Microstructural features of Co-filled carbon nanotubes

Ma, Xinlong; Cai, Yuanhua; Lun, Ning; Ao, Qing; Li, Shenli; Fengzhao, LI; Wen, Shulin

doi:10.1016/s0167-577x(02)01391-5

Cited by 20 publications

(10 citation statements)

References 19 publications

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“…High-resolution transmission electron microscopy (HRTEM) experiments have suggested that large Co particles inside CNTs have face-centered-cubic (fcc) structures, 10 instead of stable hexagonal-close-packed (hcp) structures; 11 i.e., the interaction of Co surface atoms with the inside CNT surfaces induces a structure phase change.…”

Section: Introductionmentioning

confidence: 99%

Encapsulation of small magnetic clusters in fullerene cages: A density functional theory investigation within van der Waals corrections

Tereshchuk

Silva

2012

Phys. Rev. B

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The encapsulation of magnetic transition-metal (TM) clusters inside carbon cages (fullerenes, nanotubes) has been of great interest due to the wide range of applications, which spread from medical sensors in magnetic resonance imaging to photonic crystals. Several theoretical studies have been reported; however, our atomistic understanding of the physical properties of encapsulated magnetic TM 3d clusters is far from satisfactory. In this work, we will report general trends, derived from density functional theory within the generalized gradient approximation proposed by Perdew, Burke, and Ernzerhof (PBE), for the encapsulation properties of the TM m @C n (TM = Fe, Co, Ni; m = 2−6, n = 60,70,80,90) systems. Furthermore, to understand the role of the van der Waals corrections to the physical properties, we employed the empirical Grimme's correction (PBE + D2). We found that both PBE and PBE + D2 functionals yield almost the same geometric parameters, magnetic and electronic properties, however, PBE + D2 strongly enhances the encapsulation energy. We found that the center of mass of the TM m clusters is displaced towards the inside C n surfaces, except for large TM m clusters (m = 5 and 6). For few cases, e.g., Co 4 and Fe 4 , the encapsulation changes the putative lowest-energy structure compared to the isolated TM m clusters. We identified few physical parameters that play an important role in the sign and magnitude of the encapsulation energy, namely, cluster size, fullerene equatorial diameter, shape, curvature of the inside C n surface, number of TM atoms that bind directly to the inside C n surface, and the van der Waals correction. The total magnetic moment of encapsulated TM m clusters decreases compared with the isolated TM m clusters, which is expected due to the hybridization of the d-p states, and strongly depends on the size and shape of the fullerene cages.

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Section: Introductionmentioning

confidence: 99%

Encapsulation of small magnetic clusters in fullerene cages: A density functional theory investigation within van der Waals corrections

Tereshchuk

Silva

2012

Phys. Rev. B

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“…Experimental observations suggested that the iron oxide particles had poor catalytic action for CNT growth and in-situ reduction of oxide clusters to Fe by hydrogen plasma plays a key role in discontinuous filling of the nanotubes by the catalytic particles. [12][13][14] have been used to synthesize CNTs. CVD methods (both thermal and plasma enhanced) are reliable in producing multiwalled CNTs (MWNTs) with proper control over the process parameters.…”

mentioning

confidence: 99%

“…The unique structure-properties combination of CNTs have open up a wide range of research and their potential applications such as flat panel displays [2], gas storage [3], sensors [4], scanning probe microscope tips [5], single molecular transistors [6], nanotweezers [7], high power electrochemical capacitors [8], solar cells [9], etc. Several methods such as arc discharge [10], laser ablation [11], and different forms of chemical vapor deposition (CVD) [12][13][14] have been used to synthesize CNTs. CVD methods (both thermal and plasma enhanced) are reliable in producing multiwalled CNTs (MWNTs) with proper control over the process parameters.…”

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confidence: 99%

Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes

Srivastava

Kumar

2010

Nano-Micro Lett

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The effect of hydrogen plasma treatment of iron oxide films on the growth and microstructure of carbon nanotubes (CNTs) by microwave plasma enhanced chemical vapor deposition process has been investigated. Microwave plasma was characterized in-situ using optical emission spectrometer. Morphology of the films was examined by scanning electron microscopy. Structural analysis was carried out by high resolution transmission electron microscopy (HRTEM) equipped with energy dispersive X-ray spectroscopy (EDS) and micro-diffraction attachments. It is found that oxide films without H 2 plasma pretreatment or treated for lesser time resulted in CNT films with high percentage of carbonaceous particles and with embedded particles/nanorods distributed discontinuously in the cavity of the nanotubes. The embedded particles were found to be of iron carbide (Fe-C) as confirmed by HRTEM, EDS and micro-diffraction analysis. Experimental observations suggested that the iron oxide particles had poor catalytic action for CNT growth and in-situ reduction of oxide clusters to Fe by hydrogen plasma plays a key role in discontinuous filling of the nanotubes by the catalytic particles. [12][13][14] have been used to synthesize CNTs. CVD methods (both thermal and plasma enhanced) are reliable in producing multiwalled CNTs (MWNTs) with proper control over the process parameters. Plasma enhanced CVD, however, can produce CNTs with a higher growth rate, at low temperature, and with better reproducibility. The plasma not only ionizes the gas but also causes a local surface heating [15]. Consequently, growth temperature could be significantly decreased compared to non-plasma CVD processes. In addition, the plasma atmosphere may also influence the detailed catalyst surface kinetics in many ways [16] and hence the growth of carbon nanostructures.Growth of CNTs and their microstructures depend on several parameters such as growth technique, feed gases, growth temperature, catalyst, and catalyst preparation method as well as their state (solid, liquid or vapor). In plasma assisted CVD processes, dilution gases play a critical role in the growth of CNTs and the structure of CNTs can be tailored by judicious control over gas composition [17]. In our earlier report, we investigated the effect of different dilution gases such as H 2 , NH 3 and N 2 and their different composition on the growth and microstructure of CNTs by microwave plasma enhanced CVD (MPECVD) process on Fe coated Si substrates using C 2 H 2 as feed gas [17]. Plasma pretreatment of catalyst film can also affect the growth and structure of CNTs significantly especially in a high frequency plasma process such as MPECVD. To the best of our knowledge, effect of H 2 plasma pretreatment of iron oxide films on the growth and structure of CNTs by MPECVD process have not been reported. Therefore, the motivation for the present

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“…As such, the Co 13 cluster emits less magnetism in the (6,2) tube with the diameter 5.65 Å than in the (5,3) tube with the diameter 5.48 Å, which demonstrates a nontrivial role of the carbon structure in magnetisation of Co-C complex. This finding is very interesting because the transmission electron microscopy, electron diffraction, and X-ray spectroscopy showed a structural transition of Co particles inside CNTs from hexagonal-close-packed (hcp) arrangement to face-centered-cubic (fcc) organization as a result of interaction between Co nanoparticles with CNTs [30]. Although the magnetic features of Co 13 cluster in nanotubes were noticeable in our calculations, the hidden mechanisms of magnetism and peculiarity of electron actions in filled nanotubes are out of DFT approach [31,32].…”

Section: Analysis and Discussionmentioning

confidence: 87%

Magnetism of Co<sub>13</sub>-Filled Carbon Nanotubes of Diverse Chiral Symmetry

Kuznetsov¹

2013

JMP

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The attempt to study magnetism in chiral space of single-walled carbon nanotubes (SWNTs) with embedded metal cluster is presented. Co 13 metallic cluster inside zigzag and chiral single-walled nanotubes was investigated using density functional theory (DFT). Magnetic properties of the endohedral nanotubes with the various chiral indexwere characterized by calculation of the total spin magnetic moment (S). The dependence of S on the chiral symmetry of nanotubes, as well as the orientation of Co 13 cluster within nanotubes was found. Longitudinal orientation of icosahedral Co 13 cluster was preferable for magnetization in general. However, it was shown that the magnetic landscape M f n m  of endohedral nanotubes is very complex and sharp.

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Microstructural features of Co-filled carbon nanotubes

Cited by 20 publications

References 19 publications

Encapsulation of small magnetic clusters in fullerene cages: A density functional theory investigation within van der Waals corrections

Encapsulation of small magnetic clusters in fullerene cages: A density functional theory investigation within van der Waals corrections

Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes

Magnetism of Co<sub>13</sub>-Filled Carbon Nanotubes of Diverse Chiral Symmetry

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Microstructural features of Co-filled carbon nanotubes

Cited by 20 publications

References 19 publications

Encapsulation of small magnetic clusters in fullerene cages: A density functional theory investigation within van der Waals corrections

Encapsulation of small magnetic clusters in fullerene cages: A density functional theory investigation within van der Waals corrections

Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes

Magnetism of Co&lt;sub&gt;13&lt;/sub&gt;-Filled Carbon Nanotubes of Diverse Chiral Symmetry

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Magnetism of Co<sub>13</sub>-Filled Carbon Nanotubes of Diverse Chiral Symmetry