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“The role of the VZn-NO-H complex in the p-type conductivity in ZnO”. Amini MN, Saniz R, Lamoen D, Partoens B, Physical chemistry, chemical physics 17, 5485 (2015). http://doi.org/10.1039/c4cp05894a
Abstract: Past research efforts aiming at obtaining stable p-type ZnO have been based on complexes involving nitrogen doping. A recent experiment by (J. G. Reynolds et al., Appl. Phys. Lett., 2013, 102, 152114) demonstrated a significant ([similar]1018 cm−3) p-type behavior in N-doped ZnO films after appropriate annealing. The p-type conductivity was attributed to a VZnNOH shallow acceptor complex, formed by a Zn vacancy (VZn), N substituting O (NO), and H interstitial (Hi). We present here a first-principles hybrid functional study of this complex compared to the one without hydrogen. Our results confirm that the VZnNOH complex acts as an acceptor in ZnO. We find that H plays an important role, because it lowers the formation energy of the complex with respect to VZnNO, a complex known to exhibit (unstable) p-type behavior. However, this additional H atom also occupies the hole level at the origin of the shallow behavior of VZnNO, leaving only two states empty higher in the band gap and making the VZnNOH complex a deep acceptor. Therefore, we conclude that the cause of the observed p-type conductivity in experiment is not the presence of the VZnNOH complex, but probably the formation of the VZnNO complex during the annealing process.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 4.123
Times cited: 20
DOI: 10.1039/c4cp05894a
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“Structural transitions and long-time self-diffusion of interacting colloids confined by a parabolic potential”. Euan-Diaz E, Herrera-Velarde S, Misko VR, Peeters FM, Castaneda-Priego R, The journal of chemical physics 142, 024902 (2015). http://doi.org/10.1063/1.4905215
Abstract: We report on the ordering and dynamics of interacting colloidal particles confined by a parabolic potential. By means of Brownian dynamics simulations, we find that by varying the magnitude of the trap stiffness, it is possible to control the dimension of the system and, thus, explore both the structural transitions and the long-time self-diffusion coefficient as a function of the degree of confinement. We particularly study the structural ordering in the directions perpendicular and parallel to the confinement. Further analysis of the local distribution of the first-neighbors layer allows us to identify the different structural phases induced by the parabolic potential. These results are summarized in a structural state diagram that describes the way in which the colloidal suspension undergoes a structural re-ordering while increasing the confinement. To fully understand the particle dynamics, we take into account hydrodynamic interactions between colloids; the parabolic potential constricts the available space for the colloids, but it does not act on the solvent. Our findings show a non-linear behavior of the long-time self-diffusion coefficient that is associated to the structural transitions induced by the external field. (C) 2015 AIP Publishing LLC.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.965
Times cited: 7
DOI: 10.1063/1.4905215
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“On the time scale associated with Monte Carlo simulations”. Bal KM, Neyts EC, The journal of chemical physics 141, 204104 (2014). http://doi.org/10.1063/1.4902136
Abstract: Uniform-acceptance force-bias Monte Carlo (fbMC) methods have been shown to be a powerful technique to access longer timescales in atomistic simulations allowing, for example, phase transitions and growth. Recently, a new fbMC method, the time-stamped force-bias Monte Carlo (tfMC) method, was derived with inclusion of an estimated effective timescale; this timescale, however, does not seem able to explain some of the successes the method. In this contribution, we therefore explicitly quantify the effective timescale tfMC is able to access for a variety of systems, namely a simple single-particle, one-dimensional model system, the Lennard-Jones liquid, an adatom on the Cu(100) surface, a silicon crystal with point defects and a highly defected graphene sheet, in order to gain new insights into the mechanisms by which tfMC operates. It is found that considerable boosts, up to three orders of magnitude compared to molecular dynamics, can be achieved for solid state systems by lowering of the apparent activation barrier of occurring processes, while not requiring any system-specific input or modifications of the method. We furthermore address the pitfalls of using the method as a replacement or complement of molecular dynamics simulations, its ability to explicitly describe correct dynamics and reaction mechanisms, and the association of timescales to MC simulations in general.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 2.965
Times cited: 26
DOI: 10.1063/1.4902136
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“Native point defects in CuIn1-xGaxSe2 : hybrid density functional calculations predict the origin of p- and n-type conductivity”. Bekaert J, Saniz R, Partoens B, Lamoen D, Physical chemistry, chemical physics 16, 22299 (2014). http://doi.org/10.1039/c4cp02870h
Abstract: We have performed a first-principles study of the p- and n-type conductivity in CuIn1−xGaxSe2 due to native point defects, based on the HSE06 hybrid functional. Band alignment shows that the band gap becomes larger with x due to the increasing conduction band minimum, rendering it hard to establish n-type conductivity in CuGaSe2. From the defect formation energies, we find that In/GaCu is a shallow donor, while VCu, VIn/Ga and CuIn/Ga act as shallow acceptors. Using the total charge neutrality of ionized defects and intrinsic charge carriers to determine the Fermi level, we show that under In-rich growth conditions InCu causes strongly n-type conductivity in CuInSe2. Under increasingly In-poor growth conditions, the conductivity type in CuInSe2 alters to p-type and compensation of the acceptors by InCu reduces, as also observed in photoluminescence experiments. In CuGaSe2, the native acceptors pin the Fermi level far away from the conduction band minimum, thus inhibiting n-type conductivity. On the other hand, CuGaSe2 shows strong p-type conductivity under a wide range of Ga-poor growth conditions. Maximal p-type conductivity in CuIn1−xGaxSe2 is reached under In/Ga-poor growth conditions, in agreement with charge concentration measurements on samples with In/Ga-poor stoichiometry, and is primarily due to the dominant acceptor CuIn/Ga.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 4.123
Times cited: 43
DOI: 10.1039/c4cp02870h
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“High throughput first-principles calculations of bixbyite oxides for TCO applications”. Sarmadian N, Saniz R, Partoens B, Lamoen D, Volety K, Huyberechts G, Paul J, Physical chemistry, chemical physics 16, 17724 (2014). http://doi.org/10.1039/c4cp02788d
Abstract: We present a high-throughput computing scheme based on density functional theory (DFT) to generate a class of oxides and screen them with the aim of identifying those that might be electronically appropriate for transparent conducting oxide (TCO) applications. The screening criteria used are a minimum band gap to ensure sufficient transparency, a band edge alignment consistent with easy n- or p-type dopability, and a minimum thermodynamic phase stability to be experimentally synthesizable. Following this scheme we screened 23 binary and 1518 ternary bixbyite oxides in order to identify promising candidates, which can then be a subject of an in-depth study. The results for the known TCOs are in good agreement with the reported data in the literature. We suggest a list of several new potential TCOs, including both n- and p-type compounds.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 4.123
Times cited: 23
DOI: 10.1039/c4cp02788d
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“Doping of rhenium disulfide monolayers : a systematic first principles study”. Çakir D, Sahin H, Peeters FM, Physical chemistry, chemical physics 16, 16771 (2014). http://doi.org/10.1039/c4cp02007c
Abstract: The absence of a direct-to-indirect band gap transition in ReS2 when going from the monolayer to bulk makes it special among the other semiconducting transition metal dichalcogenides. The functionalization of this promising layered material emerges as a necessity for the next generation technological applications. Here, the structural, electronic, and magnetic properties of substitutionally doped ReS2 monolayers at either the S or Re site were systematically studied by using first principles density functional calculations. We found that substitutional doping of ReS2 depends sensitively on the growth conditions of ReS2. Among the large number of non-metallic atoms, namely H, B, C, Se, Te, F, Br, Cl, As, P. and N, we identified the most promising candidates for n-type and p-type doping of ReS2. While Cl is an ideal candidate for n-type doping, P appears to be the most promising candidate for p-type doping of the ReS2 monolayer. We also investigated the doping of ReS2 with metal atoms, namely Mo, W, Ti, V. Cr, Co, Fe, Mn, Ni, Cu, Nb, Zn, Ru, Os and Pt. Mo, Nb, Ti, and V atoms are found to be easily incorporated in a single layer of ReS2 as substitutional impurities at the Re site for all growth conditions considered in this work. Tuning chemical potentials of dopant atoms energetically makes it possible to dope ReS2 with Fe, Co, Cr, Mn, W, Ru, and Os at the Re site. We observe a robust trend for the magnetic moments when substituting a Re atom with metal atoms such that depending on the electronic configuration of dopant atoms, the net magnetic moment of the doped ReS2 becomes either 0 or 1 mu(B). Among the metallic dopants, Mo is the best candidate for p-type doping of ReS2 owing to its favorable energetics and promising electronic properties.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 4.123
Times cited: 58
DOI: 10.1039/c4cp02007c
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“A quantum Monte Carlo study on electron correlation in all-metal aromatic clusters MAl4 –, (M = Li, Na, K, Rb, Cu, Ag and Au)”. Brito BGA, Hai G-Q, Teixeira Rabelo JN, Cândido L, Physical chemistry, chemical physics 16, 8639 (2014). http://doi.org/10.1039/c4cp00416g
Abstract: Using fixed-node diffusion quantum Monte Carlo (FN-DMC) simulation we investigate the electron correlation in all-metal aromatic clusters MAl4- (with M = Li, Na, K, Rb, Cu, Ag and Au). The electron detachment energies and electron affinities of the clusters are obtained. The vertical electron detachment energies obtained from the FN-DMC calculations are in very good agreement with the available experimental results. Calculations are also performed within the Hartree-Fock approximation, density-functional theory (DFT), and the couple-cluster (CCSD(T)) method. From the obtained results, we analyse the impact of the electron correlation effects in these bimetallic clusters and find that the correlation of the valence electrons contributes significantly to the detachment energies and electron affinities, varying between 20% and 50% of their total values. Furthermore, we discuss the electron correlation effects on the stability of the clusters as well as the accuracy of the DFT and CCSD(T) calculations in the present systems.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 4.123
Times cited: 10
DOI: 10.1039/c4cp00416g
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“Electronic properties of graphene nano-flakes : energy gap, permanent dipole, termination effect, and Raman spectroscopy”. Singh SK, Neek-Amal M, Peeters FM, The journal of chemical physics 140, 074304 (2014). http://doi.org/10.1063/1.4865414
Abstract: The electronic properties of graphene nano-flakes (GNFs) with different edge passivation are investigated by using density functional theory. Passivation with F and H atoms is considered: C-Nc X-Nx (X = F or H). We studied GNFs with 10 < N-c < 56 and limit ourselves to the lowest energy configurations. We found that: (i) the energy difference Delta between the highest occupied molecular orbital and the lowest unoccupied molecular orbital decreases with N-c, (ii) topological defects (pentagon and heptagon) break the symmetry of the GNFs and enhance the electric polarization, (iii) the mutual interaction of bilayer GNFs can be understood by dipole-dipole interaction which were found sensitive to the relative orientation of the GNFs, (iv) the permanent dipoles depend on the edge terminated atom, while the energy gap is independent of it, and (v) the presence of heptagon and pentagon defects in the GNFs results in the largest difference between the energy of the spin-up and spin-down electrons which is larger for the H-passivated GNFs as compared to F-passivated GNFs. Our study shows clearly the effect of geometry, size, termination, and bilayer on the electronic properties of small GNFs. This study reveals important features of graphene nano-flakes which can be detected using Raman spectroscopy. (C) 2014 AIP Publishing LLC.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.965
Times cited: 30
DOI: 10.1063/1.4865414
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“First-principles material modeling of solid-state electrolytes with the spinel structure”. Mees MJ, Pourtois G, Rosciano F, Put B, Vereecken PM, Stesmans A, Physical chemistry, chemical physics (2014). http://doi.org/10.1039/C3CP54610A
Abstract: Ionic diffusion through the novel (AlxMg1-2xLix)Al2O4 spinel electrolyte is investigated using first-principles calculations, combined with the Kinetic Monte Carlo algorithm. We observe that the ionic diffusion increases with the lithium content x. Furthermore, the structural parameters, formation enthalpies and electronic structures of (AlxMg1-2xLix)Al2O4 are calculated for various stoichiometries. The overall results indicate the (AlxMg1-2xLix)Al2O4 stoichiometries x = 0.2...0.3 as most promising. The (AlxMg1-2xLix)Al2O4 electrolyte is a potential candidate for the all-spinel solid-state battery stack, with the material epitaxially grown between well-known spinel electrodes, such as LiyMn2O4 and Li4+3yTi5O12 (y = 0...1). Due to their identical crystal structure, a good electrolyte-electrode interface is expected.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 4.123
Times cited: 8
DOI: 10.1039/C3CP54610A
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“The origin of p-type conductivity in ZnM2O4 (M = Co, Rh, Ir) spinels”. Amini MN, Dixit H, Saniz R, Lamoen D, Partoens B, Physical chemistry, chemical physics 16, 2588 (2014). http://doi.org/10.1039/c3cp53926a
Abstract: ZnM2O4 (M = Co, Rh, Ir) spinels are considered as a class of potential p-type transparent conducting oxides (TCOs). We report the formation energy of acceptor-like defects using first principles calculations with an advanced hybrid exchange-correlation functional (HSE06) within density functional theory (DFT). Due to the discrepancies between the theoretically obtained band gaps with this hybrid functional and the – scattered – experimental results, we also perform GW calculations to support the validity of the description of these spinels with the HSE06 functional. The considered defects are the cation vacancy and antisite defects, which are supposed to be the leading source of disorder in the spinel structures. We also discuss the band alignments in these spinels. The calculated formation energies indicate that the antisite defects ZnM (Zn replacing M, M = Co, Rh, Ir) and VZn act as shallow acceptors in ZnCo2O4, ZnRh2O4 and ZnIr2O4, which explains the experimentally observed p-type conductivity in those systems. Moreover, our systematic study indicates that the ZnIr antisite defect has the lowest formation energy in the group and it corroborates the highest p-type conductivity reported for ZnIr2O4 among the group of ZnM2O4 spinels. To gain further insight into factors affecting the p-type conductivity, we have also investigated the formation of localized small polarons by calculating the self-trapping energy of the holes.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT); Condensed Matter Theory (CMT)
Impact Factor: 4.123
Times cited: 47
DOI: 10.1039/c3cp53926a
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“On the low-temperature growth mechanism of single walled carbon nanotubes in plasma enhanced chemical vapor deposition”. Shariat M, Shokri B, Neyts EC, Chemical physics letters 590, 131 (2013). http://doi.org/10.1016/j.cplett.2013.10.061
Abstract: Despite significant progress in single walled carbon nanotube (SWCNT) production by plasma enhanced chemical vapor deposition (PECVD), the growth mechanism in this method is not clearly understood. We employ reactive molecular dynamics simulations to investigate how plasma-based deposition allows growth at low temperature. We first investigate the SWCNT growth mechanism at low and high temperatures under conditions similar to thermal CVD and PECVD. We then show how ion bombardment during the nucleation stage increases the carbon solubility in the catalyst at low temperature. Finally, we demonstrate how moderate energy ions sputter amorphous carbon allowing for SWCNT growth at 500 K. (C) 2013 Elsevier B. V. All rights reserved.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 1.815
Times cited: 14
DOI: 10.1016/j.cplett.2013.10.061
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“NEXAFS spectromicroscopy of suspended carbon nanohorns”. Bittencourt C, Ke X, Van Tendeloo G, Tagmatarchis N, Guttmann P, Chemical physics letters 587, 85 (2013). http://doi.org/10.1016/j.cplett.2013.09.034
Abstract: We demonstrate that near-edge X-ray-absorption fine-structure spectroscopy combined with full-field transmission X-ray microscopy can be used to study the electronic structure of suspended carbon nanohorns. Based on reports of electronic structure calculations additional spectral features observed in the π region of the NEXAFS spectrum recorded on the carbon nanohorns were associated to the presence of the pentagonal rings and the folding of the graphene sheet.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.815
Times cited: 4
DOI: 10.1016/j.cplett.2013.09.034
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“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
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“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
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“Platinum and palladium on carbon nanotubes : experimental and theoretical studies”. Adjizian JJ, De Marco P, Suarez-Martinez I, El Mel AA, Snyders R, Gengler RYN, Rudolf P, Ke X, Van Tendeloo G, Bittencourt C, Ewels CP;, Chemical physics letters 571, 44 (2013). http://doi.org/10.1016/j.cplett.2013.03.079
Abstract: Pristine and oxygen plasma functionalised carbon nanotubes (CNTs) were studied after the evaporation of Pt and Pd atoms. High resolution transmission electron microscopy shows the formation of metal nanoparticles at the CNT surface. Oxygen functional groups grafted by the plasma functionalization act as nucleation sites for metal nanoparticles. Analysis of the C1s core level spectra reveals that there is no covalent bonding between the Pt or Pd atoms and the CNT surface. Unlike other transition metals such as titanium and copper, neither Pd nor Pt show strong oxygen interaction or surface oxygen scavenging behaviour.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.815
Times cited: 23
DOI: 10.1016/j.cplett.2013.03.079
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“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
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“Stability of Ge12C48 and Ge20C40 heterofullerenes : a first principles molecular dynamics study”. Massobrio C, Djimbi DM, Matsubara M, Scipioni R, Boero M, Chemical physics letters 556, 163 (2013). http://doi.org/10.1016/j.cplett.2012.11.033
Abstract: By using first-principles molecular dynamics, we address the issue of structural stability for the C-60 Ge-m(m) family of doped heterofullerenes through a set of calculations targeting C48Ge12 and C40Ge20. Three kinds of theoretical tools are employed: (a) static structural optimization, (b) a bonding analysis based on localized orbitals (Wannier wavefunctions and centers) and (c) first-principles molecular dynamics at finite temperature. This latter tool allows concluding that the segregated form of C40Ge20 is less stable than its Si-based counterpart. However, the non-segregated forms of C40Ge20 and C40Si20 have comparable stabilities at finite temperatures. (C) 2012 Elsevier B. V. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.815
Times cited: 3
DOI: 10.1016/j.cplett.2012.11.033
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“Gold clusters on WO3 nanoneedles grown via AACVD : XPS and TEM studies”. Navío C, Vallejos S, Stoycheva T, Llobet E, Correig X, Snyders R, Blackman C, Umek P, Ke X, Van Tendeloo G, Bittencourt C;, Materials chemistry and physics 134, 809 (2012). http://doi.org/10.1016/j.matchemphys.2012.03.073
Abstract: We have prepared tungsten oxide films decorated with gold particles on Si substrates by aerosol assisted chemical vapor deposition (AACVD) and characterized them using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). SEM shows that the films are composed of needle-like structures and TEM shows that both the needles and the gold particles are crystalline. XPS indicates the presence of oxygen vacancies, i.e. the films are WO3−x, and hence the deposited material is composed of semiconducting nanostructures and that the interaction between the gold particles and the WO3 needles surface is weak. The synthesis of semiconducting tungsten oxide nanostructures decorated with metal particles represents an important step towards the development of sensing devices with optimal properties.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.084
Times cited: 52
DOI: 10.1016/j.matchemphys.2012.03.073
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“Preparation, microstructure characterization and catalytic performance of Cu/ZnO and ZnO/Cu composite nanoparticles for liquid phase methanol synthesis”. Sliem MA, Turner S, Heeskens D, Kalidindi SB, Van Tendeloo G, Muhler M, Fischer RA, Physical chemistry, chemical physics 14, 8170 (2012). http://doi.org/10.1039/c2cp40482f
Abstract: Stearate@Cu/ZnO nanocomposite particles with molar ratios of ZnO ∶ Cu = 2 and 5 are synthesized by reduction of the metalorganic Cu precursor [Cu{(OCH(CH3)CH2N(CH3)2)}2] in the presence of stearate@ZnO nanoparticles. In the case of ZnO ∶ Cu = 5, high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) combined with electron-energy-loss-spectroscopy (EELS) as well as attenuated total reflection Fourier transform infrared (ATR-IR) spectroscopy are used to localize the small amount of Cu deposited on the surface of 35 nm sized stearate@ZnO particles. For ZnO ∶ Cu = 2, the microstructure of the nanocomposites after catalytic activity testing is characterized by HAADF-STEM techniques. This reveals the construction of large Cu nanoparticles (2050 nm) decorated by small ZnO nanoparticles (35 nm). The catalytic activity of both composites for the synthesis of methanol from syn gas is evaluated.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.123
Times cited: 16
DOI: 10.1039/c2cp40482f
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“Study of the interaction between copper and carbon nanotubes”. Bittencourt C, Ke X, Van Tendeloo G, Thiess S, Drube W, Ghijsen J, Ewels CP, Chemical physics letters 535, 80 (2012). http://doi.org/10.1016/j.cplett.2012.03.045
Abstract: Copper deposited by thermal evaporation onto pristine and oxygen plasma treated carbon nanotubes (CNTs) diffuse over the CNT surface, coalescing and forming crystalline islands. The nucleation sites of the islands are preferentially defects, and more homogeneous island dispersion was observed at the CNT oxygen functionalized surface. The presence of weakly bound oxygen atoms at the CNT surface induces the formation of CuO bonds at the Cu/CNT interface, as described through density functional calculations. Exposure to air allows further oxidation to facetted crystalline Cu2O. Oxygen plasma pre-treatment represents a promising route for homogenous disperse Cu2O nanoparticle decoration of CNTs.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.815
Times cited: 27
DOI: 10.1016/j.cplett.2012.03.045
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“The electric field as a novel switch for uptake/release of hydrogen for storage in nitrogen doped graphene”. Ao ZM, Hernández-Nieves AD, Peeters FM, Li S, Physical chemistry, chemical physics 14, 1463 (2012). http://doi.org/10.1039/c1cp23153g
Abstract: Nitrogen-doped graphene was recently synthesized and was reported to be a catalyst for hydrogen dissociative adsorption under a perpendicular applied electric field (F). In this work, the diffusion of H atoms on N-doped graphene, in the presence and absence of an applied perpendicular electric field, is studied using density functional theory. We demonstrate that the applied field can significantly facilitate the binding of hydrogen molecules on N-doped graphene through dissociative adsorption and diffusion on the surface. By removing the applied field the absorbed H atoms can be released efficiently. Our theoretical calculation indicates that N-doped graphene is a promising hydrogen storage material with reversible hydrogen adsorption/desorption where the applied electric field can act as a switch for the uptake/release processes.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 4.123
Times cited: 67
DOI: 10.1039/c1cp23153g
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“Thermal behavior of Si-doped fullerenes vs their structural stability at T = 0 K : a density functional study”. Scipioni R, Matsubara M, Ruiz E, Massobrio C, Boero M, Chemical physics letters 510, 14 (2011). http://doi.org/10.1016/j.cplett.2011.05.019
Abstract: We establish the topological conditions underlying the thermal stability of C30Si30 clusters. Two topologies have been considered: a segregated one, where Si and C atoms lie on neighboring and yet, separated parts of the cage, and a non-segregated one, where the number of SiC bonds is maximized. The segregated network is energetically favored against the non-segregated one, both structures being fully relaxed at T = 0 K. Conversely, the non-segregated structure is the only one stable at finite temperatures, regardless of the nature of the local states (d or p) included in the KleynmanBylander construction.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.815
Times cited: 14
DOI: 10.1016/j.cplett.2011.05.019
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“Unexpected optical response of single ZnO nanowires probed using controllable electrical contacts”. Zeng YI, Menghini M, Li DY, Lin SS, Ye ZZ, Hadermann J, Moorkens T, Seo JW, Locquet J-P, van Haesendonck C, Physical chemistry, chemical physics 13, 6931 (2011). http://doi.org/10.1039/c1cp00012h
Abstract: Relying on combined electron-beam lithography and lift-off methods Au/Ti bilayer electrical contacts were attached to individual ZnO nanowires (NWs) that were grown by a vapor phase deposition method. Reliable Schottky-type as well as ohmic contacts were obtained depending on whether or not an ion milling process was used. The response of the ZnO NWs to ultraviolet light was found to be sensitive to the type of contacts. The intrinsic electronic properties of the ZnO NWs were studied in a field-effect transistor configuration. The transfer characteristics, including gate threshold voltage, hysteresis and operational mode, were demonstrated to unexpectedly respond to visible light. The origin of this effect could be accounted for by the presence of point defects in the ZnO NWs.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.123
Times cited: 7
DOI: 10.1039/c1cp00012h
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“Modelling of synchrotron SAXS patterns of silicalite-1 zeolite during crystallization”. Aerts A, Follens LRA, Biermans E, Bals S, Van Tendeloo G, Loppinet B, Kirschhock CEA, Martens JA, Physical chemistry, chemical physics 13, 4318 (2011). http://doi.org/10.1039/c0cp01592j
Abstract: Synchrotron small angle X-ray scattering (SAXS) was used to characterize silicalite-1 zeolite crystallization from TEOS/TPAOH/water clear sol. SAXS patterns were recorded over a broad range of length scales, enabling the simultaneous monitoring of nanoparticles and crystals occurring at various stages of the synthesis. A simple two-population model accurately described the patterns. Nanoparticles were modeled by polydisperse coreshell spheres and crystals by monodisperse oblate ellipsoids. These models were consistent with TEM images. The SAXS results, in conjunction with in situ light scattering, showed that nucleation of crystals occurred in a short period of time. Crystals were uniform in size and shape and became increasingly anisotropic during growth. In the presence of nanoparticles, crystal growth was fast. During crystal growth, the number of nanoparticles decreased gradually but their size was constant. These observations suggested that the nanoparticles were growth units in an aggregative crystal growth mechanism. Crystals grown in the presence of nanoparticles developed a faceted habit and intergrowths. In the final stages of growth, nanoparticles were depleted. Concurrently, the crystal growth rate decreased significantly.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.123
Times cited: 22
DOI: 10.1039/c0cp01592j
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“Preparation and structural characterization of SnO2 and GeO2 methanol steam reforming thin film model catalysts by (HR)TEM”. Lorenz H, Zhao Q, Turner S, Lebedev OI, Van Tendeloo G, Klötzer B, Rameshan C, Penner S, Materials chemistry and physics 122, 623 (2010). http://doi.org/10.1016/j.matchemphys.2010.03.057
Abstract: Structure, morphology and composition of different tin oxide and germanium oxide thin film catalysts for the methanol steam reforming (MSR) reaction have been studied by a combination of (high-resolution) transmission electron microscopy, selected area electron diffraction, dark-field imaging and electron energy-loss spectroscopy. Deposition of the thin films on NaCl(0 0 1) cleavage faces has been carried out by thermal evaporation of the respective SnO2 and GeO2 powders in varying oxygen partial pressures and at different substrate temperatures. Preparation of tin oxide films in high oxygen pressures (10−1 Pa) exclusively resulted in SnO phases, at and above 473 K substrate temperature epitaxial growth of SnO on NaCl(0 0 1) leads to well-ordered films. For lower oxygen partial pressures (10−3 to 10−2 Pa), mixtures of SnO and β-Sn are obtained. Well-ordered SnO2 films, as verified by electron diffraction patterns and energy-loss spectra, are only obtained after post-oxidation of SnO films at temperatures T ≥ 673 K in 105 Pa O2. Preparation of GeOx films inevitably results in amorphous films with a composition close to GeO2, which cannot be crystallized by annealing treatments in oxygen or hydrogen at temperatures comparable to SnO/SnO2. Similarities and differences to neighbouring oxides relevant for selective MSR in the third group of the periodic system (In2O3 and Ga2O3) are also discussed with the aim of cross-correlation in formation of nanomaterials, and ultimately, also catalytic properties.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 2.084
Times cited: 15
DOI: 10.1016/j.matchemphys.2010.03.057
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“Bond switching regimes in nickel and nickel-carbon nanoclusters”. Neyts E, Shibuta Y, Bogaerts A, Chemical physics letters 488, 202 (2010). http://doi.org/10.1016/j.cplett.2010.02.024
Abstract: Understanding the fundamental dynamics in carbon nanotube (CNT) catalysts is of primary importance to understand CNT nucleation. This Letter reports on calculated bond switching (BS) rates in pure and carbon containing nickel nanoclusters. The rates are analyzed in terms of their temperature dependent spatial distribution and the mobility of the cluster atoms. The BS mechanism is found to change from vibrational to diffusional at around 900 K, with a corresponding strong increase in activation energy. Furthermore, the BS activation energy is observed to decrease as the carbon content in the cluster increases, resulting in an effective liquification of the cluster.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 1.815
Times cited: 20
DOI: 10.1016/j.cplett.2010.02.024
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“Molecular dynamics simulation of oxide thin film growth: importance of the inter-atomic interaction potential”. Georgieva V, Todorov IT, Bogaerts A, Chemical physics letters 485, 315 (2010). http://doi.org/10.1016/j.cplett.2009.12.067
Abstract: A molecular dynamics (MD) study of MgxAlyOz thin films grown by magnetron sputtering is presented using an ionic model and comparing two potential sets with formal and partial charges. The applicability of the model and the reliability of the potential sets for the simulation of thin film growth are discussed. The formal charge potential set was found to reproduce the thin film structure in close agreement with the structure of the experimentally grown thin films. Graphical abstract A molecular dynamics study of growth of MgxAlyOz thin films is presented using an ionic model and comparing two potential sets with formal and partial charges. The simulation results with the formal charge potential set showed a transition in the film from a crystalline to an amorphous structure, when the Mg metal content decreases below 50% in very close agreement with the structure of the experimentally deposited films.
Keywords: A1 Journal article; Plasma Lab for Applications in Sustainability and Medicine – Antwerp (PLASMANT)
Impact Factor: 1.815
Times cited: 16
DOI: 10.1016/j.cplett.2009.12.067
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“Orientational ordering in solid C60 fullerene-cubane”. Verberck B, Vliegenthart GA, Gompper G, The journal of chemical physics 130, 154510 (2009). http://doi.org/10.1063/1.3098550
Abstract: We study the structure and phase behavior of fullerene-cubane C60·C8H8 by Monte Carlo simulation. Using a simple potential model capturing the icosahedral and cubic symmetries of its molecular constituents, we reproduce the experimentally observed phase transition from a cubic to an orthorhombic crystal lattice and the accompanying rotational freezing of the C60 molecules. We elaborate a scheme to identify the low-temperature orientations of individual molecules and to detect a pattern of orientational ordering similar to the arrangement of C60 molecules in solid C60. Our configuration of orientations supports a doubled periodicity along one of the crystal axes.
Keywords: A1 Journal article; Condensed Matter Theory (CMT)
Impact Factor: 2.965
Times cited: 8
DOI: 10.1063/1.3098550
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“Platinumcarbon nanotube interaction”. Bittencourt C, Hecq M, Felten A, Pireaux JJ, Ghijsen J, Felicissimo MP, Rudolf P, Drube W, Ke X, Van Tendeloo G, Chemical physics letters 462, 260 (2008). http://doi.org/10.1016/j.cplett.2008.07.082
Abstract: The interaction between evaporated Pt and pristine or oxygen-plasma-treated multiwall carbon nanotubes (CNTs) is investigated. Pt is found to nucleate at defect sites, whether initially present or introduced by oxygen plasma treatment. The plasma treatment induces a uniform dispersion of Pt nanoparticles at the CNT surface. The absence of additional features in the C 1s core level spectrum indicates that no mixed PtC phase is formed. The formation of COPt bonds at the cluster-CNT interface is suggested to reduce the electronic interaction between Pt nanoparticles and the CNT surface.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.815
Times cited: 62
DOI: 10.1016/j.cplett.2008.07.082
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“Silica-supported chromium oxide: colloids as building blocks”. Hermans I, Breynaert E, Poelman H, de Gryse R, Liang D, Van Tendeloo G, Maes A, Peeters J, Jacobs P, Physical chemistry, chemical physics 9, 5382 (2007). http://doi.org/10.1039/b706601e
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 4.123
Times cited: 8
DOI: 10.1039/b706601e
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