Carbon Peapods Research Articles

Vacancy defects impede the transition from peapods to diamond: a neuroevolution machine learning study.

Exploration of novel carbon allotropes has been a central subject in materials science, in which carbon peapods hold great potential as a precursor for the development of new carbon allotropes. To enable precise large-scale molecular dynamics simulations, we develop a high-accurate and low-cost machine-learned potential (MLP) for carbon materials using the neuroevolution potential framework. Based on the MLP, we conduct an investigation into the structural transitions of peapod arrays under high-temperature and high-pressure conditions and disclose the impact of vacancy defects. Defects promote the transition from the ordered crystalline structure to the disordered amorphous structure in peapods at low temperatures, while impeding the transition to the ordered diamond structure. Benefiting from the accurate MLP, we are able to reproduce the experimentally observed carbon structures in numerical simulations. We build a diagram summarizing all the structures that appear in the compression simulation of peapod arrays at various temperatures. The present work not only discloses the underlying mechanism of structural transitions from carbon peapods into various functional carbon materials, but also provides a high-accurate and low-cost interatomic potential that shall be valuable in the exploration of novel carbon allotropes.

Structure and Dynamics of Carbon Buckyballs Encapsulated to Single-Walled Carbon Nanotubes

The structural and dynamical attributes of C60 chains inserted inside Single Walled carbon Nanotubes (SWNT) have been investigated by x-ray and neutron refraction, and inelastic neutron scattering (INS). The mensuration have been performed on a large mass of a very high quality carbon peapods sample. We showed that powder refraction could hardly give definitive response on the way the C60s are bonded inside SWNT. However, the comparison of the neutron-derived generalized compression of states (GDOS) of the inserted C60 peas with the GDOS of the same objects derived from lattice dynamics computations led to unambiguous results. The witnessing of excitations in the 8-15 meV span is a clear evidence for the presence strong bonds among C60s in the sample. In the same time, the witnessing of a very weak quasi-elastic signal may be relevant to rotational motions of C60 monomers inside the SWNT. These results suggest that peapods are built of a mixed phase of C60 monomers and C60 n-mers.

Carbon Nanotube Peapods Under High-Strain Rate Conditions: A Molecular Dynamics Investigation

ABSTRACTNew forms of carbon-based materials have received great attention, and the developed materials have found many applications in nanotechnology. Interesting novel carbon structures include the carbon peapods, which are comprised of fullerenes encapsulated within carbon nanotubes. Peapod-like nanostructures have been successfully synthesized, and have been used in optical modulation devices, transistors, solar cells, and in other devices. However, the mechanical properties of these structures are not completely elucidated. In this work, we investigated, using fully atomistic molecular dynamics simulations, the deformation of carbon peapods under high-strain rate conditions, which are achieved by shooting the peapods at ultrasonic velocities against a rigid substrate. Our results show that carbon peapods experience large deformation at impact, and undergo multiple fracture pathways, depending primarily on the relative orientation between the peapod and the substrate, and the impact velocity. Observed outcomes include fullerene ejection, carbon nanotube fracture, fullerene, and nanotube coalescence, as well as the formation of amorphous carbon structures.

Strain-induced semiconductor-to-metal transitions in C36-based carbon peapods: Ab initio study

We present a density functional study of the band structure and some elastic properties of semiconductor carbon nanotube endohedrally doped with the C36 fullerenes. We found that the electronic states belonging to C36s lied inside the band gap of the pristine tube. External strain applied along the tube axis results in decreasing of the semiconducting gap from 0.3 to 0 eV. Metallic behavior of the strained system is confirmed via the additional calculations of electronic transmission coefficients. Phonons influence is accounted with the molecular dynamics approach. Strain of about 0.04 corresponds to the linear part of stress-strain curve and is found to be sufficient to observe the semiconductor-to-metal transitions at room temperature.

Vibration analysis of single-walled carbon peapods based on nonlocal Timoshenko beam theory

In this article, vibration behavior of single-walled carbon nanotube encapsulating C60 molecules is studied using the Eringen’s nonlocal elasticity theory within the frame work of Timoshenko beam theory. The governing equation and boundary conditions are derived using Hamilton’s principle. It is considered that the nanopeapod is embedded in an elastic medium and the C60 molecules are modeled as lumped masses attached to the nanobeam. The Galerkin’s method is applied to determine the natural frequency of the nanobeam with clamped–clamped boundary conditions. Effects of nonlocality, foundation stiffness, and ratio of the fullerenes’ mass to the nanotube’s mass on the natural frequencies are investigated. In addition, by vanishing effects of shear deformation and rotary inertia, the results based on Euler–Bernoulli beam theory are presented.

Isomerization of sp2‐hybridized carbon nanomaterials: structural transformation and topological defects of fullerene, carbon nanotube, and graphene

The structural transformation of various carbon nanomaterials, such as fullerene, carbon nanotube (CNT), and graphene, has been extensively studied both experimentally and theoretically. It was broadly recognized that the isomerization of the sp2‐hybridized carbon network through the generalized Stone–Wales transformation (GSWT), which is equivalent to a CC bond's in‐plane rotation, is the key mechanism facilitating most structural revolutions in carbon materials. The GSWT process also plays a crucial role in the shape change, defect healing and the growth in these carbon materials and may greatly affect their mechanical, chemical, and electronic performances. In this review, we summarize the previous studies on the GSWT and topological defects in the sp2 carbon network as well as the consequent results of sp2‐hybridized carbon materials’ isomerization, including structural shrinkage of the giant fullerenes and CNTs at high temperature, plastic deformation of CNTs, coalescence of the fullerenes and carbon peapods, topological defects evolution under high energetic irradiation, and healing of the defects during the chemical vapor deposition growth of CNT and graphene. This review provides a clear picture of the isomerization of the sp2‐hybridized carbon materials, from single step process until the large‐scale structural transformation, and many examples for the readers to get into the topic deeply step by step. WIREs Comput Mol Sci 2017, 7:e1283. doi: 10.1002/wcms.1283This article is categorized under: Structure and Mechanism > Reaction Mechanisms and Catalysis Structure and Mechanism > Computational Materials Science

Free vibrations of single walled carbon peapods

In this paper the free vibration of single walled carbon nanopeapods encapsulating C60 molecules is considered. The nanopeapod is embedded in an elastic medium and clamped at both ends. The Euler–Bernoulli beam model is used for the carbon nanotube and the C60 molecules are considered as lumped masses attached to the beam. Based on the nonlocal elasticity theory the governing equation of motion is derived and the resonance frequencies of the nanopeapod are obtained. The effects of small scale, foundation stiffness and ratio of the fullerenes' mass to the nanotube's mass on the frequencies are studied and some conclusions are drawn.

In situ X-ray diffraction observation of two-step fullerene coalescence in carbon peapods

We report an in situ X-ray diffraction study of the high-temperature coalescence of C60 and C70 peapods. The monitoring of the structural evolution with time at two successive temperatures (1000 °C and 1200 °C) allows highlighting the occurrence of a two-step process for both peapods samples. The first step of the process, slower for C70 peapods than for C60 ones, is attributed to the transformation of individual molecules into corrugated tubules recalling the fullerenes one-dimensional periodicity. Even after long annealing time at 1000 °C this transformation is found to stagnate, until the temperature is set higher than 1050 °C, where the corrugated tubules evolve into well-formed inner nanotubes.

Electronic structure and magnetic properties of 31P@C60-SWCNT as peapods

Design of the NMR quantum computer of 1D spin chains based on 31P@C60-SWCNT as peapods was studied. Electronic structure and magnetic properties of 31P@C60 encapsulating fullerenes within SWCNT as peapods was investigated by quantum chemical calculation. Characterization of chemical shifts of 13C, principle g-tensor and A-tensor of hyperfine structure for phosphorus atom with electronic spin S = 3/2 and nuclear spin I = 1/2 were studied. The excited energy and wavelength at 1512 nm and 728 nm confirmed assignment of the first and second states as van Hove transitions. Molecular design of carbon peapods is important to control quantum spin qubits, splitting by spin-local interaction and dipole-dipole interaction based on p-orbital spin density distribution under hybrization of molecular orbital at excited state and grand state.

Molecular dynamics simulations of the transformation of carbon peapods into double-walled carbon nanotubes

The transformation of carbon peapods (encapsulated fullerenes in nanotubes) into double-walled nanotubes was studied using molecular dynamics simulation. The simulations reproduce the two main trends known experimentally: the production of low-defect nanotubes and the templating effect of the outer tube. The process involves a low-temperature polymerization of the fullerenes followed by higher temperature self-assembly into a tube. Modelling of this second stage is made possible by the use of the Environment-Dependent Interaction Potential, a large number of atoms and long-time annealing. Analysis shows that the outer tube acts as a container for the self-assembly process, analogous to previous simulations and experiments in which free surfaces, either external or internal, template the formation of highly ordered sp 2 phases.

Effects of Doping on Electronic Structure and Correlations in Carbon Peapods

Sc@C(82) peapods, which form encapsulated spin-1/2 antiferromagnetic chains under doping with electrons or holes are investigated using hybrid density functional theory. The narrow fullerene bands become shifted relative to nanotube bands resulting in charge transfer and conducting channels along both the fullerene chain and the nanotube. This is accompanied by a reduction in the magnetic moments on the fullerenes, consistent with a 1D Hubbard-Anderson model description.

Energetics of carbon peapods: Elliptical deformation of nanotubes and aggregation of encapsulatedC60

The energetics of large diameter carbon nanotubes encapsulating ${\text{C}}_{60}$ molecules (peapods) have been studied by using the local density approximation in the density-functional theory (DFT). We find that the energy gain ascribed to the encapsulation of ${\text{C}}_{60}$ increases under the elliptical deformation of the nanotubes compared to that for the nanotubes with circular cross section. The energy cost of the deformation of nanotubes is found to be less than 10 meV per atom and is found to be the largest for the (20,20) nanotube. We also explore the energetics of the aggregation of encapsulated ${\text{C}}_{60}$ in the nanometer-scale space of the (10,10) nanotube. The total energy of the dimerized ${\text{C}}_{60}$ encapsulated in the (10,10) nanotube is lower by 0.2 eV per atom than that of the isolated ${\text{C}}_{60}$ indicating that the dimerization reaction is exothermic. The activation barrier for the dimerization of ${\text{C}}_{60}$ is about 1.4 eV, so that the spontaneous dimerization of ${\text{C}}_{60}$ is unlikely to take place without any external stimuli such as electron irradiation.

Modeling spin interactions in carbon peapods using a hybrid density functional theory

The $\text{Sc}@{\text{C}}_{82}$ endohedral fullerenes inside a single-wall semiconducting or metallic nanotube form a well-defined chain of antiferromagnetically coupled spins. Using hybrid density functional theory (DFT), we find that the spin resides mainly on the fullerene cage, whether or not the fullerenes are in a nanotube. The spin interactions decay exponentially with fullerene separation and the system can be described by a simple antiferromagnetic Heisenberg spin chain. Energy parameters for a generalized Hubbard-Anderson model are deduced from the DFT calculations and yield a second-order Heisenberg exchange energy, which is in good agreement with total-energy calculations for parallel and antiparallel spin configurations. Within the accuracy of the calculations, neither semiconducting nor metallic nanotubes affect the interactions between the fullerene electron spins.

Dipole polarizability of onion-like carbons and electromagnetic properties of theircomposites

Onion-like carbons (OLC) obtained by thermal transformation of nanodiamonds areagglomerates of multi-shell fullerenes, often covered by an external graphitic mantle. Forthe present work, elemental OLC units were constructed on the computer by coalescence ofseveral two-layer fullerenes, in a structure similar to carbon peapods with a corrugatedexternal wall. The electrical polarizability of such pod-of-peas fullerenes has beencomputed by a classical monopole–dipole atomistic theory. The description ofpod-of-peas fullerenes was further simplified by representing them as linear arrays ofpoint-like objects, whose polarizability matches that of the starting molecules.Calculations demonstrated that the static polarizability of spherically shapedassemblies of these arrays, modeling real OLC materials, is weakly dependent on thegeometry of its constituent molecules and is chiefly proportional to the volume ofthe whole cluster. It increases with increasing filling fraction of the pod-of-peasfullerenes in the OLC aggregate. The polarizability so obtained can be used inMaxwell–Garnett theory to predict the permittivity of OLC-based composites, atleast for static excitations. Experimental results obtained at GHz frequenciesreveal a weak attenuation for OLC- and nanodiamond-based polydimethylsiloxanecomposites. In these silicone composites, we did not find long chains of coupledOLCs. Quite separated clusters were found instead, which contribute little to thepolarizability and to the dielectric properties, in good agreement with our theoreticalpredictions.

Energetics, structure, and long-range interaction of vacancy-type defects in carbon nanotubes: Atomistic simulations

The presence of vacancy clusters in carbon nanotubes has been assumed to explain the formation of carbon peapods and the difference between the experimentally measured and theoretical fracture strength of nanotubes. We use atomistic simulations at various levels of theory to study the characteristics of large vacancies formed by up to six missing atoms. We show that the formation of big ``holes'' on nanotube walls is energetically unfavorable as the vacancies tend to split into smaller defects due to the reconstruction of the nanotube atomic network. We also demonstrate that there is a weak but long-ranged interaction between the vacancies not only through strain fields but, surprisingly, also due to electronic effects, similar to those of adatoms on metal surfaces.

Structural properties of carbon peapods under extreme conditions studied usingin situx-ray diffraction

Structural properties of carbon peapods, ${\mathrm{C}}_{60}$, trapped into single-walled carbon nanotubes (SWNT), have been studied under high-pressure/high-temperature conditions (HPHT) by in situ x-ray diffraction. The ${\mathrm{C}}_{60}$ chain structure together with the influence of the filling on the SWNT change under HPHT treatment is investigated. Synthesis of a one-dimensional polymer chain of ${\mathrm{C}}_{60}$ inside the single-walled carbon nanotubes is evidenced. At $4\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, increasing the temperature up to $1023\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ leads to a progressive ${\mathrm{C}}_{60}$ polymerization that is associated to a shortening of ${\mathrm{C}}_{60}\text{\ensuremath{-}}{\mathrm{C}}_{60}$ distance down to $8.7\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. Back to ambient conditions, the ${\mathrm{C}}_{60}$ chain remains polymerized, emphasizing the high stability of this material. In addition, our data strongly suggest a symmetry change of the two-dimensional bunde lattice under pressure.

Compressive and tensile properties of Ar filled carbon nano-peapods

In order to investigate the compressive and tensile mechanical properties of the carbon nano-peapods filled with Ar atoms outside, inside, or both outside and inside their C 60 fullerenes, the MD (molecular dynamics) method was used to simulate the compression and tension of the carbon peapods. According to the calculated results the effects of the filled pattern and amount of Ar atom on the mechanical properties of the carbon peapods were discussed systematically. It is shown that (1) the Ar filled nano-peapods have better compressive properties than the unfilled one, and the more Ar atoms are filled, the better the compressive properties are, (2) when the same amount of Ar atoms are filled, the carbon peapod with Ar atoms both outside and inside its C 60 fullerenes has the best compressive properties and the one with Ar atoms only outside has the worst compressive properties, and (3) the filled pattern and amount of Ar atom seem to have little effect on the tensile properties of the carbon peapods.

Nanoscale Lasers Based on Carbon Peapods

A scheme of nanoscale lasers based on the so-called carbon peapodsis examined in detail. Since there is considerable cylindricalempty space in the middle of a single-wall carbon nanotube(SWCNT), it can serve as a laser resonant cavity that consists oftwo highly reflecting alignment ``mirrors'' separated by adistance. These mirrors refer to the ordered arrays of C60inside SWCNTs, which have photonic bandgap structures. Meanwhile,ideally single-mode lasers are supposed to be produced in thenanoscale resonant cavity.

Raman active modes in carbon peapods

The nonresonant Raman spectra of infinite peapod were calculated in the framework of bond-polarization theory by using either direct diagonalisation of dynamical matrix or the spectral moments method. The effect of C 60 -tube interaction on the mode frequencies both of the peas and the pod has been calculated using the Lennard-Jones, potential showing that the lowest frequency mode region is more affected than the higher one. The tube chirality's and diameter effects on Raman spectra were studied. Also, we show that filling factors of C 60 molecules inside some single-walled carbon nanotubes (SWCNT) may induce a splitting of the radial breathing like mode (RBLM) into two components. Comparison with experimental results is reported.

Redox Doping of Double‐Wall Carbon Nanotubes and C60 Peapods

Electrochemical and chemical doping of double‐walled carbon nanotubes (DWCNT) and peapods, C60@SWCNT was monitored by in situ Raman spectroelectrochemistry. Chemical doping was carried out by gaseous Kor F2. The outer tube in DWCNT is more sensitive to doping. The peapods exhibit characteristic and complex feedback to chemical or electrochemical doping.