“Electronic structures of iMAX phases and their two-dimensional derivatives: A family of piezoelectric materials”. Khazaei M, Wang V, Sevik C, Ranjbar A, Arai M, Yunoki S, Physical review materials 2, 074002 (2018). http://doi.org/10.1103/PHYSREVMATERIALS.2.074002
Abstract: Recently, a group of MAX phases, (Mo2/3Y1/3)(2)AlC, (Mo2/3Sc1/3)(2)AlC, (W2/3Sc1/3)(2)AlC,(W2/3Y1/3)(2)AlC, and (V-2/3 Zr-1/3)(2)AlC, with in-plane ordered double transition metals, named iMAX phases, have been synthesized. Experimentally, some of these MAX phases can be chemically exfoliated into two-dimensional (2D) single- or multilayered transition metal carbides, so-called MXenes. Accordingly, the 2D nanostructures derived from iMAX phases are named iMXenes. Here we investigate the structural stabilities and electronic structures of the experimentally discovered iMAX phases and their possible iMXene derivatives. We show that the iMAX phases and their pristine, F, or OH-terminated iMXenes are metallic. However, upon 0 termination, (Mo2/3Y1/3)(2)C, (Mo2/3Sc1/3)(2)C, (W2/3Y1/3)(2)C, and (W2/3Sc1/3)(2)C iMXenes turn into semiconductors. Owing to the absence of centrosymmetry, the semiconducting iMXenes may find applications in piezoelectricity. Our calculations reveal that the semiconducting iMXenes possess giant piezoelectric coefficients as large as 45 x 10(-)(10) C/m.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
DOI: 10.1103/PHYSREVMATERIALS.2.074002
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“Nontarget biomolecules alter macromolecular changes induced by bactericidal low-temperature plasma”. Privat-Maldonado A, Gorbanev Y, O'Connell D, Vann R, Chechik V, van der Woude MW, IEEE transactions on radiation and plasma medical sciences 2, 121 (2018). http://doi.org/10.1109/TRPMS.2017.2761405
Abstract: Low-temperature plasmas (LTPs) have a proven bactericidal activity governed by the generated reactive oxygen and nitrogen species (RONS) that target microbial cell components. However, RONS also interact with biomolecules in the environment. Here we assess the impact of these interactions upon exposure of liquid suspensions with variable organic content to an atmospheric-pressure dielectric barrier discharge plasma jet. Salmonella enterica serovar Typhimurium viability in the suspension was reduced in the absence [e. g., phosphate buffered saline (PBS)], but not in the presence of (high) organic content [Dulbecco's Modified Eagle's Medium (DMEM), DMEM supplemented with foetal calf serum, and Lysogeny Broth]. The reduced viability of LTP-treated bacteria in PBS correlated to a loss of membrane integrity, whereas double-strand DNA breaks could not be detected in treated single cells. The lack of bactericidal activity in solutions with high organic content correlated with a relative decrease of center dot OH and O-3/O-2(a(1)Delta g)/O, and an increase of H2O2 and NO2- in the plasma-treated solutions. These results indicate that the redox reactions of LTP-generated RONS with nontarget biomolecules resulted in a RONS composition with reduced bactericidal activity. Therefore, the chemical composition of the bacterial environment should be considered in the development of LTP for antimicrobial treatment, and may affect other biomedical applications as well.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
DOI: 10.1109/TRPMS.2017.2761405
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“Plasma Technology: An Emerging Technology for Energy Storage”. Bogaerts A, Neyts EC, ACS energy letters 3, 1013 (2018). http://doi.org/10.1021/acsenergylett.8b00184
Abstract: Plasma technology is gaining increasing interest for gas conversion applications, such as CO2 conversion into value-added chemicals or renewable fuels, and N2 fixation from the air, to be used for the production of small building blocks for, e.g., mineral fertilizers. Plasma is generated by electric power and can easily be switched on/off, making it, in principle, suitable for using intermittent renewable electricity. In this Perspective article, we explain why plasma might be promising for this application. We briefly present the most common types of plasma reactors with their characteristic features, illustrating why some plasma types exhibit better energy efficiency than others. We also highlight current research in the fields of CO2 conversion (including the combined conversion of CO2 with CH4, H2O, or H2) as well as N2 fixation (for NH3 or NOx synthesis). Finally, we discuss the major limitations and steps to be taken for further improvement.
Keywords: A1 Journal article; Engineering sciences. Technology; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Times cited: 56
DOI: 10.1021/acsenergylett.8b00184
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“Recent breakthroughs in scanning transmission electron microscopy of small species”. van den Bos KHW, Altantzis T, De Backer A, Van Aert S, Bals S, Advances in Physics: X 3, 1480420 (2018). http://doi.org/10.1080/23746149.2018.1480420
Abstract: Over the last decade, scanning transmission electron microscopy has become one of the most powerful tools to characterise nanomaterials at the atomic scale. Often, the ultimate goal is to retrieve the three-dimensional structure, which is very challenging since small species are typically sensitive to electron irradiation. Nevertheless, measuring individual atomic positions is crucial to understand the relation between the structure and physicochemical properties of these (nano)materials. In this review, we highlight the latest approaches that are available to reveal the 3D atomic structure of small species. Finally, we will provide an outlook and will describe future challenges where the limits of electron microscopy will be pushed even further.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Times cited: 8
DOI: 10.1080/23746149.2018.1480420
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“Substrate-induced proximity effect in superconducting niobium nanofilms”. Rezvani SJ, Perali A, Fretto M, De Leo N, Flammia L, Milošević, M, Nannarone S, Pinto N, Condensed Matter 4, 4 (2018). http://doi.org/10.3390/CONDMAT4010004
Abstract: Structural and superconducting properties of high-quality niobium nanofilms with different thicknesses are investigated on silicon oxide (SiO2) and sapphire substrates. The role played by the different substrates and the superconducting properties of the Nb films are discussed based on the defectivity of the films and on the presence of an interfacial oxide layer between the Nb film and the substrate. The X-ray absorption spectroscopy is employed to uncover the structure of the interfacial layer. We show that this interfacial layer leads to a strong proximity effect, especially in films deposited on a SiO2 substrate, altering the superconducting properties of the Nb films. Our results establish that the critical temperature is determined by an interplay between quantum-size effects, due to the reduction of the Nb film thicknesses, and proximity effects. The detailed investigation here provides reference characterizations and has direct and important implications for the fabrication of superconducting devices based on Nb nanofilms.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Times cited: 3
DOI: 10.3390/CONDMAT4010004
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“Epitaxial stress-free growth of high crystallinity ferroelectric PbZr0.52Ti0.48O3 on GaN/AlGaN/Si(111) substrate”. Li L, Liao Z, Gauquelin N, Minh Duc Nguyen, Hueting RJE, Gravesteijn DJ, Lobato I, Houwman EP, Lazar S, Verbeeck J, Koster G, Rijnders G, Advanced Materials Interfaces 5, 1700921 (2018). http://doi.org/10.1002/ADMI.201700921
Abstract: <script type='text/javascript'>document.write(unpmarked('Due to its physical properties gallium-nitride (GaN) is gaining a lot of attention as an emerging semiconductor material in the field of high-power and high-frequency electronics applications. Therefore, the improvement in the performance and/or perhaps even extension in functionality of GaN based devices would be highly desirable. The integration of ferroelectric materials such as lead-zirconate-titanate (PbZrxTi1-xO3) with GaN has a strong potential to offer such an improvement. However, the large lattice mismatch between PZT and GaN makes the epitaxial growth of Pb(Zr1-xTix)O-3 on GaN a formidable challenge. This work discusses a novel strain relaxation mechanism observed when MgO is used as a buffer layer, with thicknesses down to a single unit cell, inducing epitaxial growth of high crystallinity Pb(Zr0.52Ti0.48)O-3 (PZT) thin films. The epitaxial PZT films exhibit good ferroelectric properties, showing great promise for future GaN device applications.'));
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.279
Times cited: 15
DOI: 10.1002/ADMI.201700921
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“Magnetic field dependence of the atomic collapse state in graphene”. Moldovan D, Masir MR, Peeters FM, 2D materials 5, 015017 (2018). http://doi.org/10.1088/2053-1583/AA9647
Abstract: <script type='text/javascript'>document.write(unpmarked('Quantum electrodynamics predicts that heavy atoms (Z \u003E Z(c) approximate to 170) will undergo the process of atomic collapse where electrons sink into the positron continuum and a new family of so-called collapsing states emerges. The relativistic electrons in graphene exhibit the same physics but at a much lower critical charge (Z(c) approximate to 1) which has made it possible to confirm this phenomenon experimentally. However, there exist conflicting predictions on the effect of a magnetic field on atomic collapse. These theoretical predictions are based on the continuum Dirac-Weyl equation, which does not have an exact analytical solution for the interplay of a supercritical Coulomb potential and the magnetic field. Approximative solutions have been proposed, but because the two effects compete on similar energy scales, the theoretical treatment varies depending on the regime which is being considered. These limitations are overcome here by starting from a tight-binding approach and computing exact numerical results. By avoiding special limit cases, we found a smooth evolution between the different regimes. We predict that the atomic collapse effect persists even after the magnetic field is activated and that the critical charge remains unchanged. We show that the atomic collapse regime is characterized: (1) by a series of Landau level anticrossings and (2) by the absence of root B scaling of the Landau levels with regard to magnetic field strength.'));
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 6.937
Times cited: 13
DOI: 10.1088/2053-1583/AA9647
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“Plasma physics of liquids—A focused review”. Vanraes P, Bogaerts A, Applied physics reviews 5, 031103 (2018). http://doi.org/10.1063/1.5020511
Abstract: The interaction of plasma with liquids has led to various established industrial implementations as well as promising applications, including high-voltage switching, chemical analysis, nanomaterial synthesis, and plasma medicine. Along with these numerous accomplishments, the physics of plasma in liquid or in contact with a liquid surface has emerged as a bipartite research field, for which we introduce here the term “plasma physics of liquids.” Despite the intensive research
investments during the recent decennia, this field is plagued by some controversies and gaps in knowledge, which might restrict further progress. The main difficulties in understanding revolve around the basic mechanisms of plasma initiation in the liquid phase and the electrical interactions at a plasma-liquid interface, which require an interdisciplinary approach. This review aims to provide the wide applied physics community with a general overview of the field, as well as the opportunities for interdisciplinary research on topics, such as nanobubbles and the floating water bridge, and involving the research domains of amorphous semiconductors, solid state physics, thermodynamics, material science, analytical chemistry, electrochemistry, and molecular dynamics simulations. In addition, we provoke awareness of experts in the field on yet underappreciated question marks. Accordingly, a strategy for future experimental and simulation work is proposed.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 13.667
Times cited: 33
DOI: 10.1063/1.5020511
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“Theoretical and experimental investigation of conjugation of 1,6-hexanedithiol on MoS2”. Gul A, Bacaksiz C, Unsal E, Akbali B, Tomak A, Zareie HM, Sahin H, Materials Research Express 5, 036415 (2018). http://doi.org/10.1088/2053-1591/AAB4A6
Abstract: We report an experimental and theoretical investigation of conjugation of 1,6-Hexaneditihiol (HDT) on MoS2 which is prepared by mixing MoS2 structure and HDT molecules in proper solvent. Raman spectra and the calculated phonon bands reveal that the HDT molecules bind covalently to MoS2. Surface morphology of MoS2/HDTstructure is changed upon conjugation ofHDTon MoS2 and characterized by using Scanning Electron Microscope (SEM). Density Functional Theory (DFT) based calculations show that HOMO-LUMO band gap of HDT is altered after the conjugation and two-S binding (handle-like) configuration is energetically most favorable among three different structures. This study displays that the facile thiol functionalization process of MoS2 is promising strategy for obtaining solution processable MoS2.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 1.068
Times cited: 2
DOI: 10.1088/2053-1591/AAB4A6
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“Exciton Fine Structure and Lattice Dynamics in InP/ZnSe Core/Shell Quantum Dots”. Brodu A, Ballottin MV, Buhot J, van Harten EJ, Dupont D, La Porta A, Prins PT, Tessier MD, Versteegh MAM, Zwiller V, Bals S, Hens Z, Rabouw FT, Christianen PCM, de Donega CM, Vanmaekelbergh D, ACS Photonics 5, 3353 (2018). http://doi.org/10.1021/ACSPHOTONICS.8B00615
Abstract: Nanocrystalline InP quantum dots (QDs) hold promise for heavy-metal-free optoelectronic applications due to their bright and size tunable emission in the visible range. Photochemical stability and high photoluminescence (PL) quantum yield are obtained by a diversity of epitaxial shells around the InP core. To understand and optimize the emission line shapes, the exciton fine structure of InP core/shell QD systems needs be investigated. Here, we study the exciton fine structure of InP/ZnSe core/shell QDs with core diameters ranging from 2.9 to 3.6 nm (PL peak from 2.3 to 1.95 eV at 4 K). PL decay measurements as a function of temperature in the 10 mK to 300 K range show that the lowest exciton fine structure state is a dark state, from which radiative recombination is assisted by coupling to confined acoustic phonons with energies ranging from 4 to 7 meV, depending on the core diameter. Circularly polarized fluorescence line-narrowing (FLN) spectroscopy at 4 K under high magnetic fields (up to 30 T) demonstrates that radiative recombination from the dark F = +/- 2 state involves acoustic and optical phonons, from both the InP core and the ZnSe shell. Our data indicate that the highest intensity FLN peak is an acoustic phonon replica rather than a zero-phonon line, implying that the energy separation observed between the F = +/- 1 state and the highest intensity peak in the FLN spectra (6 to 16 meV, depending on the InP core size) is larger than the splitting between the dark and bright fine structure exciton states.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 6.756
Times cited: 40
DOI: 10.1021/ACSPHOTONICS.8B00615
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“The conversion mechanism of amorphous silicon to stoichiometric WS2”. Heyne MH, de Marneffe J-F, Nuytten T, Meersschaut J, Conard T, Caymax M, Radu I, Delabie A, Neyts EC, De Gendt S, Journal of materials chemistry C : materials for optical and electronic devices 6, 4122 (2018). http://doi.org/10.1039/C8TC00760H
Abstract: The deposition of ultra-thin tungsten films and their related 2D chalcogen compounds on large area dielectric substrates by gas phase reactions is challenging. The lack of nucleation sites complicates the adsorption of W-related precursors and subsequent sulfurization usually requires high temperatures. We propose here a technique in which a thin solid amorphous silicon film is used as reductant for the gas phase precursor WF6 leading to the conversion to metallic W. The selectivity of the W conversion towards the underlying dielectric surfaces is demonstrated. The role of the Si surface preparation, the conversion temperature, and Si thickness on the formation process is investigated. Further, the in situ conversion of the metallic tungsten into thin stoichiometric WS2 is achieved by a cyclic approach based on WF6 and H2S pulses at the moderate temperature of 450 1C, which is much lower than usual oxide sulfurization processes.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 5.256
Times cited: 4
DOI: 10.1039/C8TC00760H
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“MXenes/graphene heterostructures for Li battery applications : a first principles study”. Aierken Y, Sevik C, Gulseren O, Peeters FM, Çakir D, Journal of materials chemistry A : materials for energy and sustainability 6, 2337 (2018). http://doi.org/10.1039/C7TA09001C
Abstract: MXenes are the newest class of two-dimensional (2D) materials, and they offer great potential in a wide range of applications including electronic devices, sensors, and thermoelectric and energy storage materials. In this work, we combined the outstanding electrical conductivity, that is essential for battery applications, of graphene with MXene monolayers (M2CX2 where M = Sc, Ti, V and X = OH, O) to explore its potential in Li battery applications. Through first principles calculations, we determined the stable stacking configurations of M2CX2/graphene bilayer heterostructures and their Li atom intercalation by calculating the Li binding energy, diffusion barrier and voltage. We found that: (1) for the ground state stacking, the interlayer binding is strong, yet the interlayer friction is small; (2) Li binds more strongly to the O-terminated monolayer, bilayer and heterostructure MXene systems when compared with the OHterminated MXenes due to the H+ induced repulsion to the Li atoms. The binding energy of Li decreases as the Li concentration increases due to enhanced repulsive interaction between the positively charged Li ions; (3) Ti2CO2/graphene and V2CO2/graphene heterostructures exhibit large Li atom binding energies making them the most promising candidates for battery applications. When fully loaded with Li atoms, the binding energy is -1.43 eV per Li atom and -1.78 eV per Li atom for Ti2CO2/graphene and V2CO2/graphene, respectively. These two heterostructures exhibit a nice compromise between storage capacity and kinetics. For example, the diffusion barrier of Li in Ti2CO2/graphene is around 0.3 eV which is comparable to that of graphite. Additionally, the calculated average voltages are 1.49 V and 1.93 V for Ti2CO2/graphene and V2CO2/graphene structures, respectively; (4) a small change in the in-plane lattice parameters (<1%), interatomic bond lengths and interlayer distances (<0.5 angstrom) proves the stability of the heterostructures against Li intercalation, and the impending phase separation into constituent layers and capacity fading during charge-discharge cycles in real battery applications; (5) as compared to bare M2CX2 bilayers, M2CX2/graphene heterostructures have lower molecular mass, offering high storage capacity; (6) the presence of graphene ensures good electrical conductivity that is essential for battery applications. Given these advantages, Ti2CO2/graphene and V2CO2/graphene heterostructures are predicted to be promising for lithium-ion battery applications.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 8.867
Times cited: 131
DOI: 10.1039/C7TA09001C
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“Tuning electronic and magnetic properties of monolayer \alpha-RuCl3 by in-plane strain”. Iyikanat F, Yagmurcukardes M, Senger RT, Sahin H, Journal of materials chemistry C : materials for optical and electronic devices 6, 2019 (2018). http://doi.org/10.1039/C7TC05266A
Abstract: By employing density functional theory-based methods, the structural, vibrational, electronic, and magnetic properties of monolayer -RuCl3 were investigated. It was demonstrated that ferromagnetic (FM) and zigzag-antiferromagnetic (ZZ-AFM) spin orders in the material have very close total energies with the latter being the ground state. We found that each Ru atom possesses a magnetic moment of 0.9 (B) and the material exhibits strong magnetic anisotropy. While both phases exhibit indirect gaps, the FM phase is a magnetic semiconductor and the ZZ-AFM phase is a non-magnetic semiconductor. The structural stability of the material was confirmed by phonon calculations. Moreover, dynamical analysis revealed that the magnetic order in the material can be monitored via Raman measurements of the crystal structure. In addition, the magnetic ground state of the material changes from ZZ-AFM to FM upon certain applied strains. Valence and conduction band-edges of the material vary considerably under in-plane strains. Owing to the stable lattice structure and unique and controllable magnetic properties, monolayer -RuCl3 is a promising material in nanoscale device applications.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 5.256
Times cited: 16
DOI: 10.1039/C7TC05266A
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“Measurement of local crystal lattice strain variations in dealloyed nanoporous gold”. Mahr C, Müller-Caspary K, Graf M, Lackmann A, Grieb T, Schowalter M, Krause FF, Mehrtens T, Wittstock A, Weissmueller J, Rosenauer A, Materials research letters 6, 84 (2018). http://doi.org/10.1080/21663831.2017.1396263
Abstract: Reversible macroscopic length changes in nanoporous structures can be achieved by applying electric potentials or by exposing them to different gases or liquids. Thus, these materials are interesting candidates for applications as sensors or actuators. Macroscopic length changes originate from microscopic changes of crystal lattice parameters. In this report, we show spatially resolved measurements of crystal lattice strain in dealloyed nanoporous gold. The results confirm theory by indicating a compression of the lattice along the axis of cylindrically shaped ligaments and an expansion in radial direction. Furthermore, we show that curved npAu surfaces show inward relaxation of the surface layer. [GRAPHICS] .
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.773
Times cited: 4
DOI: 10.1080/21663831.2017.1396263
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“Band-Tails Tunneling Resolving the Theory-Experiment Discrepancy in Esaki Diodes”. Bizindavyi J, Verhulst AS, Smets Q, Verreck D, Sorée B, Groeseneken G, IEEE journal of the Electron Devices Society 6, 633 (2018). http://doi.org/10.1109/JEDS.2018.2834825
Abstract: Discrepancies exist between the theoretically predicted and experimentally measured performance of band-to-band tunneling devices, such as Esaki diodes and tunnel field-effect transistors (TFETs). We resolve this discrepancy for highly-doped, direct-bandgap Esaki diodes by successfully calibrating a semi-classical model for high-doping-induced ballistic band-tails tunneling currents at multiple temperatures with two In0.53Ga0.47As Esaki diodes using their SIMS doping profiles, C-V characteristics and their forward-bias current density in the negative differential resistance (NDR) regime. The current swing in the NDR regime is shown not to be linked to the band-tails Urbach energy. We further demonstrate theoretically that the calibrated band-tails contribution is also the dominant band-tails contribution to the subthreshold swing of the corresponding TFETs. Lastly, we verify that the presented procedure is applicable to all direct-bandgap semiconductors by successfully applying it to InAs Esaki diodes in literature.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 3.141
Times cited: 5
DOI: 10.1109/JEDS.2018.2834825
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“Charge transfer doping modulated raman scattering and enhanced stability of black phosphorus quantum dots on a ZnO nanorod”. Hu L, Amini MN, Wu Y, Jin Z, Yuan J, Lin R, Wu J, Dai Y, He H, Lu Y, Lu J, Ye Z, Han S-T, Ye J, Partoens B, Zeng Y-J, Ruan S, Advanced Optical Materials 6, 1800440 (2018). http://doi.org/10.1002/ADOM.201800440
Abstract: Black phosphorus (BP) has recently triggered an unprecedented interest in the 2D community. However, many of its unique properties are not exploited and the well-known environmental vulnerability is not conquered. Herein, a type-I mixed-dimensional (0D-1D) van der Waals heterojunction is developed, where three-atomic-layer BP quantum dots (QDs) are assembled on a single ZnO nanorod (NR). By adjusting the indium (In) content in ZnO NRs, the degree and even the direction of surface charge transfer doping within the heterojunction can be tuned, which result in selective Raman scattering enhancements between ZnO and BP. The maximal enhancement factor is determined as 4340 for BP QDs with sub-ppm level. Furthermore, an unexpected long-term ambient stability (more than six months) of BP QDs is revealed, which is ascribed to the electron doping from ZnO:In NRs. The first demonstration of selective Raman enhancements between two inorganic semiconductors as well as the improved stability of BP shed light on this emerging 2D material.
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 6.875
Times cited: 37
DOI: 10.1002/ADOM.201800440
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“Can surface reactivity of mixed crystals be predicted from their counterparts? A case study of (Bi1-xSbx)2Te3 topological insulators”. Volykhov AA, Sanchez-Barriga J, Batuk M, Callaert C, Hadermann J, Sirotina AP, Neudachina VS, Belova AI, Vladimirova NV, Tamm ME, Khmelevsky NO, Escudero C, Perez-Dieste V, Knop-Gericke A, Yashina LV, Journal of materials chemistry C : materials for optical and electronic devices 6, 8941 (2018). http://doi.org/10.1039/C8TC02235F
Abstract: The behavior of ternary mixed crystals or solid solutions and its correlation with the properties of their binary constituents is of fundamental interest. Due to their unique potential for application in future information technology, mixed crystals of topological insulators with the spin-locked, gapless states on their surfaces attract huge attention of physicists, chemists and material scientists. (Bi1-xSbx)(2)Te-3 solid solutions are among the best candidates for spintronic applications since the bulk carrier concentration can be tuned by varying x to obtain truly bulk-insulating samples, where the topological surface states largely contribute to the transport and the realization of the surface quantum Hall effect. As this ternary compound will be evidently used in the form of thin-film devices its chemical stability is an important practical issue. Based on the atomic resolution HAADF-TEM and EDX data together with the XPS results obtained both ex situ and in situ, we propose an atomistic picture of the mixed crystal reactivity compared to that of its binary constituents. We find that the surface reactivity is determined by the probability of oxygen attack on the Te-Sb bonds, which is directly proportional to the number of Te atoms bonded to at least one Sb atom. The oxidation mechanism includes formation of an amorphous antimony oxide at the very surface due to Sb diffusion from the first two quintuple layers, electron tunneling from the Fermi level of the crystal to oxygen, oxygen ion diffusion to the crystal, and finally, slow Te oxidation to the +4 oxidation state. The oxide layer thickness is limited by the electron transport, and the overall process resembles the Cabrera-Mott mechanism in metals. These observations are critical not only for current understanding of the chemical reactivity of complex crystals, but also to improve the performance of future spintronic devices based on topological materials.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.256
Times cited: 3
DOI: 10.1039/C8TC02235F
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“Integrated X-ray fluorescence and diffuse visible-to-near-infrared reflectance scanner for standoff elemental and molecular spectroscopic imaging of paints and works on paper”. Delaney JK, Conover DM, Dooley KA, Glinsman L, Janssens K, Loew M, Heritage science 6, 31 (2018). http://doi.org/10.1186/S40494-018-0197-Y
Abstract: Prior studies have shown the improved ability to identify artists' pigments by combining results from X-ray fluorescence (XRF), which provides elemental information, with reflectance spectroscopy in the visible to near infrared (400-1000 nm) that provides information on electronic transitions. Extending the spectral range of reflectance spectroscopy into the UV, 350-400 nm, allows identification of several white pigments since their electronic transitions occur in this region (e.g., zinc white and rutile and anatase forms of titanium white). Extending the range further into the infrared, out to 2500 nm, provides information on vibrational transitions of various functional groups, such as hydroxyl, carbonate, and methyl groups. This allows better identification of mineral-based pigments and some paint binders. The combination of elemental information with electronic and vibrational transitions provides a more robust method to identify artists' materials in situ. The collection of both sets of spectral information across works of art, such as paintings and works on paper, allows generating a more complete map of artists' materials. Here, we describe a 2-D scanner that simultaneously collects XRF spectra and reflectance spectra from 350 to 2500 nm across the surfaces of works of art. The scanner consists of a stationary, single pixel XRF spectrometer and fiber optic reflectance spectrometer along with a 2-D position-controlled easel that moves the artwork in front of the two detection systems. The dual-mode scanner has been tested on a variety of works of art from illuminated manuscripts (0.1 x 0.1 m(2)) to paintings as large as 1.7 x 1.9 m(2). The scanner is described and two sets of results are presented. The first is the XRF scanning of a large warped panel painting by Andrea del Sarto titled Charity. The second is a combined XRF and reflectance scan of Georges Seurat's painting titled Haymakers at Montfermeil. The XRF was collected at 1 mm spatial sampling and the reflectance spectral data at 3 mm. Combining the results from the data sets was found to enhance the identification of pigments as well as yield distribution maps, in spite of the relatively low reflectance spatial sampling. The elemental and reflectance maps allowed the identification and mapping of lead white, cobalt blue, viridian, ochres, and likely chrome yellow. The maps also provide information on the mixing of pigments. While the reflectance image cube has 10-20x larger spatial samples than desired, the elimination of having to use two hyperspectral cameras to cover the range from 400 to 2500 nm makes for a low cost dual modality scanner.
Keywords: A1 Journal article; Art; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Times cited: 7
DOI: 10.1186/S40494-018-0197-Y
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“Separating two painting campaigns in Saul and David, attributed to Rembrandt, using macroscale reflectance and XRF imaging spectroscopies and microscale paint analysis”. Dooley KA, Gifford EM, van Loon A, Noble P, Zeibel JG, Conover DM, Alfeld M, van der Snickt G, Legrand S, Janssens K, Dik J, Delaney JK, Heritage science 6, 46 (2018). http://doi.org/10.1186/S40494-018-0212-3
Abstract: Late paintings of Rembrandt van Rijn (1606-1669) offer intriguing problems for both art historians and conservation scientists. In the research presented here, the key question addressed is whether observed stylistic differences in paint handling can be correlated with material differences. In Saul and David, in the collection of the Royal Picture Gallery Mauritshuis in The Hague, NL, the stylistic differences between the loose brushwork of Saul's cloak and the more detailed depiction of his turban and the figure of David have been associated with at least two painting stages since the late 1960s, but the attribution of each stage has been debated in the art historical literature. Stylistic evaluation of the paint handling in the two stages, based on magnified surface examination, is further described here. One of the research goals was to determine whether the stylistic differences could be further differentiated with macroscale and microscale methods of material analysis. To address this, selected areas of the painting having pronounced stylistic differences were investigated with two macroscopic chemical imaging methods, X-ray fluorescence and reflectance imaging spectroscopies. The pigments used were identified and their spatial distribution was mapped. The mapping results show that the passages rendered in more detail and associated stylistically with the first painting stage, such as the orange-red color of David's garment or the Greek key design in Saul's turban, were painted with predominately red ochre mixed with vermilion. The regions of loose, bold brushwork, such as the orange-red slashing strokes in the interior of Saul's cloak, associated with the second painting stage, were painted with predominately red ochre without vermilion. These macroscale imaging results were confirmed and extended with scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) analysis of three cross-sections taken from regions of stylistic differences associated with the two painting stages, including one sample each from the right and left sleeve of David, and one from the interior of Saul's cloak. SEM-EDX also identified a trace component, barium sulfate, associated with the red ochre of the second stage revisions. Combining mapping information from two spectroscopic imaging methods with localized information from microscopic samples has clearly shown that the stylistic differences observed in the paint handling are affiliated with differences in the chemical composition of the paints.
Keywords: A1 Journal article; Art; AXES (Antwerp X-ray Analysis, Electrochemistry and Speciation)
Times cited: 3
DOI: 10.1186/S40494-018-0212-3
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“Determinants of internal governance quality : evidence from corporations in Ethiopia”. Adane YG, Engida TG, Asfaw YA, Azadi H, Van Passel S, Cogent economics &, finance 6, 1537051 (2018). http://doi.org/10.1080/23322039.2018.1537051
Abstract: The study analysed the factors that affect the internal governance quality of corporations in Ethiopia. It performed an ordered logistic regression analysis on a randomly selected sample of 76 corporations to analyse the effect of the ownership structure, form of ownership (private or government), leverage, corporate size, and sales growth on the internal governance quality score (IGQS). The governance quality score was measured using 20 indices categorized into four perspectives: disclosure, board characteristics, ethics, and shareholder rights. In this study, a significant positive effect of the corporate size and sales growth on the IGQS was found. In addition, government-owned corporations were found to perform better than privately owned corporations. It is recommended that appropriate authorities and officials should encourage the use of the corporate governance system in privately owned corporations and the convergence of internal governance quality of the two groups of corporations to the highest level.
Keywords: A1 Journal article; Economics; Engineering Management (ENM)
DOI: 10.1080/23322039.2018.1537051
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“Epitaxial CVD Growth of Ultra-Thin Si Passivation Layers on Strained Ge Fin Structures”. Loo R, Arimura H, Cott D, Witters L, Pourtois G, Schulze A, Douhard B, Vanherle W, Eneman G, Richard O, Favia P, Mitard J, Mocuta D, Langer R, Collaert N, ECS journal of solid state science and technology 7, P66 (2018). http://doi.org/10.1149/2.0191802JSS
Abstract: Epitaxially grown ultra-thin Si layers are often used to passivate Ge surfaces in the high-k gate module of (strained) Ge FinFET and Gate All Around devices. We use Si4H10 as Si precursor as it enables epitaxial Si growth at temperatures down to 330 degrees. C-V characteristics of blanket capacitors made on Ge virtual substrates point to the presence of an optimal Si thickness. In case of compressively strained Ge fin structures, the Si growth results in non-uniform and high strain levels in the strained Ge fin. These strain levels have been calculated for different shapes of the Ge fin and in function of the grown Si thickness. The high strain is the driving force for potential (unwanted) Ge surface reflow during Si deposition. The Ge surface reflow is strongly affected by the strength of the H-passivation during Si-capping and can be avoided by carefully selected process conditions. (C) The Author(s) 2018. Published by ECS.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 1.787
Times cited: 5
DOI: 10.1149/2.0191802JSS
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“Study of the intrinsic limitations of the contact resistance of metal/semiconductor interfaces through atomistic simulations”. Dabral A, Pourtois G, Sankaran K, Magnus W, Yu H, de de Meux AJ, Lu AKA, Clima S, Stokbro K, Schaekers M, Collaert N, Horiguchi N, Houssa M, ECS journal of solid state science and technology 7, N73 (2018). http://doi.org/10.1149/2.0041806JSS
Abstract: In this contribution, we report a fundamental study of the factors that set the contact resistivity between metals and highly doped n-type 2D and 3D semiconductors. We investigate the case of n-type doped Si contacted with amorphous TiSi combining first principles calculations with Non-Equilibrium Green functions transport simulations. The evolution of the intrinsic contact resistivity with the doping concentration is found to saturate at similar to 2 x 10(-10) Omega.cm(2) for the case of TiSi and imposes an intrinsic limit to the ultimate contact resistance achievable for n-doped Silamorphous-TiSi (aTiSi). The limit arises from the intrinsic properties of the semiconductors and of the metals such as their electron effective masses and Fermi energies. We illustrate that, in this regime, contacting heavy electron effective mass metals with semiconductor helps reducing the interface intrinsic contact resistivity. This observation seems to hold true regardless of the 3D character of the semiconductor, as illustrated for the case of three 2D semiconducting materials, namely MoS2, ZrS2 and HfS2. (C) The Author(s) 2018. Published by ECS.
Keywords: A1 Journal article; Condensed Matter Theory (CMT); Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 1.787
Times cited: 2
DOI: 10.1149/2.0041806JSS
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“On the evolution of strain and electrical properties in as-grown and annealed Si:P epitaxial films for source-drain stressor applications”. Dhayalan SK, Kujala J, Slotte J, Pourtois G, Simoen E, Rosseel E, Hikavyy A, Shimura Y, Loo R, Vandervorst W, ECS journal of solid state science and technology 7, P228 (2018). http://doi.org/10.1149/2.0071805JSS
Abstract: Heavily P doped Si:P epitaxial layers have gained interest in recent times as a promising source-drain stressor material for n type FinFETs (Fin Field Effect Transistors). They are touted to provide excellent conductivity as well as tensile strain. Although the as-grown layers do provide tensile strain, their conductivity exhibits an unfavorable behavior. It reduces with increasing P concentration (P > 1E21 at/cm(3)), accompanied by a saturation in the active carrier concentration. Subjecting the layers to laser annealing increases the conductivity and activates a fraction of P atoms. However, there is also a concurrent reduction in tensile strain (<1%). Literature proposes the formation of local semiconducting Si3P4 complexes to explain the observed behaviors in Si:P [Z. Ye et al., ECS Trans., 50(9) 2013, p. 1007-10111. The development of tensile strain and the saturation in active carrier is attributed to the presence of local complexes while their dispersal on annealing is attributed to strain reduction and increase in active carrier density. However, the existence of such local complexes is not proven and a fundamental void exists in understanding the structure-property correlation in Si:P films. In this respect, our work investigates the reason behind the evolution of strain and electrical properties in the as-grown and annealed Si:P epitaxial layers using ab-initio techniques and corroborate the results with physical characterization techniques. It will be shown that the strain developed in Si:P films is not due to any specific complexes while the formation of Phosphorus-vacancy complexes will be shown responsible for the carrier saturation and the increase in resistivity in the as-grown films. Interstitial/precipitate formation is suggested to be a reason for the strain loss in the annealed films. (C) The Author(s) 2018. Published by ECS.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 1.787
Times cited: 4
DOI: 10.1149/2.0071805JSS
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“Non-thermal plasma induces immunogenic cell death in vivo in murine CT26 colorectal tumors”. Lin AG, Xiang B, Merlino DJ, Baybutt TR, Sahu J, Fridman A, Snook AE, Miller V, Oncoimmunology 7, e1484978 (2018). http://doi.org/10.1080/2162402X.2018.1484978
Abstract: Immunogenic cell death is characterized by the emission of danger signals that facilitate activation of an adaptive immune response against dead-cell antigens. In the case of cancer therapy, tumor cells undergoing immunogenic death promote cancer-specific immunity. Identification, characterization, and optimization of stimuli that induce immunogenic cancer cell death has tremendous potential to improve the outcomes of cancer therapy. In this study, we show that non-thermal, atmospheric pressure plasma can be operated to induce immunogenic cell death in an animal model of colorectal cancer. In vitro, plasma treatment of CT26 colorectal cancer cells induced the release of classic danger signals. Treated cells were used to create a whole-cell vaccine which elicited protective immunity in the CT26 tumor mouse model. Moreover, plasma treatment of subcutaneous tumors elicited emission of danger signals and recruitment of antigen presenting cells into tumors. An increase in T cell responses targeting the colorectal cancer-specific antigen guanylyl cyclase C (GUCY2C) were also observed. This study provides the first evidence that non-thermal plasma is a bone fide inducer of immunogenic cell death and highlights its potential for clinical translation for cancer immunotherapy.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Times cited: 28
DOI: 10.1080/2162402X.2018.1484978
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“TiO2 Films Modified with Au Nanoclusters as Self-Cleaning Surfaces under Visible Light”. Liao T-W, Verbruggen S, Claes N, Yadav A, Grandjean D, Bals S, Lievens P, Nanomaterials 8, 30 (2018). http://doi.org/10.3390/nano8010030
Abstract: In this study, we applied cluster beam deposition (CBD) as a new approach for fabricating efficient plasmon-based photocatalytic materials. Au nanoclusters (AuNCs) produced in the gas phase were deposited on TiO2 P25-coated silicon wafers with coverage ranging from 2 to 8 atomic monolayer (ML) equivalents. Scanning Electron Microscopy (SEM) images of the AuNCs modified TiO2 P25 films show that the surface is uniformly covered by the AuNCs that remain isolated at low coverage (2 ML, 4 ML) and aggregate at higher coverage (8 ML). A clear relationship between AuNCs coverage and photocatalytic activity towards stearic acid photo-oxidation was measured, both under ultraviolet and green light illumination. TiO2 P25 covered with 4 ML AuNCs showed the best stearic acid photo-oxidation performance under green light illumination (Formal Quantum Efficiency 1.6 x 10-6 over a period of 93 h). These results demonstrate the large potential of gas-phase AuNCs beam deposition technology for the fabrication of visible light active plasmonic photocatalysts.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT); Sustainable Energy, Air and Water Technology (DuEL)
Impact Factor: 3.553
Times cited: 29
DOI: 10.3390/nano8010030
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“Ti surface doping of LiNi0.5Mn1.5O4−δpositive electrodes for lithium ion batteries”. Ulu Okudur F, D'Haen J, Vranken T, De Sloovere D, Verheijen M, Karakulina OM, Abakumov AM, Hadermann J, Van Bael MK, Hardy A, RSC advances 8, 7287 (2018). http://doi.org/10.1039/C7RA12932G
Abstract: The particle surface of LiNi0.5Mn1.5O4−δ (LNMO), a Li-ion battery cathode material, has been modified by Ti cation doping through a hydrolysis–condensation reaction followed by annealing in oxygen. The effect of different annealing temperatures (500–850 °C) on the Ti distribution and electrochemical performance of the surface modified LNMO was investigated. Ti cations diffuse from the preformed amorphous ‘TiOx’ layer into the LNMO surface during annealing at 500 °C. This results in a 2–4 nm thick Ti-rich spinel surface having lower Mn and Ni content compared to the core of the LNMO particles, which was observed with scanning transmission electron microscopy coupled with compositional EDX mapping. An increase in the annealing temperature promotes the formation of a Ti bulk doped LiNi(0.5−w)Mn(1.5+w)−tTitO4 phase and Ti-rich LiNi0.5Mn1.5−yTiyO4 segregates above 750 °C. Fourier-transform infrared spectrometry indicates increasing Ni–Mn ordering with annealing temperature, for both bare and surface modified LNMO. Ti surface modified LNMO annealed at 500 °C shows a superior cyclic stability, coulombic efficiency and rate performance compared to bare LNMO annealed at 500 °C when cycled at 3.4–4.9 V vs. Li/Li+. The improvements are probably due to suppressed Ni and Mn dissolution with Ti surface doping.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 3.108
Times cited: 9
DOI: 10.1039/C7RA12932G
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“Enhancement of cellular glucose uptake by reactive species: a promising approach for diabetes therapy”. Kumar N, Shaw P, Razzokov J, Yusupov M, Attri P, Uhm HS, Choi EH, Bogaerts A, RSC advances 8, 9887 (2018). http://doi.org/10.1039/C7RA13389H
Abstract: It is generally known that antidiabetic activity is associated with an increased level of glucose uptake in adipocytes and skeletal muscle cells. However, the role of exogenous reactive oxygen and nitrogen species (RONS) in muscle development and more importantly in glucose uptake is largely unknown. We investigate the effect of RONS generated by cold atmospheric plasma (CAP) in glucose uptake. We show that the glucose uptake is significantly enhanced in differentiated L6 skeletal muscle cells after CAP treatment. We also observe a significant increase of the intracellular Ca++ and ROS level, without causing toxicity. One of the possible reasons for an elevated level of glucose uptake as well as intracellular ROS and Ca++ ions is probably the increased oxidative stress leading to glucose transport.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 3.108
Times cited: 1
DOI: 10.1039/C7RA13389H
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“Josephson vortex loops in nanostructured Josephson junctions”. Berdiyorov GR, Milošević, MV, Kusmartsev F, Peeters FM, Savel'ev S, Scientific reports 8, 2733 (2018). http://doi.org/10.1038/S41598-018-21015-7
Abstract: Linked and knotted vortex loops have recently received a revival of interest. Such three-dimensional topological entities have been observed in both classical-and super-fluids, as well as in optical systems. In superconductors, they remained obscure due to their instability against collapse – unless supported by inhomogeneous magnetic field. Here we reveal a new kind of vortex matter in superconductors -the Josephson vortex loops – formed and stabilized in planar junctions or layered superconductors as a result of nontrivial cutting and recombination of Josephson vortices around the barriers for their motion. Engineering latter barriers opens broad perspectives on loop manipulation and control of other possible knotted/linked/entangled vortex topologies in nanostructured superconductors. In the context of Josephson devices proposed to date, the high-frequency excitations of the Josephson loops can be utilized in future design of powerful emitters, tunable filters and waveguides of high-frequency electromagnetic radiation, thereby pushing forward the much needed Terahertz technology.
Keywords: A1 Journal article; Engineering sciences. Technology; Condensed Matter Theory (CMT)
Impact Factor: 4.259
Times cited: 10
DOI: 10.1038/S41598-018-21015-7
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“The role of the electrode surface in Na-Air batteries : insights in electrochemical product formation and chemical growth of NaO2”. Lutz L, Corte DAD, Chen Y, Batuk D, Johnson LR, Abakumov A, Yate L, Azaceta E, Bruce PG, Tarascon J-M, Grimaud A, Advanced energy materials 8, 1701581 (2018). http://doi.org/10.1002/AENM.201701581
Abstract: The Na-air battery, because of its high energy density and low charging overpotential, is a promising candidate for low-cost energy storage, hence leading to intensive research. However, to achieve such a battery, the role of the positive electrode material in the discharge process must be understood. This issue is herein addressed by exploring the electrochemical reduction of oxygen, as well as the chemical formation and precipitation of NaO2 using different electrodes. Whereas a minor influence of the electrode surface is demonstrated on the electrochemical formation of NaO2, a strong dependence of the subsequent chemical precipitation of NaO2 is identified. In the origin, this effect stems from the surface energy and O-2/O-2(-) affinity of the electrode. The strong interaction of Au with O-2/O-2(-) increases the nucleation rate and leads to an altered growth process when compared to C surfaces. Consequently, thin (3 mu m) flakes of NaO2 are found on Au, whereas on C large cubes (10 mu m) of NaO2 are formed. This has significant impact on the cell performance and leads to four times higher capacity when C electrodes with low surface energy and O-2/O-2(-) affinity are used. It is hoped that these findings will enable the design of new positive electrode materials with optimized surfaces.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 16.721
Times cited: 13
DOI: 10.1002/AENM.201701581
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“Chemical fingerprints of cold physical plasmas &ndash, an experimental and computational study using cysteine as tracer compound”. Lackmann J-W, Wende K, Verlackt C, Golda J, Volzke J, Kogelheide F, Held J, Bekeschus S, Bogaerts A, Schulz-von der Gathen V, Stapelmann K, Scientific reports 8, 7736 (2018). http://doi.org/10.1038/s41598-018-25937-0
Abstract: Reactive oxygen and nitrogen species released by cold physical plasma are being proposed as effectors in various clinical conditions connected to inflammatory processes. As these plasmas can be tailored in a wide range, models to compare and control their biochemical footprint are desired to infer on the molecular mechanisms underlying the observed effects and to enable the discrimination between different plasma sources. Here, an improved model to trace short-lived reactive species is presented. Using FTIR, high-resolution mass spectrometry, and molecular dynamics computational simulation, covalent modifications of cysteine treated with different plasmas were deciphered and the respective product pattern used to generate a fingerprint of each plasma source. Such, our experimental model allows a fast and reliable grading of the chemical potential of plasmas used for medical purposes. Major reaction products were identified to be cysteine sulfonic acid, cystine, and cysteine fragments. Less abundant products, such as oxidized cystine derivatives or S-nitrosylated cysteines, were unique to different plasma sources or operating conditions. The data collected point at hydroxyl radicals, atomic O, and singlet oxygen as major contributing species that enable an impact on cellular thiol groups when applying cold plasma in vitro or in vivo.
Keywords: A1 Journal article; Engineering sciences. Technology; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.259
Times cited: 19
DOI: 10.1038/s41598-018-25937-0
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