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  • 1.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Larsson, J. Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Communication: Origin of the difference between carbon nanotube armchair and zigzag ends2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 9, p. 091102-Article in journal (Refereed)
    Abstract [en]

    In this work, we have found that the difference between armchair and zigzag ends of carbon nanotubes (CNTs) does not pertain at close study for individual bonds and thus alternative strategies need to be developed to reach the ultimate goals in selective growth. Based on first-principles simulations, the difference between binding strengths for CNTs of different chirality was investigated using hydrogen dissociation energies at their passivated ends. When all H atoms are removed collectively we find the well-known difference: that armchair bonds are much weaker than zigzag ones, which is typically seen for both CNT ends and graphene edges. However, when individual H atoms are removed we find almost no difference in hydrogen dissociation energies, small difference in bond lengths, which by association means small difference in C-C and M-C binding energies. We show convincingly that the difference in binding energy between armchair and zigzag ends is due to a fragment stabilization effect that is only manifested when all (or several neighbouring) bonds are broken. This is because at armchair ends/edges neighbouring dangling bonds can pair-up to form C C triple bonds that constitute a considerable stabilization effect compared to the isolated dangling bonds at zigzag ends/edges. Consequently, in many processes, e. g., catalytic growth where bonds are normally created/broken sequentially, not collectively, the difference between armchair and zigzag ends/edges cannot be used to discriminate growth of one type over the other to achieve chiral selective growth. Strategies are discussed to realize chirality selective growth in the light of the results presented, including addition of C-2-fragments to favor armchair tubes. (C) 2014 AIP Publishing LLC.

  • 2.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, Tanveer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sarkar, Abir De
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hydrogen storage in polylithiated BC3 monolayer sheet2013In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 170, p. 39-43Article in journal (Refereed)
    Abstract [en]

    We perform a detailed study on the stability, electronic structure and hydrogen storage capacity of polylithiated (CLi3 functionalized) boron carbide (BC3) monolayer sheet using first-principles calculations. The binding of the CLi3 radical to the boron carbide (BC3) monolayer sheet is found to be large enough to ensure its uniform distribution without any clustering. The structural stability has been confirmed by molecular dynamics. Each lithium atom is able to accommodate 4 H2 molecules with an average binding energy of 0.21 eV, which is suitable for reversible H2 adsorption/desorption at ambient temperatures. The uptake of H2 is found to reach up to 9.83 wt% in polylithiated BC3 monolayer sheet.

  • 3.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Yan-Ling
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Single-layer MoS2 as an efficient photocatalyst2013In: Catalysis Science & Technology, ISSN 2044-4753, Vol. 3, no 9, p. 2214-2220Article in journal (Refereed)
    Abstract [en]

    The potential application of the single-layer MoS2 as a photocatalyst was revealed based on first-principles calculations. It is found that the pristine single-layer MoS2 is a good candidate for hydrogen production, and its catalysing ability can be tuned by the applied mechanical strain. Furthermore, the p-type doping could make the single layer a good photocatalyst for the overall water splitting.

  • 4.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Yan-Ling
    Sun, Weiwei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dynamic stability of the single-layer transition metal dichalcogenides2014In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 92, p. 206-212Article in journal (Refereed)
    Abstract [en]

    In the quest for advanced semi-conductors, we have expanded our knowledge on a series of single-layer TMDs by calculating the electronic structure and lattice dynamic stability based on the first-principles density functional theory. The single layers of Mo and W dichalcogenides are found to be stable with P-6m2 symmetry. The reduction of dimension opens up and increases the bandgap. The charge transfer is found to decrease from sulfide to selenide and to telluride due to the decrease of electronegativity of chalcogen, which also induces the reduction of bandgap. The TA mode softening is found along Gamma-K direction and becomes more significant from sulfide to selenide and to telluride in the single-layer TMDs of Mo and W, which corresponds to the vibration of transition metal cations along y-axis. The single layers of Nb dichalcogenides are found to be instable with P-6m2 symmetry but stable with P-3m1 symmetry. It is also speculated that the interactions of cations mediated by electron-phonon coupling are accountable for the dynamic instability of the single-layer TMDs of Nb with P-6m2 symmetry. The unstable P-6m2 single-layer Nb dichalcogenides can transform to the stable P-3m1 structure during the exfoliation from the bulk, via the displacement of two anion layers of the sandwich structure.

  • 5.
    Li, Yunguo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Nisar, Jawad
    Qian, Zhao
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Metal-decorated graphene oxide for ammonia adsorption2013In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 103, no 2, p. 28007-Article in journal (Refereed)
    Abstract [en]

    Based on the first-principles density functional theory, we have studied the stability, electronic structure and ammonia storage capacity of metal-decorated graphene oxide (GO). Metal atoms (Mg and Li) are bonded strongly to the epoxy oxygen atoms on the surface of the GO sheet, which can act as high-surface-area adsorbent for the ammonia uptake and release. Each metal atom can bind several ammonia molecules around itself with a reasonable binding energy. We find metal-decorated GO can store up to tens of moles of ammonia per kilogram, which is far better than the recently reported excellent ammonia adsorption by GO.

  • 6.
    Ramzan, Muhammed
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Yunguo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic structure, mechanical and optical properties of In2O3 with hybrid density functional (HSE06)2013In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 172, p. 37-40Article in journal (Refereed)
    Abstract [en]

    In this study, the hybrid densily correlation functional (HSE06) is used to explore the eleclronic structure and optical properties of In2O3, on the basis of density functional theory (DFT). The calculated equilibrium lattice parameters, volume and bulk modulus of this compound, are comparable with the experimental results available in the literature. The bandgap of In2O3 has been a matter of debate in literatures. However, our calculated bandgap can bridge the gap between experiment and theory, and is in good agreement with the available experimental results. Furthermore, we calculate and analyze the optical and mechanical properties of this compound. We hope that our work will help to understand the correct electronic structure and optical properties of this compound.

  • 7.
    Sagynbaeva, Myskal
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Panigrahi, Puspamitra
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Yunguo, Li
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Tweaking the magnetism of MoS2 nanoribbon with hydrogen and carbon passivation2014In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 25, no 16, p. 165703-Article in journal (Refereed)
    Abstract [en]

    Using density functional theory (DFT), we report the modulated electronic and magnetic properties of MoS2 nanoribbon by passivating the ribbon edges with H and C separately. For the modeled symmetric MoS2 nanoribbon with a zig-zag type edge, one side is terminated at Mo and the other side is terminated at S. For the zig-zag type, we have studied two ribbons of width similar to 3 angstrom and 6 angstrom respectively. Both of these pristine zig-zag type nanoribbons are found to be metallic and also ferromagnetic. However, the increase in the ribbon width results in a decrease in the net magnetic moment of the nanoribbon. Thereafter, we study the modulated electronic and magnetic properties of the nanoribbon of similar to 3 angstrom width by saturating the ribbon edges with H and C. In one case, by passivating the zig-zag type ribbon with H at the S terminated edge, we find a net increase in magnetic moment of the ribbon when compared with the pristine one. Furthermore, when the ribbon is passivated with H at both of the edges, the net magnetic moment shows a decreasing trend. In another case, the zig-zag nanoribbon is passivated with C in a similar fashion to H and we find with one edge passivation the net magnetic moment of the ribbon decreases, whereas with both edges C passivated the ribbon magnetism increases significantly. However, the nanoribbon modeled with the armchair type of edge and terminated with Mo at both sides is found to be non-magnetic and semiconducting. Passivating the armchair type nanoribbon with H and C, we find the band gap shows an increasing trend when going from one side to both sides passivation. In all cases, the armchair type nanoribbons show non-magnetic behavior.

  • 8.
    Sun, Weiwei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Li, Yunguo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zhu, Li
    Ma, Yanming
    Di Marco, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Korzhavyi, Pavel
    Gluing together metallic and covalent layers to form Ru2C under ambient conditions2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 15, p. 9730-9736Article in journal (Refereed)
    Abstract [en]

    Ru2C has recently been synthesised at high pressure and high temperature, and was assumed to have a structure with space group P (3) over bar m1. However, subsequent theoretical work has revealed that this structure is unstable under ambient conditions, which motivated us to look for the stable structure. In this work, we explore the structures of Ru2C by using an unbiased swarm structure searching algorithm. The structures with R3m and R (3) over barm symmetries have been found to be lower in energy than the P (3) over bar m1 structure, at the same time being dynamically stable under ambient conditions. These layered structures consist of alternating Ru bilayers and C monolayers in the R3m structure, and alternating Ru tetra-layers and C bilayers in the R (3) over barm structure. The C layers are more evenly distributed and more covalently bound to the Ru layers in the R3m structure than in the R (3) over barm structure. Instead, in the R (3) over barm structure there exists more Ru-Ru metallic bonding, which has a crucial role in diminishing the hardness of this material. Our findings should stimulate further explorations of the structures and properties of the heavy transition metal carbides and nitrides, potentially leading to industrial applications.

1 - 8 of 8
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