Large-diameter Single-walled Carbon Nanotubes Research Articles

Nano-confinement of biomolecules: Hydrophilic confinement promotes structural order and enhances mobility of water molecules

Molecular dynamics simulations have been used to investigate the confinement packing characteristics of small hydrophilic (N-acetyl-glycine-methylamide, Nagma) and hydrophobic (N-acetyl-leucine-methylamide, Nalma) biomolecules in large diameter single-wall carbon nanotubes (SWCNTs). We find that hydrophilic biomolecules easily fill the nanotube and self organize into a geometrical configuration which reminds the water structural organization under SWCNT confinement. The packing of hydrophilic biomolecules inside the cylinder confines all water molecules in its core, which enhances their mobility. Conversely, hydrophobic biomolecules accommodate into the nanotubes with a trend for homogeneous filling, which generate unstable small pockets of water and drive toward a state of dehydration. These results shed light on key parameters important for the encapsulation of biomolecules with direct relevance for long-term storage and prevention of degradation.

Enhanced solubilization of large-diameter single-walled carbon nanotubes with amino-functionalized dipyrene nanotweezers

Pyrene-based nanotweezers 1 consisting of two pyrenes and amino-substituted carbazole in between have been successfully synthesized via Suzuki–Miyaura coupling reaction. The supramolecular complex formation of nanotweezers 1 with single-walled carbon nanotubes (SWNTs) was studied, and it was found that nanotweezers 1 exhibited much higher the SWNTs extraction ability as compared to the analogous dipyrene nanotweezers 2 and 3 with soluble alkyl-substituents. This enhanced extraction ability of 1 can be attributed to the formation of more stable SWNT complexes in methanol. On the basis of photoluminescence excitation and UV–Vis-NIR absorption of 76-CoMoCAT SWNTs before and after the extraction, nanotweezers 1 were found to show high selectivity towards (8,4)-, (7,6)-, (9,4)-, and (8,6)-SWNTs with diameter ranging from 0.84 to 0.97 nm.

Intraexciton Transitions Observed in High Stability Doped Single-Wall Carbon Nanotube Films and Solutions

Normally hidden excited state transitions were observed in large diameter single-walled carbon nanotubes for the first time by controlling the degree of doping. With increased doping, the normally observed photoinduced bleach (PB) signal associated with the creation of excitons switched to a photoinduced absorption (PA). A delay in the onset of the PA signal made it clear that the absorption was due to an intraexcitonic transition. The study was afforded by the development of novel methods that allowed samples to be reproducibly and stably prepared in specific states. Our results further the understanding of the photophysics of large diameter single-walled carbon nanotube materials, which are promising for a variety of optoelectronic applications.

Sculpting carbon bonds for allotropic transformation through solid-state re-engineering of -sp2 carbon.

Carbon forms one of nature's strongest chemical bonds; its allotropes having provided some of the most exciting scientific discoveries in recent times. The possibility of inter-allotropic transformations/hybridization of carbon is hence a topic of immense fundamental and technological interest. Such modifications usually require extreme conditions (high temperature, pressure and/or high-energy irradiations), and are usually not well controlled. Here we demonstrate inter-allotropic transformations/hybridizations of specific types that appear uniformly across large-area carbon networks, using moderate alternating voltage pulses. By controlling the pulse magnitude, small-diameter single-walled carbon nanotubes can be transformed predominantly into larger-diameter single-walled carbon nanotubes, multi-walled carbon nanotubes of different morphologies, multi-layered graphene nanoribbons or structures with sp(3) bonds. This re-engineering of carbon bonds evolves via a coalescence-induced reconfiguration of sp(2) hybridization, terminates with negligible introduction of defects and demonstrates remarkable reproducibility. This reflects a potential step forward for large-scale engineering of nanocarbon allotropes and their junctions.

Precise determination of the threshold diameter for a single-walled carbon nanotube to collapse.

Closed-edged bilayer graphene nanoribbons were formed by the spontaneous collapse of large-diameter single-walled carbon nanotubes (SWNTs) grown on gold nanoparticles by chemical vapor deposition. Such bilayer graphene nanoribbons could adopt different stacking configurations, such as AB-stacking or stacking order with any rotation angle, correlated with the chiral angles of their parent rounded SWNTs. On the basis of the electron diffraction characterizations on a good number of collapsed and uncollapsed SWNTs, the threshold diameter for SWNTs to collapse was precisely determined to be 5.1 nm, independent of the chiral angle of the SWNTs. The determination is consistent with that calculated by both classical adaptive intermolecular reactive empirical bond order force field and density functional theory after having taken the stacking effect and thermal fluctuation into account.

Conjugated polymer-assisted dispersion of single-wall carbon nanotubes: the power of polymer wrapping.

The future application of single-walled carbon nanotubes (SWNTs) in electronic (nano)devices is closely coupled to the availability of pure, semiconducting SWNTs and preferably, their defined positioning on suited substrates. Commercial carbon nanotube raw mixtures contain metallic as well as semiconducting tubes of different diameter and chirality. Although many techniques such as density gradient ultracentrifugation, dielectrophoresis, and dispersion by surfactants or polar biopolymers have been developed, so-called conjugated polymer wrapping is one of the most promising and powerful purification and discrimination strategies. The procedure involves debundling and dispersion of SWNTs by wrapping semiflexible conjugated polymers, such as poly(9,9-dialkylfluorene)s (PFx) or regioregular poly(3-alkylthiophene)s (P3AT), around the SWNTs, and is accompanied by SWNT discrimination by diameter and chirality. Thereby, the π-conjugated backbone of the conjugated polymers interacts with the two-dimensional, graphene-like π-electron surface of the nanotubes and the solubilizing alkyl side chains of optimal length support debundling and dispersion in organic solvents. Careful structural design of the conjugated polymers allows for a selective and preferential dispersion of both small and large diameter SWNTs or SWNTs of specific chirality. As an example, with polyfluorenes as dispersing agents, it was shown that alkyl chain length of eight carbons are favored for the dispersion of SWNTs with diameters of 0.8-1.2 nm and longer alkyls with 12-15 carbons can efficiently interact with nanotubes of increased diameter up to 1.5 nm. Polar side chains at the PF backbone produce dispersions with increased SWNT concentration but, unfortunately, cause reduction in selectivity. The selectivity of the dispersion process can be monitored by a combination of absorption, photoluminescence, and photoluminescence excitation spectroscopy, allowing identification of nanotubes with specific coordinates [(n,m) indices]. The polymer wrapping strategy enables the generation of SWNT dispersions containing exclusively semiconducting nanotubes. Toward the applications in electronic devices, until now most applied approach is a direct processing of such SWNT dispersions into the active layer of network-type thin film field effect transistors. However, to achieve promising transistor performance (high mobility and on-off ratio) careful removal of the wrapping polymer chains seems crucial, for example, by washing or ultracentrifugation. More defined positioning of the SWNTs can be accomplished in directed self-assembly procedures. One possible strategy uses diblock copolymers containing a conjugated polymer block as dispersing moiety and a second block for directed self-assembly, for example, a DNA block for specific interaction with complementary DNA strands. Another strategy utilizes reactive side chains for controlled anchoring onto patterned surfaces (e.g., by interaction of thiol-terminated alkyl side chains with gold surfaces). A further promising application of purified SWNT dispersions is the field of organic (all-carbon) or hybrid solar cell devices.

Spontaneous nanoinjection with carbon nanotubes: a molecular dynamics simulation study.

Based on the interactions between the zinc finger protein (ZNF) and single-walled carbon nanotubes (SWCNTs), we design a nanodevice for injecting ZNF spontaneously. The new injection device involves four essential components: a small-diameter SWCNT as a plunger, a large-diameter SWCNT as a tube as well as the nozzle and needle, ZNF and water solution. The injection behavior is demonstrated and analyzed using molecular dynamics simulations. The effects of the diameter, chirality and length of SWCNTs on the injection behavior are analyzed with the center of mass distance, the van der Waals interaction between ZNF and SWCNTs, the root-mean-square deviation of ZNF, and the radius of gyration for ZNF.

Inner tube growth properties and electronic structure of ferrocene-filled large diameter single-walled carbon nanotubes

We study the filling of single-walled carbon nanotubes (SW- CNTs) with ferrocene molecules. Using e-DIPS SWCNTs with a mean diameter of 1.7 nm, we obtain a filling factor as high as 90%. At elevated temperatures in high vacuum the filled SWCNTs are transformed to double-walled carbon nanotubes (DWCNTs). Temperature dependence of inner tube growth is investigated by Raman spectroscopy. The electronic properties of the obtained nanostructures are studied by X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy. It is found that the growth temperature is higher for larger diameter inner tubes. It is demonstrated that ferrocene filling leads to electron doping of SWCNTs.

Stepwise design of non-covalent wrapping of large diameter carbon nanotubes by peptides

Single-walled carbon nanotube (SWCNT) is one of the most popular low-dimensional carbon materials in material science, nanomedicine, and nanoscale electronics. Yet the application of the SWCNTs was hindered by the self-aggregation. To purify and disperse the SWCNTs, non-covalent wrapping is one of the effective options to overcome such defects. In this work, two kinds of short peptides were designed to facilitate the modification of large-diameter SWCNT. The design of the peptide was carried out in a stepwise manner. The effective residues of helix-rich and sheet-rich proteins on SWCNT were studied at the first step, and then a coarse model peptide composed of the key adsorption residues above was built to investigate the adsorption dynamics on SWCNT. In the end, the residues include long alkyl side chain and that include aromatic rings were found to play key roles on the adsorption of protein/peptide on hydrophobic SWCNT. And two peptides rich in the long alkyl chain and aromatic rings were constructed respectively. The predominant adsorption capabilities of the two kinds of peptides were discerned by the adsorption details.

Helicity-Selective Photoreaction of Single-Walled Carbon Nanotubes with Organosulfur Compounds in the Presence of Oxygen

This report describes a helicity-selective photoreaction of single-walled carbon nanotubes (SWNTs) with disulfide in the presence of oxygen. The SWNTs were characterized using absorption, photoluminescence (PL), Raman, and X-ray photoelectron spectroscopy, scanning electron microscopy, and current-voltage (I-V) measurements. Results showed remarkable helicity-selective (metallic SWNTs/semiconducting SWNTs and diameter) functionalization of SWNTs. The reaction rate decreases in the order of metallic SWNTs > semiconducting SWNTs and small-diameter SWNTs > large-diameter SWNTs. Control experiments conducted under various experimental conditions and ESR and femtosecond laser flash photolysis measurements revealed that the helicity-selective reaction proceeds via a photoinduced electron transfer reaction. The PL and I-V measurements showed that the photoreaction is effective not only to control SWNT conductivity but also for the band gap modulation of semiconducting SWNTs.

CoSO4/SiO2 catalyst for selective synthesis of (9, 8) single-walled carbon nanotubes: Effect of catalyst calcination

A sulfate-promoted CoSO4/SiO2 catalyst is developed for chirally selective synthesis of large-diameter single-walled carbon nanotubes needed for electronic applications. The catalyst shows tunable nanotube chiral selectivity by changing catalyst calcination temperature. After calcination in air at 400°C, it has excellent single chiral selectivity toward large-diameter (9,8) nanotubes at 1.17nm. The selectivity shifts to small-diameter nanotubes, when it is calcined at 800°C. Catalyst characterizations by hydrogen temperature-programed reduction, X-ray absorption spectroscopy at the cobalt K-edge and sulfur K-edge suggest that the presence of chelating bidentate SO42- bonded with cobalt on the silica surface may limit the aggregation of cobalt and/or form cobalt–sulfur compounds during nanotube growth, leading to the selectivity toward the (9,8) nanotubes. Furthermore, the removal of sulfur at higher calcination temperatures may form surface cobalt oxides and silicates that shift the chiral selectivity toward small-diameter nanotubes.

Shell-like instability of large diameter single-walled carbon nanotubes conveying fluid

The instability of large diameter single-walled carbon nanotubes (SWCNTs) conveying fluid is investigated based on the molecular mechanics. Using the modal expansion for structural displacements, the governing equations of coupled fluid-structural dynamics of SWCNTs are derived. The natural frequencies and mode shape of the SWCNTs are obtained based on the molecular structural mechanics to account for the effect of chirality and discrete nature of SWCNTs. The results show that the vibrational behavior of large diameter SWCNTs conveying fluid is size dependent, but the effect of chirality is negligible. The obtained results are compared with the equivalent continuum-based model in the literature and in some cases remarkable deviations between the results are observed. Accordingly, proper values for the equivalent wall thickness and Young’s modulus of SWCNTs are proposed to adopt the results of continuum-based model with the molecular mechanics predictions.

Diameter Effect on the Sidewall Functionalization of Single‐Walled Carbon Nanotubes by Addition of Dichlorocarbene

AbstractDichlorocarbene is added to the sidewalls of single‐walled carbon nanotubes (SWNTs) with diameters ranging from 1.2 to 2.2 nm. Small diameter SWNTs are found to react much more easily than large diameter SWNTs. Upon functionalization, the conductance could be largely preserved for almost all SWNTs, while an effective bandgap increase for functionalized metallic SWNTs (m‐SWNTs) and a bandgap reduction for functionalized semiconducting SWNTs (s‐SWNTs) are generally observed. The results suggest that [2 + 1] cycloaddition is an excellent choice of processing, resulting in SWNTs over a large diameter range with electronic properties that are almost unaffected. Furthermore, possible separation of SWNTs according to their diameters could be achieved due to the apparent diameter‐dependent reactivity.

The growth mechanism of single-walled carbon nanotubes with a controlled diameter

Understanding the growth mechanism of carbon nanotube is important to control the structure and properties of carbon nanotubes. We examined several aspects of the single wall carbon nanotubes (SWCNTs) prepared by chemical vapor deposition (CVD) processes using ethanol with the additions of ferrocene and thiophene, focusing on the potential mechanisms leading to the differences in the diameters, structures, and conductivities of the SWCNTs formed. The diameter of SWCNTs could be controlled from ∼1.0 to ∼5.8nm by adjusting the concentration of thiophene used. The larger diameter SWCNTs has a higher thermal stability than smaller-diameter SWCNTs. With increasing diameter, the electrical properties of the SWCNT change from mainly semi-conducting to metallic-like. The growth mechanism of SWCNTs was subsequently studied to understand the mechanism of thiophene controlled SWCNTs formation. This study could lead to improved control over the diameter and electronic properties of SWCNTs.

Extraction of Specific Large-Diameter Single-Wall Carbon Nanotubes by Fluorene-Based Copolymers

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Confining effect of carbon-nanotube configuration on phase behavior of hard-sphere fluid

We capture the effects of the structured surface on a phase transition of hard-sphere fluids. The confining environment follows single-walled carbon nanotube (SWCNT) configuration. For careful discrimination of the surface-chirality effect, hard-core potentials are applied to carbon atoms, and further their positions are fixed. In this way, equation of states and microstructures of the confined particles are intrinsically obtained based on the SWCNT chirality as well as the diameter. We observed three branches indicating fluid-like and solid-like phases with onsets of freezing and melting. We found that freezing and melting of fluid particles are very sensitive to the surface chirality in small-diameter SWCNT, which especially holds a single layer of fluid particles. In those SWCNTs, spreading pressures are found to be lower than those of smooth-surface cylindrical pores. The surface chirality has less impact on the phase change of confined fluids for large-diameter SWCNT, of which diameter is a dominant factor.

Growth of large-diameter (∼4 nm) single-wall carbon nanotubes in the nanospace of mesoporous material SBA-15

Single-wall carbon nanotubes (SWCNTs) have been synthesized by supported-catalyst chemical vapor deposition (CCVD) using one-dimensional (1D) channels of mesoporous silica (SBA-15; mean channel diameter, 6.0 nm) functionalized with carboxyl groups where Co and Fe complexes are encapsulated. The synthesized SWCNTs have much larger diameters than the SWCNTs synthesized by conventional CCVD. Transmission electron microscope observations reveal that large-diameter SWCNTs (<4.2 nm) are grown in 1D channels of SBA-15. Large metal particles formed in the channels should play an important role in the growth of the SWCNTs with larger diameters.

Selective Extraction of Large-Diameter Single-Wall Carbon Nanotubes with Specific Chiral Indices by Poly(9,9-dioctylfluorene-alt-benzothiadiazole)

Semiconducting single-wall carbon nanotubes (SWCNTs) having large diameters (d(t) > 1.3 nm) are successfully extracted in toluene by fluorene-based polymers. In particular, poly(9,9-dioctylfluorene-alt-benzothiadiazole) shows excellent selectivity for (15,4) SWCNTs. Although the importance of structural matching between the fluorene backbone and the tube surface has already been discussed, the present photoluminescence studies reveal that matching the energy levels between fluorene-based polymers and SWCNTs is crucial for selective nanotube extractions.

Growth of single-walled carbon nanotubes with controlled diameters and lengths by an aerosol method

On the basis of combined study of the transmission electron microscopy, scanning electron microscopy, Raman spectroscopy and ultraviolet–visible–near infrared absorption spectroscopy, the properties of the single-walled carbon nanotubes (SWCNTs), synthesized by aerosol (floating catalyst) chemical vapor deposition method by ferrocene vapor decomposition in the presence of carbon monoxide, are studied in details. The results show that increasing the temperature gives rise to the formation of high quality and large diameter SWCNTs. By monitoring the water-cooled probe position, both the bundle length and the diameter of the SWCNTs are effectively tuned due to the variation of the residence time and temperature profile in the reactor. An introduction of a small amount of CO 2 suppresses the growth of small diameter nanotubes and enlarges the mean diameter of SWCNT samples. The mean diameter of SWCNTs could be easily altered in a broad range from 1.1 to 1.9 nm during growth, which is essential for the SWCNT applications in optical and electronic devices.

Synthesis of High-Density, Large-Diameter, and Aligned Single-Walled Carbon Nanotubes by Multiple-Cycle Growth Methods

A dense array of parallel single-walled carbon nanotubes (SWNTs) as the device channel can carry higher current, be more robust, and have smaller device-to-device variation, thus is more desirable for and compatible with applications in future highly integrated circuits when compared with single-tube devices. The density of the parallel SWNT arrays and the diameter of SWNTs both are key factors in the determination of the device performance. In this paper, we present a new multiple-cycle chemical vapor deposition (CVD) method to synthesize horizontally aligned arrays of SWNTs with densities of 20-40 SWNT/μm over large area and a diameter distribution of 2.4 ± 0.5 nm on the quartz surface based on a methanol/ethanol CVD method. The high nucleation efficiency of catalyst particles in multiple-cycle CVD processes has been demonstrated to be the main reason for the improvements in the density of SWNT arrays. More interestingly, we confirmed the existence of an etching effect, which strongly affects the final products in the multiple-cycle growth. This etching effect is likely the reason that only large-diameter SWNTs were obtained in the multiple-cycle CVD growth. Using these high-density and large-diameter nanotube arrays, two-terminal devices with back-gates were fabricated. The performances of these devices have been greatly improved in overall resistance and on-state current, which indicates these SWNT arrays have high potential for applications such as interconnects, high-frequency devices, and high-current transistors in future micro- or nanoelectronics.