|
“Extended Ginzburg-Landau formalism : systematic expansion in small deviation from the critical temperature”. Vagov AV, Shanenko AA, Milošević, MV, Axt VM, Peeters FM, Physical review : B : condensed matter and materials physics 85, 014502 (2012). http://doi.org/10.1103/PhysRevB.85.014502
Abstract: Based on the Gor'kov formalism for a clean s-wave superconductor, we develop an extended version of the single-band Ginzburg-Landau (GL) theory by means of a systematic expansion in the deviation from the critical temperature T(c), i.e., tau = 1 – T/T(c). We calculate different contributions to the order parameter and the magnetic field: the leading contributions (proportional to tau(1/2) in the order parameter and. t in the magnetic field) are controlled by the standard GL theory, while the next-to-leading terms (proportional to tau(3/2) in the gap and proportional to tau(2) in the magnetic field) constitute the extended GL (EGL) approach. We derive the free-energy functional for the extended formalism and the corresponding expression for the current density. To illustrate the usefulness of our formalism, we calculate, in a semianalytical form, the temperature-dependent correction to the GL parameter at which the surface energy becomes zero, and analytically, the temperature dependence of the thermodynamic critical field. We demonstrate that the EGL formalism is not just a mathematical extension to the theory: variations of both the gap and the thermodynamic critical field with temperature calculated within the EGL theory are found in very good agreement with the full BCS results down to low temperatures, which dramatically improves the applicability of the formalism compared to its standard predecessor.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 36
DOI: 10.1103/PhysRevB.85.014502
|
|
|
“Properties and thermal stability of solution processed ultrathin, high-k bismuth titanate (Bi2Ti2O7) films”. Hardy A, Van Elshocht S, De Dobbelaere C, Hadermann J, Pourtois G, De Gendt S, Afanas'ev VV, Van Bael MK, Materials research bulletin 47, 511 (2012). http://doi.org/10.1016/j.materresbull.2012.01.001
Abstract: Ultrathin bismuth titanate films (Bi2Ti2O7, 5-25 nm) are deposited onto SiO2/Si substrates by aqueous chemical solution deposition and their evolution during annealing is studied. The films crystallize into a preferentially oriented, pure pyrochlore phase between 500 and 700 degrees C, depending on the film thickness and the total thermal budget. Crystallization causes a strong increase of surface roughness compared to amorphous films. An increase of the interfacial layer thickness is observed after anneal at 600 degrees C, together with intermixing of bismuth with the substrate as shown by TEM-EDX. The band gap was determined to be similar to 3 eV from photoconductivity measurements and high dielectric constants between 30 and 130 were determined from capacitance voltage measurements, depending on the processing conditions. (C) 2012 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.446
DOI: 10.1016/j.materresbull.2012.01.001
|
|
|
“Biexciton binding energy in fractional dimensional semiconductors”. Rønnow TF, Pedersen TG, Partoens B, Physical review : B : condensed matter and materials physics 85, 045412 (2012). http://doi.org/10.1103/PhysRevB.85.045412
Abstract: Biexcitons in fractional dimensional spaces are studied using variational quantum Monte Carlo. We investigate the biexciton binding energy as a function of the electron-hole mass fraction sigma as well as study the dimensional dependence of biexcitons for sigma = 0 and sigma = 1. As our first application of this model we treat the H(2) molecule in two and three dimensions. Next we investigate biexcitons in carbon nanotubes within the fractional dimensional model. To this end we find a relation between the nanotube radius and the effective dimension. The results of both applications are compared with results obtained using different models and we find a reasonable agreement. Within the fractional dimensional model we find that the biexciton binding energy in carbon nanotubes accurately scales as E(B)(r,epsilon) = 1280 meV angstrom/(r epsilon), as a function of radius r and the dielectric screening epsilon.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 21
DOI: 10.1103/PhysRevB.85.045412
|
|
|
“Enhancement of the retrapping current of superconducting microbridges of finite length”. Vodolazov DY, Peeters FM, Physical review : B : condensed matter and materials physics 85, 024508 (2012). http://doi.org/10.1103/PhysRevB.85.024508
Abstract: We theoretically find that the resistance of a superconducting microbridge or nanowire decreases while the retrapping current I(r) for the transition to the superconducting state increases when one suppresses the magnitude of the order parameter vertical bar Delta vertical bar in the attached superconducting leads. This effect is a consequence of the increased energy interval for diffusion of the “hot” nonequilibrium quasiparticles (induced by the oscillations of vertical bar Delta vertical bar in the center of the microbridge) to the leads. The effect is absent in short microbridges (with length less than the coherence length) and it is relatively weak in long microbridges (with length larger than the inelastic relaxation length of the nonequilibrium distribution function). A nonmonotonous dependence of I(r) on the length of the microbridge is predicted. Our results are important for the explanation of the enhancement of the critical current and the appearance of negative magnetoresistance observed in many recent experiments on superconducting microbridges or nanowires.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 7
DOI: 10.1103/PhysRevB.85.024508
|
|
|
“Configuration-interaction excitonic absorption in small Si/Ge and Ge/Si core/shell nanocrystals”. de Oliveira EL, Albuquerque EL, de Sousa JS, Farias GA, Peeters FM, The journal of physical chemistry: C : nanomaterials and interfaces 116, 4399 (2012). http://doi.org/10.1021/jp2088516
Abstract: The excitonic properties of Si(core)/Ge(shell) and Ge(core)/Si(shell) nanocrystals (NC's) with diameters of similar to 1.9 nm are investigated using a combination density functional ab initio method to obtain the single particle wave functions and a configuration interaction method to compute the exciton fine structure and absorption coefficient. These core/shell structures exhibit type II confinement, which is more pronounced for the Si/Ge NC as a consequence of strain. The absorption coefficients of these NC's exhibit a single dominant peak, which has a much larger oscillator strength than the multipeaks found for pure Si and Ge NC's. The exciton lifetime in Si, Ge, and Ge/Si shows a small i:emperature dependence in the range 10-300 K, whereas in Si/Ge, the exciton lifetime decreases more than an order of magnitude in the same temperature range.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 4.536
Times cited: 44
DOI: 10.1021/jp2088516
|
|
|
“Fano resonances and electron spin transport through a two-dimensional spin-orbit-coupled quantum ring”. Nowak MP, Szafran B, Peeters FM, Physical review : B : condensed matter and materials physics 84, 235319 (2011). http://doi.org/10.1103/PhysRevB.84.235319
Abstract: Electron transport through a spin-orbit-coupled quantum ring is investigated within linear response theory. We show that the finite width of the ring results in the appearance of Fano resonances in the conductance. This turns out to be a consequence of the spin-orbit interaction that leads to a breaking of the parity of the states localized in the ring. The resonances appear when the system is close to maxima of Aharonov-Casher conductance oscillations where spin transfer is heavily modified. When the spin-orbit coupling strength is detuned from the Aharonov-Casher maxima the resonances are broadened resulting in a dependence of the spin transport on the electron Fermi energy in contrast to predictions from one-dimensional models.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 19
DOI: 10.1103/PhysRevB.84.235319
|
|
|
“Direct observation of ferrielectricity at ferroelastic domain boundaries in CaTiO3 by electron microscopy”. Van Aert S, Turner S, Delville R, Schryvers D, Van Tendeloo G, Salje EKH, Advanced materials 24, 523 (2012). http://doi.org/10.1002/adma.201103717
Abstract: High-resolution aberration-corrected transmission electron microscopy aided by statistical parameter estimation theory is used to quantify localized displacements at a (110) twin boundary in orthorhombic CaTiO3. The displacements are 36 pm for the Ti atoms and confined to a thin layer. This is the first direct observation of the generation of ferroelectricity by interfaces inside this material which opens the door for domain boundary engineering.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 150
DOI: 10.1002/adma.201103717
|
|
|
“New insights into the early stages of nanoparticle electrodeposition”. Ustarroz J, Ke X, Hubin A, Bals S, Terryn H, The journal of physical chemistry: C : nanomaterials and interfaces 116, 2322 (2012). http://doi.org/10.1021/jp210276z
Abstract: Electrodeposition is an increasingly important method to synthesize supported nanoparticles, yet the early stages of electrochemical nanoparticle formation are not perfectly understood. In this paper, the early stages of silver nanoparticle electrodeposition on carbon substrates have been studied by aberration-corrected TEM, using carbon-coated TEM grids as electrochemical electrodes. In this manner we have access to as-deposited nanoparticle size distribution and structural characterization at the atomic scale combined with electrochemical measurements, which represents a breakthrough in a full understanding of the nanoparticle electrodeposition mechanisms. Whereas classical models, based upon characterization at the nanoscale, assume that electrochemical growth is only driven by direct attachment, the results reported hereafter indicate that early nanoparticle growth is mostly driven by nanocluster surface movement and aggregation. Hence, we conclude that electrochemical nulceation and growth models should be revised and that an electrochemical aggregative growth mechanism should be considered in the early stages of nanoparticle electrodeposition.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.536
Times cited: 104
DOI: 10.1021/jp210276z
|
|
|
“Importance of twinning in static and dynamic compression of a Ti-6Al-4V titanium alloy with an equiaxed microstructure”. Coghe F, Tirry W, Rabet L, Schryvers D, Van Houtte P, Materials science and engineering: part A: structural materials: properties, microstructure and processing 537, 1 (2012). http://doi.org/10.1016/j.msea.2011.12.047
Abstract: Whereas deformation twinning is known to be an important deformation mechanism for hexagonal materials like magnesium and pure titanium, so far almost no literature exists on the twinning behaviour of the Ti-6Al-4V alloy. In this work it was shown that the activation of twinning as a deformation mechanism could have a pronounced effect on the mechanical behaviour of the Ti-6Al-4V alloy. This effect is even more pronounced under dynamic loading conditions. Transmission electron microscopy showed that only the {1 0 1 2}{1 0 1 1} tensile twin system was activated under certain loading conditions. Light-optical microscopy and electron backscatter diffraction data were afterwards used to experimentally determine the twin fractions. The importance of twinning for the texture evolution was also studied. It was shown that even small twin fractions can lead to distinct texture features, especially due to the discrete reorientation of the c-axes. The experimental results were compared to simulated results that were obtained with a viscoplastic self-consistent crystal plasticity code, after experimental validation that twinning can be reliably modelled as a unidirectional slip system. Although good agreement was obtained for the experimental and simulated stress-strain curves, the simulated results concerning twinning correlated well only on a qualitative basis as the simulated twin fractions were systematically higher than the experimental fractions. This seems to strengthen the hypothesis made by other research groups that complete grains might reorient by twinning. (C) 2011 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 3.094
Times cited: 35
DOI: 10.1016/j.msea.2011.12.047
|
|
|
“Hardening in relation with microstructure evolution of high purity \alpha-titanium deformed under monotonic and cyclic simple shear loadings at room temperature”. Bouvier S, Benmhenni N, Tirry W, Gregory F, Nixon ME, Cazacu O, Rabet L, Materials science and engineering: part A: structural materials: properties, microstructure and processing 535, 12 (2012). http://doi.org/10.1016/j.msea.2011.12.033
Abstract: The aim of this paper is to gain understanding of the quasi-static, large strain deformation behavior at room-temperature of high-purity alpha-Ti with an initial split-basal texture. Simple shear tests were conducted along different directions in order to quantify the material's anisotropy and hardening evolution for different strain paths such as monotonic, Bauschinger, and cyclic loadings. The stress-strain curves indicate that the material displays strong anisotropy in the flow behavior. In order to capture the link between microstructure evolution (occurrence of twinning, grain size evolution, etc.) and the macroscopic response, a thoroughly detailed multi-scale characterization using scanning electron microscope (SEM) observations and electron backscattered diffraction (EBSD) analysis was also conducted. Specifically, EBSD analyses indicate that the twin activity and grain fragmentation are responsible for the observed difference between the macroscopic hardening rates corresponding to different directions and loading paths. (C) 2011 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 3.094
Times cited: 22
DOI: 10.1016/j.msea.2011.12.033
|
|
|
“Parity-fluctuation induced enlargement of the ratio \DeltaE/kBTc in metallic grains”. Croitoru MD, Shanenko AA, Peeters FM, Axt VM, Physical review : B : condensed matter and materials physics 84, 214518 (2011). http://doi.org/10.1103/PhysRevB.84.214518
Abstract: We investigate how the interplay of quantum confinement and particle number-parity fluctuations affects superconducting correlations in ultra-small metallic grains. Using the number-parity projected BCS formalism we calculate the critical temperature and the excitation gap as a function of the grain size for grains with even and odd number of confined carriers. We show that the experimentally observed anomalous increase of the coupling ratio ΔE/kBTc with decreasing superconducting grain size can be attributed to an enhancement of the number-parity fluctuations in ultra-small grains.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 14
DOI: 10.1103/PhysRevB.84.214518
|
|
|
“Fluctuations in superconducting rings with two order parameters”. Berger J, Milošević, MV, Physical review : B : condensed matter and materials physics 84, 214515 (2011). http://doi.org/10.1103/PhysRevB.84.214515
Abstract: Motivated by two-band superconductivity in, e.g., borides and pnictides, starting from the two-band Ginzburg-Landau energy functional, we discuss how the presence of two order parameters and the coupling between them influence a superconducting ring in the fluctuative regime. Our method is an extension of the von OppenRiedel formalism for rings; it is exact, but requires numerical implementation. We also study approximations for which analytic expressions can be obtained, and check their ranges of validity. We provide estimates for the temperature ranges where fluctuations are important, calculate the persistent current in MgB2 rings as a function of temperature and enclosed flux, and point out its additional dependence on the cross-section area of the wire from which the ring is made. We find temperature regions in which fluctuations enhance the persistent currents and regions where they inhibit the persistent current. The presence of two order parameters that can fluctuate independently always leads to larger averages of the order parameters at Tc, but yields larger persistent current only for appropriate parameters. In cases of very different material parameters for the two coupled condensates, the persistent current is inhibited.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 7
DOI: 10.1103/PhysRevB.84.214515
|
|
|
“Scattering of Dirac electrons by circular mass barriers : valley filter and resonant scattering”. Masir MR, Matulis A, Peeters FM, Physical review : B : condensed matter and materials physics 84, 245413 (2011). http://doi.org/10.1103/PhysRevB.84.245413
Abstract: The scattering of two-dimensional (2D) massless Dirac electrons is investigated in the presence of a random array of circular mass barriers. The inverse momentum relaxation time and the Hall factor are calculated and used to obtain parallel and perpendicular resistivity components within linear transport theory. We found a nonzero perpendicular resistivity component which has opposite sign for electrons in the different K and K′ valleys. This property can be used for valley filter purposes. The total cross section for scattering on penetrable barriers exhibits resonances due to the presence of quasibound states in the barriers that show up as sharp gaps in the cross section while for Schrödinger electrons they appear as peaks.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 32
DOI: 10.1103/PhysRevB.84.245413
|
|
|
“Energy levels of triangular and hexagonal graphene quantum dots : a comparative study between the tight-binding and Dirac equation approach”. Zarenia M, Chaves A, Farias GA, Peeters FM, Physical review : B : condensed matter and materials physics 84, 245403 (2011). http://doi.org/10.1103/PhysRevB.84.245403
Abstract: The Dirac equation is solved for triangular and hexagonal graphene quantum dots for different boundary conditions in the presence of a perpendicular magnetic field. We analyze the influence of the dot size and its geometry on their energy spectrum. A comparison between the results obtained for graphene dots with zigzag and armchair edges, as well as for infinite-mass boundary condition, is presented and our results show that the type of graphene dot edge and the choice of the appropriate boundary conditions have a very important influence on the energy spectrum. The single-particle energy levels are calculated as a function of an external perpendicular magnetic field that lifts degeneracies. Comparing the energy spectra obtained from the tight-binding approximation to those obtained from the continuum Dirac equation approach, we verify that the behavior of the energies as a function of the dot size or the applied magnetic field are qualitatively similar, but in some cases quantitative differences can exist.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 145
DOI: 10.1103/PhysRevB.84.245403
|
|
|
“Superconducting proximity effect in graphene under inhomogeneous strain”. Covaci L, Peeters FM, Physical review : B : condensed matter and materials physics 84, 241401 (2011). http://doi.org/10.1103/PhysRevB.84.241401
Abstract: The interplay between quantum Hall states and Cooper pairs is usually hindered by the suppression of the superconducting state due to the strong magnetic fields needed to observe the quantum Hall effect. From this point of view, graphene is special since it allows the creation of strong pseudomagnetic fields due to strain. We show that in a Josephson junction made of strained graphene, Cooper pairs will diffuse into the strained region. The pair correlation function will be sublattice polarized due to the polarization of the local density of states in the zero pseudo-Landau level. We uncover two regimes: (1) one in which the cyclotron radius is larger than the junction length, in which case the supercurrent will be enhanced, and (2) the long junction regime where the supercurrent is strongly suppressed because the junction becomes an insulator. In the latter case quantized Hall states form and Andreev scattering at the normal/superconducting interface will induce edge states. Our numerical calculation has become possible due to an extension of the Chebyshev-Bogoliubovde Gennes method to computations on video cards (GPUs).
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 27
DOI: 10.1103/PhysRevB.84.241401
|
|
|
“G0W0 band gap of ZnO : effects of plasmon-pole models”. Stankovski M, Antonius G, Waroquiers D, Miglio A, Dixit H, Sankaran K, Giantomassi M, Gonze X, Côté, M, Rignanese G-M, Physical review : B : condensed matter and materials physics 84, 241201 (2011). http://doi.org/10.1103/PhysRevB.84.241201
Abstract: Carefully converged calculations are performed for the band gap of ZnO within many-body perturbation theory (G0W0 approximation). The results obtained using four different well-established plasmon-pole models are compared with those of explicit calculations without such models (the contour-deformation approach). This comparison shows that, surprisingly, plasmon-pole models depending on the f-sum rule gives less precise results. In particular, it confirms that the band gap of ZnO is underestimated in the G0W0 approach as compared to experiment, contrary to the recent claim of Shih et al. [ Phys. Rev. Lett. 105 146401 (2010)].
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 81
DOI: 10.1103/PhysRevB.84.241201
|
|
|
“Study of dpa distributions in electron irradiated YBCO slabs through MCCM algorithm”. Piñera I, Cruz CM, van Espen P, Abreu Y, Leyva A, Nuclear instruments and methods in physics research: B: beam interactions with materials and atoms 274, 191 (2012). http://doi.org/10.1016/J.NIMB.2011.11.021
Abstract: The Monte Carlo assisted Classical Method (MCCM) consists on a calculation procedure for determining the displacements per atom (dpa) distribution in solid materials. This algorithm allows studying the gamma and electron irradiation damage in different materials. It is based on the electrons elastic scattering classic theories and the use of Monte Carlo simulation for the physical processes involved. The present study deals with the Monte Carlo simulation of electron irradiation effects on YBa2Cu3O7-x (YBCO) slabs using the MCNPX code system. Displacements per atom distributions are obtained through the MCCM for electron irradiation up to 10 MeV. In-depth dpa profiles for electrons and positrons are obtained and analysed. Also, dpa contributions from each atomic specie in the material are calculated. It was found that the dpa distribution is more homogeneous in the material volume when increasing energy of incident electrons. Also, the dpa produced by positrons has no relevance when irradiating with electrons, in contrast with previous similar gamma irradiation studies. All the results are presented and discussed in this contribution. (C) 2011 Elsevier B.V. All rights reserved.
Keywords: A1 Journal article; Engineering sciences. Technology; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
DOI: 10.1016/J.NIMB.2011.11.021
|
|
|
“Measuring the corrugation amplitude of suspended and supported graphene”. Kirilenko DA, Dideykin AT, Van Tendeloo G, Physical review : B : condensed matter and materials physics 84, 235417 (2011). http://doi.org/10.1103/PhysRevB.84.235417
Abstract: Nanoscale corrugation is a fundamental property of graphene arising from its low-dimensional nature. It places a fundamental limit to the conductivity of graphene and influences its properties. However the degree of the influence of the corrugation has not been well established because of the little knowledge about its spectrum in suspended graphene. We present a transmission electron microscopy technique that enables us to measure the average corrugation height and length. We applied the technique also to measure the temperature dependence of the corrugation. The difference in corrugation between suspended and supported graphene has been illustrated.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.836
Times cited: 31
DOI: 10.1103/PhysRevB.84.235417
|
|
|
“Cultural heritage and archaeology materials studied by synchrotron spectroscopy and imaging”. Bertrand L, Robinet L, Thoury M, Janssens K, Cohen SX, Schöder S, Applied physics A : materials science &, processing 106, 377 (2012). http://doi.org/10.1007/S00339-011-6686-4
Abstract: The use of synchrotron radiation techniques to study cultural heritage and archaeological materials has undergone a steep increase over the past 10-15 years. The range of materials studied is very broad and encompasses painting materials, stone, glass, ceramics, metals, cellulosic and wooden materials, and a cluster of organic-based materials, in phase with the diversity observed at archaeological sites, museums, historical buildings, etc. Main areas of investigation are: (1) the study of the alteration and corrosion processes, for which the unique non-destructive speciation capabilities of X-ray absorption have proved very beneficial, (2) the understanding of the technologies and identification of the raw materials used to produce archaeological artefacts and art objects and, to a lesser extent, (3) the investigation of current or novel stabilisation, conservation and restoration practices. In terms of the synchrotron methods used, the main focus so far has been on X-ray techniques, primarily X-ray fluorescence, absorption and diffraction, and Fourier-transform infrared spectroscopy. We review here the use of these techniques from recent works published in the field demonstrating the breadth of applications and future potential offered by third generation synchrotron techniques. New developments in imaging and advanced spectroscopy, included in the UV/visible and IR ranges, could even broaden the variety of materials studied, in particular by fostering more studies on organic and complex organic-inorganic mixtures, while new support activities at synchrotron facilities might facilitate transfer of knowledge between synchrotron specialists and users from archaeology and cultural heritage sciences.
Keywords: A1 Journal article; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Impact Factor: 1.455
Times cited: 55
DOI: 10.1007/S00339-011-6686-4
|
|
|
“Electronic and optical properties of a circular graphene quantum dot in a magnetic field : influence of the boundary conditions”. Grujić, M, Zarenia M, Chaves A, Tadić, M, Farias GA, Peeters FM, Physical review : B : condensed matter and materials physics 84, 205441 (2011). http://doi.org/10.1103/PhysRevB.84.205441
Abstract: An analytical approach, using the Dirac-Weyl equation, is implemented to obtain the energy spectrum and optical absorption of a circular graphene quantum dot in the presence of an external magnetic field. Results are obtained for the infinite-massand zigzag boundary conditions. We found that the energy spectrum of a dot with the zigzag boundary condition exhibits a zero-energy band regardless of the value of the magnetic field, while for the infinite-mass boundary condition, the zero-energy states appear only for high magnetic fields. The analytical results are compared to those obtained from the tight-binding model: (i) we show the validity range of the continuum model and (ii) we find that the continuum model with the infinite-mass boundary condition describes rather well its tight-binding analog, which can be partially attributed to the blurring of the mixed edges by the staggered potential.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 78
DOI: 10.1103/PhysRevB.84.205441
|
|
|
“Landau levels in asymmetric graphene trilayer”. Sena SHR, Pereira JM, Peeters FM, Farias GA, Physical review : B : condensed matter and materials physics 84, 205448 (2011). http://doi.org/10.1103/PhysRevB.84.205448
Abstract: The electronic spectrum of three coupled graphene layers (graphene trilayers) is investigated in the presence of an external magnetic field. We obtain analytical expressions for the Landau level spectrum for both the ABA and ABC type of stacking, which exhibit very different dependence on the magnetic field. We show that layer asymmetry and an external gate voltage can strongly influence the properties of the system.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 30
DOI: 10.1103/PhysRevB.84.205448
|
|
|
“Anisotropic cation exchange in PbSe/CdSe core/shell nanocrystals of different geometry”. Casavola M, van Huis MA, Bals S, Lambert K, Hens Z, Vanmaekelbergh D, Chemistry of materials 24, 294 (2012). http://doi.org/10.1021/cm202796s
Abstract: We present a study of Cd2+-for-Pb2+ exchange in PbSe nanocrystals (NCs) with cube, star, and rod shapes. Prolonged temperature-activated cation exchange results in PbSe/CdSe heterostructured nanocrystals (HNCs) that preserve their specific overall shape, whereas the PbSe core is strongly faceted with dominance of {111} facets. Hence, cation exchange proceeds while the Se anion lattice is preserved, and well-defined {111}/{111} PbSe/CdSe interfaces develop. Interestingly, by quenching the reaction at different stages of the cation exchange new structures have been isolated, such as coreshell nanorods, CdSe rods that contain one or two separated PbSe dots and fully zinc blende CdSe nanorods. The crystallographically anisotropic cation exchange has been characterized by a combined HRTEM/HAADF-STEM study of heterointerface evolution over reaction time and temperature. Strikingly, Pb and Cd are only intermixed at the PbSe/CdSe interface. We propose a plausible model for the cation exchange based on a layer-by-layer replacement of Pb2+ by Cd2+ enabled by a vacancy-assisted cation migration mechanism.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 136
DOI: 10.1021/cm202796s
|
|
|
“Can we control the thickness of ultrathin silica layers by hyperthermal silicon oxidation at room temperature?”.Khalilov U, Neyts EC, Pourtois G, van Duin ACT, The journal of physical chemistry: C : nanomaterials and interfaces 115, 24839 (2011). http://doi.org/10.1021/jp2082566
Abstract: Using reactive molecular dynamics simulations by means of the ReaxFF potential, we studied the growth mechanism of ultrathin silica (SiO2) layers during hyperthermal oxidation at room temperature. Oxidation of Si(100){2 × 1} surfaces by both atomic and molecular oxygen was investigated in the energy range 15 eV. The oxidation mechanism, which differs from thermal oxidation, is discussed. In the case of oxidation by molecular O2, silica is quickly formed and the thickness of the formed layers remains limited compared to oxidation by atomic oxygen. The Si/SiO2 interfaces are analyzed in terms of partial charges and angle distributions. The obtained structures of the ultrathin SiO2 films are amorphous, including some intrinsic defects. This study is important for the fabrication of silica-based devices in the micro- and nanoelectronics industry, and more specifically for the fabrication of metal oxide semiconductor devices.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.536
Times cited: 36
DOI: 10.1021/jp2082566
|
|
|
“Nickel/carbon composite materials based on expanded graphite”. Afanasov IM, Lebedev OI, Kolozhvary BA, Smirnov AV, Van Tendeloo G, New carbon materials 26, 335 (2011). http://doi.org/10.1016/S1872-5805(11)60085-1
Abstract: Monolithic nickel/carbon (Ni/C) composites were prepared from coal tar pitch-impregnated compressed expanded graphite pre-decorated with NiO particles (EGNiO) by pyrolysis at 550 °C and subsequent steam activation at 800 °C. The microstructural arrangement of the Ni-comprising nanoparticles in the composites was investigated using transmission electron microscopy. The specific surface area and porosity of the composites were analyzed by nitrogen adsorption. The catalytic activity of the composites was compared with the material obtained by the conventional H2 treatment of EGNiO using hydrocracking of 2,2,3-trimethylpentane as a model reaction.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 7
DOI: 10.1016/S1872-5805(11)60085-1
|
|
|
“Depth strain profile with sub-nm resolution in a thin silicon film using medium energy ion scattering”. Jalabert D, Pelloux-Gervais D, Béché, A, Hartmann JM, Gergaud P, Rouvière JL, Canut B, Physica Status Solidi A-Applications And Materials Science 209, 265 (2012). http://doi.org/10.1002/PSSA.201127502
Abstract: The depth strain profile in silicon from the Si (001) substrate to the surface of a 2 nm thick Si/12 nm thick SiGe/bulk Si heterostructure has been determined by medium energy ion scattering (MEIS). It shows with sub-nanometer resolution and high strain sensitivity that the thin Si cap presents residual compressive strain caused by Ge diffusion coming from the fully strained SiGe layer underneath. The strain state of the SiGe buffer have been checked by X-ray diffraction (XRD) and nano-beam electron diffraction (NBED) measurements.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.775
Times cited: 3
DOI: 10.1002/PSSA.201127502
|
|
|
“Iron catalysts for the growth of carbon nanofibers : Fe, Fe3C or both?”.He Z, Maurice J-L, Gohier A, Lee CS, Pribat D, Cojocaru CS, Chemistry of materials 23, 5379 (2011). http://doi.org/10.1021/cm202315j
Abstract: Iron is a widely used catalyst for the growth of carbon nanotubes (CNTs) or carbon nanofibers (CNFs) by catalytic chemical vapor deposition. However, both Fe and FeC compounds (generally, Fe3C) have been found to catalyze the growth of CNTs/CNFs, and a comparison study of their respective catalytic activities is still missing. Furthermore, the control of the crystal structure of iron-based catalysts, that is α-Fe or Fe3C, is still a challenge, which not only obscures our understanding of the growth mechanisms of CNTs/CNFs, but also complicates subsequent procedures, such as the removal of catalysts for better industrial applications. Here, we show a partial control of the phase of iron catalysts (α-Fe or Fe3C), obtained by varying the growth temperatures during the synthesis of carbon-based nanofibers/nanotubes in a plasma-enhanced chemical vapor deposition reactor. We also show that the structure of CNFs originating from Fe3C is bamboo-type, while that of CNFs originating from Fe is not. Moreover, we directly compare the growth rates of carbon-based nanofibers/nanotubes during the same experiments and find that CNFs/CNTs grown by α-Fe nanoparticles are longer than CNFs grown from Fe3C nanoparticles. The influence of the type of catalyst on the growth of CNFs is analyzed and the corresponding possible growth mechanisms, based on the different phases of the catalysts, are discussed.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 9.466
Times cited: 91
DOI: 10.1021/cm202315j
|
|
|
“Effect of heat-treatment on luminescence and structure of Ag nanoclusters doped oxyfluoride glasses and implication for fiber drawing”. Kuznetsov AS, Cuong NT, Tikhomirov VK, Jivanescu M, Stesmans A, Chibotaru LF, Velázquez JJ, Rodríguez VD, Kirilenko D, Van Tendeloo G, Moshchalkov VV, Optical materials 34, 616 (2012). http://doi.org/10.1016/j.optmat.2011.09.007
Abstract: The effect of heat treatment on the structure and luminescence of Ag nanoclusters doped oxyfluoride glasses was studied and the implication for drawing the corresponding fibers doped with luminescent Ag nanoclusters has been proposed. The heat treatment results, first, in condensation of the Ag nanoclusters into larger Ag nanoparticles and loss of Ag luminescence, and further heat treatment results in precipitation of a luminescent-loss nano- and microcrystalline Ag phases onto the surface of the glass. Thus, the oxyfluoride fiber doped with luminescent Ag nanoclusters was pulled from the viscous glass melt and its attenuation loss was 0.19 dB/cm in the red part of the spectrum; i.e. near to the maximum of Ag nanoclusters luminescence band. The nucleation centers for the Ag nanoclusters in oxyfluoride glasses have been suggested to be the fluorine vacancies and their nanoclusters.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.238
Times cited: 25
DOI: 10.1016/j.optmat.2011.09.007
|
|
|
“Ginzburg-Landau theory of the zigzag transition in quasi-one-dimensional classical Wigner crystals”. Galván Moya JE, Peeters FM, Physical review : B : condensed matter and materials physics 84, 134106 (2011). http://doi.org/10.1103/PhysRevB.84.134106
Abstract: We present a mean-field description of the zigzag phase transition of a quasi-one-dimensional system of strongly interacting particles, with interaction potential r−ne−r/λ, that are confined by a power-law potential (yα). The parameters of the resulting one-dimensional Ginzburg-Landau theory are determined analytically for different values of α and n. Close to the transition point for the zigzag phase transition, the scaling behavior of the order parameter is determined. For α=2, the zigzag transition from a single to a double chain is of second order, while for α>2, the one-chain configuration is always unstable and, for α<2, the one-chain ordered state becomes unstable at a certain critical density, resulting in jumps of single particles out of the chain.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 16
DOI: 10.1103/PhysRevB.84.134106
|
|
|
“Influence of impurities and surface defects on the flux-induced current in mesoscopic d-wave superconducting loops”. Zha G-Q, Milošević, MV, Zhou S-P, Peeters FM, Physical review : B : condensed matter and materials physics 84, 132501 (2011). http://doi.org/10.1103/PhysRevB.84.132501
Abstract: We investigated the magnetic flux dependence of the supercurrent in mesoscopic d-wave superconducting loops, containing impurities and surface defects, by numerically solving the Bogoliubovde Gennes equations self-consistently. In the presence of impurities, bound states arise close to the Fermi energy. In the case of a single impurity, the flux-induced current is found to be suppressed. This can be different when more impurities are introduced in the sample due to the quantum interference effect, which depends sensitively on the relative position between the impurities. We further analyze the effect of small surface defects at the inner or outer edge of the loop, and show that indentation and bulge defects have pronounced and different effects on the supercurrent.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 13
DOI: 10.1103/PhysRevB.84.132501
|
|
|
“Rectification of vortex motion in a circular ratchet channel”. Lin NS, Heitmann TW, Yu K, Plourde BLT, Misko VR, Physical review : B : condensed matter and materials physics 84, 144511 (2011). http://doi.org/10.1103/PhysRevB.84.144511
Abstract: We study the dynamics of vortices in an asymmetric (i.e., consisting of triangular cells) ring channel driven by an external ac current I in a Corbino setup. The asymmetric potential rectifies the motion of vortices and induces a net vortex flow without any unbiased external drive, i.e., the ratchet effect. We show that the net flow of vortices strongly depends on vortex density and frequency of the driving current. Depending on the density, we distinguish a single-vortex rectification regime (for low density, when each vortex is rectified individually) determined by the potential-energy landscape inside each cell of the channel (i.e., hard and easy directions) and multi-vortex, or collective, rectification (high-density case) when the inter-vortex interaction becomes important. We analyze the average angular velocity ω of vortices as a function of I and study commensurability effects between the numbers of vortices and cells in the channel and the role of frequency of the applied ac current. We have shown that the commensurability effect results in a stepwise ω-I curve. Besides the integer steps, i.e., the large steps found in the single-vortex case, we also found fractional steps corresponding to fractional ratios between the numbers of vortices and triangular cells. We have performed preliminary measurements on a device containing a single weak-pinning circular ratchet channel in a Corbino geometry and observed a substantial asymmetric vortex response.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.836
Times cited: 27
DOI: 10.1103/PhysRevB.84.144511
|
|