C60 Peapods Research Articles

Raman active modes in defective peapods

The vibrational properties of defective single-walled carbon nanotube filled with C60 fullerene is the subject of the current study. For this aim we use the spectral moments method in the framework of the bond-polarization theory to calculate the non-resonant Raman spectra of hexa-vacancy defective C60 peapods. Essentially, the vibrational properties are closely coupled with the atomic structure of the system. The evolution of the Raman spectrum as a function of the spatial arrangement of defects in carbon nanotubes is discussed. This work provides benchmark theoretical results to understand the experimental data of defective C60 peapods. #single_wall_carbon_nanotube #C60_peapods #hexa-vacancy_defect #Raman_spectroscopy #pectral_moment_method

C60 Filling Rate in Carbon Peapods: A Nonresonant Raman Spectra Analysis

We calculated the nonresonant Raman spectra of C60 peapods to determine the concentration of C60 fullerenes inside single-walled carbon nanotubes. We focus on peapods with large diameters for which C60 molecules can adopt a double helix configuration or a two-molecule layer configuration. Our calculations are performed within the framework of the bond-polarizability model combined with the spectral moment’s method. The changes in the Raman spectra as a function of C60 filling rate and the configuration of C60 molecules inside the nanotubes are identified and discussed. Our calculations support the experimental method proposed by Kuzmany to evaluate the concentration of C60 molecules inside nanotubes.

Filling rate dependence on theoretical Raman spectra of carbon C60 peapods

We use the spectral moments method in the framework of the bond-polarization theory to calculate nonresonant Raman spectra of C60 peapods as a function of the concentration of fullerenes inside the single wall carbon nanotubes. The evolution of the average Raman intensity ratios between Raman mode of C60 molecules and nanotube as a function of the concentration of fullerenes has been analyzed and a general good agreement is found between calculations and measurements. #CARBON_NANOTUBES #PEAPODS #RAMAN_SPECTROSCOPY #SIMULATION #SPECTRAL_MOMENT_METHOD

Influence of packing on the vibrations of homogeneous bundles of C60 peapods

The non-resonant Raman spectra of homogeneous bundles of C60 peapods (C60 inserted in single-walled carbon nanotubes) are calculated in the framework of spectral moment method, together with a bond-polarizability model. The evolutions of the low wavenumber range of the Raman spectrum of homogeneous bundles of C60 peapods as a function of the nanotube diameter and the size of bundles are discussed. The effect of the C60 filling factor is investigated in detail. The results are compared to experimental Raman data measured on various samples of C60 peapods.

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.

Carbon nanotube and boron nitride nanotube hosted C60–V nanopeapods

We investigate electronic and transport properties of a novel form of nanopeapod structure, where the “pod” component is either a carbon nanotube (CNT) or a boron-nitride nanotube (BNNT) while the “pea” component is a chain of C60–V dimers. Compared to the conventional carbon peapod where the “pea” is a chain of C60 fullerenes, marked changes in the electronic structures are found due to the formation of coordination bonds between V and two neighboring C60 molecules. The local spins in the (η6-C60–V)@CNT or (η6-C60–V)@BNNT peapod are coupled via antiferromagnetic (AFM) exchange interaction. In particular, the C60–V chain in BNNT yields a well-defined spin qubit. Density-functional theory calculation suggests that the (η6-C60–V)@CNT peapod is metallic with characteristics of multiple carriers contributed from CNTs, C60, and V. The (η6-C60–V)@BNNT peapod is predicted to be semiconducting with a narrow band gap, and its charge carriers are contributed by the C60–V chain. Evidently, the insertion of a V atom between every two C60 fullerenes can enhance the conductivity of the peapod. Binding H atoms on all the α positions of the pentagons in C60 can further strengthen the V–C60 interaction. Both AFM and FM states of the H-containing peapod are nearly degenerate in energy. The FM state gives rise to a magnetic moment of 3.0 μB per unit cell, three times greater than that of the V–benzene or V–cyclopentadiene multidecker complexes. The binding of H atoms to the C60 however cannot enhance electron transport due to the removal of the π channel of C60. Previous experiments have demonstrated that C60 molecules can enter BNNTs through the open tips of the BNNTs, offering a strategy that the V–C60 dimers may be encapsulated into nanotubes through the open tips of the nanotubes to form M–C60 peapods.

Hydrogen-Driven Collapse of C60Inside Single-Walled Carbon Nanotubes

A small intruder: The reaction of C60 peapods with hydrogen was studied at elevated pressure and temperature and compared with the reaction of bulk C60 powder. At temperatures above 500 °C the reaction results in a collapse of the fullerene cage structure and formation of various hydrocarbon molecules. Direct evidence was given for the surprising ability of hydrogen to penetrate into the inner space of C60 peapods and to react with the fullerenes (see picture).

Pressure studies on fullerene peapods

We carried out pressure-dependent transmission measurements on single-walled carbon nanotubes (SWCNTs) filled with C60 molecules, so-called C60 peapods, in the near-infrared and visible frequency range, where the optical transitions between the Van Hove singularities of the carbon nanotubes are excited. The pressure-induced shifts of the optical transitions exhibit an anomaly associated with the deformation of the carbon nanotubes. The results are compared with those for empty SWCNTs. Furthermore, the importance of the pressure transmitting medium used in the measurements is discussed.

Study of C60 Peapods After a High-Pressure–High-Temperature Treatment

The present work is devoted to studying the products formed from C60 peapods after treatment at 8 GPa, from 200°C to 1200°C by SEM, TEM, XRD, and Raman techniques. It is confirmed that at temperatures up to 600°C the C60 molecules polymerize in forming the known 1D polymeric crystal with a C60 – C60 distance of 9 Å. In addition, we also find that at 1000°C the peapods begin to transform into different products including nanodiamond particles, amorphous carbon, and graphitic ribbons. At 1200°C only well-formed graphite is observed.

Investigation of fullerene encapsulation in carbon nanotubes using a complex approach based on vibrational spectroscopy

AbstractFor carbon nanotubes filled with fullerenes (“peapods”), it is a key issue to find an analytical method that distinguishes the molecules inside the nanotube from those adsorbed on its surface. High‐resolution transmission electron microscopy (HRTEM) detects both encapsulated and adsorbed molecules which are large enough (e.g., fullerenes), but being a local‐probe method, it cannot be applied to large amounts of sample. In Raman spectroscopy, the empirical rules for line shifts and splitting are nanotube‐type dependent and often ambiguous. We prepared C60 peapods by nano‐extraction using supercritical CO2 as a solvent, and subsequently removed the adsorbed fullerene molecules by washing the samples. We analyzed the samples by the combination of HRTEM, Raman, and midinfrared attenuated total reflectance (MIR‐ATR) spectroscopy. Although the TEM images proved that the nanotubes were filled with fullerenes, we did not observe any shift in the fullerene's Ag(2) Raman mode compared to C60 crystals. ATR spectra, on the other hand, were found to detect only the adsorbed molecules. Therefore, the combination of the two methods provide good basis for determining the success of nanotube filling by spectroscopy alone.

Photoinduced electron transfer in C60 encapsulated single-walled carbon nanotube

The transport properties of field-effect transistors based on C60 fullerene peapods have been investigated and our findings indicate that the transport characteristics of single-walled carbon nanotubes (SWNTs) are highly sensitive to the encapsulated fullerenes due to the charge-transfer effect. Under light illumination, the photoinduced electron transfer characteristics are found in C60 peapods, which is different from those observed for empty SWNTs. The response characteristic of peapod devices to light is reflected in a shift of threshold voltage toward negative values, indicating an electron-doping process. After removing light the photoresponse is fully recoverable, indicating complete restoration of transferred electrons.

Thermomechanical Stresses in Fullerenes at Nanotube

The thermomechanical stresses acting between a nanotube and fullerenes encapsulated on it are computed. After a general formulation, based on elasticity, we have applied the analysis to C82@(10,10) or C60@(10,10) peapods finding stresses in the gigapascal range or vanishing, respectively. The analysis suggests that a thermal control could be used to produce smart fullerenes at nanotube systems, for example, as two‐stage nanovectors for drug delivery.

Fullerene derivatives encapsulated in carbon nanotubes

AbstractWe report on the preparation and subsequent Raman analysis of carbon nanotube peapods, using the fullerene C60 and its heterofullerene derivative (C59N)2 as filling materials. The filling with (C59N)2 was done from liquid solution at room temperature and from the gas phase at elevated temperatures. The success of the encapsulation procedure is confirmed through the identification of fingerprint Raman modes and the conversion to double wall nanotubes through heating to 1250 °C. The 2D mode of double wall nanotubes made from (C59N)2 peapods is observed to be downshifted compared to the same mode in double wall nanotubes made from C60 peapods. We interpret this downshift as an evidence for the integration of the nitrogen into the lattice of the inner tube. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth mechanisms of inner‐shell tubes in double‐wall carbon nanotubes

AbstractThe growth process of inner‐shell tubes from C60 peapods and ferrocene (FeCp2) filled single‐wall carbon nanotubes was studied with Raman spectroscopy and X‐ray diffraction (XRD). In the peapod case, it is shown that the Raman signal of the fullerenes decays about a factor five faster than the XRD peak of the 1D fullerene chain. The growth of the inner‐shell tubes coincides well with the 1D chain decay. In the FeCp2 case, the inner tubes grow already at 600 °C in about one hour. Additionally, even for the same starting material, the inner‐outer tube pair distribution is different than for C60 based inner tubes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

In Situ Raman Spectroelectrochemical Study of 13C‐Labeled Fullerene Peapods and Carbon Nanotubes

C60 fullerene peapods and double-walled carbon nanotubes (DWCNTs) containing highly 13C enriched C60 and inner tubes, respectively, are studied using Raman spectroscopy and in situ Raman spectroelectrochemistry in order to follow the influence of 13C enrichment on the vibrational pattern of these carbon nanostructures. The Raman response of 13C60 after encapsulation in fullerene peapods differs from that of isotope-natural species, (Nat)C60. The Raman A(g)(2) mode of encapsulated 13C60 is upshifted in frequency compared to that of the (Nat)C60 peapods with the same filling factor. The chemical doping of 13C60 peapods (peapod = C(60)@SWCNT) with K-vapor leads to the downshift of the A(g)(2) mode, similar to the case of (Nat)C60 peapods. The 13C60 peapods were successfully transformed into DWCNTs, which confirms high filling of single-walled (SW) CNTs with 13C60. The DWCNTs exhibited distinctly downshifted G and D Raman modes for inner tubes, which proves that only inner tubes were enriched by 13C. The in situ Raman spectroelectrochemistry of (Nat)C60 exhibits strong anodic enhancement, while for 13C60 peapods the enhancement is only weak. On the other hand, the electrochemical charging of the inner-tube-labeled DWCNTs (13C(i)-DWCNTs) followed the behavior of ordinary (Nat)C(i)-DWCNTs as indicated by in situ Raman spectroelectrochemistry. In addition, the spectroelectrochemical behavior of the G mode of inner tubes in 13C(i)-DWCNTs is followed from the start of the electrochemical doping, which was not feasible for (Nat)C(i)-DWCNTs.

A photoemission study of the metallic ground state of potassium‐doped C60 peapods

AbstractWe report on the doping dependence of the electronic structure of the valence band of mats of C60‐filled single wall carbon nanotubes (C60 peapods) studied by high resolution photoemission spectroscopy. In the pristine state, the bundles consist of approximately one third metallic tubes which are Tomonaga–Luttinger liquids (TLL) and thus show a power law scaling of the density of states near the Fermi level. The power law scaling factor of the pristine peapods is hardly increased compared to that of single‐walled carbon nanotubes (SWCNT). Upon doping we find a complex doping behavior and charge distribution between the electronic states of the SWCNT and the encaged C60 chains. Close to the Fermi level this has consequences on the doping induced crossover from a TLL to a conventional Fermi liquid which is found at a higher charge transfer as compared to intercalated SWCNT bundles. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of fluorination on electrical properties of single walled carbon nanotubes and C60 peapods in networks

Abstract We present a comparative study of fluorinated single wall carbon nanotubes and C 60 peapods. The fluorination was carried out by xenon difluoride treatment at moderate temperature (100 °C). The fluorination level was determined by EDX. In empty nanotubes a fluorination level of 0.8 at.% was obtained, whereas the same treatment leads to 18 at.% in peapods (corresponding to a gross stoichiometry of C 4 F). TEM images show that this fluorination procedure does not affect the peapod structure. The elemental mapping carried out by EELS reveals homogenous distribution of fluorine along the carbon nanotube bundle. This chemical treatment is found to change the electrical properties of carbon nanotubes in bucky papers. Four-probe measurements indicate a conductivity decrease by up to two orders of magnitude at room temperature. The temperature dependence of the conductivity indicates a significant change in the charge carrier density of this system. Moreover, a non-linear behavior of the I – V characteristic is observed below 50 K in fluorinated peapods.

Single-electron transistor mediated by C60 insertion inside a carbon nanotube

Electrical properties of C60 encapsulated peapod are investigated at various temperatures from room temperature down to T=1.8K. The current behavior induced by the applied gate and source-drain voltage shows that C60 peapods exhibit single-electron transistor properties. Gate-dependent conductance is enhanced at negative gate voltage and is suppressed and oscillate at positive gate voltage. This behavior is ascribed to the modulation of density of states by the insertion of C60s inside a carbon nanotube.

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.

Direct Imaging of the Alkali Metal Site in K-Doped Fullerene Peapods

The structure of K-doped fullerene peapods has been investigated by means of high-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS). It is proven that the potassium atoms can be doped at the intermolecular sites within C60 peapods. The EELS spectrum of potassium (K) L edge clearly exhibits the feature of K+ in the doped peapod and consequently suggests n-type doping. These results encourage the realization of a one-dimensional superconducting wire based on the nanotube peapods.