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  • 1.
    Björk, Hans
    et al.
    University of Borås, School of Engineering.
    Lindecrantz, Kaj
    University of Borås, School of Engineering.
    Ericsson, Dag
    University of Borås, School of Engineering.
    Sarv, Hans
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Börjesson, Anders
    University of Borås, School of Engineering.
    Bazooyar, Faranak
    University of Borås, School of Engineering.
    Ahlström, Peter
    University of Borås, School of Engineering.
    Taherzadeh, Mohammad
    University of Borås, School of Engineering.
    Andersson, Bengt-Åke
    University of Borås, School of Engineering.
    Johansson, Andreas
    University of Borås, School of Engineering.
    Skrifvars, Mikael
    University of Borås, School of Engineering.
    20 år med Institutionen Ingenjörshögskolan: historik, nuläge och framtid2009Report (Other academic)
  • 2.
    Bolton, Kim
    et al.
    University of Borås, School of Engineering.
    Börjesson, Anders
    University of Borås, School of Engineering.
    Computational studies of single-walled carbon nanotube growth2011In: SNIC Progress Report (2008-2009), p. 40-46Article in journal (Other academic)
    Abstract [en]

    Allocation of time on the Swedish national supercomputing facilities since 2000, as well as support from other sources, has allowed us to perform computational studies on a wide variety of systems. These include properties and growth of carbon nanotubes [1–36], icecatalysed reactions of importance to stratospheric ozone depletion[37], calculations of vapour-liquid, liquid-liquid and vapour-liquid-liquid phase equilibrium of single, binary and ternary component systems[38], and, more recently, carbonaceous polymer nanocomposites and cellulose decomposition. More details of these projects are available at the web page given above.

  • 3.
    Bolton, Kim
    et al.
    University of Borås, School of Engineering.
    Börjesson, Anders
    University of Borås, School of Engineering.
    Ahlström, Peter
    University of Borås, School of Engineering.
    Bazooyar, Faranak
    University of Borås, School of Engineering.
    Beräkningsteknik2009In: Vetenskap för profession, ISSN 1654-6520, no 10, p. 63-68Article in journal (Other academic)
  • 4.
    Bolton, Kim
    et al.
    University of Borås, School of Engineering.
    Börjesson, Anders
    University of Borås, School of Engineering.
    Zhu, Wuming
    Amara, Hakim
    Bichara, Christophe
    Density functional theory and tight binding-based dynamical studies of carbon metal systems of relevance to carbon nanotube growth2009In: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 2, no 10, p. 774-782Article in journal (Refereed)
    Abstract [en]

    Density functional theory (DFT) and tight binding (TB) models have been used to study systems containing single-walled carbon nanotubes (SWNTs) and metal clusters that are of relevance to SWNT growth and regrowth. In particular, TB-based Monte Carlo (TBMC) simulations at 1000 or 1500 K show that Ni atoms that are initially on the surface of the SWNT or that are clustered near the SWNT end diffuse to the nanotube end so that virtually none of the Ni atoms are located inside the nanotube. This occurs, in part, due to the lowering of the Ni atom energies when they retract from the SWNT to the interior of the cluster. Aggregation of the atoms at the SWNT end does not change the chirality within the simulation time, which supports the application of SWNT regrowth (seeded growth) as a potential route for chirality-controlled SWNT production. DFT-based geometry optimisation and direct dynamics at 2000 K show that Cr and Mo atoms in Cr5Co50 and Mo5Co50 clusters prefer to be distributed in the interior of the clusters. Extension of these calculations should deepen our understanding of the role of the various alloy components in SWNT growth.

  • 5.
    Börjesson, A.
    et al.
    University of Borås, School of Engineering.
    Zhu, W.
    Amara, H.
    Bichara, C.
    Ducastelle, F.
    Bolton, Kim
    University of Borås, School of Engineering.
    Theoretical investigation of the Nanotube-metal junction2008Conference paper (Other academic)
  • 6.
    Börjesson, Anders
    University of Borås, School of Engineering.
    Computational Studies of Metal Clusters and Carbon Nanotubes2008Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Carbon nanotubes constitute a promising candidate material in the realisation of nanoscaled electronics. This requires the ability for systematic production of carbon nanotubes with certain properties. This is called selective carbon nanotube growth. Two important aspects related to carbon nanotube growth are investigated in order to shed some light on this issue. First the melting behaviour of nanometer sized iron particles is investigated using molec- ular dynamics simulations. The iron nanoparticles studied are mounted on a porous Al2 O3 substrate in order to mimic the experimental situation during nanotube growth with the chemical vapour deposition method. This showed that the melting temperature of a cluster on a porous substrate may be lower than the melting temperature of a cluster on a flat sub- strate. This means that the catalyst particles used for nanotube growth may be liquid. In association with these studies the role of surface curvature to melting behaviour is explored further. The second presented study concerns the docking of nickel clusters to open single wall carbon nanotube ends. The motivation for this study was the possibility to continue growth of a carbon nanotube by docking of catalyst particles to its end. This work may also be of importance for the creation of electric junctions between carbon nanotubes and metal elec- trodes. This study showed that independent of whether the metal was gently put on the nanotube end or brutally forced to the end, it is the metal that adapts to the nanotube and not vice versa. For forced docking it was seen that carbon might dissolve in to the metal. This was not seen for the gently docked clusters. Carbon dissolution might affect the electronic properties of the metal (carbide) and nanotube-metal junction.

  • 7.
    Börjesson, Anders
    University of Borås, School of Engineering.
    In silico studies of carbon nano tubes and metal clusters2010Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Carbon nanotubes have been envisioned to become a very important material in various applications. This is due to the unique properties of carbon nanotubes which can be exploited in applications on length scales spanning from the nano world to our macroscopic world. For example, the electronic properties of carbon nanotubes makes them utterly suitable for nano electronics while the strength of them makes them suitable for reinforcements in plastics. Both of these applications do however require... mer the ability for systematic production of carbon nanotubes with certain properties. This is called selective carbon nanotube growth and today this has not been achieved with total success. In the work presented in the thesis several different computational methods have been applied in our contribution to the systematic search for selective carbon nanotube growth. Put in a context of previous knowledge about carbon nanotube growth our results provide valuable clues to which parameters that control the carbon nanotube growth. In association with the latest results we even dare to, with all modesty, speculate about a plausible control mechanism. The studies presented in the thesis addressed different stages of carbon nanotube growth, spanning from the properties affecting the initiation of the growth to the parameters affecting the termination of the growth. In some more detail this included studies of the melting temperatures of nanoscaled metal clusters. The expected size dependence of the melting temperatures was confirmed and the melting temperatures of clusters on substrates were seen to depend both on the material and shape of the surface. As this constitute the premises prior to the carbon nanotube growth it was followed by studies of the interaction between carbon nanotubes and metal clusters of different size and constitution. This was done using different computational methods and at different temperatures. It soon became apparent that the clusters adapted to the carbon nanotube and not vice versa. This held true irrespectively of the constitution of the cluster, that is for both pure metal and metal carbide. It was also seen that there exist a minimum cluster size that prevent the carbon nanotube end from closing. Closure of the carbon nanotube end is likely to lead to the termination of the growth which lead to studies of other reasons for growth termination, e.g., Ostwald ripening of the catalyst particles. This was investigated with the result that the rate of the Ostwald ripening may depend on both the chirality and diameter of the carbon nanotubes. It is suggested that this may provide some answers to the controlled growth of carbon nanotubes.

  • 8.
    Börjesson, Anders
    et al.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    First Principles Studies of the Effect of Nickel Carbide Catalyst Composition on Carbon Nanotube Growth2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 42, p. 18045-18050Article in journal (Refereed)
    Abstract [en]

    Density functional theory calculations were used to investigate the stability of single-walled carbon nanotubes (CNTs) attached to nanoparticles. The total energies and the adhesion energies between the CNTs and the nanoparticles were calculated for systems where the nanoparticles were either pure Ni or Ni carbide. It was found that the adhesion between the CNT and a pure Ni cluster is stronger than between the same CNT and a Ni carbide cluster although the energy difference was small compared to the total adhesion energies. This adhesion strength implies that CNTs are likely to remain attached to both pure Ni and Ni carbide clusters and that either pure Ni or Ni carbide clusters may be docked onto the open CNT ends to achieve continued growth or electronic contacts between CNTs and electrode materials. The system with a CNT attached to a pure Ni cluster was found to be energetically favored compared to a system containing the same CNT attached to a Ni carbide. The difference in total energy implies that a CNT should act as a sink for C atoms dissolved in the Ni carbide cluster, which means that the dissolved C atoms will be drained from the cluster, yielding a pure metal in the zero Kelvin thermodynamic limit. It is argued that this draining procedure is likely to occur even if carbon is added to the cluster at a proper rate, for example, during CNT growth.

  • 9.
    Börjesson, Anders
    et al.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    First Principles Studies of the Effect of Ostwald Ripening on Carbon Nanotube Chirality Distributions2011In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 5, no 2, p. 771-779Article in journal (Refereed)
    Abstract [en]

    The effect of Ostwald ripening of metal particles attached to carbon nanotubes has been studied using density functional theory. It has been confirmed that Ostwald ripening may be responsible for the termination of growth of carbon nanotube forests. It was seen that the Ostwald ripening of metal particles attached to carbon nanotubes is governed by a critical factor that depends on both the cluster size and the carbon nanotube chirality. For example, clusters attached to armchair and zigzag nanotubes of similar diameters will have different critical factors although the exact behavior may depend on which molecules are present in the surrounding medium. The critical factor was also observed to have a critical point with the effect that clusters with a narrow size distribution close to the critical point may experience a narrowing rather than a widening of the size distribution, as is the case for free clusters.

  • 10.
    Börjesson, Anders
    et al.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering. University of Borås, Swedish School of Textiles.
    Modelling of Ostwald ripening of metal clusters attached to carbon nanotubes2011In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 50, p. 24454-24462Article in journal (Refereed)
    Abstract [en]

    We present a model of Ostwald ripening of nanosized clusters and apply it to study the time evolution of metal particles attached to carbon nanotubes. The Ostwald ripening of metal clusters attached to carbon nanotubes differs from that of free metal clusters. While free clusters experience a rapid broadening in the size dispersion, this may be delayed by the nanotubes, which may therefore limit the ripening. The diameter and chirality of the carbon nanotubes were also seen to affect the Ostwald ripening of the catalyst particles. For a collection of carbon nanotubes that contains different diameters and chiralities, the clusters attached to carbon nanotubes with large diameters and strong carbon–metal adhesion are the most likely to survive the Ostwald ripening.

  • 11.
    Börjesson, Anders
    et al.
    University of Borås, School of Engineering.
    Curtarolo, Stefano
    Harutyunyan, Avetik R.
    Bolton, Kim
    University of Borås, School of Engineering.
    Computational study of the thermal behavior of iron clusters on a porous substrate2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, no 11Article in journal (Refereed)
    Abstract [en]

    The thermal behavior of iron nanoclusters on a porous substrate has been studied using classical molecular dynamics simulations. The substrate has been modeled with a simple Morse potential and pores with different shapes have been modeled in order to mimic the porous substrates used for carbon nanotube growth. It has been confirmed that the presence of the substrate increases the cluster melting temperature compared to the free cluster. In addition, the magnitude of this increase in melting point depends on the existence, shape, and diameter of the pore. For example, the increase in melting point is larger for clusters supported on flat (nonporous) substrates than for clusters which straddle pores with smaller diameters than the cluster diameter.

  • 12.
    Börjesson, Anders
    et al.
    University of Borås, School of Engineering.
    Erdtman, Edvin
    University of Borås, School of Engineering.
    Ahlström, Peter
    University of Borås, School of Engineering.
    Berlin, Mikael
    Andersson, Thorbjörn
    Bolton, Kim
    University of Borås, School of Engineering.
    Molecular modelling of oxygen and water permeation in polyethylene2013In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 54, no 12, p. 2988-Article in journal (Refereed)
    Abstract [en]

    Monte Carlo and molecular dynamics simulations were performed to calculate solubility, S, and diffusion, D, coefficients of oxygen and water in polyethylene, and to obtain a molecular-level understanding of the diffusion mechanism. The permeation coefficient, P, was calculated from the product of S and D. The AMBER force field, which yields the correct polymer densities under the conditions studied, was used for the simulations, and it was observed that the results were not sensitive to the inclusion of atomic charges in the force field. The simulated S for oxygen and water are higher and lower than experimental data, respectively. The calculated diffusion coefficients are in good agreement with experimental data. Possible reasons for the discrepancy in the simulated and experimental solubilities, which results in discrepancies in the permeation coefficients, are discussed. The diffusion of both penetrants occurs mainly by large amplitude, infrequent jumps of the molecules through the polymer matrix.

  • 13.
    Börjesson, Anders
    et al.
    University of Borås, School of Engineering.
    Harutyunyan, Avetik R.
    Curtarolo, Stefano
    Bolton, Kim
    University of Borås, School of Engineering.
    Computational study of the thermal behavior of iron clusters on a porous substrate2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, no 11Article in journal (Refereed)
  • 14.
    Börjesson, Anders
    et al.
    University of Borås, School of Engineering.
    Zhu, Wuming
    Amara, Hakim
    Bichara, Christophe
    Bolton, Kim
    University of Borås, School of Engineering.
    Computational studies of metal-carbon nanotube interfaces for regrowth and electronic transport2009In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 9, no 3, p. 1117-1120Article in journal (Refereed)
    Abstract [en]

    First principles and tight binding Monte Carlo simulations show that junctions between single-walled carbon nanotubes (SWNTs) and nickel clusters are on the cluster surface, and not at subsurface sites, irrespective of the nanotube chirality, temperature, and whether the docking is gentle or forced. Gentle docking helps to preserve the pristine structure of the SWNT at the metal interface, whereas forced docking may partially dissolve the SWNT in the cluster. This is important for SWNT-based electronics and SWNT-seeded regrowth.

  • 15. Jiang, A.
    et al.
    Awasthi, N.
    Kolmogorov, A. N.
    Setyawan, W.
    Börjesson, A.
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    Harutyunyan, A.
    Curtarolo, S.
    Theoretical study of the thermal behaviour of free and alumina-supported Fe-C nanoparticles2007In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 75, no 20Article in journal (Refereed)
    Abstract [en]

    The thermal behavior of free and alumina-supported iron-carbon nanoparticles is investigated via molecular-dynamics simulations, in which the effect of the substrate is treated with a simple Morse potential fitted to ab initio data. We observe that the presence of the substrate raises the melting temperature of medium and large Fe1-xCx nanoparticles (x=0-0.16, N=80-1000, nonmagic numbers) by 40-60 K; it also plays an important role in defining the ground state of smaller Fe nanoparticles (N=50-80). The main focus of our study is the investigation of Fe-C phase diagrams as a function of the nanoparticle size. We find that as the cluster size decreases in the 1.1-1.6-nm-diameter range, the eutectic point shifts significantly not only toward lower temperatures, as expected from the Gibbs-Thomson law, but also toward lower concentrations of C. The strong dependence of the maximum C solubility on the Fe-C cluster size may have important implications for the catalytic growth of carbon nanotubes by chemical-vapor deposition.

  • 16. Zhu, Wuming
    et al.
    Börjesson, Anders
    University of Borås, School of Engineering.
    Bolton, Kim
    University of Borås, School of Engineering.
    DFT and tight binding Monte Carlo calculations related to single-walled carbon nanotube nucleation and growth2010In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 48, no 2, p. 470-478Article in journal (Refereed)
    Abstract [en]

    Density-functional theory (DFT) calculations for idealized nucleation processes of (5,5) and (10,0) single-walled carbon nanotubes (SWCNTs) on a 55 atom nickel cluster (Ni-55) showed that it requires a larger chemical potential to grow a carbon island (which is the simplest structure that can lead to formation of the SWCNTs) on the cluster than to extend the island into a SWCNT or to have the carbon atoms dispersed on the cluster surface. Hence, in the thermodynamic limit the island will only form once the (surface of the) cluster is saturated with carbon, and the island will spontaneously form a SWCNT at the chemical potentials required to create the island. The DFT (zero Kelvin) and tight binding Monte Carlo (1000 K) also show that there is a minimum cluster size required to support SWCNT growth, and that this cluster size can be used to control the diameter, but probably not the chirality, of the SWCNT at temperatures relevant to carbon nanotube growth. It also imposes a minimum size of clusters that are used for SWCNT regrowth. (C) 2009 Elsevier Ltd. All rights reserved.

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