Structures of ultrathin copper nanowires encapsulated in carbon nanotubes

Choi, Wook; Kang, Jeong Won; Hwang, Ho Jung

doi:10.1103/physrevb.68.193405

Cited by 120 publications

(96 citation statements)

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“…The cylindrical concentric shell structures predicted for solidified Cu and Au in SWCNTs, 7,8 are also found for mercury in ͑20,20͒ and smaller nanotubes. Figure 6͑a͒ illustrates radial snapshots of the encapsulated mercury in a ͑20,20͒ SWCNT at various temperatures above and below the solidification point ͑ϳ173 K͒.…”

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confidence: 72%

“…6 Depending on the nanotube diameter, helical-strand, cylindrical-shell, and fcc structures were predicted for Cu and Au confined inside nanotube cavities. 7,8 Experimental evidence for the existence of such new structures in nanotube cavities has been sparse. Using highresolution transmission electron microscopy, Fan et al 9 demonstrated the formation of a double-strand helix of iodine atoms inside a ͑10,10͒ single-walled nanotube ͑SWCNT͒.…”

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Contact angles, ordering, and solidification of liquid mercury in carbon nanotube cavities

Kutana

Giapis

2007

Phys. Rev. B

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Optimized model potentials for mercury-mercury and mercury-carbon interactions are used in molecular dynamics simulations to study wetting and solidification of liquid mercury encapsulated in single-walled carbon nanotubes. The contact angle of mercury in the nanotube cavity increases linearly with wall curvature. The solid-liquid transition becomes less well defined as nanotube diameter decreases, while the melting temperature drops exponentially. A concentric cylindrical-shell structure is predicted for solidified mercury in small ͑20,20͒ nanotubes, while a polycrystalline structure appears in larger ͑40,40͒ nanotubes. DOI: 10.1103/PhysRevB.76.195444 PACS number͑s͒: 65.80.ϩn, 02.70.Ns, 64.70.Dv Liquid mercury does not wet graphite spontaneously. Indeed, fresh mercury forms droplets on highly ordered pyrolytic graphite with a contact angle of 152.5°. 1 Being equivalent to graphene scrolls, carbon nanotubes too cannot be wetted spontaneously by mercury, or for that matter, by any liquid metal with surface tension greater than 180 mN/ m. 2 However, wetting and filling of the inner cavity of a carbon nanotube with mercury have been shown to occur as a result of electrowetting. 3 Continuous columns of liquid mercury form inside carbon nanotubes with their open end immersed into a mercury droplet, following the application of a voltage exceeding a threshold value between the nanotube and the droplet. Once confined in a nanotube cavity, the wetting behavior of a nonwetting fluid becomes of fundamental and practical interest for nanofluidics. Furthermore, studies of freezing or melting transitions of metals under onedimensional confinement could lead to the discovery of new crystalline phases and possibly to the existence of a solidliquid critical point. 4 New solid metal phases could lead to unexpected mechanical, electrical, magnetic, and catalytic properties.Ordering and crystallization of materials in carbon nanotube cavities have attracted intense theoretical interest. New ice phases, including ordered ice nanotubes, were predicted to form by freezing water inside carbon nanotubes. 5 Simulations of CCl 4 in nanotube cavities showed liquid ordering in concentric layers, which solidify into two-dimensional hexagonal crystals unlike those observed for bulk crystallization. 6 Depending on the nanotube diameter, helical-strand, cylindrical-shell, and fcc structures were predicted for Cu and Au confined inside nanotube cavities. 7,8 Experimental evidence for the existence of such new structures in nanotube cavities has been sparse. Using highresolution transmission electron microscopy, Fan et al. 9 demonstrated the formation of a double-strand helix of iodine atoms inside a ͑10,10͒ single-walled nanotube ͑SWCNT͒. In slightly larger SWCNTs, Guan et al. 10 found a new crystalline phase of iodine, in addition to a triple-strand helix. Using x-ray diffraction, Maniwa et al. 11 studied water freezing in SWCNT bundles and found a new peak appearing in the diffraction spectrum at 235 K, which was attributed to the formati...

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confidence: 99%

Contact angles, ordering, and solidification of liquid mercury in carbon nanotube cavities

Kutana

Giapis

2007

Phys. Rev. B

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“…[4][5][6] Pure metals, in particular, were predicted to form cylindrically layered structures. 7,8 Although they have received markedly less attention, metallic alloys should also form cylindrical shell structures when solidified in CNTs. However, differences in the interaction energy between the alloy components and the graphitic walls may allow one element to accumulate near the wall while the other is displaced toward the tube center.…”

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confidence: 99%

Surface segregation of bimetallic alloys in nanoscale confinement

Giapis

Goicochea

et al. 2010

Applied Physics Letters

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The surface segregation of Pt atoms in liquid bimetallic alloys confined in carbon nanotube cavities was studied using molecular dynamics simulations. Considerable enrichment in the Pt-atom surface density was found to occur in Pt alloys, when the complementary metal has surface energy higher than Pt and simultaneously metal-wall interaction strength lower than that of Pt with the confining wall. The results suggest that solidification of liquid binary alloys in nanochannels could produce core-shell nanorods with the shell enriched in one of the components for catalytic and other applications. © 2010 American Institute of Physics. ͓doi:10.1063/1.3500825͔The influence of nanoscale confinement on the thermodynamic behavior and physical properties of materials has attracted widespread interest in the last two decades. 1 Constraints in the packing of atoms or molecules confined in one dimension could influence the freezing of liquids and lead to the formation of new solid phases. 2 Carbon nanotubes ͑CNTs͒, with their hollow inner cavity, offer an ideal nanochannel for performing such studies. 2,3 Indeed, both helical strand and cylindrical shell structures-not present in bulk phases-have been demonstrated for single-element materials confined in CNTs. [4][5][6] Pure metals, in particular, were predicted to form cylindrically layered structures. 7,8 Although they have received markedly less attention, metallic alloys should also form cylindrical shell structures when solidified in CNTs. However, differences in the interaction energy between the alloy components and the graphitic walls may allow one element to accumulate near the wall while the other is displaced toward the tube center. This surface segregation process may lead to the spontaneous formation of core-shell nanostructures from impure mixtures, with possibly unexpected electrical, magnetic, or catalytic properties.Here we report on the propensity of the Pt atoms to segregate near confining walls in Pt-based metallic alloys. We simulate the solidification of binary liquid mixtures inside CNTs using molecular dynamics. We seek mixtures of low initial Pt concentration for which the surface density of the segregated Pt atoms is maximized. Our model structure consists of a binary alloy column confined in a ͑20,20͒ single-walled CNT, which is composed of 7680 carbon atoms ͑diameter= 2.7 nm, length= 23.4 nm͒. We consider various Pt-based alloys and focus on the effect of the initial concentration, metal-wall interaction, and surface energy on the quality of the final core-shell structure. The alloy column ͑initially ϳ18-nm-long͒ is taken from the equilibrium configuration for bulk alloy of the same composition. The alloy column has two free ends and contains ϳ4000 atoms with Pt concentration ranging from 5 to 95 at. %. The entire system is confined within a rectangular simulation box of 8 ϫ 23.4 ϫ 8 nm 3 , long enough in the x and z directions to avoid self-imaging interactions. Periodic boundary conditions are used in all directions, resulting in an alloy nanoro...

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“…These observed characteristics indicate the encapsulated Cu nanowire forms a polycrystal with a fcc structure. The fcc structure is predicted for a Cu nanowire encapsulated in a CNT by a theoretical study (Choi et al, 2003). TEM examination of outer regions of the sphere like particles formed together with Cu-filled CNTs indicated that the particles were Cu-filled CNCs (Fig.…”

Section: Cu-filled Cnts and Cncs From Graphite Containing Cumentioning

confidence: 99%

Formation of Various Nanocarbon and Composite Structures by Laser Ablation

Kokai¹

2011

Advances in Composite Materials for Medicine and Nanotechnology

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Structures of ultrathin copper nanowires encapsulated in carbon nanotubes

Cited by 120 publications

References 45 publications

Contact angles, ordering, and solidification of liquid mercury in carbon nanotube cavities

Contact angles, ordering, and solidification of liquid mercury in carbon nanotube cavities

Surface segregation of bimetallic alloys in nanoscale confinement

Formation of Various Nanocarbon and Composite Structures by Laser Ablation

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