-edged NRs we find odd-even oscillations in the band gap width, although their band structures show similar features. Moreover, our detailed magnetic-ground-state analysis reveals that zigzag and armchair edged ribbons have non-magnetic ground states. Passivating the dangling bonds with hydrogen at the edges of the structures influences the band dispersion. Our results shed light on the characteristic properties of T phase NRs of similar crystal structures.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 20
DOI: 10.1088/2053-1583/2/4/044002
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“Two-shell vortex and antivortex dynamics in a Corbino superconducting disk”. Cabral LRE, de Aquino BRCHT, de Souza Silva CC, Milošević, MV, Peeters FM, Physical review : B : condensed matter and materials physics 93, 014515 (2016). http://doi.org/10.1103/PhysRevB.93.014515
Abstract: We examine theoretically the dynamics of two vortex shells in pinning-free superconducting thin disks in the Corbino geometry. In the first considered case, the inner shell is composed of vortices and the outer one of antivortices, corresponding to a state induced by the stray field of an off-plane magnetic dipole placed on top of the superconductor. In the second considered case, both shells comprise vortices induced by a homogeneous external field. We derive the equation of motion for each shell within the Bardeen-Stephen model and study the dynamics analytically by assuming both shells are rigid and commensurate. In both cases, two distinct regimes for vortex shell motion are identified: For low applied currents the entire configuration rotates rigidly, while above a threshold current the shells decouple from each other and rotate at different angular velocities. Analytical expressions for the decoupling current, the recombination time in the decoupled phases, as well as the voltage-current characteristics are presented. Our analytical results are in excellent agreement with numerical molecular dynamics simulations of the full many-vortex problem.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 7
DOI: 10.1103/PhysRevB.93.014515
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“Quantum effects in a free-standing graphene lattice : path-integral against classical Monte Carlo simulations”. Brito BGA, Candido L, Hai G-Q, Peeters FM, Physical review : B : condensed matter and materials physics 92, 195416 (2015). http://doi.org/10.1103/PhysRevB.92.195416
Abstract: In order to study quantum effects in a two-dimensional crystal lattice of a free-standing monolayer graphene, we have performed both path-integral Monte Carlo (PIMC) and classical Monte Carlo (MC) simulations for temperatures up to 2000 K. The REBO potential is used for the interatomic interaction. The total energy, interatomic distance, root-mean-square displacement of the atom vibrations, and the free energy of the graphene layer are calculated. The obtained lattice vibrational energy per atom from the classical MC simulation is very close to the energy of a three-dimensional harmonic oscillator 3k(B)T. The PIMC simulation shows that quantum effects due to zero-point vibrations are significant for temperatures T < 1000 K. The quantum contribution to the lattice vibrational energy becomes larger than that of the classical lattice for T < 400 K. The lattice expansion due to the zero-point motion causes an increase of 0.53% in the lattice parameter. A minimum in the lattice parameter appears at T similar or equal to 500 K. Quantum effects on the atomic vibration amplitude of the graphene lattice and its free energy are investigated.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 22
DOI: 10.1103/PhysRevB.92.195416
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“Quantum magnetotransport properties of a MoS2 monolayer”. Tahir M, Vasilopoulos P, Peeters FM, Physical review : B : condensed matter and materials physics 93, 035406 (2016). http://doi.org/10.1103/PhysRevB.93.035406
Abstract: We study transport properties of a MoS2 monolayer in the presence of a perpendicular magnetic field B. We derive and discuss its band structure and take into account spin and valley Zeeman effects. Compared to a conventional two-dimensional electron gas, these effects lead to new quantum Hall plateaus and new peaks in the longitudinal resistivity as functions of the magnetic field. The field B leads to a significant enhancement of the spin splitting in the conduction band, to a beating of the Shubnikov-de Haas (SdH) oscillations in the low-field regime, and to their splitting in the high-field regime. The Zeeman fields suppress significantly the beating of the SdH oscillations in the low-field regime and strongly enhance their splitting at high fields. The spin and valley polarizations show a similar beating pattern at low fields and are clearly separated at high fields in which they attain a value higher than 90%.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 42
DOI: 10.1103/PhysRevB.93.035406
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“Heterostructures of graphene and nitrogenated holey graphene: Moire pattern and Dirac ring”. Kang J, Horzum S, Peeters FM, Physical review : B : condensed matter and materials physics 92, 195419 (2015). http://doi.org/10.1103/PhysRevB.92.195419
Abstract: Nitrogenated holey graphene (NHG) is a recently synthesized two-dimensional material. In this paper the structural and electronic properties of heterostructures of graphene and NHG are investigated using first-principles and tight-binding calculations. Due to the lattice mismatch between NHG and graphene, the formation of a moire pattern is preferred in the graphene/NHG heterostructure, instead of a lattice-coherent structure. In moire-patterned graphene/NHG, the band gap opening at the K point is negligible, and the linear band dispersion of graphene survives. Applying an electric field modifies the coupling strength between the two atomic layers. The Fermi velocity upsilon(F) is reduced as compared to the one of pristine graphene, and its magnitude depends on the twist angle theta between graphene and NHG: For theta = 0 degrees, upsilon(F) is 30% of that of graphene, and it increases rapidly to a value of 80% with increasing theta. The heterostructure exhibits electron-hole asymmetry in upsilon(F), which is large for small theta. In NHG encapsulated between two graphene layers, a “Dirac ring” appears around the K point. Its presence is robust with respect to the relative stacking of the two graphene layers. These findings can be useful for future applications of graphene/NHG heterostructures.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 33
DOI: 10.1103/PhysRevB.92.195419
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“Spin- and valley-dependent transport through arrays of ferromagnetic silicene junctions”. Missault N, Vasilopoulos P, Vargiamidis V, Peeters FM, Van Duppen B, Physical review : B : condensed matter and materials physics 92, 195423 (2015). http://doi.org/10.1103/PhysRevB.92.195423
Abstract: We study ballistic transport of Dirac fermions in silicene through arrays of barriers, of width d, in the presence of an exchange field M and a tunable potential of height U or depth-U. The spin-and valley-resolved conductances as functions of U or M, exhibit resonances away from the Dirac point (DP) and close to it a pronounced dip that becomes a gap when a critical electric field E-z is applied. This gap widens by increasing the number of barriers and can be used to realize electric field-controlled switching of the current. The spin p(s) and valley p(v) polarizations of the current near the DP increase with Ez or M and can reach 100% for certain of their values. These field ranges widen significantly by increasing the number of barriers. Also, ps and pv oscillate nearly periodically with the separation between barriers or wells and can be inverted by reversing M.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 54
DOI: 10.1103/PhysRevB.92.195423
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