| Alexandrou, I., Scheibe, H. J., Kiely, C. J., Papworth, A. J., Amaratunga, G. A. J., and Schultrich, B. |
| Carbon films with an sp(2) network structure. |
| Physical Review B: Condensed Matter v.60, n.15, pp.10903-10907. (1999). |
| Abstract: Laser-arc evaporation of a graphite target has been used to deposit carbon films that exhibit high hardness (45 Cpa) and elastic recovery (85%). High-resolution electron microscopy (HREM) and electron energy loss spectroscopy (EELS) were subsequently used to study the microstructure and bonding of the resultant layers. The structure of the films from HREM is seen to consist of a dense array of parallel curved graphene sheet segments packed in various orientations. EELS reveals that the films are comprised of mainly sp(2)-bonded carbon. The results suggest that a form of carbon thin film with fullerenelike structure can be realized. In order to explain how a predominantly sp(2)-bonded material can exhibit such a high hardness, a simple model is proposed to correlate the excellent mechanical properties with the observed structure. [S0163-1829(99)00439-7] |
| Internal Reference: [ID: 1603]
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|
| Alinchenko, M. G., Anikeenko, A. V., Medvedev, N. N., Voloshin, V. P., Mezei, M., and Jedlovszky, P. |
| Morphology of voids in molecular systems. A Voronoi-Delaunay analysis of a simulated DMPC membrane. |
| Journal of Physical Chemistry B v.108, n.49, pp.19056-19067. (2004). |
| Abstract: A generalized version of the Voronoi-Delaunay method is used to study relatively large intermolecular voids in a model of the hydrated DMPC bilayer, obtained from all-atom Monte Carlo simulation. Application of the original version of the method for molecular systems has been hampered by the fact that these systems geometrically represent ensembles of partially overlapping spheres of different radii. The generalized version of the method is based on using the additively weighed Voronoi diagram, representing the locus of spatial points being equally far from the surface rather than the center of the corresponding pair of atoms. This version of the Voronoi-Delaunay method can be readily used to reveal and analyze voids accessible for probes of different radii even in rather complex molecular systems. When the properties of the voids present in the simulated DMPC membrane are investigated, their shape, size, and orientation have been analyzed in detail in the different regions of the membrane located at different depths along the membrane normal axis. The characteristics of the voids are found to be different in different regions of the bilayer, namely (i) at the middle of the membrane, in the region of the hydrophobic lipid tails, (ii) in the region of the hydrophilic zwitterionic headgroups, and (iii) in the region of the bulklike water adjacent to the bilayer. The largest and oblong voids are found in the middle of the membrane, with a preferred orientation that is parallel to the bilayer normal axis. A clear correlation between the orientation of the voids and the orientation of the lipid chains is observed. In the bulk water region the fraction of the empty space is even higher than at the middle of the membrane; however, here the voids are distributed more uniformly. Finally, in the high-density region of the hydrophilic headgroups the voids are found, on average, smaller than in the other parts of the system |
| Internal Reference: [ID: 2453]
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|
| Barborini, E., Piseri, P., Milani, P., Benedek, G., Ducati, C., and Robertson, J. |
| Negatively curved spongy carbon. |
| Applied Physics Letters v.81, n.18, pp.3359-3361. (2002). |
| Abstract: We describe the production and characterization of a form of nanostructured carbon consisting of fully connected, three-dimensional (3D) sp2 networks. This form of carbon is characterized by interconnected thin layers forming a spongy structure with meso- and macroporosity. It is produced by a pulsed microplasma cluster source in the presence of a very low concentration of metallorganic catalyst. The unique 3D structure and topology of the spongy carbon are very interesting for catalysis and electrochemical applications and for the investigation of negatively curved forms of carbon such as schwarzites. |
| Internal Reference: [ID: 1805]
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|
| Biggs, M. J. and Buts, A. |
| Virtual porous carbons: what they are and what they can be used for. |
| Molecular Simulation v.32, n.7, pp.579-593. (2006). |
| Abstract: We use the term "virtual porous carbon" (VPC) to describe computer-based molecular models of nanoporous carbons that go beyond the ubiquitous slit pore model and seek to engage with the geometric, topological and chemical heterogeneity that characterises almost every form of nanoporous carbon. A small number of these models have been developed and used since the early 1990s. These models and their use are reviewed. Included are three more detailed examples of the use of our VPC model. The first is concerned with the study of solid-like adsorbate in nanoporous carbons, the second with the absolute assessment of multi-isotherm based methods for determining the fractal dimension, and the final one is concerned with the fundamental study of diffusion in nanoporous carbons |
| Internal Reference: [ID: 2431]
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|
| Bogana, M. P. and Colombo, L. |
| Atomic scale simulations of vapor cooled carbon clusters. |
| Applied Physics A: Materials Science & Processing v.86, n.3, pp.275-281. (2007). |
| Abstract: By means of atomistic simulations we observed the
formation of many topologically non-equivalent carbon clusters
formed by the condensation of liquid droplets, including:
(i) standard fullerenes and onion-like structures, (ii) clusters
showing extremely complex surfaces with both positive and
negative curvatures and (iii) complex endohedral structures. In
this work we offer a thorough structural characterization of the
above systems, as well as an attempt to correlate the resulting
structure to the actual protocol of growth. The IR and Raman
responses of some exotic linear carbon structures have been
further investigated, finding good agreement with experimental
evidence of carbinoid structures in cluster-assembled films.
Towards the aimof fully understanding the process of cluster-tocluster
coalescence dynamics, we further simulated an aerosol
of amorphous carbon clusters at controlled temperatures. Various
annealing temperatures and times have been observed,
identifying different pathways for cluster ripening, ranging from
simple coalescence to extensive reconstruction. |
| Internal Reference: [ID: 2465]
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|
| Bourgeois, L. N. and Bursill, L. A. |
| High-resolution transmission electron microscopy and energetics of flattened carbon nanoshells. |
| Chemical Physics Letters v.277, n.5-6, pp.571-578. (1997). |
| Abstract: When examined under a high-resolution transmission electron microscope, carbon soot produced alongside buckytubes in an arc-discharge is found to contain a small percentage of flattened carbon shells. These objects are shown to be small graphite flakes which have eliminated their dangling bonds by terminating their edges with highly curved junctions. Ideal models for these structures are presented and their energies estimated. Thecalculations show that the establishment of highly curved junctions is energetically favourable for a graphite flake in an inert atmosphere. Flattened shells also appear more stable than their `inflated' counterparts (fullerene `onions' and buckytubes) when the shell dimensions obey specific criteria |
| Internal Reference: [ID: 2389]
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|
| Brodka, A., Zerda, T. W., and Burian, A. |
| Graphitization of small diamond cluster -- Molecular dynamics simulation. |
| Diamond and Related Materials v.15, n.11-12, pp.1818-1821. (2006). |
| Abstract: Molecular dynamics simulation was used to study graphitization process of a small diamond cluster at 1200, 1500, and 1800 K. The cluster was in the shape of a sphere of about 3 nm in diameter, and interaction between carbon atoms was described by the reactive bond order potential. Results obtained for 1500 K showed transformation of diamond nanoparticle into a carbon onion with diamond-like core and graphite layers in its outer shell. At 1800 K the process was faster and graphitization more effective. The whole final cluster was basically comprised of the onion structure, but it was irregular and separation between layers ranged from 0.2 to 0.3 nm |
| Internal Reference: [ID: 2387]
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|
| Burket, C. L., Rajagopalan, R., and Foley, H. C. |
| Synthesis of nanoporous carbon with pre-graphitic domains. |
| Carbon v.45, n.11, pp.2307-2310. (2007). |
| Abstract: Herein we describe the discovery of a new route to the synthesis of a pure nanoporous carbon containing pre-graphitic structures with both high surface area and high nano- and mesoporosity from the readily available polymer precursor polyfurfuryl alcohol. |
| Internal Reference: [ID: 2433]
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|
| Cabioc'h, T., Thune, E., and Jaouen, M. |
| Mechanisms involved in the formation of onionlike carbon nanostructures synthesized by ion implantation at high temperature. |
| Physical Review B: Condensed Matter v.65, n.13, (2002). |
| Abstract: The origin of the formation of multishell fullerenes (carbon onions) produced by carbon ion-implantations performed at high-temperature into silver is discussed on the basis of high-resolution transmission electron microscopy observations. For low carbon fluences, one observes the formation inside the silver matrix of poorly organized carbon nanostructures the shape of which is roughly spherical. They progressively evolve towards perfect onionlike structures when the implanted carbon fluence increases. The catalytic effect of silver, which lowers the graphitization temperature of the carbon, the irradiation-induced displacements of the carbon atoms, and the effect of the temperature are proposed to be the key mechanisms that control the formation of the onionlike structures observed in such experiments |
| Internal Reference: [ID: 2474]
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|
| Carey, J. D. and Silva, S. R. P. |
| Disorder, clustering, and localization effects in amorphous carbon. |
| Physical Review B: Condensed Matter v.70, n.23, pp.235417 (2004). |
| Abstract: The nanostructure of amorphous carbon thin films is described in terms of a disordered nanometer-sized conductive sp(2) phase embedded in an electrically insulating sp(3) matrix. It is shown that the degree of clustering and disorder within the sp(2) phase plays a determining role in the electronic properties of these films. Clustering of the sp(2) phase is shown to be important in explaining several experimental results including the reduction of the electron spin resonance linewidth with increasing spin density and the dispersion associated with the width of the Raman active G band. The influence of structural disorder, associated with sp(2) clusters of similar size, and topological disorder, due to undistorted clusters of different sizes, on both spin density and Raman measurements, is discussed. An extension of this description to intercluster interactions to explain some of the electrical transport and electron field emission behavior is also presented |
| Internal Reference: [ID: 2229]
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|
| Carey, J. D. |
| Quantifying clustering in disordered carbon thin films. |
| Thin Solid Films v.515, n.3, pp.996-999. (2006). |
| Abstract: The quantification of disorder and the effects of clustering in the sp(2) phase of amorphous carbon thin films are discussed. The sp(2) phase is described in terms of disordered nanometer-sized conductive sp(2) clusters embedded in a less conductive sp(3) matrix. Quantification of the clustering of the sp(2) phase is estimated from optical as well as from electron and nuclear magnetic resonance methods. Unlike in other disordered group IV thin film semiconductors, we show that care must be exercised in attributing a meaning to the Urbach energy extracted from absorption measurements in the disordered carbon system. The influence of structural disorder, associated with sp(2) clusters of similar size, and topological disorder due to undistorted clusters of different sizes is also discussed. Extensions of this description to other systems are also presented. (c) 2006 Elsevier B.V. All rights reserved |
| Internal Reference: [ID: 2228]
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|
| Chen, X. D., Sullivan, J. P., Friedmann, T. A., and Gibson, J. M. |
| Fluctuation microscopy studies of medium-range ordering in amorphous diamond-like carbon films. |
| Applied Physics Letters v.84, n.15, pp.2823-2825. (2004). |
| Abstract: In this letter, we report fluctuation microscopy studies of medium-range ordering in amorphous diamond-like carbon films and the effect of annealing on this ordering. Annealed and unannealed diamond-like carbon films have almost identical short-range order. Our fluctuation microscopy results, however, indicate the presence of medium range order or clustering in the films on a lateral length scale that exceeds 1 nm. Within the clustered regions, the dominant local ordering appears to be diamond-like, and graphite-like ordering is not observed. Thermal annealing up to 600degreesC leads to an increase in diamond-like clustering with no onset of graphite-like clustering. However, after high temperature annealing up to 1000degreesC, graphite-like clustering becomes apparent as a result of the conversion of diamond-like carbon to graphite-like carbon. The results on the as-deposited films and films annealed up to 600degreesC suggest that a spontaneous medium range ordering process occurs in diamond-like carbon films during and subsequent to film growth, and this may play an important role in stress relaxation. (C) 2004 American Institute of Physics |
| Internal Reference: [ID: 1468]
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|
| Du, G. X., Song, C., Zhao, J. H., Feng, S., and Zhu, Z. P. |
| Solid-phase transformtion of glass-like carbon nanoparticles into nanotubes and the related mechanism. |
| Carbon v.46, n.1, pp.92-98. (2008). |
| Abstract: Multi-walled carbon nanotubes have been synthesized through the solid-phase transformation of metal-containing glass-like carbon nanoparticles by heating at temperatures of 800-1000 degrees C. From microscopic observations on the morphologies and structures of the nanotubes and various intermediate objects, it is shown that the transformation occurs by nanoparticles first assembling into wire-like nanostructures, and then transforming into nanotubes via p article-p article coalescence and structural crystallization. (c) 2007 Elsevier Ltd. All rights reserved |
| Internal Reference: [ID: 2441]
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|
| Franzblau, D. S. |
| Computation of Ring Statistics for Network Models of Solids. |
| Physical Review B: Condensed Matter v.44, n.10, pp.4925-4930. (1991). |
| Abstract: In random-network models of amorphous solids, ring statistics provide a measure of medium-range order. However, many criteria used so far to determine the set of rings to count have serious drawbacks. Here, a "shortest-path" (SP) criterion is shown to give ring statistics that agree well with intuition, and to avoid problems inherent in other criteria. The SP criterion arises naturally in a hierarchy of criteria for "irreducible" rings. It falls exactly midway between the least restrictive and most restrictive criteria in the hierarchy, suggesting that it may give the optimal balance between the two extremes. Since SP rings are simple to characterize and enumerate, SP ring statistics appear to be the most promising means for characterizing network topology |
| Internal Reference: [ID: 2231]
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|
| Harris, P. J. F. and Tsang, S. C. |
| High-resolution electron microscopy studies of non-graphitizing carbons. |
| Philosophical Magazine A-Physics of Condensed Matter Structure Defects and Mechanical Properties v.76, n.3, pp.667-677. (1997). |
| Abstract: High-resolution electron microscopy is used to study the structure of two typical non-graphitizing carbons before and after heat treatment at temperatures in the range 2100-2600 degrees C. It is found that these heat treatments can result in the formation of closed carbon nanoparticles, which are apparently fullerene-like in structure. This suggests that fullerene-like elements were present in the original carbons and leads us to propose a new model for the structure of non-graphitizing carbons |
| Internal Reference: [ID: 2444]
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|
| Harris, P. J. F. |
| Fullerene-related structure of commercial glassy carbons. |
| Philosophical Magazine v.84, n.29, pp.3159-3167. (2004). |
| Abstract: Glassy carbon is a technologically important material widely used in products such as electrodes and high-temperature crucibles. However, the properties which make glassy carbon so valuable in these applications are poorly understood, since its detailed atomic structure is not known. A model for the structure of glassy carbon put forward many years ago has gained wide acceptance, but appears to suffer from serious shortcomings. In particular, it fails to account for the chemical inertness of the carbon, and for its high proportion of closed porosity. Here I show, using high-resolution transmission electron microscopy, that glassy carbons obtained from commercial suppliers contain a high proportion of fullerene-related structures. On the basis of these observations, models are put forward for the structures of 'low-temperature' and 'high-temperature' glassy carbons which incorporate non-six-membered rings |
| Internal Reference: [ID: 1616]
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|
| Harris, P. J. F. |
| New perspectives on the structure of graphitic carbons. |
| Critical Reviews in Solid State and Materials Sciences v.30, n.4, pp.235-253. (2005). |
| Abstract: Graphitic forms of carbon are important in a wide variety of applications, ranging from pollution control to composite materials, yet the structure of these carbons at the molecular level is poorly understood. The discovery of fullerenes and fullerene-related structures such as carbon nanotubes has given a new perspective on the structure of solid carbon. This review aims to show how the new knowledge gained as a result of research on fullerene-related carbons can be applied to well-known forms of carbon such as microporous carbon, glassy carbon, carbon fibers, and carbon black |
| Internal Reference: [ID: 1840]
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|
| Hawelek, L., Koloczek, J., Brodka, A., Dore, J. C., Honkimaki, V., and Burian, A. |
| Structural studies of disordered carbons by high-energy X-ray diffraction. |
| Philosophical Magazine v.87, n.32, pp.4973-4986. (2007). |
| Abstract: X-ray diffraction measurements were carried out on three samples of disordered, commercially produced carbons, AX21, CXV and BP71, on the ID15B beam-line at the European Synchrotron Radiation Facility (ESRF), Grenoble. Intensity data were converted to pair correlation functions via the Fourier transform. The results obtained show that the structure of the studied samples consists of one four graphite-like layers, stacked without spatial correlations. The size of the ordered regions is in the range of 9-16 angstrom. The atomic arrangement within an individual layer can be described in terms of the paracrystalline ordering, in which lattice distortions propagate proportionally to the square root of interatomic distances. The paracrystalline structure was simulated by introducing the Stone Wales defects (pair of two pentagons and two heptagons), randomly distributed in the network. The resulting structures were relaxed using the reactive empirical bond order potential for carbon-carbon interaction and the Lennard-Jones potential with parameters for interlayer interactions. Such defects lead to curvature of individual layers |
| Internal Reference: [ID: 2447]
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|
| Huang, J. Y., Chen, S., Ren, Z. F., Chen, G., and Dresselhaus, M. S. |
| Real-time observation of tubule formation from amorphous carbon nanowires under high-bias Joule heating. |
| Nano Letters v.6, n.8, pp.1699-1705. (2006). |
| Abstract: The tubule formation process from amorphous carbon nanowires under high-bias-caused Joule heating was observed in real time in a high-resolution transmission electron microscope. The crystallization of the amorphous carbon nanowires occurred in two distinct ways: the formation of tubular graphitic basal planes parallel to the nanowire axis on the surface and the formation of nano-onions in the interior of the nanowire. The tubule formation mechanism is a process of solid-state atom diffusion at high temperatures. Energetically, the tubule formation is caused by the exceptionally low surface energy of the (0002) plane of graphite. Higher input power to the amorphous nanowires generally leads to improved graphitization and, in turn, to increased conductance. The results suggest that nanotube formation in the arc-discharge growth process may involve the formation and crystallization of amorphous carbon |
| Internal Reference: [ID: 2439]
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|
| Huang, J. Y., Ding, F., Jiao, K., and Yakobson, B. I. |
| Self-templated growth of carbon-nanotube walls at high temperatures. |
| Small v.3, n.10, pp.1735-1739. (2007). |
|
| Internal Reference: [ID: 2442]
Online at: Link to Online Reference
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|
| Huang, J. Y. |
| Real time microscopy, kinetics, and mechanism of giant fullerene evaporation. |
| Physical Review Letters v.99, n.17, pp.175503 (2007). |
| Abstract: We report in situ high-resolution transmission electron microscopy observing the shrinkage of single-layer giant fullerenes (GF). At temperatures similar to 2000 degrees C, the GF volume reduces by greater than one 100-fold while the fullerene shell remains intact, evolving from a slightly polygonized to a nearly spherical shape with a smaller diameter. The number of carbon atoms in the GF decreases linearly with time until the small subbuckyball cage opens and rapidly disappears. Theoretical modeling indicates that carbon atoms are removed predominantly from the weakest binding energy sites, i. e., the pentagons, leading to the constant evaporation rate. The fullerene cage integrity is attributed to the collective behavior of interacting defects. These results constitute the first experimental evidence for the "shrink-wrapping'' and "hot-giant'' fullerene formation mechanisms |
| Internal Reference: [ID: 2440]
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|
| Kawai, T., Okada, S., Miyamoto, Y., and Oshiyama, A. |
| Carbon three-dimensional architecture formed by intersectional collision of graphene patches. |
| Physical Review B: Condensed Matter v.72, n.3, pp.035428 (2005). |
| Abstract: Graphite is the most stable form of carbon under room temperature and atmospheric pressure, and consists of two-dimensional honeycomb lattices with intralayer sp(2) bonding and rather weak van der Waals like interlayer interaction. When we supply gaseous small carbonic molecules such as methane to a patch of graphene, the patch will grow into graphite. Now, let us imagine a slightly different situation. Is a layered structure of graphite always formed, when we supply not methane molecules but another graphene patch? The answer from our computer simulations is "No." Some graphene patches collide in parallel, but others at right angles, which result in a formation of junction structures (graphitic Y junctions). These junction structures are different from those of common sense for graphitic materials. Performing density functional calculations, we found that the reaction barrier height required for the formation of graphitic Y junctions are almost zero, and the binding energies per bond for each structure are similar to 1 eV. Furthermore, tight-binding molecular dynamics simulations showed high thermal stability and high formation probabilities for these junction structures. As applications of graphitic Y junctions, we will present two interesting structures, where we focus on the magnetic properties of junction structures and nanotube T-junction structures which are different from conventional models. We expect that graphitic Y junctions might be hidden in graphitic soot and not characterized yet in experiment. 3D architectures constructed from those unit structures are expected to have various applications with lightweight, ferromagnet, high molecular storage and high thermal conductor |
| Internal Reference: [ID: 2381]
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|
| Kumar, A., Lobo, R. F., and Wagner, N. J. |
| Porous amorphous carbon models from periodic Gaussian chains of amorphous polymers. |
| Carbon v.43, n.15, pp.3099-3111. (2005). |
| Abstract: An algorithm has been developed to create structural models for amorphous carbons using Monte Carlo simulations in the canonical ensemble. The simulation method used follows the experimental preparation of nanoporous carbons (NPC) by pyrolysis from polyfurfuryl alcohol as a guideline. The resulting structure exhibits properties that compare favorably to those observed experimentally for real NPCs. These atomistic NPC models are approaching a realistic representation of NPCs used for gas separations and as such, are being used to study the diffusion of small gas molecules in these materials. Limitations of the method and possible improvements are discussed. (C) 2005 Elsevier Ltd. All rights reserved |
| Internal Reference: [ID: 2429]
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|
| Kuznetsov, V. L., Chuvilin, A. L., Butenko, Y. V., Malkov, I. Y., and Titov, V. M. |
| Onion-Like Carbon from Ultra-Disperse Diamond. |
| Chemical Physics Letters v.222, n.4, pp.343-348. (1994). |
| Abstract: A new material containing macroscopic quantities of onion-like carbon (OLC) particles is produced by heat treatment of ultra-disperse diamond (UDD) powder (2-6 nm) - Annealing products (characterized by high-resolution electron microscopy) are presented by: (a) quasi-spherical particles with closed concentric graphite shells, (b) polyhedron particles with closed shells, (c) elongated particles with linked external graphite-like layers and closed quasi-spherical internal shells. The intermediates of UDD transformation have been registered. The structural transformation of UDD begins from the surface of the diamond particles towards a crystal bulk. The transformation rate of (111) diamond planes to graphite-like sheets is higher than that of other planes |
| Internal Reference: [ID: 2472]
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|
| Lau, D. W. M., McCulloch, D. G., Marks, N. A., Madsen, N. R., and Rode, A. V. |
| High-temperature formation of concentric fullerene-like structures within foam-like carbon: Experiment and molecular dynamics simulation. |
| Physical Review B: Condensed Matter v.75, n.23, pp.233408-4. (2007). |
| Abstract: The formation mechanism of carbon onions is investigated. The microstructure of onions formed using pulsed-laser deposition is found to depend critically on the background gas pressure. Molecular dynamics simulations show that an optimal annealing temperature of 4000 K is required to form well-ordered onions (concentric fullerene-like spheres), in agreement with experiment. The onions form from the outer layer first, and a model is presented in which the background pressure must be sufficient to allow atoms to cluster, yet low enough to allow annealing into well-ordered onions. |
| Internal Reference: [ID: 2391]
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|
| Leyssale, J. M. and Vignoles, G. L. |
| Molecular dynamics evidences of the full graphitization of a nanodiamond annealed at 1500 K. |
| Chemical Physics Letters v.454, n.4-6, pp.299-304. (2008). |
| Abstract: The annealing of a small nanodiamond cluster at 1500 K is studied by molecular dynamics. The transformation of the particle in an almost fully graphitized carbon onion is observed. The remaining 17% of sp(3) atoms are delocalized on the whole particle, both under the form of isolated point defects and of small diamond-like clusters separating large graphite-like domains. It is also shown, that the Berendsen thermostat, previously used to fix temperature in such simulations, transfers kinetic energy from internal to global motions of the cluster. This can lead to severe artifacts like the freezing of the graphitization process. (c) 2008 Elsevier B.V. All rights reserved |
| Internal Reference: [ID: 2460]
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|
| Liu, A. C. Y., Arenal, R., and Chen, X. D. |
| Clustering in a highly hydrogenated diamondlike carbon determined using fluctuation electron microscopy and phenomenological atomistic simulations. |
| Physical Review B: Condensed Matter v.76, n.12, pp.121401 (2007). |
| Abstract: We compare fluctuation electron microscopy data to simulations from phenomenological atomic models and demonstrate a strong correspondence between some features in the experimental data and certain atomic configurations. This allows the nature of atomic clustering in a highly hydrogenated diamondlike carbon to be determined more closely. We compare the structural information garnered from fluctuation electron microscopy and Raman spectroscopy for a particular diamondlike carbon and find consistency between the two techniques in the region where their information overlaps |
| Internal Reference: [ID: 2449]
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|
| Mariwala, R. K. and Foley, H. C. |
| Evolution of Ultramicroporous Adsorptive Structure in Poly(furfuryl alcohol)-Derived Carbogenic Molecular Sieves. |
| Industrial & Engineering Chemistry Research v.33, n.3, pp.607-615. (1994). |
|
| Internal Reference: [ID: 2432]
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|
| Marks, N. |
| Modelling diamond-like carbon with the environment-dependent interaction potential. |
| Journal of Physics : Condensed Matter v.14, n.11, pp.2901-2927. (2002). |
| Abstract: The environment-dependent interaction potential is a transferable empirical potential for carbon which is well suited for studying disordered systems. Ab initio data are used to motivate and parametrize the functional form, which includes environment-dependence in the pair and triple terms, and a generalized aspherical coordination describing dihedral rotation and non-bonded pi-repulsion. Simulations of liquid carbon compare very favourably with Car-Parrinello calculations, while amorphous networks generated by liquid quench have properties superior to Tersoff, Brenner and orthogonal tight-binding calculations. The efficiency of the method enables the first simulations of tetrahedral amorphous carbon by deposition, and a new model for the formation of diamond-like bonding is presented |
| Internal Reference: [ID: 2135]
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|
| Marks, N. A. |
| Thin film deposition of tetrahedral amorphous carbon: a molecular dynamics study. |
| Diamond and Related Materials v.14, n.8, pp.1223-1231. (2005). |
| Abstract: Molecular dynamics simulations of carbon thin film deposition are performed using the Environment Dependent Interaction Potential. Films deposited with carbon beams in the range 1-100 eV reproduce the energy dependence of the biaxial stress, density and tetrahedral bonding fraction observed experimentally. The transition from low-density, graphite-like amorphous carbon to the high-density tetrahedral phase occurs at an energy at which impacting ions do not penetrate the surface of the film. This result is incompatible with the generally accepted subplantation explanation for the diamond-like properties, and a new model of energetic burial is deduced from the simulations. Radial distribution functions compare well with experiment, and represent a significant improvement over Tersoff and Brenner simulations which contain unphysical distances. (c) 2005 Elsevier B.V All rights reserved |
| Internal Reference: [ID: 2470]
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|
| Marks, N. A., Cover, M. F., and Kocer, C. |
| Simulating temperature effects in the growth of tetrahedral amorphous carbon: The importance of infrequent events. |
| Applied Physics Letters v.89, n.13, pp.131924 (2006). |
| Abstract: This thin-film deposition study of tetrahedral amorphous carbon shows that including infrequent processes on the millisecond scale substantially improves the accuracy of molecular dynamics simulations. Elevated temperature between energetic impacts is used to activate processes which are typically ignored. In agreement with experiment, the simulations show an abrupt transition in which diamondlike carbon transforms into vertically oriented graphitic sheets. The simulations also highlight the importance of infrequent events in combination with energetic impact. In the absence of the latter, the transition temperature is significantly higher, in good correlation with experiment. (c) 2006 American Institute of Physics |
| Internal Reference: [ID: 2296]
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|
| Maruyama, S. and Yamaguchi, Y. |
| A molecular dynamics demonstration of annealing to a perfect C60 structure. |
| Chemical Physics Letters v.286, n.3-4, pp.343-349. (1998). |
| Abstract: The formation process of imperfect fullerenes C60 and C70 was simulated using the molecular dynamics method as described in our previous report. These imperfect fullerenes were kept at 2500 K to evaluate annealing effects. Through successive Stone-Wales transformations, perfect fullerene structures were achieved both for C60 and C70 in about 200 ns. The annealing temperature and time scale were plausible, compared to experimental conditions as seen in an Arrhenius plot. Similar simulations were performed for smaller clusters at each stage of the clustering process. Based on these simulations, a fullerene formation model is proposed |
| Internal Reference: [ID: 2462]
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|
| McKenzie, D. R., Muller, D., and Pailthorpe, B. A. |
| Compressive-Stress-Induced Formation of Thin-Film Tetrahedral Amorphous-Carbon. |
| Physical Review Letters v.67, n.6, pp.773-776. (1991). |
| Abstract: Thin tetrahedrally coordinated amorphous carbon (ta-C) films have been grown using a filtered vacuum are. ta-C is a new allotrope of carbon whose existence was previously thought to be unlikely. A model is proposed which accounts for the formation and structure of these films on the basis of the compressive stress generated by the shallow implantation of carbon ions. An optimal range of beam energies between 15 and 70 eV, a high film stress, and a graphitic surface are predicted and confirmed by experimental evidence. Computer simulation of the growth confirms that high compressive stress is generated by impact energies in this range |
| Internal Reference: [ID: 2469]
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|
| Medvedev, N. N., Voloshin, V. P., Luchnikov, V. A., and Gavrilova, M. L. |
| Algorithm for three-dimensional Voronoi S-network. |
| Journal of Computational Chemistry v.27, n.14, pp.1676-1692. (2006). |
| Abstract: The paper presents an algorithm for calculating the three-dimensional Voronoi-Delaunay tessellation for an ensemble of spheres of different radii (additively-weighted Voronoi diagram). Data structure and output of the algorithm is oriented toward the exploration of the voids between the spheres. The main geometric construct that we develop is the Voronoi S-network (the network of vertices and edges of the Voronoi regions determined in relation to the surfaces of the spheres). General scheme of the algorithm and the key points of its realization are discussed. The principle of the algorithm is that for each determined site of the network we find its neighbor sites. Thus, starting from a known site of the network, we sequentially find the whole network. The starting site of the network is easily determined based on certain considerations. Geometric properties of ensembles of spheres of different radii are discussed, the conditions of applicability and limitations of the algorithm are indicated. The algorithm is capable of working with a wide variety of physical models, which may be represented as sets of spheres, including computer models of complex molecular systems. Emphasis was placed on the issue of increasing the efficiency of algorithm to work with large models (tens of thousands of atoms). It was demonstrated that the experimental CPU time increases linearly with the number of atoms in the system, O(n). (C) 2006 Wiley Periodicals, Inc |
| Internal Reference: [ID: 2266]
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|
| Pettifor, D. G. |
| Bonding and Structure of Molecules and Solids. |
| (1995). |
| Abstract: This book is intended to introduce advanced undergraduate and beginning graduate students to the quantum mechanical concepts employed in materials science. With its exposition of essential ideas from density functional theory, the work will also interest practicing solid-state physicists and theoretical chemists. Topics range from experimental trends in bonding and structure to the bonding of transition metals and semiconductors. |
| Internal Reference: [ID: 2476]
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| Qiao, Z. J., Li, J. J., Zhao, N. Q., Shi, C. S., and Nash, P. |
| Graphitization and microstructure transformation of nanodiamond to onion-like carbon. |
| Scripta Materialia v.54, n.2, pp.225-229. (2006). |
| Abstract: Onion-like carbons were synthesized by annealing diamond nanoparticles at 1100-1400 degrees C. The diamond nanoparticles begin to graphitize in the range of 1100-1200 degrees C and all the particles transform into onion-like carbons at 1400 degrees C. The transformation temperature changes with the nanoparticle size. The onion-like carbons exhibit similarity to the original nanoparticles in shape. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved |
| Internal Reference: [ID: 2399]
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| Ravagnan, L., Siviero, F., Lenardi, C., Piseri, P., Barborini, E., Milani, P., Casari, C. S., Li Bassi, A., and Bottani, C. E. |
| Cluster-Beam Deposition and in situ Characterization of Carbyne-Rich Carbon Films. |
| Physical Review Letters v.89, n.28, pp.285506 (2002). |
| Abstract: Nanostructured carbon films produced by supersonic cluster beam deposition have been studied by in situ Raman spectroscopy. Raman spectra show the formation of a sp2 solid with a very large fraction of sp-coordinated carbyne species with a long-term stability under ultrahigh vacuum. Distinct Raman contributions from polyyne and cumulene species have been observed, as well as different stabilities under gas exposure. Our experiments confirm theoretical predictions and demonstrate the possibility of producing a carbyne-rich pure carbon solid. The stability of the sp2-sp network has important implications for astrophysics and for the production of novel carbon-based systems. |
| Internal Reference: [ID: 2466]
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|
| Roussel, T., Jagiello, J., Pellenq, R. J. M., Thommes, M., and Bichara, C. |
| Testing the feasibility of using the density functional theory route for pore size distribution calculations of ordered microporous carbons. |
| Molecular Simulation v.32, n.7, pp.551-555. (2006). |
| Abstract: The pore size distribution (PSD) characterization of microporous carbon materials is traditionally obtained from the analysis of N-2 adsorption isotherms at 77 K. In this work, we aim at testing the feasibility of using the density functional theory (DFT) route for PSD calculations of interconnected carbon pore structures. The first step of this study was to generate using an atomistic simulation approach, an ordered porous carbon material with well-defined porosity using NaY zeolite as a templating matrix. For this purpose, we used the grand canonical Monte-Carlo (GCMC) technique in which the carbon-carbon interactions were described within the frame of a newly developed tight binding approach and the carbon-zeolite interactions assumed to be characteristic of physisorption. We calculated the PSD of such a carbon porous material. At a second stage, we calculated nitrogen adsorption isotherms at different temperatures. These data were subsequently used as inputs for DFT calculation to obtain the PSD. Comparisons between DFT-PSD and MC-PSD are made. In particular, we show that with an appropriate wall thickness of two graphene layers, the PSD obtained from DFr calculation agrees well with that from direct analysis of the simulated structure |
| Internal Reference: [ID: 2446]
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| Sano, N., Wang, H., Alexandrou, I., Chhowalla, M., Teo, K. B. K., Amaratunga, G. A. J., and Iimura, K. |
| Properties of carbon onions produced by an arc discharge in water. |
| Journal of Applied Physics v.92, n.5, pp.2783-2788. (2002). |
| Abstract: A simple method to fabricate high-quality nanoparticles including spherical carbon onions and elongated fullerene-like nanoparticles similar to nanotubes in large quantities without the use of vacuum equipment is reported. The nanoparticles are obtained in the form of floating powder on the water surface following an arc discharge between two graphite electrodes submerged in water. High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy images confirm the presence of spherical carbon onions with diameters ranging from 4 to 36 nm. The specific surface area of the floating powder was found to be very large, 984.3 m(2)/g, indicating that the material is promising for gas storage. From the surface area measurements, the mean particle diameter was calculated to be 3.7 nm. This value is close to the lower limit of the carbon onions observed in HRTEM. However, closer HRTEM observations also reveal that some carbon onions are not well crystallized. The large specific surface area can be attributed to the "surface roughness" induced by the defective nature of the carbon onion shells. To explain the formation mechanism of the carbon onions, a model of arc discharge in water with two quenching zones is proposed: (1) the presence of ion current conducive for elongated nanoparticles growth and (2) the absence of ion current for isotropic growth of carbon onions. Based on this model, we propose that the physical characteristics of the product can be controlled. (C) 2002 American Institute of Physics |
| Internal Reference: [ID: 2475]
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|
| Sastry, S., Debenedetti, P. G., and Stillinger, F. H. |
| Statistical geometry of particle packings .2. ''Weak spots'' in liquids. |
| Physical Review E: Statistical, Nonlinear and Soft Matter Physics v.56, n.5, pp.5533-5543. (1997). |
| Abstract: We investigate the statistical geometry of inherent structures (mechanically stable arrangements of particles generated by a steepest-descent mapping of equilibrium configurations to local potential minima) of liquid configurations of the shifted-force Lennard-Jones system, as an approach to elucidating mechanisms for the decay of metastable states. For a wide range of densities, including some higher than the triple point density, inherent structures are found to display remarkably heterogeneous geometry, with an apparently bicontinuous structure consisting of a compact phase and a void region. The void region is found to consist of a single system-spanning cavity. The volume fraction of this cavity vanishes above the density rho* = 0.89. This density coincides with the minimum in the pressure vs density curve for inherent structures, at negative pressure, indicating that the observed heterogeneity of the inherent structures is triggered by the crossing of a threshold of mechanical instability, much like the familiar spinodal concept. Analysis of spontaneous density fluctuations in the equilibrium and superheated liquid reveals that atoms present in regions of low density (weak spots) map predominantly to the cavity interface in the inherent structures. We discuss the relevance of these observations to limits of stability of the metastable liquid, nucleation, and, possibly, the glass transition |
| Internal Reference: [ID: 2164]
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|
| Sastry, S., Corti, D. S., Debenedetti, P. G., and Stillinger, F. H. |
| Statistical geometry of particle packings .1. Algorithm for exact determination of connectivity, volume, and surface areas of void space in monodisperse and polydisperse sphere packings. |
| Physical Review E: Statistical, Nonlinear and Soft Matter Physics v.56, n.5, pp.5524-5532. (1997). |
| Abstract: Packings of spheres serve as useful models of the geometry of many physical systems; in particular, the description of the void region in such packings (the region not occupied by the spheres) is crucial in many studies, The void region is, in general, composed of disconnected cavities. We present an algorithm for decomposing void spate into cavities and determining the exact volumes and surface areas of such cavities-in three-dimensional packings of monodisperse and polydisperse spheres |
| Internal Reference: [ID: 2163]
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|
| Smith, M. A., Foley, H. C., and Lobo, R. F. |
| A simple model describes the PDF of a non-graphitizing carbon. |
| Carbon v.42, n.10, pp.2041-2048. (2004). |
| Abstract: A model for the structure of a non-graphitizing carbon is built by randomly incorporating between 0.5% and 4% non-hexagonal rings into an extended sp2 carbon sheet. The sheets are created using Cerius2 Modeling software, optimized using a DREIDING force-field, and turbostratically layered to create a three-dimensional structure. We show that the calculated pair distribution function (PDF) for models containing approximately 1% non-hexagonal rings is remarkable similar to the experimental PDF obtained from neutron scattering by a non-graphitizing carbon prepared from polyfurfuryl alcohol pyrolyzed at 1200 [degree sign]C. No attempt was made to fit the model to the experimental data, and the model has no adjustable parameters except for the fraction of non-hexagonal rings |
| Internal Reference: [ID: 2379]
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|
| Stuart, S. J., Knippenberg, M. T., Kum, O., and Krstic, P. S. |
| Simulation of amorphous carbon with a bond-order potential. |
| Physica Scripta v.T124, pp.58-64. (2006). |
| Abstract: Simulations of amorphous carbon were performed at densities ranging from 2.0 to 3.0 g cm(-3) with a reactive bond-order potential. The fraction of sp(3) bonding increases with increasing density, as is observed experimentally, but with generally too much sp(2) content. Ring size distributions are calculated, with a number of large rings observed. It is suggested that structural quantities that are more directly related to physical properties-such as void volumes and coordination numbers-are more useful than ring size distributions in characterizing the structure of amorphous carbon. Void fractions and void volume distributions are calculated, indicating that a percolating void network exists at 2.0 g cm(-3), large, non-percolating voids exist at intermediate density, and no voids are found larger than atomic volumes at 3.0 g cm(-3) |
| Internal Reference: [ID: 2287]
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|
| Terzyk, A. P., Furmaniak, S., Gauden, P. A., Harris, P. J. F., Wloch, J., and Kowalczyk, P. |
| Hyper-parallel tempering Monte Carlo simulations of Ar adsorption in new models of microporous non-graphitizing activated carbon: effect of microporosity. |
| Journal of Physics : Condensed Matter v.19, n.40, pp.406208 (2007). |
| Abstract: The adsorption of gases on microporous carbons is still poorly understood, partly because the structure of these carbons is not well known. Here, a model of microporous carbons based on fullerene- like fragments is used as the basis for a theoretical study of Ar adsorption on carbon. First, a simulation box was constructed, containing a plausible arrangement of carbon fragments. Next, using a new Monte Carlo simulation algorithm, two types of carbon fragments were gradually placed into the initial structure to increase its microporosity. Thirty six different microporous carbon structures were generated in this way. Using the method proposed recently by Bhattacharya and Gubbins ( BG), the micropore size distributions of the obtained carbon models and the average micropore diameters were calculated. For ten chosen structures, Ar adsorption isotherms ( 87 K) were simulated via the hyper- parallel tempering Monte Carlo simulation method. The isotherms obtained in this way were described by widely applied methods of microporous carbon characterisation, i. e. Nguyen and Do, Horvath - Kawazoe, high- resolution alpha(a)s plots, adsorption potential distributions and the Dubinin - Astakhov ( DA) equation. From simulated isotherms described by the DA equation, the average micropore diameters were calculated using empirical relationships proposed by different authors and they were compared with those from the BG method |
| Internal Reference: [ID: 2445]
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|
| Tomanek, D., Berber, S., Umemoto, K., and Saito, S. |
| Hierarchical assembly of nanostructured carbon foam. |
| Molecular Crystals and Liquid Crystals v.386, pp.189-195. (2002). |
| Abstract: This contribution addresses the unusual structural and electronic properties of carbon foam, a hypothetical new system that may form by a hierarchical self-assembly process from nanostructured graphite. Due its topological relationship to bulk forms of carbon, the postulated foam covers the structural phase space extending from hexagonal diamond to graphite. Ab initio results for the optimized structure indicate that carbon foam should be stable, structurally rigid, and metallic |
| Internal Reference: [ID: 2430]
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|
| Ugarte, D. |
| Curling and Closure of Graphitic Networks Under Electron-Beam Irradiation. |
| Nature v.359, n.6397, pp.707-709. (1992). |
| Abstract: THE discovery1 of buckminsterfullerene (C60) and its production in macroscopic quantities2 has stimulated a great deal of research. More recently, attention has turned towards other curved graphitic networks, such as the giant fullerenes (C(n), n > 100)3,4 and carbon nanotubes5-8. A general mechanism has been proposed9 in which the graphitic sheets bend in an attempt to eliminate the highly energetic dangling bonds present at the edge of the growing structure. Here, I report the response of carbon soot particles and tubular graphitic structures to intense electron-beam irradiation in a high-resolution electron microscope; such conditions resemble a high-temperature regime, permitting a degree of structural fluidity. With increased irradiation, there is a gradual reorganization of the initial material into quasi-spherical particles composed of concentric graphitic shells. This lends weight to the nucleation scheme proposed9 for fullerenes, and moreover, suggests that planar graphite may not be the most stable allotrope of carbon in systems of limited size |
| Internal Reference: [ID: 2471]
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|
| Umemoto, K., Saito, S., Berber, S., and Tomanek, D. |
| Carbon foam: Spanning the phase space between graphite and diamond. |
| Physical Review B: Condensed Matter v.64, n.19, pp.193409 (2001). |
| Abstract: We study an unusual class of carbon structures, based on rigidly interconnected segments of graphite. The resulting foamlike systems cover the structural phase space extending from hexagonal diamond to graphite. Related to the most stable phases of carbon, these hybrid systems show an unusually high structural stability at low mass densities. Our density-functional calculations indicate that carbon foam is metallic, stable, and structurally rigid |
| Internal Reference: [ID: 2382]
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|
| Valencia, F., Romero, A. H., Hernandez, E., Terrones, M., and Terrones, H. |
| Theoretical characterization of several models of nanoporous carbon. |
| New Journal of Physics v.5, pp.123.1-123.16. (2003). |
| Abstract: Elastic, electronic and vibrational properties of seven models of nanoporous carbon are reported. The studied structures are periodic graphitic arrangements with heptagonal and octagonal rings of carbon, known as Schwarzites. The calculations were performed within a non-orthogonal tight binding framework which has been shown to be reliable for diamond, graphene layers, fullerenes and carbon nanotubes. In contrast with previous studies, each structure was properly relaxed, so that differences between each model must be assigned to intrinsic properties rather than to differences in their construction. Thermodynamic properties were calculated from the vibrational density of states |
| Internal Reference: [ID: 2448]
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|
| Yamaguchi, Y. and Maruyama, S. |
| A molecular dynamics simulation of the fullerene formation process. |
| Chemical Physics Letters v.286, n.3-4, pp.336-342. (1998). |
| Abstract: A molecular dynamics simulation starting from 500 isolated carbon atoms resulted in several closed caged structures under suitable temperature control. A caged C70 cluster that appeared in the simulation was traced back to study the dynamics and structure of Cn precursors: simple chain and ring for n<20, tangled poly-cyclic structure for 2030. Furthermore, it was found that the final caged structure was obtained when the control temperature was roughly in the range from 2500 to 3000 K, and a graphitic flat structure resulted in lower control temperatures |
| Internal Reference: [ID: 2463]
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|
| Yamaguchi, Y. and Wakabayashi, T. |
| Coagulation of linear carbon molecules into nanoparticles: a molecular dynamics study. |
| Chemical Physics Letters v.388, n.4-6, pp.436-440. (2004). |
| Abstract: Using molecular dynamics (MD) simulations, the coagulation of carbon chain molecules that occurs on the subliming surface of a carbon-containing rare-gas matrix is investigated. Intermolecular connections with dangling bonds enhance the sublimation of the matrix and that results in the emission of a layer of nested carbon chains into vacuum at a velocity about 100 m/s. The following conversion from carbon sp- to more stable sp2-type bonds heats up the carbon material above 3000 K. During this process, the nested carbon layer self-anneals via a graphitic mono-layer into a conjunct array of particles with a dimension about 10 nm |
| Internal Reference: [ID: 2464]
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|
| Yamaguchi, Y., Colombo, L., Piseri, P., Ravagnan, L., and Milani, P. |
| Growth of sp-sp2 nanostructures in a carbon plasma. |
| Physical Review B: Condensed Matter v.76, n.13, pp.134119-7. (2007). |
| Abstract: The growth of sp and sp2 nanostructures in a carbon plasma is simulated by tight-binding molecular dynamics. The simulations are arranged so as to mimic the cluster formation conditions typical of a pulsed microplasma cluster source which is used to grow nanostructured sp-sp2 carbon films [L. Ravagnan et al., Phys. Rev. Lett. 98, 216103 (2007)]. The formation of linear, ring, and fullerenelike objects in the carbon plasma is found to proceed through a very long multistep process. Therefore, tight-binding simulations of unprecedented duration have been performed by exploiting the disconnected topology of the simulated carbon plasma which made it possible to implement a computationally efficient divide-and-diagonalize procedure. Present simulations prove that topologically different structures can be formed in experiments, depending on the plasma temperature and density. A thorough characterization of the observed structures as well as their evolution (caused both by thermal annealing and by cluster ripening) is provided. |
| Internal Reference: [ID: 2467]
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|
| Zhu, Z., Lu, Y., Qiao, D., Bai, S., Hu, T., Li, L., and Zheng, J. |
| Self-Catalytic Behavior of Carbon Nanotubes. |
| Journal of the American Chemical Society v.127, n.45, pp.15698-15699. (2005). |
| Abstract: Self-catalytic behavior of multi-walled carbon nanotubes is proposed and validated experimentally under the conditions in which metal catalysis was previously figured to work only. The self-catalysis could support the nanotube nucleation and radial and axial developing processes. This result should lead to a new and better understanding of the growth mechanism of carbon nanotubes in a metal catalytic process. |
| Internal Reference: [ID: 2458]
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|