|
“Novel functional imaging of changes in small airways of patients treated with extrafine beclomethasone/formoterol”. Vos W, de Backer J, Poli G, De Volder A, Ghys L, Van Holsbeke C, Vinchurkar S, De Backer L, de Backer W, Respiration 86, 393 (2013). http://doi.org/10.1159/000347120
Abstract: Background: Inhaled formulations using extrafine particles of long-acting beta(2)-agonists and corticosteroids were developed to optimize asthma treatment. Findings that these combinations reach and treat smaller airways more effectively are predominantly based on general non-specific outcomes with little information on regional characteristics. Objectives: This study aims to assess long-term effects of extrafine beclomethasone/formoterol on small airways of asthmatic patients using novel functional imaging methods. Methods: Twenty-four stable asthma patients were subdivided into three groups (steroid naive, n = 7; partially controlled, n = 6; well controlled, n = 11). Current treatment was switched to a fixed combination of extrafine beclomethasone/formoterol (Foster (R); Chiesi Pharmaceuticals, Parma, Italy). Patients underwent lung function evaluation and thorax high-resolution computerized tomography (HRCT) scan. Local airway resistance was obtained from computational fluid dynamics (CFD). Results: After 6 months, the entire population showed improvement in pre-bronchodilation imaging parameters, including small airway volume (p = 0.0007), resistance (p = 0.011), and asthma control score (p = 0.016). Changes in small airway volume correlated with changes in asthma control score (p = 0.004). Forced expiratory volume in 1 s (p = 0.044) and exhaled nitric oxide (p = 0.040) also improved. Functional imaging provided more detail and clinical relevance compared to lung function tests, especially in the well-controlled group where only functional imaging parameters showed significant improvement, while the correlation with asthma control score remained. Conclusions: Extrafine beclomethasone/formoterol results in a significant reduction of small airway obstruction, detectable by functional imaging (HRCT/CFD). Changes in imaging parameters correlated significantly with clinically relevant improvements. This indicates that functional imaging is a useful tool for sensitive assessment of changes in the respiratory system after asthma treatment. Copyright (C) 2013 S. Karger AG, Basel
Keywords: A1 Journal article; Biophysics and Biomedical Physics; Condensed Matter Theory (CMT); Laboratory Experimental Medicine and Pediatrics (LEMP)
Impact Factor: 2.772
Times cited: 30
DOI: 10.1159/000347120
|
|
|
“Electron-hole symmetry and solutions of Richardson pairing model”. Pogosov WV, Lin N, Misko VR, European physical journal : B : condensed matter and complex systems 86, 235 (2013). http://doi.org/10.1140/epjb/e2013-40234-9
Abstract: Richardson approach provides an exact solution of the pairing Hamiltonian. This Hamiltonian is characterized by the electron-hole pairing symmetry, which is however hidden in Richardson equations. By analyzing this symmetry and using an additional conjecture, fulfilled in solvable limits, we suggest a simple expression of the ground state energy for an equally-spaced energy-level model, which is applicable along the whole crossover from the superconducting state to the pairing fluctuation regime. Solving Richardson equations numerically, we demonstrate a good accuracy of our expression.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.461
Times cited: 6
DOI: 10.1140/epjb/e2013-40234-9
|
|
|
“Optoelectronic properties of ABC-stacked trilayer graphene”. Xiao YM, Xu W, Zhang YY, Peeters FM, Physica status solidi: B: basic research 250, 86 (2013). http://doi.org/10.1002/pssb.201248169
Abstract: We present a theoretical study on the optoelectronic properties of ABC-stacked trilayer graphene (TLG). The optical conductance and light transmittance are evaluated through using the energy-balance equation derived from the Boltzmann equation for an air/graphene/dielectric-wafer system in the presence of linearly polarized radiation field. The results obtained from two band structure models are examined and compared. For short wavelength radiation, the universal optical conductance sigma(0) = 3e(2)/(4h) can be obtained. Importantly, there exists an optical absorption window in the radiation wavelength range 10-200 mu m, which is induced by different transition energies required for inter- and intra-band optical absorption channels. As a result, we find that the position and width of this window depend sensitively on temperature and carrier density of the system, especially the lower frequency edge. There is a small characteristic absorption peak at about 82 mu m where the largest interband transition states exist in the ABC-stacked TLG model, in contrast to the relatively smooth curves in a simplified model. These theoretical results indicate that TLG has some interesting and important physical properties which can be utilized to realize infrared or THz optoelectronic devices.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.674
Times cited: 6
DOI: 10.1002/pssb.201248169
|
|
|
“The ageing effect in topological insulators : evolution of the surface electronic structure of Bi2Se3 upon K adsorption”. Park K, De Beule C, Partoens B, New journal of physics 15, 113031 (2013). http://doi.org/10.1088/1367-2630/15/11/113031
Abstract: Topological insulators (TIs) have attracted a lot of interest in recent years due to their topologically protected surface states, as well as exotic proximity-induced phenomena and device applications for TI heterostructures. Since the first experimental studies of TIs, angle-resolved photoemission spectra (ARPES) showed that the electronic structure of the topological surface states significantly changes as a function of time after cleavage. The origin and underlying mechanism of this ageing effect are still under debate, despite its importance. Here we investigate the evolution of the surface Dirac cone for Bi2Se3 films upon asymmetric potassium (K) adsorption, using density-functional theory and a tight-binding model. We find that the K adatoms induce short-ranged downward band bending within 2-3 nm from the surface, due to charge transfer from the adatoms to the TI. These findings are in contrast to earlier proposals in the literature, that propose a long-ranged downward band bending up to 15 nm from the surface. Furthermore, as the charge transfer increases, we find that a new Dirac cone, localized slightly deeper into the TI than the original one, appears at the K-adsorbed surface, originating from strong Rashba-split conduction-band states. Our results suggest possible reinterpretations of experiments because the new Dirac cone might have been observed in ARPES measurements instead of the original one that appears immediately after cleavage. Our findings are consistent with ARPES data and provide insight into building TI-heterostructure devices by varying the band-bending potential or film thickness.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.786
Times cited: 45
DOI: 10.1088/1367-2630/15/11/113031
|
|
|
“Controlling magnetic flux motion by arrays of zigzag-arranged magnetic bars”. Kapra AV, Misko VR, Peeters FM, Superconductor science and technology 26, 025011 (2013). http://doi.org/10.1088/0953-2048/26/2/025011
Abstract: Recent advances in manufacturing arrays of artificial pinning sites, i.e., antidots, blind holes and magnetic dots, allowed an effective control of magnetic flux in superconductors. An array of magnetic bars deposited on top of a superconducting film was shown to display different pinning regimes depending on the direction of the in-plane magnetization of the bars. Changing the sign of their magnetization results in changes in the induced magnetic pinning potentials. By numerically solving the time-dependent Ginzburg-Landau equations in a superconducting film with periodic arrays of zigzag-arranged magnetic bars, we revealed various flux dynamics regimes. In particular, we demonstrate flux pinning and flux flow, depending on the direction of the magnetization of the magnetic bars. Remarkably, the revealed different flux-motion regimes are associated with different mechanisms of vortex-antivortex dynamics. For example, we found that for an 'antiparallel' configuration of magnetic bars this dynamics involves a repeating vortex-antivortex generation and annihilation. We show that the depinning transition and the onset of flux flow can be manipulated by the magnetization of the bars and the geometry of the array. This provides an effective control of the depinning critical current that can be useful for possible fluxonics applications.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.878
Times cited: 5
DOI: 10.1088/0953-2048/26/2/025011
|
|
|
“Electron bounce resonance heating in dual-frequency capacitively coupled oxygen discharges”. Liu Y-X, Zhang Q-Z, Liu L, Song Y-H, Bogaerts A, Wang Y-N, Plasma sources science and technology 22, 025012 (2013). http://doi.org/10.1088/0963-0252/22/2/025012
Abstract: The electron bounce resonance heating (BRH) in dual-frequency capacitively coupled plasmas operated in oxygen is studied by different experimental methods and a particle-in-cell/Monte Carlo collision (PIC/MCC) simulation, and compared with the electropositive argon discharge. In comparison with argon, the experimental results show that in an oxygen discharge the resonance peaks in positive-ion density and light intensity tend to occur at larger electrode gaps. Moreover, at electrode gaps L > 2.5 cm, the positive-ion (and electron) density and the light emission drop monotonically in the oxygen discharge upon increasing L, whereas they rise (after an initial drop) in the argon case. At resonance gap the electronegativity reaches its maximum due to the BRH. All these experimental observations are explained by PIC/MCC simulations, which show that in the oxygen discharge the bulk electric field becomes quite strong and is out of phase with the sheath field. Therefore, it retards the resonance electrons when traversing the bulk, resulting in a suppressed BRH. Both experiment and simulation results show that this effect becomes more pronounced at lower high-frequency power, when the discharge mode changes from electropositive to electronegative. In a pure oxygen discharge, the BRH is suppressed with increasing pressure and almost diminishes at 12 Pa. Finally, the driving frequency significantly affects the BRH, because it determines the phase relation between bulk electric field and sheath electric field.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.302
Times cited: 20
DOI: 10.1088/0963-0252/22/2/025012
|
|
|
“Etching of low-k materials for microelectronics applications by means of a N2/H2 plasma : modeling and experimental investigation”. Van Laer K, Tinck S, Samara V, de Marneffe JF, Bogaerts A, Plasma sources science and technology 22, 025011 (2013). http://doi.org/10.1088/0963-0252/22/2/025011
Abstract: In this paper, we investigate the etch process of so-called low-k organic material by means of a N2/H2 capacitively coupled plasma, as applied in the micro-electronics industry for the manufacturing of computer chips. In recent years, such an organic material has emerged as a possible alternative for replacing bulk SiO2 as a dielectric material in the back-end-of-line, because of the smaller parasitic capacity between adjacent conducting lines, and thus a faster propagation of the electrical signals throughout the chip. Numerical simulations with a hybrid plasma model, using an extensive plasma and surface chemistry set, as well as experiments are performed, focusing on the plasma properties as well as the actual etching process, to obtain a better insight into the underlying mechanisms. Furthermore, the effects of gas pressure, applied power and gas composition are investigated to try to optimize the etch process. In general, the plasma density reaches a maximum near the wafer edge due to the so-called 'edge effect'. As a result, the etch rate is not uniform but will also reach its maximum near the wafer edge. The pressure seems not to have a big effect. A higher power increases the etch rate, but the uniformity becomes (slightly) worse. The gas mixing ratio has no significant effect on the etch process, except when a pure H2 or N2 plasma is used, illustrating the synergistic effects of a N2/H2 plasma. In fact, our calculations reveal that the N2/H2 plasma entails an ion-enhanced etch process. The simulation results are in reasonable agreement with the experimental values. The microscopic etch profile shows the desired anisotropic shape under all conditions under study.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.302
Times cited: 13
DOI: 10.1088/0963-0252/22/2/025011
|
|
|
“Gas ratio effects on the Si etch rate and profile uniformity in an inductively coupled Ar/CF4 plasma”. Zhao S-X, Gao F, Wang Y-N, Bogaerts A, Plasma sources science and technology 22, 015017 (2013). http://doi.org/10.1088/0963-0252/22/1/015017
Abstract: In this work, a hybrid model is used to investigate the effect of different gas ratios on the Si etching and polymer film deposition characteristics in an Ar/CF4 inductively coupled plasma. The influence of the surface processes on the bulk plasma properties is studied, and also the spatial characteristics of important gas phase and etched species. The densities of F and CF2 decrease when the surface module is included in the simulations, due to the species consumption caused by etching and polymer deposition. The influence of the surface processes on the bulk plasma depends on the Ar/CF4 gas ratio. The deposited polymer becomes thicker at high CF4 content because of more abundant CFx radicals. As a result of the competition between the polymer thickness and the F flux, the etch rate first increases and then decreases upon increasing the CF4 content. The electron properties, more specifically the electron density profile, affect the Si etch characteristics substantially by determining the radical density and flux profiles. In fact, the radial profile of the etch rate is more uniform at low CF4 content since the electron density has a smooth distribution. At high CF4 content, the etch rate is less uniform with a minimum halfway along the wafer radius, because the electron density distribution is more localized. Therefore, our calculations predict that it is better to work at relatively high Ar/CF4 gas ratios, in order to obtain high etch rate and good profile uniformity for etch applications. This, in fact, corresponds to the typical experimental etch conditions in Ar/CF4 gas mixtures as found in the literature, where Ar is typically present at a much higher concentration than CF4.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.302
Times cited: 11
DOI: 10.1088/0963-0252/22/1/015017
|
|
|
“Heating mechanism in direct current superposed single-frequency and dual-frequency capacitively coupled plasmas”. Zhang Q-Z, Liu Y-X, Jiang W, Bogaerts A, Wang Y-N, Plasma sources science and technology 22, 025014 (2013). http://doi.org/10.1088/0963-0252/22/2/025014
Abstract: In this work particle-in-cell/Monte Carlo collision simulations are performed to study the heating mechanism and plasma characteristics in direct current (dc) superposed radio-frequency (RF) capacitively coupled plasmas, operated both in single-frequency (SF) and dual-frequency (DF) regimes. An RF (60/2 MHz) source is applied on the bottom electrode to sustain the discharge, and a dc source is fixed on the top electrode. The heating mechanism appears to be very different in dc superposed SF and DF discharges. When only a single source of 60 MHz is applied, the plasma bulk region is reduced by the dc source, thus the ionization rate and hence the electron density decrease with rising dc voltage. However, when a DF source of 60 and 2 MHz is applied, the electron density can increase upon addition of a dc voltage, depending on the gap length and applied dc voltage. This is explained from the spatiotemporal ionization rates in the DF discharge. In fact, a completely different behavior is observed for the ionization rate in the two half-periods of the LF source. In the first LF half-period, the situation resembles the dc superposed SF discharge, and the reduced plasma bulk region due to the negative dc bias results in a very small effective discharge area and a low ionization rate. On the other hand, in the second half-period, the negative dc bias is to some extent counteracted by the LF voltage, and the sheath close to the dc electrode becomes particularly thin. Consequently, the amplitude of the high-frequency sheath oscillations at the top electrode is largely enhanced, while the LF sheath at the bottom electrode is in its expanding phase and can thus well confine the high-energy electrons. Therefore, the ionization rate increases considerably in this second LF half-period. Furthermore, in addition to the comparison between SF and DF discharges and the effect of gap length and dc voltage, the effect of secondary electrons is examined.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.302
Times cited: 9
DOI: 10.1088/0963-0252/22/2/025014
|
|
|
“In-phase motion of Josephson vortices in stacked SNS Josephson junctions : effect of ordered pinning”. Berdiyorov GR, Savel'ev SE, Kusmartsev FV, Peeters FM, Superconductor science and technology 26, 125010 (2013). http://doi.org/10.1088/0953-2048/26/12/125010
Abstract: The dynamics of Josephson vortices (fluxons) in artificial stacks of superconducting-normal-superconducting Josephson junctions is investigated using the anisotropic time-dependent Ginzburg-Landau theory in the presence of a square/rectangular array of pinning centers (holes). For small values of the applied drive, fluxons in different junctions move out of phase, forming a periodic triangular lattice. A rectangular lattice of moving fluxons is observed at larger currents, which is in agreement with previous theoretical predictions (Koshelev and Aranson 2000 Phys. Rev. Lett. 85 3938). This 'superradiant' flux-flow state is found to be stable in a wide region of applied current. The stability range of this ordered state is considerably larger than the one obtained for the pinning-free sample. Clear commensurability features are observed in the current-voltage characteristics of the system with pronounced peaks in the critical current at (fractional) matching fields. The effect of density and strength of the pinning centers on the stability of the rectangular fluxon lattice is discussed. Predicted synchronized motion of fluxons in the presence of ordered pinning can be detected experimentally using the rf response of the system, where enhancement of the Shapiro-like steps is expected due to the synchronization.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.878
Times cited: 5
DOI: 10.1088/0953-2048/26/12/125010
|
|
|
“Interlayer structure in YBCO-coated conductors prepared by chemical solution deposition”. Molina L, Egoavil R, Turner S, Thersleff T, Verbeeck J, Holzapfel B, Eibl O, Van Tendeloo G, Superconductor science and technology 26, 075016 (2013). http://doi.org/10.1088/0953-2048/26/7/075016
Abstract: The functionality of YBa2Cu3O7−δ (YBCO)-coated conductor technology depends on the reliability and microstructural properties of a given tape or wire architecture. Particularly, the interface to the metal tape is of interest since it determines the adhesion, mechanical stability of the film and thermal contact of the film to the substrate. A trifluoroacetate (TFA)metal organic deposition (MOD) prepared YBCO film deposited on a chemical solution-derived buffer layer architecture based on CeO2/La2Zr2O7 and grown on a flexible Ni5 at.%W substrate with a {100}⟨001⟩ biaxial texture was investigated. The YBCO film had a thickness was 440 nm and a jc of 1.02 MA cm−2 was determined at 77 K and zero external field. We present a sub-nanoscale analysis of a fully processed solution-derived YBCO-coated conductor by aberration-corrected scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS). For the first time, structural and chemical analysis of the valence has been carried out on the sub-nm scale. Intermixing of Ni, La, Ce, O and Ba takes place at these interfaces and gives rise to nanometer-sized interlayers which are a by-product of the sequential annealing process. Two distinct interfacial regions were analyzed in detail: (i) the YBCO/CeO2/La2Zr2O7 region (10 nm interlayer) and (ii) the La2Zr2O7/Ni5 at.%W substrate interface region (20 nm NiO). This is of particular significance for the functionality of these YBCO-coated conductor architectures grown by chemical solution deposition.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.878
Times cited: 11
DOI: 10.1088/0953-2048/26/7/075016
|
|
|
“Monodisperse spherical mesoporous silica particles : fast synthesis procedure and fabrication of photonic-crystal films”. Trofimova EY, Kurdyukov DA, Yakovlev SA, Kirilenko DA, Kukushkina YA, Nashchekin AV, Sitnikova AA, Yagovkina MA, Golubev VG, Nanotechnology 24, 155601 (2013). http://doi.org/10.1088/0957-4484/24/15/155601
Abstract: A procedure for the synthesis of monodisperse spherical mesoporous silica particles (MSMSPs) via the controlled coagulation of silica/surfactant clusters into spherical aggregates with mean diameters of 250-1500 nm has been developed. The synthesis is fast (taking less than 1 h) because identical clusters are simultaneously formed in the reaction mixture. The results of microscopic, x-ray diffraction, adsorption and optical measurements allowed us to conclude that the clusters are similar to 15 nm in size and have hexagonally packed cylindrical pore channels. The channel diameters in MSMSPs obtained with cethyltrimethylammonium bromide and decyltrimethylammonium bromide as structure-directing agents were 3.1 +/- 0.15 and 2.3 +/- 0.12 nm, respectively. The specific surface area and the pore volume of MSMSP were, depending on synthesis conditions, 480-1095 m(2) g(-1) and 0.50-0.65 cm(3) g(-1). The MSMSP were used to grow opal-like photonic-crystal films possessing a hierarchical macro-mesoporous structure, with pores within and between the particles. A selective filling of mesopore channels with glycerol, based on the difference between the capillary pressures in macro- and mesopores, was demonstrated. It is shown that this approach makes it possible to control the photonic bandgap position in mesoporous opal films by varying the degree of mesopore filling with glycerol. Online supplementary data available from stacks.iop.org/Nano/24/155601/mmedia
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 3.44
Times cited: 49
DOI: 10.1088/0957-4484/24/15/155601
|
|
|
“Probing the dynamic response of antivortex, interstitial and trapped vortex lattices on magnetic periodic pinning potentials”. Gomez A, Gonzalez EM, Gilbert DA, Milošević, MV, Liu K, Vicent JL, Superconductor science and technology 26, 085018 (2013). http://doi.org/10.1088/0953-2048/26/8/085018
Abstract: The dynamics of the pinned vortex, antivortex and interstitial vortex have been studied in superconducting/magnetic hybrids consisting of arrays of Co/Pd multilayer nanodots embedded in Nb films. The magnetic nanodots show out-of-plane magnetization at the remanent state. This magnetic state allows for superconducting vortex lattices of different types in an applied homogeneous magnetic field. We experimentally and theoretically show three such lattices: (i) a lattice containing only antivortices; (ii) a vortex lattice entirely pinned on the dots; and (iii) a vortex lattice with pinned and interstitial vortices. Between the flux creep (low vortex velocity) and the free flux flow (high vortex velocity) regimes the interaction between the magnetic array and the vortex lattice governs the vortex dynamics, which in turn enables distinguishing experimentally the type of vortex lattice which governs the dissipation. We show that the vortex lattice with interstitial vortices has the highest onset velocity where the lattice becomes ordered, whereas the pinned vortex lattice has the smallest onset velocity. Further, for this system, we directly estimate that the external force needed to depin vortices is 60% larger than the one needed to depin antivortices; therefore we are able to decouple the antivortex-vortex motion.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.878
Times cited: 7
DOI: 10.1088/0953-2048/26/8/085018
|
|
|
“Sorting the modes contributing to guidance in strain-induced graphene waveguides”. Villegas CEP, Tavares MRS, Hai G-Q, Peeters FM, New journal of physics 15, 023015 (2013). http://doi.org/10.1088/1367-2630/15/2/023015
Abstract: We propose a simple way of probing the number of modes contributing to the channeling in graphene waveguides which are formed by a gauge potential produced by mechanical strain. The energy mode structure for both homogeneous and non-homogeneous strain regimes is carefully studied using the continuum description of the Dirac equation. We found that high strain values privilege negative (instead of positive) group velocities throughout the guidance, sorting the types of modes flowing through it. We also show how the effect of a substrate-induced gap competes against the strain.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.786
Times cited: 7
DOI: 10.1088/1367-2630/15/2/023015
|
|
|
“Vortex transport in a channel with periodic constrictions”. Kapra AV, Vodolazov DY, Misko VR, Superconductor science and technology 26, 095010 (2013). http://doi.org/10.1088/0953-2048/26/9/095010
Abstract: By numerically solving the time-dependent Ginzburg-Landau equations in a type-II superconductor, characterized by a critical temperature T-c1, and the coherence length xi(1), with a channel formed by overlapping rhombuses (diamond-like channel) made of another type-II superconductor, characterized, in general, by different T-c2 and xi(2), we investigate the dynamics of driven vortex matter for varying parameters of the channel: the width of the neck connecting the diamond cells, the cell geometry, and the ratio between the coherence lengths in the bank and the channel. We analyzed samples with periodic boundary conditions (which we call 'infinite' samples) and finite-size samples (with boundaries for vortex entry/exit), and we found that by tuning the channel parameters, one can manipulate the vortex dynamics, e.g., change the transition from flux-pinned to flux-flow regime and tune the slope of the IV-curves. In addition, we analyzed the effect of interstitial vortices on these characteristics. The critical current of this device was studied as a function of the applied magnetic field, j(c)(H). The function j(c)(H) reveals a striking commensurability peak, in agreement with recent experimental observations. The obtained results suggest that the diamond channel, which combines the properties of pinning arrays and flux-guiding channels, can be a promising candidate for potential use in devices controlling magnetic flux motion.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.878
Times cited: 2
DOI: 10.1088/0953-2048/26/9/095010
|
|
|
“An electric field tunable energy band gap at silicene/(0001) ZnS interfaces”. Houssa M, van den Broek B, Scalise E, Pourtois G, Afanas'ev VV, Stesmans A, Physical chemistry, chemical physics 15, 3702 (2013). http://doi.org/10.1039/c3cp50391g
Abstract: The interaction of silicene, the silicon counterpart of graphene, with (0001) ZnS surfaces is investigated theoretically, using first-principles simulations. The charge transfer occurring at the silicene/(0001) ZnS interface leads to the opening of an indirect energy band gap of about 0.7 eV in silicene. Remarkably, the nature (indirect or direct) and magnitude of the energy band gap of silicene can be controlled by an external electric field: the energy gap is predicted to become direct for electric fields larger than about 0.5 V angstrom(-1), and the direct energy gap decreases approximately linearly with the applied electric field. The predicted electric field tunable energy band gap of the silicene/(0001) ZnS interface is very promising for its potential use in nanoelectronic devices.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.123
Times cited: 74
DOI: 10.1039/c3cp50391g
|
|
|
“Atomistic modelling of CVD synthesis of carbon nanotubes and graphene”. Elliott JA, Shibuta Y, Amara H, Bichara C, Neyts EC, Nanoscale 5, 6662 (2013). http://doi.org/10.1039/c3nr01925j
Abstract: We discuss the synthesis of carbon nanotubes (CNTs) and graphene by catalytic chemical vapour deposition (CCVD) and plasma-enhanced CVD (PECVD), summarising the state-of-the-art understanding of mechanisms controlling their growth rate, chiral angle, number of layers (walls), diameter, length and quality (defects), before presenting a new model for 2D nucleation of a graphene sheet from amorphous carbon on a nickel surface. Although many groups have modelled this process using a variety of techniques, we ask whether there are any complementary ideas emerging from the different proposed growth mechanisms, and whether different modelling techniques can give the same answers for a given mechanism. Subsequently, by comparing the results of tight-binding, semi-empirical molecular orbital theory and reactive bond order force field calculations, we demonstrate that graphene on crystalline Ni(111) is thermodynamically stable with respect to the corresponding amorphous metal and carbon structures. Finally, we show in principle how a complementary heterogeneous nucleation step may play a key role in the transformation from amorphous carbon to graphene on the metal surface. We conclude that achieving the conditions under which this complementary crystallisation process can occur may be a promising method to gain better control over the growth processes of both graphene from flat metal surfaces and CNTs from catalyst nanoparticles.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 7.367
Times cited: 52
DOI: 10.1039/c3nr01925j
|
|
|
“Band structure quantization in nanometer sized ZnO clusters”. Schouteden K, Zeng Y-J, Lauwaet K, Romero CP, Goris B, Bals S, Van Tendeloo G, Lievens P, Van Haesendonck C, Nanoscale 5, 3757 (2013). http://doi.org/10.1039/c3nr33989k
Abstract: Nanometer sized ZnO clusters are produced in the gas phase and subsequently deposited on clean Au(111) surfaces under ultra-high vacuum conditions. The zinc blende atomic structure of the approximately spherical ZnO clusters is resolved by high resolution scanning transmission electron microscopy. The large band gap and weak n-type conductivity of individual clusters are determined by scanning tunnelling microscopy and spectroscopy at cryogenic temperatures. The conduction band is found to exhibit clear quantization into discrete energy levels, which can be related to finite-size effects reflecting the zero-dimensional confinement. Our findings illustrate that gas phase cluster production may provide unique possibilities for the controlled fabrication of high purity quantum dots and heterostructures that can be size selected prior to deposition on the desired substrate under controlled ultra-high vacuum conditions.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 13
DOI: 10.1039/c3nr33989k
|
|
|
“Chemical insight into electroforming of resistive switching manganite heterostructures”. Borgatti F, Park C, Herpers A, Offi F, Egoavil R, Yamashita Y, Yang A, Kobata M, Kobayashi K, Verbeeck J, Panaccione G, Dittmann R;, Nanoscale 5, 3954 (2013). http://doi.org/10.1039/c3nr00106g
Abstract: We have investigated the role of the electroforming process in the establishment of resistive switching behaviour for Pt/Ti/Pr0.5Ca0.5MnO3/SrRuO3 layered heterostructures (Pt/Ti/PCMO/SRO) acting as non-volatile Resistance Random Access Memories (RRAMs). Electron spectroscopy measurements demonstrate that the higher resistance state resulting from electroforming of as-prepared devices is strictly correlated with the oxidation of the top electrode Ti layer through field-induced electromigration of oxygen ions. Conversely, PCMO exhibits oxygen depletion and downward change of the chemical potential for both resistive states. Impedance spectroscopy analysis, supported by the detailed knowledge of these effects, provides an accurate model description of the device resistive behaviour. The main contributions to the change of resistance from the as-prepared (low resistance) to the electroformed (high resistance) states are respectively due to reduced PCMO at the boundary with the Ti electrode and to the formation of an anisotropic np junction between the Ti and the PCMO layers.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 40
DOI: 10.1039/c3nr00106g
|
|
|
“Dimethylformamide-mediated synthesis of water-soluble platinum nanodendrites for ethanol oxidation electrocatalysis”. Mourdikoudis S, Chirea M, Altantzis T, Pastoriza-Santos I, Perez-Juste J, Silva F, Bals S, Liz-Marzan LM, Nanoscale 5, 4776 (2013). http://doi.org/10.1039/c3nr00924f
Abstract: Herein we describe the synthesis of water-soluble platinum nanodendrites in dimethylformamide (DMF), in the presence of polyethyleneimine (PEI) as a stabilizing agent. The average size of the dendrites is in the range of 20-25 nm while their porosity can be tuned by modifying the concentration of the metal precursor. Electron tomography revealed different crystalline orientations of nanocrystallites in the nanodendrites and allowed a better understanding of their peculiar branching and porosity. The high surface area of the dendrites (up to 22 m(2) g(-1)) was confirmed by BET measurements, while X-ray diffraction confirmed the abundance of high-index facets in the face-centered-cubic crystal structure of Pt. The prepared nanodendrites exhibit excellent performance in the electrocatalytic oxidation of ethanol in alkaline solution. Sensing, selectivity, cycleability and great tolerance toward poisoning were demonstrated by cyclic voltammetry measurements.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 50
DOI: 10.1039/c3nr00924f
|
|
|
“Formation of single layer graphene on nickel under far-from-equilibrium high flux conditions”. Neyts EC, van Duin ACT, Bogaerts A, Nanoscale 5, 7250 (2013). http://doi.org/10.1039/c3nr00153a
Abstract: We investigate the theoretical possibility of single layer graphene formation on a nickel surface at different substrate temperatures under far-from-equilibrium high precursor flux conditions, employing state-of-the-art hybrid reactive molecular dynamics/uniform acceptance force bias Monte Carlo simulations. It is predicted that under these conditions, the formation of a single layer graphene-like film may proceed through a combined depositionsegregation mechanism on a nickel substrate, rather than by pure surface segregation as is typically observed for metals with high carbon solubility. At 900 K and above, nearly continuous graphene layers are obtained. These simulations suggest that single layer graphene deposition is theoretically possible on Ni under high flux conditions.
Keywords: A1 Journal article; Engineering sciences. Technology; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 7.367
Times cited: 25
DOI: 10.1039/c3nr00153a
|
|
|
“Ordered and disordered packing of coronene molecules in carbon nanotubes”. Verberck B, Okazaki T, Tarakina NV, Physical chemistry, chemical physics 15, 18108 (2013). http://doi.org/10.1039/c3cp52797b
Abstract: Monte Carlo simulations of coronene molecules in single-walled carbon nanotubes (SWCNTs) and dicoronylene molecules in SWCNTs are performed. Depending on the diameter D of the encapsulating SWCNT, regimes favoring the formation of ordered, one-dimensional (1D) stacks of tilted molecules (D <= 1.7 nm for coronene@SWCNT, 1.5 nm <= D <= 1.7 nm for dicoronylene@SWCNT) and regimes with disordered molecular arrangements and increased translational mobilities enabling the thermally induced polymerization of neighboring molecules resulting in the formation of graphene nanoribbons (GNRs) are observed. The results show that the diameter of the encapsulating nanotube is a crucial parameter for the controlled synthesis of either highly ordered 1D structures or GNR precursors.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 4.123
Times cited: 9
DOI: 10.1039/c3cp52797b
|
|
|
“Reactive molecular dynamics simulations on SiO2-coated ultra-small Si-nanowires”. Khalilov U, Pourtois G, Bogaerts A, van Duin ACT, Neyts EC, Nanoscale 5, 719 (2013). http://doi.org/10.1039/c2nr32387g
Abstract: The application of coreshell SiSiO2 nanowires as nanoelectronic devices strongly depends on their structure, which is difficult to tune precisely. In this work, we investigate the formation of the coreshell nanowires at the atomic scale, by reactive molecular dynamics simulations. The occurrence of two temperature-dependent oxidation mechanisms of ultra-small diameter Si-NWs is demonstrated. We found that control over the Si-core radius and the SiOx (x ≤ 2) oxide shell is possible by tuning the growth temperature and the initial Si-NW diameter. Two different structures were obtained, i.e., ultrathin SiO2 silica nanowires at high temperature and Si core|ultrathin SiO2 silica nanowires at low temperature. The transition temperature is found to linearly decrease with the nanowire curvature. Finally, the interfacial stress is found to be responsible for self-limiting oxidation, depending on both the initial Si-NW radius and the oxide growth temperature. These novel insights allow us to gain control over the exact morphology and structure of the wires, as is needed for their application in nanoelectronics.
Keywords: A1 Journal article; Engineering sciences. Technology; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 7.367
Times cited: 17
DOI: 10.1039/c2nr32387g
|
|
|
“Stability of Si epoxide defects in Si nanowires : a mixed reactive force field/DFT study”. Schoeters B, Neyts EC, Khalilov U, Pourtois G, Partoens B, Physical chemistry, chemical physics 15, 15091 (2013). http://doi.org/10.1039/c3cp51621k
Abstract: Modeling the oxidation process of silicon nanowires through reactive force field based molecular dynamics simulations suggests that the formation of Si epoxide defects occurs both at the Si/SiOx interface and at the nanowire surface, whereas for flat surfaces, this defect is experimentally observed to occur only at the interface as a result of stress. In this paper, we argue that the increasing curvature stabilizes the defect at the nanowire surface, as suggested by our density functional theory calculations. The latter can have important consequences for the opto-electronic properties of thin silicon nanowires, since the epoxide induces an electronic state within the band gap. Removing the epoxide defect by hydrogenation is expected to be possible but becomes increasingly difficult with a reduction of the diameter of the nanowires.
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.123
Times cited: 3
DOI: 10.1039/c3cp51621k
|
|
|
“Synthesis of uniformly dispersed anatase nanoparticles inside mesoporous silica thin films via controlled breakup and crystallization of amorphous TiO2 deposited using atomic layer deposition”. Sree SP, Dendooven J, Masschaele K, Hamed HM, Deng S, Bals S, Detavernier C, Martens JA, Nanoscale 5, 5001 (2013). http://doi.org/10.1039/c3nr00594a
Abstract: Amorphous titanium dioxide was introduced into the pores of mesoporous silica thin films with 75% porosity and 12 nm average pore diameter via Atomic Layer Deposition (ALD) using alternating pulses of tetrakis(dimethylamino)titanium and water. Calcination provoked fragmentation of the deposited amorphous TiO2 phase and its crystallization into anatase nanoparticles inside the nanoporous film. The narrow particle size distribution of 4 ± 2 nm and the uniform dispersion of the particles over the mesoporous silica support were uniquely revealed using electron tomography. These anatase nanoparticle bearing films showed photocatalytic activity in methylene blue degradation. This new synthesis procedure of the anatase nanophase in mesoporous silica films using ALD is a convenient fabrication method of photocatalytic coatings amenable to application on very small as well as very large surfaces
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 7.367
Times cited: 22
DOI: 10.1039/c3nr00594a
|
|
|
“Annular dark-field transmission electron microscopy for low contrast materials”. Leroux F, Bladt E, Timmermans J-P, Van Tendeloo G, Bals S, Microscopy and microanalysis 19, 629 (2013). http://doi.org/10.1017/S1431927613000020
Abstract: Imaging soft matter by transmission electron microscopy (TEM) is anything but straightforward. Recently, interest has grown in developing alternative imaging modes that generate contrast without additional staining. Here, we present a dark-field TEM technique based on the use of an annular objective aperture. Our experiments demonstrate an increase in both contrast and signal-to-noise ratio in comparison to conventional bright-field TEM. The proposed technique is easy to implement and offers an alternative imaging mode to investigate soft matter.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.891
Times cited: 5
DOI: 10.1017/S1431927613000020
|
|
|
“Electron microscopy, nanoscopy, and scanning micro- and nanoanalysis”. Oleshko VP, Gijbels R, Amelinckx S Wiley, Chichester, page 1 (2013).
Keywords: H1 Book chapter; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
|
|
|
“Nonvolatile resistive switching in Pt/LaAlO3/SrTiO3 heterostructures”. Wu S, Luo X, Turner S, Peng H, Lin W, Ding J, David A, Wang B, Van Tendeloo G, Wang J, Wu T;, Physical review X 3, 041027 (2013). http://doi.org/10.1103/PhysRevX.3.041027
Abstract: Resistive switching heterojunctions, which are promising for nonvolatile memory applications, usually share a capacitorlike metal-oxide-metal configuration. Here, we report on the nonvolatile resistive switching in Pt/LaAlO3/SrTiO3 heterostructures, where the conducting layer near the LaAlO3/SrTiO3 interface serves as the unconventional bottom electrode although both oxides are band insulators. Interestingly, the switching between low-resistance and high-resistance states is accompanied by reversible transitions between tunneling and Ohmic characteristics in the current transport perpendicular to the planes of the heterojunctions. We propose that the observed resistive switching is likely caused by the electric-field-induced drift of charged oxygen vacancies across the LaAlO3/SrTiO3 interface and the creation of defect-induced gap states within the ultrathin LaAlO3 layer. These metal-oxide-oxide heterojunctions with atomically smooth interfaces and defect-controlled transport provide a platform for the development of nonvolatile oxide nanoelectronics that integrate logic and memory devices.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 12.789
Times cited: 77
DOI: 10.1103/PhysRevX.3.041027
|
|
|
“Small-angle X-ray scattering and light scattering study of hybrid nanoparticles composed of thermoresponsive triblock copolymer F127 and thermoresponsive statistical polyoxazolines with hydrophobic moieties”. Bogomolova A, Hruby M, Panek J, Rabyk M, Turner S, Bals S, Steinhart M, Zhigunov A, Sedlacek O, Stepanek P, Filippov SK;, Journal of applied crystallography 46, 1690 (2013). http://doi.org/10.1107/S0021889813027064
Abstract: A combination of new thermoresponsive statistical polyoxazolines, poly[(2-butyl-2-oxazoline)-stat-(2-isopropyl-2-oxazoline)] [pBuOx-co-piPrOx], with different hydrophobic moieties and F127 surfactant as a template system for the creation of thermosensitive nanoparticles for radionuclide delivery has recently been tested [Pánek, Filippov, Hrubý, Rabyk, Bogomolova, Kučka Stěpánek (2012). Macromol. Rapid Commun.33, 16831689]. It was shown that the presence of the thermosensitive F127 triblock copolymer in solution reduces nanoparticle size and polydispersity. This article focuses on a determination of the internal structure and solution properties of the nanoparticles in the temperature range from 288 to 312 K. Here, it is demonstrated that below the cloud point temperature (CPT) the polyoxazolines and F127 form complexes that co-exist in solution with single F127 molecules and large aggregates. When the temperature is raised above the CPT, nanoparticles composed of polyoxazolines and F127 are predominant in solution. These nanoparticles could be described by a spherical shell model. It was found that the molar weight and hydrophobicity of the polymer do not influence the size of the outer radius and only slightly change the inner radius of the nanoparticles. At the same time, molar weight and hydrophobicity did affect the process of nanoparticle formation. In conclusion, poly(2-oxazoline) molecules are fully incorporated inside of F127 micelles, and this result is very promising for the successful application of such systems in radionuclide delivery.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 18
DOI: 10.1107/S0021889813027064
|
|
|
“Functional Respiratory Imaging as a tool to personalize respiratory treatment in subjects with unilateral diaphragmatic paralysis”. Van Holsbeke CS, Leemans G, Vos WG, de Backer JW, Vinchurkar SC, Geldof M, Verdonck PR, Parizel PM, van Schil PE, de Backer WA, Respiratory care , 1 (2013). http://doi.org/10.4187/respcare.02756
Abstract: In two subjects with a unilateral diaphragmatic paralysis and complaints of dyspnea, a completely different treatment approach was chosen despite similar anatomical and physiological abnormalities. These decisions were supported by the results generated by Functional Respiratory Imaging (FRI). FRI was able to generate functional information with respect to lobar ventilation and local drug deposition. In one subject, it was found that some lobes were poorly ventilated and drug deposition simulation showed that some regions were undertreated. This subject underwent a diaphragm plication to restore the ventilation. In the other subject, it was found that all lobes were still ventilated. A conservative approach with regular follow-up was chosen to wait for spontaneous recovery of the diaphragmatic function. Both subjects improved subjectively and objectively. These cases demonstrate how novel medical imaging techniques such as FRI can be used to personalize respiratory treatment in subjects with unilateral diaphragmatic paralysis.
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Antwerp Surgical Training, Anatomy and Research Centre (ASTARC); Laboratory Experimental Medicine and Pediatrics (LEMP)
Impact Factor: 1.733
Times cited: 5
DOI: 10.4187/respcare.02756
|
|