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  • 1.
    Atumi, M.K.
    et al.
    Newcastle University.
    Goss, J.P.
    Newcastle University.
    Briddon, P.R.
    Newcastle University.
    Shirf, F.E.
    Newcastle University.
    Rayson, Mark
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Hyperfine interactions at nitrogen interstitial defects in diamond2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 6Article in journal (Refereed)
    Abstract [en]

    Diamond has many extreme physical properties and it can be used in a wide range of applications. In particular it is a highly effective particle detection material, where radiation damage is an important consideration. The WAR9 and WAR10 are electron paramagnetic resonance centres seen in irradiated, nitrogen-containing diamond. These S = 1/2 defects have C2v and C1h symmetry, respectively, and the experimental spectra have been interpreted as arising from nitrogen split-interstitial centres. Based upon the experimental and theoretical understanding of interstitial nitrogen defect structures, the AIMPRO density functional code has been used to assess the assignments for the structures of WAR9 and WAR10. Although the calculated hyperfine interaction tensors are consistent with the measured values for WAR9, the thermal stability renders the assignment problematic. The model for the WAR10 centre yields principal directions of the hyperfine tensor at variance with observation. Alternative models for both centres are discussed in this paper, but no convincing structures have been found.

  • 2.
    Blumenau, A.T.
    et al.
    University of Exeter.
    Elsner, J.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Heggie, M.I.
    University of Sussex.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Frauenheim, T.
    Universität Paderborn.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Dislocations in hexagonal and cubic GaN2000In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, p. 10223-10233Article in journal (Refereed)
    Abstract [en]

    The structure and electronic activity of several types of dislocations in both hexagonal and cubic GaN are calculated using first-principles methods. Most of the stoichiometric dislocations investigated in hexagonal GaN do not induce deep acceptor states and thus cannot be responsible for the yellow luminescence. However, it is shown that electrically active point defects, in particular gallium vacancies and oxygen-related defect complexes, can be trapped at the stress field of the dislocations and may be responsible for this luminescence. For cubic GaN, we find the ideal stoichiometric 60° dislocation to be electrically active and the glide set to be more stable than the shuffle. The dissociation of the latter is considered

  • 3.
    Blumenau, A.T.
    et al.
    Theoretische Physik, Universität Paderborn.
    Fall, C.J.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Heggie, M.I.
    CPES, University of Sussex, Falmer, Brighton.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Frauenheim, T.
    Theoretische Physik, Universität Paderborn.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Straight and kinked 90° partial dislocations in diamond and 3C-SiC2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 48, p. 12741-12747Article in journal (Refereed)
    Abstract [en]

    Density-functional based calculations are used to investigate low energy core structures of 90° partial dislocations in diamond and 3C-SiC. In both materials dislocation glide is analysed in terms of kink formation and migration and the fundamental steps to kink migration are investigated. We find the C terminated core structure in SiC to be more mobile than the Si core. However, the Si partial is electrically active and this opens the possibility of recombination-enhanced glide under ionizing conditions or an enhanced mobility in doped material.

  • 4.
    Blumenau, A.T.
    et al.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Frauenheim, T.
    Universität Paderborn.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Optical bands related to dislocations in Si2000In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, p. 10123-10129Article in journal (Refereed)
    Abstract [en]

    First-principles calculations are used to investigate the interaction of self-interstitial aggregates with the 90° partial dislocation in Si. We find that I4 is bound to the line with an energy of around 3 eV. The defect causes deep levels to appear in the band gap and optical transitions between these levels may account for the luminescent bands relating to plastically deformed Si.

  • 5.
    Carvalho, A.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Janke, C.
    School of Physics, University of Exeter.
    Goss, J.P.
    School of Natural Science, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    First-principles study of the diffusion mechanisms of the self-interstitial in germanium2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 13Article in journal (Refereed)
    Abstract [en]

    The self-interstitial in germanium can assume multiple configurations depending on the temperature and charge state. Here, we employ a first-principles density functional method to investigate the diffusion mechanisms of this defect. The energy barriers associated with the transformation between different structures are determined by the climbing nudged elastic band method, as a function of the charge state. The relation between the thermodynamic properties of the self-interstitial and the temperature evolution of electron radiation damage in germanium are discussed.

  • 6. Cataudella, Vittorio
    et al.
    Minnhagen, Petter
    Weber, Hans
    Renormalisation equations for the two-dimensional Coulomb gas: inclusion of the single-particle charge distribution and comparison with Monte Carlo simulations1990In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 2, p. 2345-2354Article in journal (Refereed)
    Abstract [en]

    A set of self-consistent equations for the high-temperature phase of the two-dimensional Coulomb gas is solved numerically. These equations explicitly include the charge distribution of a single particle. Comparisons are made with Monte Carlo simulations as well as with the 'point-charge'-limit of the equations. The results are discussed in the context of type II superconducting films

  • 7. Chen, W.
    et al.
    Paul, Jan
    Barbieri, A.
    Hove, M.A. van
    Cameron, S.
    Structure determination of Pt3Ti(111) by automated tensor LEED1993In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 5, p. 4585-4594Article in journal (Refereed)
    Abstract [en]

    An analysis of low-energy electron diffraction (LEED) I-V spectra from the clean Pt3Ti(111) surface was performed by comparing measured intensities with data calculated using an automated tensor LEED program, which employs a directed search optimization procedure. It was found that the topmost layer is pure Pt and that the other layers have the bulk composition. The first and second interlayer spacings are 2.23+or-0.03 AA and 2.21+or-0.03 AA respectively, corresponding to a contraction of 0.9% and 1.8% of the bulk value. The perpendicular buckling is 0.04 AA +or-0.05 AA in the top layer and 0.15 AA +or-0.04 AA in the second layer. The results are in full accordance with previous investigations of the physical and chemical properties of this surface.

  • 8.
    Coomer, B.J.
    et al.
    School of Physics, University of Exeter.
    Goss, J.P.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Identification of the tetra-interstitial in silicon2001In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 13, no 1, p. L1-L7Article in journal (Refereed)
    Abstract [en]

    First-principles computational methods are employed to investigate the structural, vibrational, optical and electronic properties of the self-interstitial aggregate, I4 in silicon. We find the defect to be electrically active and identify it with the B3 EPR centre. We also show that its properties are consistent with DLTS and optical spectra observed following implantation of silicon.

  • 9.
    Coutinho, J.
    et al.
    Department of Physics, University of Aveiro, Campus Santiago.
    Jones, R.
    School of Physics, University of Exeter.
    Torres, V.J.B.
    Department of Physics, University of Aveiro, Campus Santiago.
    Barroso, M.
    Department of Physics, University of Aveiro, Campus Santiago.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Electronic structure and Jahn-Teller instabilities in a single vacancy in Ge2005In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, no 48, p. L521-L527Article in journal (Refereed)
    Abstract [en]

    Density functional modelling studies of the single vacancy in large Ge clusters are presented. We take a careful look at the origin of Jahn-Teller instabilities as a function of the vacancy net charge, resulting in a variety of structural relaxations. By comparing electron affinities of the vacancy with those from defects with well established gap states, we were able to estimate three acceptor states for the vacancy at E(-/0) ≤ Ev+0.2 eV, E(≤/-) ≤ Ec-0.5 eV and eV. As opposed to the Si vacancy, the defect in Ge is not a donor. We also show that these dissimilarities have fundamental consequences for the electronic/atomic picture of other centres, such as transition metals in germanium crystals.

  • 10.
    Coutinho, J.
    et al.
    Department of Physics, University of Aveiro.
    Torres, V.J.B.
    Department of Physics, University of Aveiro.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Electronic structure of divacancy-hydrogen complexes in silicon2003In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 15, no 39, p. S2809-S2814Article in journal (Refereed)
    Abstract [en]

    Divacancy-hydrogen complexes (V2H and V2H2) in Si are studied by ab initio modelling using large supercells. Here we pay special attention to their electronic structure, showing that these defects produce deep carrier traps. Calculated electrical gap levels indicate that V2H2 is an acceptor, whereas V2H is amphoteric, with levels close to those of the well known divacancy. Finally our results are compared with the available data from deep level transient spectroscopy and electron paramagnetic resonance experiments.

  • 11.
    Etz, Corina
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Uppsala universitet.
    Bergqvist, Lars
    KTH, Royal Institute of Technology, Department of Materials and Nano Physics.
    Bergman, Anders
    Department of Physics and Astronomy, Uppsala University.
    Taroni, Andrea
    Department of Physics and Astronomy, Uppsala University.
    Bergman, Olle
    Department of Physics and Astronomy, Uppsala University.
    Atomistic spin dynamics and surface magnons2015In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 24, article id 243202Article in journal (Refereed)
    Abstract [en]

    Atomistic spin dynamics simulations have evolved to become a powerful and versatile tool for simulating dynamic properties of magnetic materials. It has a wide range of applications, for instance switching of magnetic states in bulk and nano-magnets, dynamics of topological magnets, such as skyrmions and vortices and domain wall motion. In this review, after a brief summary of the existing investigation tools for the study of magnons, we focus on calculations of spin-wave excitations in low-dimensional magnets and the effect of relativistic and temperature effects in such structures. In general, we find a good agreement between our results and the experimental values. For material specific studies, the atomistic spin dynamics is combined with electronic structure calculations within the density functional theory from which the required parameters are calculated, such as magnetic exchange interactions, magnetocrystalline anisotropy, and Dzyaloshinskii-Moriya vectors

  • 12.
    Goss, J.P.
    et al.
    School of Natural Science, University of Newcastle upon Tyne.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    The lattice location of Ni in diamond: a theoretical study2004In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 16, no 25, p. 4567-4578Article in journal (Refereed)
    Abstract [en]

    Experiment unambiguously shows substitutional nickel is present in as-grown synthetic diamond where Ni is present in the solvent-catalyst. There is less convincing evidence for the presence of an interstitial species. We present the results of first-principles calculations of the properties of substitutional and interstitial Ni in diamond. The formation energy and mobility of the interstitial species suggest that nickel will be predominantly of the substitutional form. We also present possible models for the trigonal 1.404 eV optical centre correlated with the NIRIM-2 paramagnetic defect.

  • 13.
    Goss, J.P.
    et al.
    University of Exeter.
    Coomer, B.J.
    University of Exeter.
    Jones, R.
    University of Exeter.
    Fall, C.J.
    University of Exeter.
    Latham, Chris
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    University of Newcastle Upon Tyne.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Small aggregates of interstitials and models for platelets in diamond2000In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 12, no 49, p. 10257-10261Article in journal (Refereed)
    Abstract [en]

    By examining the structure of small clusters of self-interstitials in diamond using local-density-functional techniques, we have developed models for the planar defects called platelets. We present the structures, energies and vibrational properties

  • 14.
    Goss, J.P.
    et al.
    School of Physics, University of Exeter.
    Eberlein, T.A.G.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Pinho, N.
    School of Physics, University of Exeter.
    Blumenau, A.T.
    Theoretische Physik, Universität Paderborn.
    Frauenheim, T.
    Theoretische Physik, Universität Paderborn.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Planar interstitial aggregates in Si2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 48, p. 12843-12853Article in journal (Refereed)
    Abstract [en]

    Self-interstitials in silicon aggregate to form rod-like defects aligned along [110] directions and inhabiting either {111} or {113} crystallographic planes. These systems are known to be electrically and optically active. We present the results of first-principles calculations on the structure and energetics for candidate structures contained within the {113}, {111} and {001} planes and compare the results with experiment.

  • 15.
    Hourahine, B.
    et al.
    Department of Physics, Universität Paderborn.
    Jones, R.
    School of Physics, University of Exeter.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Frauenheim, T.
    Department of Physics, Universität Paderborn.
    Germanium-hydrogen pairs in silicon2003In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 15, no 39, p. S2803-S2807Article in journal (Refereed)
    Abstract [en]

    Hydrogen in a dilute SiGe alloy is considered theoretically in comparison with hydrogen in Si and Ge. Structural, vibrational and electronic properties of crystalline alloys containing ~1.6 at.% Ge complexed with single hydrogen atoms are considered. The behaviour of bond-centred hydrogen is found to be weakly perturbed, when compared to hydrogen in pure Si.

  • 16.
    Iwata, H.
    et al.
    Department of Physics and Measurement Technology, Linköping University.
    Lindefelt, U.
    Department of Physics and Measurement Technology, Linköping University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Theoretical study of planar defects in silicon carbide2002In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, no 48, p. 12733-12740Article in journal (Refereed)
    Abstract [en]

    We report on a theoretical investigation of extended planar defects in 3C-, 4H-, 6H-, and 15R-SiC which can be formed without breaking any bonds, covering a wide range of planar defects: twin boundaries, stacking faults, and polytype inclusions. Their electronic structures have been intensively studied using an ab initio supercell approach based on the density functional theory. Stacking fault energies are also calculated using both the supercell method and the axial next-nearest-neighbour Ising model. We discuss the electronic properties and energies of these defects in terms of the geometrical differences of stacking patterns.

  • 17.
    Koumpouras, Konstantinos
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Yudin, Dmitry
    Sankt Peterburgskij nacional'nyj issledovatel'skij universitet informacionnyh tehnologij mehaniki i optiki.
    Adelmann, Christoph
    IMEC, Heverlee, Vlaams .
    Bergman, Anders
    Uppsala University.
    Eriksson, Olle
    Uppsala University.
    Pereiro, Manuel
    Department of Physics and Astronomy, Uppsala Universitet.
    A majority gate with chiral magnetic solitons2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 37, article id 375801Article in journal (Refereed)
    Abstract [en]

    In magnetic materials, nontrivial spin textures may emerge due to the competition among different types of magnetic interactions. Among such spin textures, chiral magnetic solitons represent topologically protected spin configurations with particle-like properties. Based on atomistic spin dynamics simulations, we demonstrate that these chiral magnetic solitons are ideal to use for logical operations, and we demonstrate the functionality of a three-input majority gate, in which the input states can be controlled by applying an external electromagnetic field or spin-polarized currents. One of the main advantages of the proposed device is that the input and output signals are encoded in the chirality of solitons, that may be moved, allowing to perform logical operations using only minute electric currents. As an example we illustrate how the three input majority gate can be used to perform logical relations, such as Boolean AND and OR.

  • 18. Latham, Chris
    et al.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, P.R.
    School of Natural Science, University of Newcastle upon Tyne.
    Louchet, F.
    LGGE, Saint Martin d'Hères.
    A pseudopotential density functional theory study of native defects and boron impurities in FeAl2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 39, p. 8859-8876Article in journal (Refereed)
    Abstract [en]

    The structures and energies of point defects and point defect complexes in B 2 iron aluminium FeAl are calculated using a local density functional theory based method with large supercells. Particular emphasis is given to pseudopotential quality, choice of chemical potentials used to calculate defect formation energies, and how these are affected by magnetism. Both purely native defects and those containing boron atoms are considered. It is found that the relative stabilities of isolated point defects versus defect complexes depends on whether the material contains excess iron or aluminium. The situation in material containing boron is further complicated by the existence of iron borides in more than one form. We propose that the interaction between point defects, dislocations, and antiphase boundaries, where the local atomic environment has some similarities with antisite defects, also depends on the alloy composition. It is likely that these interactions are part of the underlying mechanism responsible for the unusual mechanical properties of iron aluminides.

  • 19.
    Latham, Christopher D.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Heggie, Malcolm I.
    University of Surrey.
    Alatalo, Matti
    Lappeenranta University of Technology.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, Patrick R.
    University of Newcastle Upon Tyne.
    The contribution made by lattice vacancies to the Wigner effect in radiation-damaged graphite2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 13, article id 135403Article in journal (Refereed)
    Abstract [en]

    Models for radiation damage in graphite are reviewed and compared, leading to a re-examination of the contribution made by vacancies to annealing processes. A method based on density functional theory, using large supercells with orthorhombic and hexagonal symmetry, is employed to calculate properties and behaviour of lattice vacancies and displacement defects. It is concluded that annihilation of intimate Frenkel defects marks the onset of recovery in electrical resistivity, which occurs when the temperature exceeds about 160 K. Migration of isolated monovacancies is estimated to have an activation energy Ea ≈ 1.1 eV. Coalescence into divacancy defects occurs in several stages, with different barriers at each stage, depending on the path. The formation of pairs ultimately yields up to 8.9 eV energy, which is nearly 1.0 eV more than the formation energy for an isolated monovacancy. Processes resulting in vacancy coalescence and annihilation appear to be responsible for the main Wigner energy release peak in radiation-damaged graphite, occurring at about 475 K.

  • 20. Mofidi, Mohammad
    et al.
    Prakash, Braham
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Persson, B.N.J.
    IFF, Jülich.
    Albohr, O.
    Pirelli Deutschland AG, Höchst/Odenwald.
    Rubber friction on (apparently) smooth lubricated surfaces2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 8Article in journal (Refereed)
    Abstract [en]

    We study rubber sliding friction on hard lubricated surfaces. We show that even if the hard surface appears smooth to the naked eye, it may exhibit short-wavelength roughness, which may make the dominant contribution to rubber friction. That is, the observed sliding friction is mainly due to the viscoelastic deformations of the rubber by the counterface surface asperities. The results presented are of great importance for rubber sealing and other rubber applications involving ( apparently) smooth surfaces.

  • 21.
    Pinho, N.M.C.
    et al.
    Department of Physics, University of Aveiro.
    Torres, V.J.B.
    Department of Physics, University of Aveiro.
    Jones, R.
    School of Physics, University of Exeter.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Mg-H and Be-H complexes in cubic boron nitride2001In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 13, no 40, p. 8951-8956Article in journal (Refereed)
    Abstract [en]

    Ab initio calculations on hydrogen complexes with Mg and Be impurities in c-BN are reported. We find that both impurities are acceptors and both bind H to form passive defects. However, their structures are different. For Be-H, the H atom lies at a puckered bond-centre configuration similar to that of C-H in GaAs, while in Mg-H, the H atom lies at a site anti-bonding to a N neighbour of the impurity. The hydrogen-related vibrational modes of the two complexes are also reported.

  • 22.
    Pinto, H.
    et al.
    COMP, Department of Applied Physics, Aalto University.
    Haapasilta, Ville
    COMP, Department of Applied Physics, Aalto University.
    Lokhandwala, M.
    COMP, Department of Applied Physics, Aalto University.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Foster, Adam S.
    COMP, Department of Applied Physics, Aalto University.
    Adsorption and migration of single metal atoms on the calcite (10.4) surface2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 13, article id 135001Article in journal (Refereed)
    Abstract [en]

    Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3d (Ti, Cr, Fe, Ni, Cu), 4d (Zr, Nb, Mo, Pd, Ag) and 5d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating calcite (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca–Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the calcite surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the calcite surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the calcite surface.

  • 23.
    Sque, S.J.
    et al.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Goss, J.P.
    Physics Centre, School of Natural Sciences, University of Newcastle upon Tyne.
    Briddon, P.R.
    Physics Centre, School of Natural Sciences, University of Newcastle upon Tyne.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    First-principles study of C60 and C60F36 as transfer dopants for p-type diamond2005In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, no 2, p. L21-L26Article in journal (Refereed)
    Abstract [en]

    Ab initio density-functional-theory has been used to investigate transfer doping between C60 monolayers and the hydrogenated (100) diamond surface. An electron transfer from diamond to C60 is predicted for a C60 coverage of around one monolayer, and the possibility of electron transfer is expected to increase for higher coverages, leading to an accumulation of holes at the diamond surface. It has been found that the greater electron affinity of fluorinated C60 is likely to enhance the effect. Results are reported on the structural and electronic properties of isolated C60 and C60F36 molecules, solid C60, and a monolayer of each material adjacent to the (100)-(2 × 1):H diamond surface.

  • 24.
    Stoeffler, Daniel C.A.
    et al.
    Institut de Physique et de Chimie des Matériaux de Strasbourg.
    Etz, Corina
    Institut de Physique et de Chimie des Matériaux de Strasbourg.
    Ab initio electronic structure and magnetism in Sr2XMoO 6 (X ≤ Fe or Co) double perovskite systems: A GGA and GGA+U comparative study2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 49, p. 11291-11300, article id 20Article in journal (Refereed)
    Abstract [en]

    Using the full potential linearized augmented plane wave ab initio method, we investigate bulk magnetic properties of Sr2XMoO6 (X ≤ Fe, Co) double perovskites by comparing the results obtained with the generalized gradient approximation (GGA) and GGA+U methods in order to discuss their magnetic configuration in relation with the experiments. We show that both methods lead to significantly different results and that a good agreement with experimental results - antiferromagnetic insulator for X ≤ Co - can be obtained only when the GGA+U method is used. For X ≤ Fe, we exhibit the role played by oxygen vacancies in the stabilization of a negative magnetic moment on the Fe antisite with preserved half-metallicity. We show that such a negative moment can be obtained only when an oxygen vacancy occurs in the direct neighbourhood of the Fe antisite with the GGA+U method

  • 25.
    Wagner, Philipp
    et al.
    Université de Nantes.
    Ivanovskaya, Viktoria V
    Université de Nantes.
    Rayson, Mark
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Briddon, Patrick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Ewels, Christopher P
    Université de Nantes.
    Mechanical properties of nanosheets and nanotubes investigated using a new geometry independent volume definition2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 15, p. 155302-Article in journal (Refereed)
    Abstract [en]

    Cross-sectional area and volume become difficult to define as material dimensions approach the atomic scale. This limits the transferability of macroscopic concepts such as Young's modulus. We propose a new volume definition where the enclosed nanosheet or nanotube average electron density matches that of the parent layered bulk material. We calculate the Young's moduli for various nanosheets (including graphene, BN and MoS2) and nanotubes. Further implications of this new volume definition such as a Fermi level dependent Young's modulus and out-of-plane Poisson's ratio are shown.

  • 26.
    Wright, E.
    et al.
    Department of Physics and I3N, University of Aveiro, Campus Santiago.
    Coutinho, J.
    Department of Physics and I3N, University of Aveiro, Campus Santiago.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Torres, V.J.B.
    Department of Physics and I3N, University of Aveiro, Campus Santiago.
    A first-principles model of copper-boron interactions in Si: for the light-induced degradation of solar Si2017In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 6, article id 065701Article in journal (Refereed)
    Abstract [en]

    The recent discovery that Cu contamination of Si combined with light exposure has a significant detrimental impact on carrier life-time has drawn much concern within the solar-Si community. The effect, known as the copper-related light-induced degradation (Cu-LID) of Si solar cells, has been connected to the release of Cu interstitials within the bulk (2016 Sol. Energy Mater. Sol. Cells 147 115-26). In this paper, we describe a comprehensive analysis of the formation/dissociation process of the CuB pair in Si by means of first-principles modelling, as well as the interaction of CuB defects with photo-excited minority carriers. We confirm that the long-range interaction between the Cu-i(+) cation and the B-s(-) anion has a Coulomb-like behaviour, in line with the trapping-limited diffusivity of Cu observed by transient ion drift measurements. On the other hand, the short-range interaction between the d-electrons of Cu and the excess of negative charge on B-s(-) produces a repulsive effect, thereby decreasing the binding energy of the pair when compared to the ideal point-charge Coulomb model. We also find that metastable CuB pairs produce acceptor states just below the conduction band minimum, which arise from the Cu level emptied by the B acceptor. Based on these results, we argue that photo-generated minority carriers trapped by the metastable pairs can switch off the Coulomb interaction that holds the pairs together, enhancing the release of Cu interstitials, and acting as a catalyst for Cu-LID.

1 - 26 of 26
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