The first synthesis of a conjugated hybrid of C60-fullerene and a single-wall carbon nanotube

The first synthesis of a conjugated hybrid of C₆₀-fullerene and a single-wall carbon nanotube (SWCNT) is reported. The new nanohybrid material has been prepared by amidation of acid functionalized SWCNTs by an amine functionalized-fullerene derivative. The formation of this new nanomaterial was demonstrated by high resolution TEM, attenuated total reflectance/FTIR and Raman spectroscopy. Acid hydrolysis of the new material produced carboxylic-SWCNTs and the recovery of the aminofullerene derivative as complementary evidence of their covalent link. This new SWCNT-fullerene material may be of interest in optoelectronic applications.     

Advanced carbon nanotube/polymer composite infrared sensors

We demonstrate that both single-walled carbon nanotube (SWCNT) types and nanotube-matrix polymer-nanotube (CNT-P-CNT) junctions have profound impact on electro-optical properties of SWCNT/polymer composites. Composite IR sensors based on CoMoCAT^®-produced SWCNTs (SWCNTs_CoMoCAT) significantly outperform those based on HiPco^®-produced SWCNTs (SWCNTs_HiPco). Higher semiconducting nanotube concentration in a SWCNT material is critical to enhance the photo effect of IR light on SWCNT/polymer nanocomposites, whereas CNT-P-CNT junctions play a dominant role in the thermal effect of IR light on supported SWCNT/polymer composite films.     

Crosstalk analysis of carbon nanotube bundle interconnects

ABSTRACT: Carbon nanotube (CNT) has been considered as an ideal interconnect material for replacing copper for future nanoscale IC technology due to its outstanding current carrying capability, thermal conductivity, and mechanical robustness. In this paper, crosstalk problems for single-walled carbon nanotube (SWCNT) bundle interconnects are investigated; the interconnect parameters for SWCNT bundle are calculated first, and then the equivalent circuit has been developed to perform the crosstalk analysis. Based on the simulation results using SPICE simulator, the voltage of the crosstalk-induced glitch can be reduced by decreasing the line length, increasing the spacing between adjacent lines, or increasing the diameter of SWCNT.     

Improvement of the mechanical properties of single-walled carbon nanotube networks by carbon plasma coatings

Carbon vacuum arc was used to deposit 5–25 nm thick carbon coatings on single-walled carbon nanotube (SWCNT) networks. The SWCNT bundles thus embedded in conformal coatings maintained their optical transparency and electrical conductivity. Sheet resistances of the networks were measured during the vacuum arc deposition, revealing initially a 100-fold increase, followed by significant recovery after exposing the samples to an ambient atmosphere. Nanoindentation measurements revealed improved elasticity of the network after applying the carbon coating. Pristine SWCNT networks were easily deformed permanently, but a 20 nm carbon coating strengthened the nanostructure, resulting in a fully elastic recovery from a 20 μN load applied with a Berkovich tip. In nano-wear tests on selected areas, the coated SWCNT maintained its networking integrity after two passes raster scan at loads up to 25 μN. On the other hand, the pristine networks were badly damaged under a 10 μN scan load and completely displaced under 25 μN. Raman and electron energy loss spectroscopies indicated the carbon coating on bundles to be mainly sp² bonded. Finite element modeling suggests that the low content of sp³ bonds may be due to heating by the intense ion flux during the plasma pulse.     

Study of fire retardant behavior of carbon nanotube membranes and carbon nanofiber paper in carbon fiber reinforced epoxy composites

Single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) membranes (buckypaper) and carbon nanofiber (CNF) paper were incorporated onto the surface of epoxy carbon fiber composites, as proposed fire shields. Their flammability behaviors were investigated by a cone calorimeter. SWCNT buckypaper and CNF paper did not show notable improvement on fire retardancy. However, MWCNT buckypaper acted as an effective flame-retardant shield, reducing the peak heat release rate by more than 60% and reducing smoke generation by 50% during combustion. The pore structures of buckypapers and CNF paper were characterized by scanning electron microscopy (SEM), mercury intrusion porosimetry, and N₂ adsorption isotherms. Gas permeability of buckypaper and carbon nanofiber paper was measured. The correlation between buckypaper and CNF paper properties and their fire retardancy was discussed.     

Micropatterning of single-walled carbon nanotube forest

In this work, high-aligned single-walled carbon nanotube (SWCNT) forest have been grown using a high-density plasma chemical vapor deposition technique (at room temperature) and patterned into micro-structures by photolithographic techniques, that are commonly used for silicon integrated circuit fabrication. The SWCNTs were obtained using pure methane plasma and iron as precursor material (seed). For the growth carbon SWCNT forest the process pressure was 15 mTorr, the RF power was 250 W and the total time of the deposition process was 3 h. The micropatterning processes of the SWCNT forest included conventional photolithography and magnetron sputtering for growing an iron layer (precursor material). In this situation, the iron layer is patterned and high-aligned SWCNTs are grown in the where iron is present, and DLC is formed in the regions where the iron precursor is not present. The results can be proven by Scanning Electronic Microscopy and Raman Spectroscopy. Thus, it is possible to fabricate SWCNT forest-based electronic and optoelectronic devices.     

Nanoindentation of diamond,graphite and fullerene films

The recently developed method of nanoindentation is applied to various forms of carbon materials with different mechanical properties, namely diamond, graphite and fullerite films. A diamond indenter was used and its actual shape determined by scanning force microscopy with a calibration grid. Nanoindentation performed on different surfaces of synthetic diamond turned out to be completely elastic with no plastic contributions. From the slope of the force–depth curve the Young's modulus as well as the hardness were obtained reflecting a very large hardness of 95 GPa and 117 GPa for the {100} and {111} crystal surfaces, respectively. Investigation of a layered material such as highly oriented pyrolytic graphite again showed elastic deformation for small indentation depths but as the load increased, the induced stress became sufficient to break the layers after which again an elastic deformation occurred. The Young’s modulus was calculated to be 10.5 GPa for indentation in a direction perpendicular to the layers. Plastic deformation of a thin fullerite film during the indentation process takes place in the softer material of a molecular crystalline solid formed by C₆₀ molecules. The hardness values of 0.24 GPa and 0.21 GPa for these films grown by layer epitaxy and island growth on mica and glass, respectively, vary with the morphology of the C₆₀ films. In addition to the experimental work, molecular dynamics simulations of the indentation process have been performed to see how the tip–crystal interaction turns into an elastic deformation of atomic layers, the creation of defects and nanocracks. The simulations are performed for both graphite and diamond but, because of computing power limitations, for indentation depths an order of magnitude smaller than the experiment and over indentation times several orders of magnitude smaller. The simulations capture the main experimental features of the nanoindentation process showing the elastic deformation that takes place in both materials. However, if the speed of indentation is increased, the simulations indicate that permanent displacements of atoms are possible and permanent deformation of the material takes place.     

Analysis of multiaxial properties of carbon nanotubes/polypropylene and nanocrystalline cellulose/polypropylene composites

Using the beam element to simulate single wall carbon nanotube (SWCNT) and nanocrystalline cellulose (NCC), finite element method is adopted to perform multi‐axial numerical tests to compare SWCNT and NCC reinforced polypropylene (PP). As a first step, SWCNT and NCC are assumed to be isotropic and linear elastic materials, while PP is assumed to be linear elastic or elastic–plastic. Using the same reinforcement volume fraction, the elastic and elastic–plastic properties of the nanocomposites are compared under biaxial and triaxial loading conditions. Then, the effect of particle volume fraction and particle size is presented. When NCC and SWCNT have equal particle length and number but different particle diameter, both can produce similar improvement on biaxial mechanical properties. Finally, NCC and SWCNT are compared from an economic point of view to get similar mechanical performance (biaxial properties). The results show that NCC is about 646 times cheaper than SWCNT and is an interesting prospect for future work. POLYM. COMPOS., 37:1180–1189, 2016. © 2014 Society of Plastics Engineers     

Single-walled carbon nanotube buckypaper and mesophase pitch carbon/carbon composites

Carbon/carbon composites consisting of single-walled carbon nanotube (SWCNT) buckypaper (BP) and mesophase pitch resin have been produced through impregnation of BP with pitch using toluene as a solvent. Drying, stabilization and carbonization processes were performed sequentially, and repeated to increase the pitch content. Voids in the carbon/carbon composite samples decreased with increasing impregnation process cycles. Electrical conductivity and density of the composites increased with carbonization by two to three times that of pristine BP. These results indicate that discontinuity and intertube contact barriers of SWCNTs in the BP are partially overcome by the carbonization process of pitch. The temperature dependence of the Raman shift shows that mechanical strain is increased since carbonized pitch matrix surrounds the nanotubes.     

Length dependent foam-like mechanical response of axially indented vertically oriented carbon nanotube arrays

The axial compressive mechanical response of substrate-supported carbon nanotube (CNT) arrays with heights from 35 to 1200 μm is evaluated using flat punch nanoindentation with indentation depths to 200 μm. The compressive behavior is consistent with that of an open-cell foam material with array height playing a role similar to that of occupation density for traditional foam. Mechanical yielding of all arrays is initiated between 0.03 and 0.12 strain and arises from localized coordinated plastic buckling. For intermediate CNT array heights between 190 and 650 μm, buckle formation is highly periodic, with characteristic wavelengths between 3 and 6 μm. Buckle formation produced substantial force oscillations in both the compressive and lateral directions. The compressive elastic modulus of the arrays is obtained as a continuous function of penetration depth and attains a value between 10 and 20 MPa for all arrays during mechanical yield. A qualitative model based upon concepts of cellular foam geometry is advanced to explain the observed CNT buckling behavior.     

Energetics and stability of C60 molecules encapsulated in carbon nanotubes

An energetic analysis was performed to study the interactions of C₆₀ molecules encapsulated in carbon nanotubes. Both direct interaction between C₆₀ molecules through van der Waals forces and indirect interaction between encapsulated C₆₀ molecules through the elastic deformation of their host carbon nanotubes were considered. For C₆₀s encapsulated in a (9, 9) nanotube, the indirect interaction dominates and a relatively large energy barrier exists for the formation of a uniform, stable, one-dimensional (1-D) C₆₀ array. For a (10, 10) nanotube, the indirect interaction leads to a small energy barrier to form a 1-D C₆₀ array, while for a (11, 11) nanotube the influence of the indirect interaction is negligible. Molecular dynamics simulations were performed to confirm the present energetic analysis, suggesting that the indirect interaction between encapsulated molecules/particles through the elastic deformation of their host nanotubes may affect the stability of nanotube-based structures.     

Moderating carbon supply and suppressing Ostwald ripening of catalyst particles to produce 4.5-mm-tall single-walled carbon nanotube forests

Millimeter-tall single-walled carbon nanotube (SWCNT) forests were grown by chemical vapor deposition (CVD) from C₂H₂/H₂O/Ar using Fe/Al–Si–O catalysts. Using combinatorial catalyst libraries coupled with real-time monitoring of SWCNT growth, the catalyst and CVD conditions were systematically studied. The keys for this growth are to maintain the C₂H₂ pressure below its upper limit to prevent the killing of the catalysts and to grow the SWCNTs before the catalyst particles lose their activity because of coarsening through Ostwald ripening. Lower temperatures lead to lower limits for the C₂H₂ pressure which result in lower growth rates but also lead to even lower coarsening rates which result in even longer growth lifetimes. Using these principles, we grew 4.5-mm-tall SWCNT forests in 2.5 h at 750 °C.     

Poly(l-lactide)/nano-structured carbon composites: Conductivity, thermal properties, crystallization, and biodegradation

The effects of nano-structured carbon fillers [fullerene C₆₀, single wall carbon nanotube (SWCNT), carbon nanohorn (CNH), carbon nanoballoon (CNB), and ketjenblack (KB)] and conventional carbon fillers [conductive grade and graphitized carbon black (CB)] on conductivity (resistance), thermal properties, crystallization, and proteinase K-catalyzed enzymatic degradation of poly(l-lactide) [i.e., poly(l-lactic acid) (PLLA)] films were investigated. Even at low filler concentrations such as 1 wt%, the addition of SWCNT effectively decreased the resistivity of PLLA film compared with that of conventional CB, and PLLA-SWCNT film with filler concentration of 10 wt% attained the resistivity lower than 100 Ω cm. The crystallization of PLLA further decreased the resistivity of films. The addition of carbon fillers, except for C₆₀ and CNB at 5 wt%, lowered the glass transition temperature, whereas the addition of carbon fillers, excluding C₆₀, elevated softening temperatures, if an appropriate filler concentration was selected. On heating from room temperature, cold crystallization temperature was determined mainly by the molecular weight of PLLA, whereas on cooling from the melt, the carbon fillers, excluding KB, elevated the cold crystallization temperature, reflecting the effectiveness of most of the carbon fillers as nucleating agents. Despite the nucleating effects, the addition of carbon fillers decreased the enthalpy of cold crystallization of PLLA on both heating and cooling. The addition of CNH, CNB, and CB elevated the starting temperature of thermal degradation of PLLA, whereas the addition of SWCNT reduced the thermal stability. Furthermore, the addition of C₆₀ and SWCNT enhanced the enzymatic degradation of PLLA, whereas the addition of KB and CNB disturbed the enzymatic degradation of PLLA. The reasons for the effects of carbon fillers on the physical properties, crystallization, and enzymatic degradation of PLLA films are discussed.     

A molecular dynamics simulation of methane adsorption in single walled carbon nanotube bundles

The physisorption of methane in idealized bundles of single walled carbon nanotubes (SWCNT) is investigated in detail in this work employing computational. Several aspects related to the possible application of nanotubes as fuel gas containers are analyzed employing molecular dynamics simulations. The influence of the nanotube diameter on the adsorption capacity of the material and the distribution of the adsorbate are examined by considering bundles of carbon nanotubes with different morphologies. An increase of the load capacity with the nanotube diameter is observed, together with a qualitative change in the distribution of the adsorbed molecules. The effect of porosity is also studied from the point of view of the nanotube separation, finding that this leads to a significant increase in storage capacity in the case of bundles made of small diameter nanotubes. The role of temperature as a possible uptake/release triggering variable is also examined.     

Nondestructive purification of single-walled carbon nanotube rope through a battery-induced ignition and chemical solution approach

A two-step method for the purification of single-walled carbon nanotube (SWCNT) rope containing substantial catalyst particles embedded in carbonaceous shells was developed. The first step was the triggering of rope ignition using a 9-V battery, which resulted in pre-oxidization of the carbon shells on the Fe₃C catalyst and oxidation of the exposed Fe₃C to form Fe₂O₃. In addition, SWCNTs with open-end structures due to ignition-induced cutting remained. In the second step, both oxalic acid (H₂C₂O₄) and hydrochloric acid (HCl) were used as the reactants to remove the Fe₂O₃ particles. No damage on the SWCNT walls after H₂C₂O₄ or HCl purification was found. In addition, adsorption of H₂C₂O₄ was also found on the H₂C₂O₄ purified SWCNT rope and it can be effectively removed by heating the rope at 200 °C in vacuum for 40 min. Samples were characterized by SEM, TEM, Raman spectroscopy, TGA, FTIR, XPS, and UV-Vis-NIR.     

Fluidized-bed synthesis of sub-millimeter-long single walled carbon nanotube arrays

The rapid growth method for vertically aligned, single walled carbon nanotube (SWCNT) arrays on flat substrates was applied to a fluidized-bed, using ceramic beads as catalyst supports as a means to mass produce sub-millimeter-long SWCNT arrays. Fe/Al₂O_x catalysts were deposited on the surface of Al₂O₃ beads by sputtering and SWCNTs were grown on the beads by chemical vapor deposition (CVD) using C₂H₂ as a feedstock. Scanning electron microscopy and transmission electron microscopy showed that SWCNTs of 2–4 nm in diameter grew and formed vertically aligned arrays of 0.5 mm in height. Thermogravimetric analysis showed that the SWCNTs had a catalyst impurity level below 1 wt.%. Furthermore, they were synthesized at a carbon yield as high as 65 at.% with a gas residence time as short as <0.2 s. Our fluidized-bed CVD, which efficiently utilizes the three-dimensional space of the reactor volume while retaining the characteristics of SWCNTs on substrates, is a promising option for mass-production of high-purity, sub-millimeter-long SWCNT arrays.     

Growth of novel carbon phases by methane infiltration of free-standing single-walled carbon nanotube films

High-temperature methane infiltration of thin, free-standing films of acid-treated single-walled carbon nanotubes (SWCNT) has been studied by means of scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. In the early stages of infiltration, carbon nuclei form predominantly at SWCNT bundle intersections. Further growth proceeds via the formation of graphite nanosheets - without further influence of the nanotube support. Both sheet edges and their structural imperfections act as reaction centers for subsequent deposition, likely giving rise to autocatalytic deposition kinetics. In contrast, infiltration with a H₂:CH₄ (24:1) mixture leads to the reductive activation of residual Ni/Co impurities embedded in the precursor SWCNT-felt. This is associated with a different predominant carbon deposition mode in which multiwalled carbon nanotubes grow out from the substrate.     

Possibility of driving water molecules along a single-walled carbon nanotube using methane molecules

Molecular dynamics simulation is used to study the transport behavior of water molecules along an open-ended single-walled carbon nanotube (SWCNT) under the driving force of methane molecules. The methane molecules pull the water molecules from the inside of a SWCNT along the axial direction. The transport velocity of water molecules increases with increasing number of methane molecules, but decreases with increasing diameter of the SWCNT.     

Temperature and time dependence study of single-walled carbon nanotube growth by catalytic chemical vapor deposition

The temperature and time dependence of single-walled carbon nanotube (SWCNT) growth by chemical vapor deposition of ethanol on Fe₂O₃/MgO catalyst are compared at both low (∼27 Pa) and atmospheric pressure limits. SWCNTs are synthesized in two reactors with different geometries and operating pressures and are characterized by Raman spectroscopy. Both reactors show SWCNT growth within a relatively narrow temperature window of 700-850 °C, with an optimum growth time of 35 min for the cold wall reactor and 75 min for the quartz tube reactor. A kinetic model comprising of ethanol decomposition, SWCNT formation, and water etching is developed to better understand the growth mechanism. The existence of a temperature window and an optimum growth time in both reactors can be well described by the kinetic model. Simulation results suggest that the temperature and time dependence can be explained by the competition between the growth of SWCNTs and that of amorphous carbon.     

High temperature activation and deactivation of single-walled carbon nanotube growth investigated by in situ Raman measurements

A decrease of nanotube yield is usually observed at high temperature. Here, we report on the origins of the activation and deactivation of the SWCNT growth in this high temperature range (between 700 °C and 850 °C) based on in situ Raman measurements. We observed that, at high temperature, carbon precursors such as ethanol and methane readily reduce metal oxide such as Co₃O₄. Once reduced, the size distribution of the catalyst particles quickly evolves at high temperature leading to a dramatic deactivation of the nanotube growth. An oxidizing pre-treatment has a stabilizing effect on the catalyst. In addition, we evidenced a threshold partial pressure of the carbon precursor to initiate the growth. This threshold partial pressure sets a second requirement for activating the nanotube growth in addition to the requirement of reducing the catalyst.