Diameter Of Single-walled Carbon Nanotubes Research Articles

Stability and conformation of DNA-hairpin in cylindrical confinement

We conducted atomistic Molecular Dynamics (MD) simulations of DNA-Hairpin molecules encapsulated within Single-Walled Carbon Nanotubes (SWCNTs) at a temperature of 300 K. Our investigation revealed that the structural integrity of the DNA-Hairpin can be maintained within SWCNTs, provided that the diameter of the SWCNT exceeds a critical threshold value. Conversely, when the SWCNT diameter falls below this critical threshold, the DNA-Hairpin undergoes denaturation, even at a temperature of 300 K. The DNA-Hairpin model we employed consisted of a 12-base pair stem and a 3-base loop, and we studied various SWCNTs with different diameters. Our analyses identified a critical SWCNT diameter of 3.39 nm at 300 K. Examination of key structural features, such as hydrogen bonds (H-bonds), van der Waals (vdW) interactions, and other inter-base interactions, demonstrated a significant reduction in the number of H-bonds, vdW energy, and electrostatic energies among the DNA hairpin's constituent bases when confined within narrower SWCNTs (with diameters of 2.84 nm and 3.25 nm). However, it was observed that the increased interaction energy between the DNA-Hairpin and the inner surface of narrower SWCNTs promoted the denaturation of the DNA-Hairpin. In-depth analysis of electrostatic mapping and hydration status further revealed that the DNA-Hairpin experienced inadequate hydration and non-uniform distribution of counter ions within SWCNTs having diameters below the critical value of 3.39 nm. Our inference is that the inappropriate hydration of counter ions, along with their non-uniform spatial distribution around the DNA hairpin, contributes to the denaturation of the molecule within SWCNTs of smaller diameters. For DNA-Hairpin molecules that remained undenatured within SWCNTs, we investigated their mechanical properties, particularly the elastic properties. Our findings demonstrated an increase in the persistence length of the DNA-Hairpin with increasing SWCNT diameter. Additionally, the stretch modulus and torsional stiffness of the DNA-Hairpin were observed to increase as a function of SWCNT diameter, indicating that confinement within SWCNTs enhances the mechanical flexibility of the DNA-Hairpin.

MODELING OF THE GEOMETRY AND ELECTRONIC BANDGAP STRUCTURE OF CHIRAL SINGLE WALLED CARBON NANOTUBES

Carbon Nanotubes (CNTs) are one-dimensional nanostructured materials that will play a key role in future electronics. All properties of the carbon nanotubes are determined by its electronic structure. The main focus of this study has been to investigate the basic electronic bandgap structure of the chiral single walled carbon nanotubes (SWCNTs). A simple algorithm is presented in order to model the geometry of the chiral single-walled CNTs with any desired structure. The electronic bandgap structure of the chiral single-walled carbon nanotubes has been studied by employing an extended tight binding model (TBM). The changes in the energy band gap due to the chirality effect in case of metallic (6, 3) SWCNT and in the semiconducting (12, 7) SWCNT are discussed here. The value of the SWCNTs diameter is calculated also. The computed results indicates that the bandgap depends inversely on the diameter of the tube. The present results were found to be in consistent with those reported in the literature and indicated the correctness of the process of simulation technique process.

Encapsulation of linear carbon chains in single-walled carbon nanotubes: Towards 1D van der Waals heterostructures for high-efficiency excitonic solar cells

One-dimensional van der Waals heterostructures (1D vdW HTs) based on single-walled carbon nanotubes (SWCNTs) encapsulating linear carbon chains (LCCs) with tunable optoelectronic properties provide a fresh ground for efficient excitonic solar cells (XSCs) alternative to those based on 2D monolayer materials. As an effort to identify for the first time 1D vdW HTs for efficient XSCs application, we perform here a systematic theoretical investigation on the energetic and structural stability, optoelectronic and photovoltaic properties of 1D vdW HTs based on SWCNTs encapsulating 50 symmetrical LCCs of different lengths, and capped with different conjugated endgroups through comprehensive first-principles calculations. We showed the fundamental role of the length and the endgroups effects in modulating the optoelectronic properties of LCCs. Through exploration of the energetic stability of the 1D vdW HTs of LCCs@SWCNTs from the universal force field (UFF) including vdW interactions, we determined the optimal SWCNTs diameters for which the resulting 1D vdW HTs are stable. Then, the band alignment in the 50 stable 1D vdW HTs of LCCs@SWCNTs is examined. Intriguingly, stable LCCs@SWCNTs are identified as type-II 1D vdW HTs complying the prerequisite of XSCs with strong optical absorption in the UV–visible-NIR spectral regions, and power conversion efficiency (PCE) reaching well over 21 %. These findings unravel the enormous potential of the 1D vdW HTs in designing next-generation XSCs devices competitive with state-of-the-art solar cells.

Realizing n-type carbon nanotubes via halide perovskite nanowires Cs4MX5 inner filling

N-type carbon nanotubes (CNTs)-based field-effect transistors (FETs) have huge potential applications in low-power consumption tunnel FETs. However, the low-work function metal electrodes can achieve n-type CNTs, but they are easily oxidized due to poor environmental stability. Therefore, based on first-principles calculations, we proposed halide perovskite nanowires Cs4MX5 (M = Pb, Sn; X = Cl, Br, I) inner filling to achieve n-type single-walled CNTs (SWCNTs). The results indicated that all the perovskite nanowires located at the center of the SWCNTs possess high stability. Moreover, the diameter of SWCNTs is a crucial factor affecting the inner filling of perovskite nanowires with an optimal diameter of about 1.4 nm. Furthermore, all the perovskite nanowires Cs4MX5 are excellent electron donors, and the largest charge transfer is up to 1.72 e/nm for Cs4SnI5. Their interaction mechanism reveals that the low work function and the large internal bandgap are two important factors for cubic-phase nanowires to realize the n-type CNTs. Our findings provide some candidate materials and a feasible way to achieve n-type CNTs for applying CNTs-based FETs.

Impact of Surfactant to DNA Exchange on Carbon Nanotube Emission for Biosensing Applications

Synthesis methods of single walled carbon nanotubes (SWCNTs) result in mixtures of different chiralites. Chirality affects SWCNT diameter as well electronic and optical properties. For use in optical sensors, mono-chirality SWCNTs offer better signal compared to chirality mixtures. A common chirality separation method is aqueous two-phase extraction, where solutions of surfactants are used to partition SWCNTs based on chirality. The process results in a mono-chiral solution of SWCNTs wrapped in surfactant, however for sensing applications SWCNTs need to be exchanged from this surfactant wrapping to single stranded DNA wrapping. Concerns have been raised about residual surfactant remaining on the SWCNT surface after the exchange process and the effect this would have on the sensing capabilities of the SWCNT. To investigate this, we compared the emission spectra of covalently modified SWCNTs sonicated directly in DNA to that of SWCNTs exchanged from surfactant into DNA. We observed that emission from exchanged SWCNTs was red shifted compared to direct DNA sonicated SWCNTs, however exchanged SWCNTs had similar environmental responsivity to direct DNA sonicated SWCNTs.

Diameter-selective extraction of single-walled carbon nanotubes by interlocking with Cu-tethered square nanobrackets.

We have been working with carbon nanotube separation through host-guest chemistry. Herein, a new macrocyclic host molecule, Cu-tethered square nanobrackets, is designed, synthesized and applied to single-walled carbon nanotubes (SWNTs) for their diameter-based separation. The complexation between copper ions and dipyrrin moieties of the nanobracket gives Cu-tethered square nanobrackets, which is confirmed by absorption, Raman and MALDI-TOF mass spectra. Upon extraction of SWNTs with the nanobracket and copper(II), in situ-formed square Cu-nanobrackets are found to interlock SWNTs to disperse them in 2-propanol. The interlocking is confirmed by Raman spectroscopy after thorough washing of the extracted SWNTs. Pristine SWNTs were recovered through demetalation of the interlocked ones along with the nanobracket. Raman and absorption spectroscopies of the extracted SWNTs reveals the diameter enrichment of only several kinds of SWNTs in the diameter range from 0.94 to 1.10 nm among ≈20 kinds of SWNTs from 0.76 to 1.20 nm in their diameter range. The diameter selectivity is supported by the theoretical calculations with the GFN2-xTB method, indicating that the most preferred SWNT diameter for the square Cu-nanobrackets is 1.04 nm.

Encapsulation and Evolution of Polyynes Inside Single-Walled Carbon Nanotubes.

Polyyne is an sp-hybridized linear carbon chain (LCC) with alternating single and triple carbon-carbon bonds. Polyyne is very reactive; thus, its structure can be easily damaged through a cross-linking reaction between the molecules. The longer the polyyne is, the more unstable it becomes. Therefore, it is difficult to directly synthesize long polyynes in a solvent. The encapsulation of polyynes inside carbon nanotubes not only stabilizes the molecules to avoid cross-linking reactions, but also allows a restriction reaction to occur solely at the ends of the polyynes, resulting in long LCCs. Here, by controlling the diameter of single-walled carbon nanotubes (SWCNTs), polyynes were filled with high yield below room temperature. Subsequent annealing of the filled samples promoted the reaction between the polyynes, leading to the formation of long LCCs. More importantly, single chiral (6,5) SWCNTs with high purity were used for the successful encapsulation of polyynes for the first time, and LCCs were synthesized by coalescing the polyynes in the (6,5) SWCNTs. This method holds promise for further exploration of the synthesis of property-tailored LCCs through encapsulation inside different chiral SWCNTs.

Towards the preparation of single-walled carbon nanotubes with average diameter of 1.2 nm

Preparation of single-walled carbon nanotubes (SWNTs) with diameters ranging from 1.2 to 1.5 nm has been highly demanded for field-effect transistors with superior properties. In the work, we report the chemical vapor deposition synthesis of SWNTs with an average diameter of 1.2 nm from a rationally designed nickel catalyst supported by magnesia. The high metal dispersion, the suitable reaction temperature, and the use of a methane carbon source co-determine the SWNT diameter distribution. Furthermore, through the synergistic application of poly(9,9-dioctylfluorene-2,7-diylalt-pyridine-2,6-diyl) wrapping and ultracentrifugation, SWNTs with enriched (10,8) species of 1.24 nm are successfully extracted, which is attributed to the selective interaction between the polymer molecules and the targeted SWNTs. This work not only sheds light on the growth of SWNTs with relatively large diameter, but also paves the way towards the preparation of high purity (n,m) species that could meet the requirements of advanced high-tech applications.

Single-walled carbon nanotube synthesis with RuRhPdIrPt high entropy alloy catalysts

Using high-entropy alloy nanoparticles (HEA NPs) composed of five platinum-group metals (5PGM), Ru, Rh, Pd, Ir, and Pt, as catalysts, we succeeded in growing single-walled carbon nanotubes (SWCNTs) via chemical vapor deposition (CVD). After CVD growth with C2H2 feedstock at 750 ℃ for 10 min, high-density SWCNTs were grown from 5PGM HEA NPs. The diameters of most SWCNTs were in the range of 0.83–1.1 nm, exhibiting the growth of small-diameter SWCNTs. Compared with monometal PGM catalysts, the SWCNT yield with the 5PGM HEA NP catalysts was much higher and was compatible even with those with Fe and Co.

On the Magnetization and Entanglement Plateaus in One-Dimensional Confined Molecular Magnets

One-dimensional (1D) magnetic systems offer rich phenomena in the quantum limit, proving more chemically accessible than zero-dimensional or higher-dimensional frameworks. Single-walled carbon nanotubes (SWCNT) have recently been used to encapsulate trimetric nickel(II) acetylacetonate [Nanoscale, 2019, 11, 10615–10621]. Here, we investigate the magnetization on spin chains based on nickel trimers by Matrix Product State (MPS) simulations. Our findings reveal plateaus in the exchange/magnetic-field phase diagram for three coupling configurations, showcasing effective dimeric and trimeric spin-ordering with similar or staggered entanglement across chains. These ordered states allow the qubit-like tuning of specific local magnetic moments, exhibiting disengagement or uniform coupling in entanglement plateaus. This behavior is consistent with the experimental transition from frustrated (3D) to non-frustrated (1D) molecules, corresponding to large and smaller SWCNT diameters. Our study offers insights into the potential of 1D-confined trimers for quantum computation, extending beyond the confinement of trimetric nickel-based molecules in one dimension.

Structures and dynamics of protic [EtNH3][NO3] and aprotic [Emim][NO3] ionic liquid mixtures around the single-walled carbon nanotubes: The critical role of imidazolium-based cations

Molecular dynamics (MD) simulations and a series of ab initio calculations have been applied to systematically investigate the structural and dynamic properties for ionic liquid (IL) mixture of equimolar protic [EtNH3][NO3] and aprotic [Emim][NO3] around the single-walled carbon nanotubes (SWCNTs) of (4,4), (8,8) and (12,12). Our simulation results demonstrated that ions of IL mixtures display a well-defined shell structures at the interface irrespective of the diameters of SWCNTs. The aprotic [Emim]+ cations adsorb preferentially over protic [EtNH3]+ at the interface of SWCNTs irrespective of its diameters. Further analysis reveals that these two cations and the [NO3]– anions display ordered arrangement in the first solvation shell. Accordantly, the rotational dynamics of interfacial [Emim]+ and [EtNH3]+ cations decay much slower than those of the bulk curves, suggesting the rotational motions of these two cations at the interface of the SWCNTs are significantly restricted. Interfacial [Emim]+ cations decay much slower rotational motions as the SWCNTs diameter increases. However, for interfacial [EtNH3]+ cations, because they are far from the interface, they display similar rotations regardless of the SWCNTs diameters. More importantly, the HB lifetime of interfacial [Emim]+–[NO3]– and [EtNH3]+–[NO3]– are much longer than the corresponding bulk values due to the restrictions on the rotational motions of cations, suggesting the strength of these two HBs are enhanced at the interface. The binding energies for the above HBs were determined by the ab initio calculations, which are in accordance with the MD simulation results. Our results provide a molecular-level understanding the structural and dynamic properties of [EtNH3][NO3] and [Emim][NO3] IL mixtures around the SWCNTs, which highlighted the critical role of the imidazolium-based cations.

Kinetics of Single-Wall Carbon Nanotube Coating Displacement by Single-Stranded DNA Depends on Nanotube Structure.

Time-resolved fluorescence spectroscopy has been used to study the displacement of adsorbed sodium dodecyl sulfate (SDS) from the surface of single-wall carbon nanotubes (SWCNTs) by short strands of single-stranded DNA. Intensity changes in near-infrared emission peaks of various SWCNT structures were analyzed following the addition of six different (GT)n oligomers (n from 3 to 20) to SDS-coated nanotube samples. There is a strong kinetic dependence on the oligomer length, with (GT)3 giving an initial rate more than 300 times greater than that of (GT)20. For shorter oligos in the (GT)n series, we observe an inverse dependence of the displacement rate on the SWCNT diameter, with SDS displaced from (6,5) more than twice as fast as from (8,7). However, this diameter dependence is reversed for oligos with more than six (GT) units. There is also a systematic dependence of the displacement rate on the nanotube chiral angle that is strongest for (GT)5, leading to a factor of ∼3 initial rate difference between (9,1) and (6,5) despite their identical diameters. To account for these findings, we propose a simple two-step kinetic model in which disruption of the original SDS coating is followed by conformational relaxation of ssDNA on the nanotube surface. The relaxation is relatively fast for ssDNA oligos shorter than 12 bp, making the first step rate-determining. Conversely, relaxation of the longer oligomers is slow enough that the second step becomes rate-determining.

Assembly and Characterization of Length-Sorted, Aligned Boron Nitride/Carbon Nanotube Thin Film Composites Via Slow Vacuum Filtration

Globally aligned single-wall carbon nanotubes (SWCNTs) are a promising, scalable platform for studying fundamental physical phenomena and an important vehicle for optoelectronic device applications. Recent work by Rust et al. [1] has identified nanotube length as an important mediating factor in the degree and scale of SWCNT alignment via slow vacuum filtration (SVF).Building on this work and that of Walker et al. [2,3], we explore the co-assembly of length-sorted SWCNTs and boron nitride nanotubes (BNNTs) atop polycarbonate track-etched membranes. BNNTs have recently gained interest as a chirality-agnostic, wide-bandgap material for encapsulation, insulation, thermal/mechanical robustness, and visible-light transparency, while also having a similar high aspect ratio morphology, making them an exceptional and alignable host matrix for individualized CNT species. To prepare such hybrid assemblies, a polymer-assisted, depletion-based method was first used to length-sort different diameter SWCNT (alkane filled electric-arc, CoMoCAT, metallic-sorted Tuball), and BNNT nanotube populations. Thereafter, we investigated the impacts of tube lengths, relative BN/C fraction, mass loading, and presence of a global director force on the multi-scale assembly behavior. A combination of birefringence microscopy and polarized Raman spectroscopy probed and identified trends in global and local ordering under these conditions.[1] Rust, C., Shapturenka, P., Spari, M., Jin, Q., Li, H., Bacher, A., Guttmann, M., Zheng, M., Adel, T., Hight Walker, A. R., Fagan, J. A., & Flavel, B. S. (2022). The Impact of Carbon Nanotube Length and Diameter on their Global Alignment by Dead-End Filtration. Small (forthcoming).[2] Walker, J. S., Fagan, J. A., Biacchi, A. J., Kuehl, V. A., Searles, T. A., Hight Walker, A. R., & Rice, W. D. (2019). Global Alignment of Solution-Based Single-Wall Carbon Nanotube Films via Machine-Vision Controlled Filtration. Nano Letters, 19(10), 7256–7264.[3] Walker, J. S., Macdermid, Z. J., Fagan, J. A., Kolmakov, A., Biacchi, A. J., Searles, T. A., Walker, A. R. H., & Rice, W. D. (2022). Dependence of Single‐Wall Carbon Nanotube Alignment on the Filter Membrane Interface in Slow Vacuum Filtration. Small, 18, 2105619.

(Invited) Diameter-Dependent Stacking of Squaraine Dye Molecules inside Chirality-Sorted Single-Wall Carbon Nanotubes

Filling of single-wall carbon nanotubes (SWCNTs) with organic dye molecules is a promising strategy to add new functionalities, for instance by aligning dipolar dyes in a one-dimensional (1D) head-to-tail coupled chain to obtain a giant enhancement of their nonlinear optical response,[1] or by photo-sensitizing the tubes in new wavelength ranges by excitation energy transfer (EET) from the dye to the SWCNTs, useful for photo-conversion applications.[2] The 1D stacking of molecules inside SWCNTs modulates both the properties of the molecules and of the SWCNTs. We found that the EET of squaraine-dye-filled SWCNTs reveals a pronounced SWCNT-diameter-dependence of the dye absorption, indicating a diameter-dependent stacking. By performing IR fluorescence excitation spectroscopy on a range of chirality-enriched samples of dye-filled SWCNTs with different chirality distributions, each shifted dye absorption wavelength observed through the EET can be unambiguously assigned to a specific encapsulating SWCNT chirality.[3] This reveals a systematic trend with diameter that can be associated with the J-aggregate- and H-aggregate-like interactions expected in close-packed single- and double-file stackings, as corroborated by a simple geometric model, and enables tuning of the optical properties of the 1D molecular arrays through the selection of proper SWCNT diameters.[1] S. Cambré, J. Campo, C. Beirnaert, C. Verlackt, P. Cool, W. Wenseleers, Nature Nanotechnol. 10(3) 248-252 (2015). [2] S. van Bezouw, D.H. Arias, R. Ihly, S. Cambré, A.J. Ferguson, J. Campo, J.C. Johnson, J. Defillet, W. Wenseleers, J.L. Blackburn, ACS Nano 12(7) 6881-6894 (2018). [3] S. Forel, H. Li, S. van Bezouw, J. Campo, L. Wieland, W. Wenseleers, B.S. Flavel, S. Cambré, Nanoscale 14, 8385-8397 (2022).

The distinguished hydrogen sensibility by selecting diameters of single-walled carbon nanotubes and adding sensitive materials

Hydrogen sensors based on palladium (Pd)/semiconducting single-walled carbon nanotube(s-SWNTs) have showed great performance in sensitivity, limit of detection (LOD), and response time. With the development of research, it is proved that diameters and chirality of s-SWNTs strongly influence the detection. In this paper, we fabricated two kinds of sensors with different diameters, and that results showed response of sensor with 0.7–1.2 nm s-SWNTs was almost 6 times higher than that of the one with 1.2–1.6 nm s-SWNTs. The former could achieve the response of change ≈6.09 for 1 ppm H2 in N2, and the latter was ≈1.07. Furthermore, with Pd/HKUST-1 as functionalization for capturing more hydrogen (H2), the system formed a synergistic effect to enhance the change of resistance. The fabricated Pd/HKUST-1/s-SWNTs film (0.7–1.2 nm) H2 sensor presents a very fast recovery time of 8 s at 10 ppm and a detection limit of 1 ppm H2 in nitrogen(N2). In addition, in the air the sensor can also work. Its response time of the sensor to 0.05% H2 in air are 0.183 s. By choosing the diameter of s-SWNTs and adding H2-sensitive materials, the sensors are expected to achieve the fast response and recovery with high sensitivity and low LOD.

Molecular modeling investigation on mechanism of diazinon pesticide removal from water by single- and multi-walled carbon nanotubes

In this study, the mechanism of diazinon adsorption on single-walled carbon nanotubes (SWNTs), as well as multi-walled carbon nanotubes (MWNTs), was investigated using molecular modelling. Determination of the lowest energy sites of different types of carbon nanotubes (CNTs) was demonstrated. The adsorption site locator module was used for this purpose. It was found that the 5-walled CNTs are the best MWNTs for diazinon elimination from water due to their higher interactions with diazinon. In addition, the adsorption mechanism in SWNT and MWNTs was determined to be wholly adsorption on the lateral surface. It is because the geometrical size of diazinon molecules is larger than the inner diameter of SWNT and MWNTs. Furthermore, the contribution of diazinon adsorption on the 5-wall MWNTs was the highest, for the lowest diazinon concentration in the mixture.

Radial-tangential mode of single-wall carbon nanotubes manifested by Landau regulation: reinterpretation of low- and intermediate-frequency Raman signals

The low-frequency Raman signals of single-wall carbon nanotubes (SWNTs), appearing in the range of 100–300 cm−1, have been interpreted as radial-breathing mode (RBM) comprising pure radial Eigenvectors. Here, we report that most of the low-frequency and intermediate-frequency signals of SWNTs are radial-tangential modes (RTMs) coexisting radial and tangential Eigenvectors, while only the first peak at the low-frequency side is the RBM. Density functional theory simulation for SWNTs of ~ 2 nm in diameter shows that dozens of RTMs exhibit following the RBM (~ 150 cm−1) up to G-mode (~ 1592 cm−1) in order with Landau regulation. We specify the RBM and the RTM on Raman spectra obtained from SWNTs, where both appear as prominent peaks between 149 and 170 cm−1 and ripple-like peaks between 166 and 1440 cm−1, respectively. We report that the RTMs have been regarded as RBM (~ 300 cm−1) and ambiguously named as intermediate-frequency mode (300–1300 cm−1) without assignment. The RTMs gradually interlink the RBM and the G-mode resulting in the symmetric Raman spectra in intensity. We reveal high-resolution transmission microscope evidence for a helical structure of SWNTs, informing the typical diameter of commercial SWNTs to be 1.4–2 nm.

Determine the Complete Configuration of Single-Walled Carbon Nanotubes by One Photograph of Transmission Electron Microscopy.

Developing a convenient method to determine the complete structure of single-walled carbon nanotubes (SWNTs) is important to achieve the fully controlled growth of this nanomaterial. However, approaches that can identify handedness at the atomic level with simple equipment, operation, and data analysis are still lacking. Here, the SWNTs/graphene (Gr) vertical heterostructures are artificially constructed with aligned interfaces to realize the lattice interpretation of SWNT upper and lower walls separately by only one transmission electron microscopy image, thus transforming the 3D handedness information to projected 2D space. Gr displays prominent out-of-plane deformation at the interface, promoting the energetic advantage for the aligned interface construction. The interfacial alignment between the SWNT and Gr shows no obvious dependence on either the helical angle or diameter of SWNTs. The half-wrapping of SWNTs by deformed Gr also triggers diversified alterations in electronic structures based on theoretical calculations. 27 specimens with SWNTs prepared by two disparate methods are examined, implying equal handedness distribution in the randomly aligned SWNTs grown on quartz and potential handedness enrichment in horizontal SWNT arrays grown on a-sapphire. This work provides a simple strategy for chiral discrimination and lays a characterization foundation for handedness-selective growth of nanomaterials.

Measuring the Diameter of Single-Wall Carbon Nanotubes Using AFM.

In this work, we identify two issues that can significantly affect the accuracy of AFM measurements of the diameter of single-wall carbon nanotubes (SWCNTs) and propose a protocol that reduces errors associated with these issues. Measurements of the nanotube height under different applied forces demonstrate that even moderate forces significantly compress several different types of SWCNTs, leading to errors in measured diameters that must be minimized and/or corrected. Substrate and nanotube roughness also make major contributions to the uncertainty associated with the extraction of diameters from measured images. An analysis method has been developed that reduces the uncertainties associated with this extraction to <0.1 nm. This method is then applied to measure the diameter distribution of individual highly semiconducting enriched nanotubes in networks prepared from polyfluorene/SWCNT dispersions. Good agreement is obtained between diameter distributions for the same sample measured with two different commercial AFM instruments, indicating the reproducibility of the method. The reduced uncertainty in diameter measurements based on this method facilitates: (1) determination of the thickness of the polymer layer wrapping the nanotubes and (2) measurement of nanotube compression at tube-tube junctions within the network.

Chirality Dependence of Triplet Excitons in (6,5) and (7,5) Single-Wall Carbon Nanotubes Revealed by Optically Detected Magnetic Resonance.

The excitonic structure of single-wall carbon nanotubes (SWCNTs) is chirality dependent and consists of multiple singlet and triplet excitons (TEs) of which only one singlet exciton (SE) is optically bright. In particular, the dark TEs have a large impact on the integration of SWCNTs in optoelectronic devices, where excitons are created electrically, such as in infrared light-emitting diodes, thereby strongly limiting their quantum efficiency. Here, we report the characterization of TEs in chirality-purified samples of (6,5) and (7,5) SWCNTs, either randomly oriented in a frozen solution or with in-plane preferential orientation in a film, by means of optically detected magnetic resonance (ODMR) spectroscopy. In both chiral structures, the nanotubes are shown to sustain three types of TEs. One TE exhibits axial symmetry with zero-field splitting (ZFS) parameters depending on SWCNT diameter, in good agreement with the tighter confinement expected in narrower-diameter nanotubes. The ZFS of this TE also depends on nanotube environment, pointing to slightly weaker confinement for surfactant-coated than for polymer-wrapped SWCNTs. A second TE type, with much smaller ZFS, does not show the same systematic trends with diameter and environment and has a less well-defined axial symmetry. This most likely corresponds to TEs trapped at defect sites at low temperature, as exemplified by comparing SWCNT samples from different origins and after different treatments. A third triplet has unresolved ZFS, implying it originates from weakly interacting spin pairs. Aside from the diameter dependence, ODMR thus provides insights in both the symmetry, confinement, and nature of TEs on semiconducting SWCNTs.